Stratospheric ozone transported to the troposphere is
estimated to account for 5 %–15 % of the tropospheric ozone sources.
However, the chances of intruded stratospheric ozone reaching the surface are
low. Here, we report an event of a strong surface ozone surge of
stratospheric origin in the North China Plain (NCP, 34–40∘ N,
114–121∘ E) during the night of 31 July 2021. The hourly
measurements reveal surface ozone concentrations of up to 80–90 ppbv at several
cities over the NCP from 23:00 LST (Local Standard time, = UTC +8 h) on 31
July to 06:00 LST on 1 August 2021. The ozone enhancement was 40–50 ppbv
higher than the corresponding monthly mean. A high-frequency surface
measurement indicates that this ozone surge occurred abruptly, with an
increase reaching 40–50 ppbv within 10 min. A concurrent decline in
surface carbon monoxide (CO) concentrations suggests that this surface ozone
surge might have resulted from the downward transport of a stratospheric ozone-rich and
CO-poor air mass. This is further confirmed by the vertical evolutions of
humidity and ozone profiles based on radiosonde and satellite data
respectively. Such an event of stratospheric impact on surface ozone is
rarely documented in view of its magnitude, coverage, and duration.
We find that this surface ozone surge was induced by a combined effect of
dying Typhoon In-fa and shallow local mesoscale convective systems (MCSs)
that facilitated transport of stratospheric ozone to the surface. This
finding is based on analysis of meteorological reanalysis and radiosonde
data, combined with high-resolution Weather Research and Forecasting (WRF)
simulation and backward trajectory analysis using the FLEXible
PARTicle (FLEXPART) particle dispersion model. Although Typhoon In-fa on the
synoptic scale was at its dissipation stage when it passed through the NCP,
it could still bring down a stratospheric dry and ozone-rich air mass. As a
result, the stratospheric air mass descended to the middle-to-low troposphere
over the NCP before the MCSs formed. With the pre-existing stratospheric
air mass, the convective downdrafts of the MCSs facilitated the final descent
of stratospheric air mass to the surface. Significant surface ozone
enhancement occurred in the convective downdraft regions during the
development and propagation of the MCSs. This study underscores the
substantial roles of weak convection in transporting stratospheric ozone to
the lower troposphere and even to the surface, which has important implications
for air quality and climate change.
Introduction
The exchange between the stratosphere and the troposphere, between which
atmospheric compositions and static stability are fundamentally different,
is crucial to atmospheric chemistry, global climate change, and ecosystem
health (Holton et al., 1995; Stohl et al., 2003). The stratosphere stores
approximately 90 %–95 % of atmospheric ozone (O3), and hence is
characterized by a high abundance of ozone. Meanwhile, the stratosphere
contains little water vapor, and little carbon monoxide (CO), which is
primarily emitted from combustion processes near the surface (Hartmann et
al., 2001; Pan et al., 2014b, 2018; D. Li et al., 2020). In contrast, the
troposphere contains only 5 %–15 % of atmospheric ozone, as well as high
water vapor and CO concentrations owing to its closeness to the surface
sources. Therefore, a tropospheric air mass is rich in CO and water vapor,
and poor in ozone relative to the stratospheric air mass. The transport of
these trace gases from the stratosphere to the troposphere can occur under
the influences of synoptic-scale and mesoscale atmospheric processes. Among
these processes, deep convection is of great interest because it can
effectively redistribute the trace gases vertically by modulating the flows
of air mass upward or downward (Dickerson et al., 1987; Lelieveld and
Crutzen, 1994; Pickering et al., 1991, 1992; Li et al., 2017). For example,
intensive updrafts of deep convection can transport ozone and its precursors
such as CO, nitrogen oxides (NOx), and volatile organic compounds (VOC) in
the atmospheric boundary layer (ABL) to the upper troposphere and lower
stratosphere (UTLS), and hence alter the chemical nature and promote
substantial ozone formation in the UTLS. The stratospheric ozone-rich
air mass can also be transported downward to the lower troposphere by deep
convection. Therefore, deep convection is deemed important to the ozone
budgets in the stratosphere and troposphere.
Previous studies on convective redistribution of vertical atmospheric
composition mainly focus on the upward injection of pollutants from the ABL
to the UTLS, whereas recent field campaigns and numerical analysis have started to
pay attention to the downward transport of a stratospheric air mass and its
influences on the troposphere (e.g., Baray et al., 1999; Betts et al., 2002;
Sahu and Lal, 2006; Hu et al., 2010; Pan et al., 2014a; Phoenix et al., 2020,
2021). It is known that ozone is important for the radiation balance
of the climate system and atmospheric oxidative capability. In recent years,
continuous increases in surface ozone levels have been reported over many areas in China (Li et al., 2019; Han et al., 2020), whereas the contributions from
the stratosphere-to-troposphere processes to the increasing surface ozone
have been rarely studied. There are great uncertainties in the estimation of
stratospheric impacts on the tropospheric ozone budget, because most studies
are based on global models that have coarse spatiotemporal resolutions
and a simplified representation of convection. Although events of stratospheric
intrusions directly influencing surface ozone concentrations appear rarely and
sporadically (Davies and Schuepbach, 1994; Akritidis et al., 2019; Dreessen,
2019; Knowland et al., 2017), the frequency and intensity of convection are
projected to increase significantly in the future owing to global warming (Del
Genio et al., 2007; Akritidis et al., 2019; Meul et al., 2018; Raupach et
al., 2021). As a result, the likelihood of frequent convection-triggered
transport from the stratosphere to the troposphere is also expected to rise
in the future. Therefore, detailed analysis of simulations with high
spatiotemporal resolution models can enhance our understanding of
stratospheric intrusion related to convection.
The variation in ozone concentrations in the troposphere has close links
to stratospheric intrusions of ozone-rich air mass through convection. For
example, Pan et al. (2014a), based on aircraft observations, found that the
stratospheric ozone-rich air mass can be transported downward and wrapped
around the anvil by mesoscale convective systems (MCSs) with overshooting
convection. Pan et al. (2014a) and Phoenix et al. (2020) revealed that
vigorous atmospheric motions of tropopause-penetrating convection can
perturb the tropopause and drive subsidence flow containing
stratospheric ozone-rich air around the storm edges. Researchers also
observed that small-scale convective downdrafts over tropical regions such
as the Amazon rainforest are able to enhance surface ozone by 3–30 ppbv (Betts
et al., 2002; Grant et al., 2008; Gerken et al., 2016; Melo et al., 2019).
Jiang et al. (2015) reported a typhoon-induced high ozone episode at night
with large surface ozone increases reaching 21–42 ppbv over the southeastern
coast of China. Along the downward transport of stratospheric ozone-rich
air mass, the upper and middle troposphere are most frequently impacted by
the intrusions that mix with ambient air and contribute to the general free
tropospheric ozone burden (Zanis et al., 2003; Tarasick et al., 2019). In
some cases, a stratospheric air mass can sink to the surface (e.g., Davies
and Schuepbach, 1994; Dreessen, 2019), whereas the fine-scale transport
pathways of stratospheric air to reach the surface still require in-depth
investigation. In this study, we report an event of substantial surface
ozone enhancement observed at midnight on 31 July 2021 over the North China
Plain (NCP) (34–40∘ N, 114–121∘ E, geographical
location is shown in Fig. 1). Impacted by Typhoon In-fa and local MCSs, the
surface ozone concentrations reached 80–90 ppbv at several cities over the
NCP from 23:00 LST on 31 July to 06:00 LST on 1 August 2021. Compared with the
monthly mean ozone concentrations, the surface ozone was enhanced by up to
40–50 ppbv. We expect that a direct stratospheric intrusion over the NCP was
responsible for this vigorous surface ozone enhancement event, which would
be analyzed in detail in the following sections. Such a significant
ozone surge is impressive, given the rareness of direct stratospheric
intrusions into the ground level and severe threats to the ecosystem. In
addition, several features of atmospheric processes responsible for this
night-time surface ozone surge event are worth noting. First, upon the
occurrence of the ozone surge, Typhoon In-fa, which caused the
record-breaking rainfall over Henan province of northern China in the summer of
2021, had been downgraded to tropical depression (TD, with a wind speed of
10.8–17.1 m s-1) category and evolved into its dissipation stage. Chen
et al. (2021) evaluated the impacts of typhoons on tropospheric ozone and
showed that typhoons can induce stratospheric intrusions to the lower
troposphere when typhoons are intensive over the ocean. Although in this case,
Typhoon In-fa had made landfall on 25 July 2021, and was weak when it moved
into the NCP on 29 July, it could still have substantial influences on
tropospheric ozone. Second, instead of showing significant
tropopause-penetrating features in the convection case of Pan et al. (2014a),
the local MCSs associated with the ozone surge were shallow in terms of
vertical development and did not penetrate into the tropopause. As there
are few studies that documented and analyzed the stratospheric impact on the
troposphere over the NCP (Li et al., 2015a, b), the variations, magnitudes,
transport pathways, and mechanisms of how the stratospheric air mass can
reach the surface remain less well understood. Specifically, how the
stratospheric air mass finally descends to the ground level is not clear,
despite some detrainment processes of stratospheric ozone to ambient air in
the upper and middle troposphere. Therefore, based on the observations and
model simulations with high spatiotemporal resolutions, we intend to address
the following key scientific issues related to this surface ozone surge that
is induced by stratospheric intrusions:
The fine-scale spatiotemporal variations and magnitudes of surface ozone
enhancement induced by the stratospheric intrusions.
The interactions between synoptic-scale and mesoscale atmospheric
processes responsible for the rapid and direct stratospheric influences.
The transport pathways of stratospheric ozone-rich air to reach the
surface.
The remaining paper is structured as follows. Section 2 describes the
atmospheric composition observational data and meteorological data. Details
of high-resolution simulations of the MCSs and backward trajectories
analysis are also introduced. Section 3 presents the fine-scale variations
in surface atmospheric composition. In Sect. 4, we analyze the multi-scale
interactions of atmospheric processes responsible for the stratospheric
intrusion to the surface, and present the transport pathways of ozone-rich
air mass. Section 5 offers the conclusions and discussions.
Topography of North China Plain (NCP; unit: m a.s.l., indicated with different colors (color bar)) and
locations of cities Hengshui (HS), Jinan (JN), Binzhou (BZ), Weifang (WF),
Qingdao (QD), and Weihai (WH). Three radar stations, located in JN, QD, and WH, are marked by red triangles.
The ground-based air quality monitoring stations are shown by magenta dots,
and the station with high-frequency measurement of air quality located in
Zhanhua (ZH) county of Binzhou city is marked by a magenta star. The
locations of Bohai Sea and the Yellow Sea are also indicated. The thin gray
lines indicate the borders of provinces.
Data and ModelAtmospheric composition observations
Ground-based air pollutant data were collected from two sources. First, a
nationwide observation network with more than 1500 stations distributed over
454 cities is maintained by the China National Environmental Monitoring Center
(CNEMC), which measures air pollutants, including surface fine particles with
an aerodynamic diameter of up to 2.5 µm (PM2.5) and of up to 10 µm (PM10), ozone, CO, nitrogen dioxide (NO2), and sulfur
dioxide (SO2) (Lu et al., 2018).
The air pollutant observations from the CNEMC are strictly quality controlled and released with a 1 h temporal
resolution (https://quotsoft.net/air, last access: 21 January 2022).
Correspondingly, city-scale air pollutant concentrations were obtained by
averaging all available station observations in cities such as Hengshui
(HS), Jinan (JN), Binzhou (BZ), Weifang (WF), Qingdao (QD), and Weihai (WH)
(Fig. 1). Second, continuous measurements of ozone, CO, and NOx were
made in July–August 2021 at a rural station (37.82∘ N, 118.11∘ E) located in Zhanhua (ZH), a county of Binzhou city, where the
field campaign of the 2021 Shandong Triggering Lightning Experiment (SHATLE) was
performed by the Institute of Atmospheric Physics (IAP) of the Chinese Academy
of Sciences (CAS) (Qie et al., 2009; Jiang et al., 2013). The applied
atmospheric composition instruments include an ultraviolet photometric ozone
analyzer (Model 49i), a NOx analyzer (Model 42i-TL), and a CO analyzer
(Model 48i-TLE) produced by Thermo Fisher Scientific Inc. Detailed
calibrations and daily maintenance were performed to ensure data quality.
Ozone, CO, and NOx concentrations (in ppbv) were output at a frequency
of 30 s, originally designed to track the fast variations in
atmospheric compositions during the triggered lightning flashes. In this
study, we averaged these high-frequency observations into a 3 min temporal
resolution.
In addition to the ground-based observations, tropospheric ozone vertical
profiles from satellite observations were also analyzed. The vertical
distributions of ozone are measured by the Atmospheric Infrared
Sounder (AIRS) on the Earth Observing System (EOS) Aqua satellite, and the Ozone Monitoring Instrument (OMI) on the EOS Aura satellite under the NASA
TRopospheric Ozone and Precursors from Earth System Sounding (TROPESS)
project (Verstraeten et al., 2013; Fu et al., 2018;
https://tes.jpl.nasa.gov/tropess/products/o3/, last access: 20 June 2022). The ozone profiles are produced via an optimal estimation algorithm
using multi-spectra, multi-species, and multi-sensors. These satellite-based
ozone profiles have a spatial resolution of 13 km × 24 km with 26 vertical levels from the surface to 0.1 hPa, and the temporal resolution is
1 d. Fu et al. (2018) compared the joint AIRS + OMI against ozonesonde
measurements, showing that the mean and standard deviation of the
differences are within the estimated measurement error of these space
sensors (2–5 ppbv).
Meteorological observations and atmospheric reanalysis data
The operational radiosonde data from the cities Jinan, Qingdao, and Weihai
(Fig. 1) were utilized to capture the meteorological evolution responsible
for the stratospheric intrusion. Regional radar mosaic products were
produced and analyzed using three Doppler radars, including two S-band radars
located in Jinan and Qingdao and one C-band radar in Binzhou, because radar
reflectivity and radial velocity are indicative of storm microphysical and
dynamical structure, as well as the horizontal coverage and vertical
extension of convection. Cloud-to-ground (CG) lightning flashes were also
referenced to infer the storm development and intensity provided by a
nationwide lightning detection network operated by the State Grid Electric
Power Research Institute (Chen et al., 2012).
Three-dimensional atmospheric Modern-Era Retrospective Analysis
for Research and Applications, Version 2 (MERRA-2) reanalysis data were used to
reveal the synoptic-scale evolutions impacted by Typhoon In-fa
(https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/, last access: 20 June 2022). MERRA-2 reanalysis has a horizontal resolution of 0.5∘× 0.625∘, 72 vertical levels from the surface to 0.01 hPa and a 3 h update temporal cycle. The following gridded meteorological
variables were extracted from MERRA-2. Dynamical variables including
horizontal wind and vertical wind velocity were analyzed to reveal dominant
flow patterns when Typhoon In-fa began dissipate. Potential vorticity (PV)
and relative humidity (RH), which are indicative of stratospheric intrusion,
were used to track the variation in tropopause height and the penetration of
dry stratospheric air.
WRF simulations and FLEXPART backward trajectories
The relatively coarse spatiotemporal resolution of observations and
reanalysis data mentioned above cannot explicitly capture atmospheric
processes at the storm scale, especially for the evolving convective
dynamics responsible for the downward transport of ozone-rich air mass. For
example, the 3 h cycle of MERRA-2 reanalysis data can easily miss the
details of the MCS evolution and is insufficient for conducting storm-scale
backward trajectory analysis. Therefore, the dynamical evolution of the MCSs
under the influence of Typhoon In-fa was simulated using the Weather
Research and Forecasting with the Advanced Research core (WRF-ARW, Version
3.9.1; Skamarock et al., 2008). Table 1 offers the basic parameters used in
WRF simulation. The numerical simulation employed two-way, three-domain
nested grid cells. The outermost domain has 232 × 182 grids with a
27-km horizontal grid spacing and covers approximately East Asia and the
neighboring oceans. The inner domain has 490 × 430 grids with a
9-km horizontal resolution covering the whole of China. The innermost domain
is placed over the NCP with 610 × 610 grids and a 3-km horizontal
resolution that guarantees to resolve the storm-scale features (Fig. S1 in the Supplement). To
explicitly resolve the dynamical structure in the vertical direction, the
number of terrain-following levels was set to 95, and the model top was set
to 50 hPa. As a result, the vertical spacing between each layer is
approximately 100 m in the ABL (<1.5 km) and 200 m in the free
atmosphere (between 1.5 and 20 km).
The applied physics options in the WRF model include the Kain–Fritsch
cumulus parameterization scheme (Kain and Frisch, 1993), which was applied
only to the outermost domain and inner domain but turned off for the
innermost domain. The microphysical parameterization is the Morrison
two-moment scheme (Morrison et al., 2009), the planetary boundary layer
physics parameterization is the Yonsei University (YSU) scheme (Hong et al., 2006), and the land
surface model is the Noah land surface model (Chen and Dudhia, 2001). For
the longwave and shortwave radiation processes, the Rapid Radiant Transfer Model (RRTM) scheme (Mlawer et
al., 1997) and the Dudhia scheme (Dudhia, 1989) were utilized. A
24 h period simulation starting from 08:00 LST (Local Standard time,
= UTC +8 h) on 31 July covering the entire lifespan of the MCSs was
performed, which was initialized by the 0.5∘ and 3 h Global
Forecast System (GFS) analysis of the National Centers for Environmental
Prediction (NCEP). Simulation results of the innermost domain with a 3-km
horizontal resolution were output every 3 min to analyze the evolution of
storm-scale features.
WRF Model Configuration and Physics Options.
Initial and boundary conditions0.5∘ and 3 h Global forecast system analysisSimulation domains27 km (232 × 182), 9 km (490 × 430), 3 km (610 × 610)Vertical levels95 levelsCumulus parameterizationKain–Fritsch scheme (applied in 27 and 9 km domain)MicrophysicsMorrison two-moment schemePlanetary boundary layerYonsei University schemeLand surface modelNoah schemeLongwave radiationRapid Radiative Transfer Model schemeShortwave radiationDudhia scheme
Backward trajectories for the analysis of the surface ozone surge were
simulated using the Flexible Lagrangian particle dispersion model (FLEXPART),
which works with the WRF model (FLEXPART-WRF, Version 3.3.2; Brioude et al.,
2013; https://www.flexpart.eu/wiki/FpLimitedareaWrf, last access: 20 June
2022). The FLEXPART model (Stohl et al., 2005) was originally developed at
the Norwegian Institute for Air Research in the Department of Atmospheric
and Climate Research, and was further tailored to WRF models so that the
model can be widely used to study the influence of mesoscale processes on
pollution transport (e.g., Aliaga et al., 2021; Nathan et al., 2021). Based
on the WRF simulation results of the innermost domain with a 3-km horizontal
resolution, we conducted backward trajectory calculations using
FLEXPART-WRF. Ten thousand particles were released at each defined location
and timing, which is described in the following section. The FLEXPART-WRF
output was saved every 10 min to track the three-dimensional particle
backward trajectories.
Confirmation of surface ozone surge with stratospheric origin
Before analyzing this surface ozone surge case of stratospheric origin, it
is beneficial to provide some statistics of surface ozone background
concentrations over the NCP. In the summer of 2021, the daily mean and maximum 8 h
average (MDA8) ozone concentrations in the NCP were 43.9 and 70.8 ppbv
respectively, whereas the mean night-time ozone concentration (19:00–06:00 LST) was 36.6 ppbv, calculated from observations. Figure 2 shows a 10 d
averaged surface ozone concentration (from 27 July to 5 August 2021) in each
city, used as the baseline for assessing ozone variations. Generally, the
10 d averaged ozone concentration in each city is close to the summertime
mean ozone concentration of 45–50 ppbv. During 28–30 July 2021, under the
cloudy conditions produced by Typhoon In-fa, surface ozone is apparently
lower than the 10 d average. After 31 July, as Typhoon In-fa had moved
over the NCP and entered the Bohai Sea, the photochemical reactions
accelerated, as seen in the steady increase in surface ozone at daytime and
subsequent diurnal cycles since. However, instead of continuously decreasing
after sunset, the concentrations of surface ozone over some cites in the NCP
increased abruptly and intensively between 23:00 LST on 31 July and 06:00 LST on 1 August (between the vertical black lines in Fig. 2 and the
zoomed-in Fig. S2), which were 40–50 ppbv larger than their corresponding
monthly mean values during the night and almost comparable with the daytime
high ozone concentrations (Fig. S3). In the cities of Hengshui, Binzhou, Jinan, and
Weifang, a peak ozone concentration at night-time reaching 80–90 ppbv
appeared in succession, which was in accordance with the southeastward
propagation of the MCSs (see Sect. 4.2, where impacts of the MCSs on
surface ozone are addressed in detail). Although in the eastern cities such
as Qingdao and Weihai (Fig. 2e–f), where convective activities were mostly
absent, the ozone evolution at midnight was different from the cities
experiencing storm passage shown in Fig. 2a–d.
(a)–(f) Temporal variation in surface ozone concentrations (unit: ppbv) in
local standard time (LST) from 28 July to 3 August 2021 using the 10 d
averaged ozone value as a baseline for comparison in cities Hengshui,
Binzhou, Jinan, Weifang, Qingdao, and Weihai. Positive (negative) departure
from the 10 d averaged ozone concentration is shown in red (blue) color.
The two vertical black lines represent the observed ozone surge period
between 23:00 LST on 31 July and 06:00 LST on 1 August 2021. Daily cycles
(00:00–00:00 LST) are denoted by vertical dashed pink lines. Labels along the
horizontal axis represent the observation times (month/day/hour).
During the ozone surge period, an obvious decrease in surface CO was also
observed. Figure 3 shows the variations in surface CO with a 10 d mean
concentration serving as the baseline. Although the temporal variations in
surface CO were complex, a systematic low-concentration phase of CO appeared
at midnight on 31 July (between the vertical black lines in Fig. 3 and the
zoomed-in Fig. S4), when surface ozone surged (Fig. 2) during the MCS event.
The surface CO concentrations were greatly reduced in cities such as
Hengshui, Binzhou, and Jinan, although the concentrations were reduced in
Weifang during partial night-time, and were not reduced in Qingdao and
Weihai, which were outside the path of influence of the MCSs, as noted in
the preceding paragraph. CO is often used as a tracer for both anthropogenic
pollution and biomass burning (e.g., Pochanart et al., 2003; Lin et al.,
2018); therefore, the high surface ozone synchronized with low CO in the
time series supports the case that the surface ozone surge was caused by
stratospheric intrusions of ozone-rich and CO-poor air mass. The area
impacted by stratospheric intrusions was larger than these cities covered,
and was at least 300 km × 300 km based on the nationwide
atmospheric composition measurements (Fig. 1).
(a)–(f) Same as Fig. 2, but for surface carbon monoxide (CO)
concentrations (unit: ppbv) from 28 July to 3 August 2021.
The atmospheric composition data from the national monitoring network
captured well this surface ozone surge event with stratospheric origin spatially,
although these observations were smoothed during each hour. To better identify
the magnitude and timing of surface ozone surge, high-frequency atmospheric
composition measurements collected during the SHATLE field campaign at
Zhanhua were analyzed. Figure 4 shows the 3 min variations in surface ozone
and CO concentrations relative to their 10 d averaged baseline
concentrations. As a rural county of Binzhou city, the ozone baseline
concentration (approximately 60 ppbv) in Zhanhua was higher than that in
Binzhou city (approximately 45 ppbv), whereas the CO baseline concentration in
Zhanhua, which is closely related to anthropogenic emissions, was lower than
that in Binzhou. The active photochemical reactions in the afternoon
elevated ozone concentrations, which fluctuated between 100 and 120 ppbv. After
sunset at 19:00 LST, surface ozone concentrations continuously decreased via the
titration effect and dry deposition of vegetation, and thus was lower than
its background concentration at 21:00 LST. However, at 22:36 LST, the
continuous decrease in surface ozone stopped. Instead, ozone concentrations
surged abruptly from 31 to 80 ppbv in the next 10 min and remained
high for the next 8 h. The averaged surface ozone concentrations in
the night were 79 ppbv, and the maximum concentrations reached 93 ppbv at
01:54 LST on 1 August 2021. Based on the observations with finer temporal
resolution, a synchronous reduction of surface CO concentrations occurred
exactly when ozone rose abruptly, which further confirmed that the ozone
surge was caused by intrusions of a stratospheric air mass. Compared with the
normal night-time ozone concentrations (an average of 36.6 ppbv), the
magnitudes of surface ozone surge due to stratospheric intrusions were
approximately 40–50 ppbv. The Chinese National Ambient Air Quality Standard
for ozone exceedance level is approximately 82 ppbv (K. Li et al., 2020), as a
result, the vigorous ozone surge can pose a threat to human health and
agricultural crops and other plants.
(a), (b) Surface ozone and CO concentrations (unit: ppbv) at the SHATLE
field campaign site located in Zhanhua county of Binzhou city, measured with
a 3 min temporal resolution from 16:00 LST on 31 July to 08:00 LST on 1
August 2021. The 10 d averaged ozone and CO concentrations at the site are
used as the baseline, and positive (negative) departure from the 10 d
averaged concentration is shown in red (blue) color. The two vertical black
lines represent the observed ozone surge period between 22:36 LST on 31 July
and 06:00 LST on 1 August 2021. Labels along the horizontal axis represent
the observation times (month/day/hour).
Multi-scale interactions responsible for the stratospheric intrusion
Several mechanisms have been proposed to explain higher tropospheric ozone
concentrations than normal. For example, the STE associated with
synoptic-scale dynamical exchange processes, such as tropopause folding near
the polar jet and subtropical jet (Stohl et al., 2003; Pan et al., 2014b; Li
et al., 2015a), cut-off low (Wirth, 1995; Li et al., 2015b), and
typhoons (Baray et al., 1999; Jiang et al., 2015; Preston et al., 2019; Chen
et al., 2021; Meng et al., 2022), are well studied. Local photochemical
production of ozone using the precursors anthropogenic emissions, biomass
burning (Chan et al., 2003; Brioude et al., 2007), and lightning-generated
nitrogen oxides (LNOx) (Cooper et al., 2006; Schumann and Huntrieser,
2007) are also able to increase tropospheric ozone burden. Particular to
this study is that convection with overshooting tops can force subsidence air
motions near the cloud edge owing to mass continuity and hence transport
stratospheric ozone-rich air downward (Hu et al., 2010; Pan et al., 2014a; Phoenix et
al., 2020). In this night-time surface ozone surge event associated with
stratospheric intrusions, the dominant atmospheric processes are dying
Typhoon In-fa and the local MCSs, with no significant influences from ozone
precursors from biomass burning or LNOx. In the following, we provide
detailed analyses of the interactions between synoptic-scale and
convective-scale processes that finally bring ozone from the stratosphere to
the surface and lead to the intensive midnight ozone surge.
Large-scale descent of stratospheric air attributed to the dying Typhoon
In-fa
Previous studies indicated that typhoons can perturb the tropopause and
hence induce stratospheric intrusion that brings an ozone-rich air mass to the
lower troposphere and even the ABL. Using a large ensemble of landfalling
typhoon cases, Chen et al. (2021) found significant positive ozone anomalies
at the middle and upper troposphere due to stratospheric intrusion when
typhoons are intensive, and negative ozone anomalies within the entire
troposphere when typhoons have made landfall. In this study, Typhoon In-fa
shows different features from the ensemble-averaged behaviors. Typhoon
In-fa made landfall in southern China approximately at 12:00 LST on 25 July
2021 with a maximum wind speed of 38 m s-1 (typhoon category) and
gradually weakened along its northward passage over land. At 08:00 LST on 29
July 2021, Typhoon In-fa entered the NCP (magenta cross symbols in Figs. 5a
and S5) with a maximum wind speed of 15 m s-1 (TD category) and
propagated slightly northeastward to the Bohai Sea (Fig. 1). The monitoring
of Typhoon In-fa's track and intensity by the Meteorology Administration of
China was terminated after 20:00 LST on 30 July 2021, given its weaker
intensity than TD category. Consequently, Typhoon In-fa maintained its
existence over land for more than 5 d (128 h). Figure 5a shows the
700 hPa vertical air motions superimposed on the 850 hPa horizontal wind
flows at 20:00 LST on 30 July 2021 based on MERRA-2 reanalysis data. Although
the intensity of Typhoon In-fa declined steadily and could not even satisfy
the TD category, Typhoon In-fa was still capable of maintaining systematic
upward air motions with counterclockwise circulations at the Bohai Sea and
inducing downward air motions over land. In the vertical direction (Fig. 5b), the downward air motions over land were deep, extending from surface to
500 hPa. The dynamical tropopause represented by the 2.5 PVU (potential
vorticity unit, 1 PVU = 10-6 K m2 s-1 kg-1; Wirth,
2003) contour line mainly located at approximately 100 hPa, and the
stratospheric dryness with relative humidity (RH) less than 30 % had reached
around 300 hPa. The next day, a significant downward placement of 2.5 PVU
dynamical tropopause and dryness occurred under the influences of Typhoon
In-fa (Fig. 5c–d). At 14:00 LST on 31 July 2021, the tropopause descended to
300 hPa and the dry air mass filled the upper troposphere above 500 hPa,
yielding great potential for stratospheric intrusions, even though Typhoon
In-fa was in its dissipation stage.
(a) Vertical velocity (shaded; 0.01 Pa s-1) at 700 hPa
overlaid with 850 hPa horizontal wind flows (gray vector; reference vector
is 12 m s-1) at 20:00 LST on 30 July 2021. The magenta crosses
represent the tracks of Typhoon In-fa during its dissipation stage, with a
time interval of 6 h. (b–d) Cross sections of vertical velocity (shaded;
unit: 0.01 Pa s-1; the positive values represent the downward air
motions and the negative values represent the upward air motions), relative
humidity (solid black lines with values of 10 % and 30 %) and the
2.5 PVU dynamical tropopause height (solid magenta lines) at 20:00 LST on 30
July (b), 08:00 LST on 31 July (c), and 14:00 LST on 31 July 2021 (d). The
time in (b)–(d) is indicated as month/day/hour at the bottom right corners.
The cross sections are performed along the dashed black line in Fig. 5a.
Vertical profile observations can reveal details of the large-scale descent
of a stratospheric air mass attributed to the dying Typhoon In-fa. Water
vapor and ozone are tracers commonly used to detect the stratospheric
air mass. Previous observations collected at mountain peaks suggest that the
frequency of stratospheric intrusions is at a minimum in summer, and
stratospheric intrusions that directly influence ozone concentrations below
700 hPa are rare (Elbern et al., 1997; Stohl et al., 2000). Here, we averaged
the moisture and ozone of the air mass below 700 hPa over the 10 d (28
July to 3 August 2021) and used the averages as the baselines to track
stratospheric intrusions induced by the dissipating Typhoon In-fa. The
operational radiosondes provide temperature (T) and dew-point (Td)
profiles, and the differences between them, dew-point depressions (=T-Td), can imply the saturation of air masses. Figure 6 shows the
vertical profiles of dew-point depressions relative to the 10 d averaged
baseline between the surface and 700 hPa using radiosonde observations
collected in Jinan. Consistent with the continuous downward penetration of
stratospheric dryness shown in Fig. 5, the dry air mass associated with large
dew-point depressions over Jinan sunk down to 900 hPa at 20:00 LST on 31 July. The dry stratospheric air further replaced the low-level moist air and
reached the ground level as seen in the profile at 08:00 LST on 1 August.
The timing of the surface ozone surge in Jinan was in agreement with variations
in atmospheric moisture profile (Fig. 2c). Radiosonde observations at
Qingdao and Weihai also confirmed the large-scale descent of dry
stratospheric air impacted by Typhoon In-fa. However, the near-surface
air mass in Qingdao and Weihai were moister than their baseline values (Figs. S6 and S7) on 31 July and 1 August, suggesting weaker impacts of
stratospheric intrusion at the surface.
Profiles of dew-point depressions (T-Td, unit: ∘C)
from Jinan radiosonde observations at (a) 20:00 LST on 29 July, (b) 20:00 LST on 30 July, (c) 08:00 LST, (d) 20:00 LST on 31 July, (e) 08:00 LST 01, and (f) 20:00 LST on 1 August 2021. These times are indicated as
month/day/hour at the bottom right corners. The 10 d averaged dew-point
depressions between the surface and 700 hPa are used as the baseline, and
positive (negative) departure from the 10 d averaged value is shown in red
(blue) color.
Behaviors of vertical ozone profiles under the influence of Typhoon In-fa
were examined using satellite ozone observations. Figure 7 shows the mean
profiles of ozone concentrations over the NCP against the baseline ozone
concentration (56 ppbv) averaged between the surface and 700 hPa based on
TROPESS AIRS L2 ozone products. Compared with the ozone profile on 29 July,
a significant increase in tropospheric ozone occurred over the following 3 d. Impacted by the stratospheric ozone-rich air mass, the positive ozone
anomalies relative to the baseline concentration extended downward to the
lower troposphere. Despite possible bias of AIRS ozone profiles, especially
at low levels, the relative variations in vertical ozone concentrations
between those days clearly reveal the large-scale downward propagation of
ozone enhancement under the influence of dissipating Typhoon In-fa. The
concurrent trends of atmospheric moisture and ozone provide a piece of clear
evidence that the stratospheric air mass had descended to the middle-to-low
troposphere (at least 900–500 hPa) during the evening of 31 July over the
NCP, which was adequate for initiating the subsequent vigorous surface ozone
surge.
Spatially averaged profiles of ozone concentrations (unit: ppbv)
over the NCP from the TROPESS AIRS L2 ozone products on (a) 29 July, (b) 30
July, (c) 31 July, and (d) 1 August 2021, all indicated as month/day at the
bottom right corners. The 10 d averaged ozone concentrations between the
surface and 700 hPa over the NCP are used as the baseline, and positive
(negative) departure from the 10 d averaged concentrations is shown in red
(blue) color.
Convection-facilitated stratospheric intrusion and transport pathways of
ozone-rich air mass
The above analyses reveal a large-scale downward intrusion of stratospheric
air to the lower troposphere under the influence of dissipating Typhoon
In-fa. However, the responses of surface ozone concentrations differed
spatially (Fig. 2), which leaves an important question: how was stratospheric
ozone-rich air transported to the surface? To be more exact, what are
the mechanisms responsible for the final descent of a stratospheric air mass
to the surface? Previous studies indicated that deep convection with
overshooting tops can effectively transport stratospheric ozone-rich air to
the surface (e.g., Poulida et al., 1996; Hu et al., 2010; Pan et al., 2014a).
Such convective redistribution of ozone in vertical profile is driven by
dynamical processes, in which vigorous upward motions penetrate into the
stratosphere and induce compensating subsidence of stratospheric ozone-rich
air. Here, the MCSs formed and passed through the NCP at night on 31 July
2021. In this section, we illustrate how the MCSs facilitated the final
descent of a stratospheric air mass to the surface.
Figure 8 shows the hourly radar mosaic observations on the night of 31 July
and 1 August 2021 during which ozone concentrations at the ground stations
exceeded 80 ppbv. At 20:00 LST on 31 July 2021 (1 h after sunset; Fig. 8a), two convective cells were located southwest and northeast of Hengshui,
and many stations still maintained high ozone concentrations accumulated
from the daytime photochemical reactions. The northeastern convective cell
developed rapidly, with increasing horizontal areal coverage, and evolved into
bow-echo MCSs, whereas the southwestern cell gradually weakened (Fig. 8b–f).
Bow echoes are the bow-shaped segment of radar reflectivity structures
within squall lines that can persist for several hours and are associated
with damaging winds near the apex of the bow, particularly when the rear
inflows descend to the surface. The rear inflows originate from the rear
anvil cloud of the stratiform region and descend toward the leading
convective line. They are driven by the diabatic cooling processes at the
middle levels, in which precipitation particles falling from the stratiform
clouds evaporate, melt, and cool the air (Keene and Schumacher, 2013; French
and Parker, 2014). The number of stations with high ozone concentrations
decreased as a result of titration effect and dry deposition; however,
significant surface ozone enhancement occurred in the convective downdraft
regions along with the development and propagation of bow-echo MCSs. For
example, the surface ozone (CO) concentrations increased (decreased)
abruptly when the bow echoes passed through Binzhou and Jinan. As the
bow-echo MCSs kept traveling southeastward, the downstream of regions of
convection such as Weifang experienced convective downdrafts and hence ozone
surge subsequently (Fig. 2). Although in regions where convective activities
were weak or absent such as Qingdao and Weihai, despite the high ozone
episode that lasted more than several hours, the surface ozone enhancement
at midnight was not coincident with CO reduction, suggesting that the
stratospheric air mass might not have reached the surface.
(a)–(f) Observed radar reflectivity structure (shaded; dBZ) of the
bow-echo MCSs at night on 31 July 2021. Stations with high ozone
concentrations are mapped by large circles in different colors.
Stations with ozone concentrations less than 80 ppbv are not displayed for
clearness.
With reference to radar radial wind observations (not shown here), the
descending rear inflows of bow echoes exceeded 25 m s-1 from the
trailing cloud region and hence brought down the stratospheric ozone-rich
air mass located at 900–500 hPa. Different than the case studies of deep
convection with overshooting tops reaching stratosphere (e.g., Pan et al.,
2014a), the bow-echo MCSs in this case were relatively weak and did not
penetrate to the tropopause altitudes. Figure S8 shows the temporal
evolution of vertical radar reflectivity profiles over Jinan and Binzhou.
Following the standard World Meteorology Organization (WMO) lapse-rate
criterion (Reichler et al., 2003), the thermal tropopause height was 15.8 km
based on the nearest sounding collected in Jinan station at 20:00 LST on 31
July 2021. The overall radar reflectivity structure over Jinan and Binzhou
did not reach the thermal tropopause height, and the strong radar
reflectivities were confined below an altitude of 6 km (480 hPa, -9∘C)
suggesting limited vertical extension of convective storms. Lightning
flashes are indicative of vertical development of a thunderstorm (e.g., Qie
et al., 2021). A total of 362 cloud-to-ground lightning flashes were
detected from 21:00 LST on 31 July to 06:00 LST on 1 August 2021 within a
50-km radius of Zhanhua station. It is inferred that the bow-echo MCSs were
weakly electrified owing to shallow extension above the freezing level. Owing
to the pre-existing stratospheric ozone-rich air mass located in the lower
troposphere under the influences of the dying typhoon (Fig. 5), the middle
level rear inflows can facilitate the downward transport of ozone to the
surface even though the convection was relatively shallow and weak. This
case provides new insights into the interactions between synoptic-scale and
mesoscale atmospheric processes that enable the direct stratospheric
intrusion to the surface.
To better depict the convective-scale transport pathways facilitating the
final descent of a stratospheric ozone-rich air mass to the surface,
high-resolution WRF simulations of the bow-echo MCSs were performed and used
to drive backward trajectories using the FLEXPART model. Figure 9 shows the
WRF-simulated radar reflectivity structure of the bow-echo MCSs. Compared
with the radar observations shown in Fig. 8, the WRF simulation reproduced the
two convective cells distributed in the southwestern and northeastern
regions of Hengshui, respectively (Fig. 9a), although the regions associated
with high radar reflectivity are larger than the observations. Despite
slightly overforecasted convection coverage, the WRF simulation does a good
job capturing the subsequent dissipation of the southwestern cell and the
evolution of the northeastern cell into bow echoes passing through Binzhou
and Jinan (Fig. 8b–f vs. Fig. 9b–f). Furthermore, the simulations were
quantitatively evaluated against observations as represented in the
categorical performance diagram, which is an evaluation technique commonly
used in convective-scale data assimilation and forecasting (Roebber, 2009).
The performance diagram merges multiple metrics, including bias, POD
(probability of detection), SR [success ratio, = 1-FAR (false alarm
rate)], and CSI (critical success index) into one graph, and simulations lie
on the upper-right corner of the diagram. As shown in Fig. S9, the POD for
30 dBZ radar reflectivity threshold exceeds 0.7, and the SR and CSI
increased steadily as the MCSs pass through Binzhou and Jinan, suggesting the
satisfactory simulations from WRF. Given the general agreement between the
simulations and observations, we use the output from this high-resolution
model to address the transport pathways of stratospheric ozone-rich air from
the upper troposphere to the surface.
(a)–(f) WRF-simulated radar reflectivity structure (shaded; dBZ) of the
bow-echo MCSs that occurred during the night of 31 July 2021. The solid lines
represent regions with high tracer particle counts released in Binzhou
between 0 and 3 km (blue lines), 3 and 6 km (magenta lines), and 6 and 10 km (purple
lines). The dashed black lines are the cross-section lines used in Fig. 11.
The red and black arrows highlight the movements of the tracer particles.
In this large-scale stratospheric intrusion event, the surface ozone
concentrations increased abruptly and vigorously at cities Jinan, Binzhou,
and Weifang (Fig. 2) when the bow-echo MCSs passed through. Although the
surface ozone enhancement was not coincident with CO reduction in Qingdao
and Weihai (Figs. 2 and 3) where convection was weaker or absent.
Through the FLEXPART simulations driven by the meteorology field from the WRF model,
two scenarios concerning ozone transport were designed and the backward
trajectories of tracer particles were analyzed. In the first scenario,
tracer particles were released in Binzhou between 1000 and 950 hPa at 04:00 LST
on 1 August, when the stratospheric air mass had reached the surface (referred
to in Figs. 2 and 4). In the second scenario, tracers were released at
Qingdao in order to examine the contribution of convection to the surface
ozone surge. Figure 10 shows the temporal variations in vertical tracer
particle counts in each of the scenarios. with reference to the
three-dimensional location of tracers in backward time. In the Binzhou
release scenario, the upper boundary of vertical distributions of tracers
was approximately 11 km on 31 July 2021, whereas the thermal tropopause height
was 15.8 km. Therefore, it can be inferred that the stratospheric ozone-rich
air mass that reached the surface was not freshly produced from wrapping and
shedding of stratospheric air by the MCSs (Pan et al., 2014a). Before
convection formed (09:00–20:00 LST here), the tracer particles concentrated
between 4 and 6 km, corresponding to the large-scale intrusion of stratospheric
air toward the middle-to-low troposphere under the influence of the dying
Typhoon In-fa. During this slow descending phase, the distribution of
tracers was typical of a filamentary structure owing to the weak large-scale
descending motions. As convection developed and evolved into bow-echo MCSs,
there were two periods with rapidly descending tracers. The former rapidly
descending phase took place at 20:00 LST at 2 km, whereas the latter occurred
at 23:00 LST at 3 km, which is analyzed in detail in the following
part. In the Qingdao release scenario, although the distribution of tracers
extended up to 10 km, quite a large portion of tracers remained below 1 km
on 31 July 2021, suggesting that surface ozone in Qingdao mainly originated
within the boundary layer and hence was faintly influenced by the
stratospheric air mass. The distinctly different distribution patterns
between the two scenarios indicate that convection has a considerable
influence on facilitating the final descent of stratospheric air to the
surface.
Temporal variations in vertical tracer particle counts released
at (a) Binzhou and (b) Qingdao. Tracer particle counts with a value of 100
(equalling 1 % of the total number of released tracers) are highlighted by
magenta lines. The black arrows highlight the two rapidly descending phases
of stratospheric air.
A key scientific aspect concerning stratospheric impacts on surface ozone is
how the stratospheric air mass reaches the surface. The backward trajectories
of tracers during the two rapidly descending phases in the Binzhou release
scenario were used here to address the convective-scale transport pathways
of stratospheric air to the surface. We separated the distributions of
tracer particles within the low (0–3 km), middle (3–6 km), and high (6–10 km)
levels, and superimposed them on the radar reflectivity evolution of the
MCSs (Fig. 9). During the first rapidly descending phase at 20:00 LST on
31 July, a low-level region with high tracer particle counts (black arrow in
Fig. 9) appeared in the northern flank of the southwestern convective cell
and propagated northeastward to Binzhou. The cross-section of southwestern
cell and tracer distributions (Fig. 11a) indicates that the low-level
tracers were transported by the widespread outflow winds between 0 and 3 km. At
20:00 LST, the stratospheric ozone-rich air mass had likely been transported
to the surface by the dissipation of the southwestern cell (referred to in the
high surface ozone concentrations in Fig. 8a–c), and the ozone-rich air mass
was transported horizontally by the downdraft outflows of the southwestern
cell toward Binzhou.
Cross sections of WRF-simulated radar reflectivity structure
(shaded; dBZ), tracer particle counts from the FLEXPART model (magenta lines,
the value of the outmost contour line is 1 and the contour interval is 2)
and wind flows (vectors) at (a) 20:00 LST and (b) 23:00 LST on 31 July, and at (c) 00:00 LST and 01:00 LST on 1 August 2021. The red circles represent
the thermal tropopause height calculated from WRF simulations. The
cross-section lines are shown in Fig. 9.
In addition to the horizontal transport of ozone at low levels by the
southwestern cell, the middle- and high-level regions with high tracer
particle counts expanded in the rear part of the northeastern convective
cell that evolved into bow echoes. During the second rapidly descending
phase, a significant rearward-sloping configuration of regions with high
tracer particle counts was noticeable from low to high levels (red arrow in
Fig. 9). We performed cross-section analyses of the bow-echo MCSs (Fig. 11b–c), and the results clearly show a rearward pathway through which the
stratospheric ozone-rich air mass was transported to the surface by the rear
inflows descending from stratiform clouds to the leading convective line.
Although the tropopause was perturbed and hence deformed by convective
dynamics, the bow-echo MCSs did not penetrate the tropopause significantly
and were not likely to bring down fresh stratospheric air from the cloud
edges. Instead, because of the pre-existing stratospheric air mass located at
3–6 km, rear inflows of the MCSs originating at the middle level could
easily facilitate the downward transport pathways for stratospheric ozone to
reach the surface. Previous studies documented the downward transport
of stratospheric ozone occurring both in the rearward anvil and in the forward
anvil (Stenchikov et al., 1996; Pan et al., 2014a), and that the transport in
the forward anvil is more rapid (Phoenix et al., 2020), although in this case,
there only existed rearward transport pathways for a stratospheric
ozone-rich air mass, probably because of the relatively weak and shallow structure
of the MCSs.
Conclusions and discussions
In this paper, we report an unusual surface ozone surge event of
stratospheric origin that occurred at night (from 23:00 LST on 31 July to 06:00 LST on 1 August 2021) over the North China Plain (NCP), where the population is
high and agricultural crops are plentiful. However, the impact of stratospheric
influence on surface ozone over the NCP is rarely documented. According to
ground-based atmospheric composition observations, satellite ozone profile
products, meteorological data, including radiosonde and radar observations
and MERRA-2 reanalysis products, we confirmed the stratospheric influences
of this unusual night=time surface enhancement and documented the evolution
and magnitude of the surface ozone surge in detail. The mechanisms
responsible for this direct stratospheric intrusion to reach the surface and
the transport pathways of ozone-rich air were investigated using
high-resolution model simulations and backward trajectory analyses. The
conclusions are drawn as follows:
Evolution and magnitude of the surface ozone surge.
The surface ozone surge mainly occurred between 23:00 LST on 31 July and
06:00 LST on 1 August 2021 over the NCP and swept southeastward with a
large spatial coverage (at least 300 km × 300 km). Instead of
decreasing continuously after sunset as normal, surface ozone increased
abruptly and significantly. Surface ozone concentrations at midnight in
the cities of Hengshui, Binzhou, Jinan, and Weifang reached 80–90 ppbv in succession
and were nearly twice as large as the baseline ozone
concentrations. Referring to the high-frequency measurements, the ozone
concentrations at Zhanhua station surged from 31 to 80 ppbv within 10 min, indicating that the stratospheric air mass can enhance
surface ozone by 40–50 ppbv within a short time period. A concurrent
vigorous decline in surface CO concentrations was observed, which suggested
that the surface ozone surge might have been caused by stratospheric intrusion of
ozone-rich and CO-poor air. This is further confirmed by the vertical
evolutions of humidity and ozone profiles during the night, based on radiosonde
and satellite data respectively. In terms of magnitude, covering areas,
abruptness, and duration, such a stratospheric impact on surface ozone is
rarely documented.
Mechanisms for the direct stratospheric intrusion to reach the surface.
The vigorous surface ozone enhancement was induced by the multi-scale
interactions between the dying Typhoon In-fa and local MCSs. Although the typhoon
was in its dissipation stage after a 5 d journey over land, it can still
perturb the tropopause and maintain the downward motions over the NCP that
brought down a dry and ozone-rich air mass, as seen in the reanalysis data as
well as moisture and ozone profiles. Before the local MCSs occurred, the
air mass with stratospheric origin had descended to the middle-to-low
troposphere (900–500 hPa) over the NCP. The local bow-echo MCSs facilitated
the final descent of a stratospheric air mass to the surface through the
development of convective downdrafts. Significant surface ozone enhancement
occurred in the convective downdraft regions during the development and
propagation of the bow-echo MCSs, whereas at stations where convective
activities were weak or absent, the surface ozone and CO evolutions during
the night were not in a high-ozone and low-CO pattern, suggesting that
stratospheric air mass did not reach the surface.
Transport pathways of ozone-rich air to the surface.
In the face of pre-existing stratospheric air mass, the rear inflows of the
bow-echo MCSs transported the ozone-rich air mass downward from the mid-level
rear stratiform cloud to the leading convective line and eventually to the
surface. Compared with the large-scale descending processes associated with
the dying typhoon, the convection-facilitated transport processes of ozone
were faster. Based on high-resolution simulations and trajectory analysis,
two convective-scale transport pathways responsible for ozone enhancement at
station sites were identified. The direct pathway was the vertical transport
of ozone through rear inflows of convection, which can effectively bring
down the ozone-rich air mass to the surface. The indirect pathway mainly
involved the horizontal transport of ozone by mature storms that had already
brought down the ozone-rich air mass.
Previous studies found the association between stratospheric intrusions and
strong convection, for example, intensive typhoons before making landfall
(e.g., Meng et al., 2022) and thunderstorms with over-shooting tops. This
study provides new insight into the interactions between synoptic-scale and
mesoscale atmospheric processes that enable a direct stratospheric
intrusion to reach the surface. The typhoon in this case was in its
dissipation stage, and the local MCSs were relatively shallow (up to 6 km)
and weak without any obvious over-shooting features. However, the dying typhoon
can still induce substantial stratospheric intrusions reaching the
middle-to-low troposphere, and the weak MCSs further facilitated the
intrusion-carried ozone to contact the surface. This kind of multi-scale
stratospheric intrusions with great ozone
enhancement can pose unexpected threats to human health and vegetation growth. Over a short timescale,
the timely warning and prediction of such ozone surges associated with
multi-scale interactions of atmospheric processes are important for
ecosystem wellbeing, which requires a deeper understanding of the mechanisms
of convective redistribution of vertical ozone profiles in the atmosphere.
In addition, the chemical consequences of vigorous ozone surges for air
quality should be further explored in order to issue appropriate management
policies. Over longer timescales, a proper analysis of the frequency and
magnitude of convection-driven (including weak convection) ozone changes is
crucial to better differentiate the natural and anthropogenic contributions
to the rapid ozone increase in the region (Lu et al., 2018; Li et al., 2019;
Han et al., 2020). As such dynamical transports of ozone associated with
convection are inexplicitly expressed in global chemistry climate models,
the stratospheric ozone input to the troposphere and the ABL is probably
underestimated (Pan et al., 2014a). In the context of global warming, the
frequency and intensity of convection are projected to increase, which
underscores the necessity of incorporating these processes into the global
models.
Data availability
The surface air pollutant observations obtained from the China National Environmental Monitoring Centre are archived at https://quotsoft.net/air (Wang, 2022) and are available from the authors upon request.
The MERRA-2 reanalysis meteorological data can be downloaded from https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2 (Gelaro et al., 2017).
Satellite-based ozone vertical profiles measured by the AIRS and the OMI under the NASA TRopospheric Ozone and Precursors from Earth System Sounding (TROPESS) project were obtained from https://tes.jpl.nasa.gov/tropess/products/o3/ (Verstraeten et al., 2013; Fu et al., 2018). The applied Weather Research and Forecasting with the Advanced Research core (WRF-ARW, Version 3.9.1) model is open-source code in the public domain maintained by the National Center for Atmospheric Research (NCAR; https://www2.mmm.ucar.edu/wrf/users/download/get_source.html; Skamarock et al., 2008). The Flexible Lagrangian particle dispersion model (FLEXPART) which uses the WRF model (FLEXPART-WRF, Version 3.3.2) was downloaded from https://www.flexpart.eu/wiki/FpLimitedareaWrf (Brioude et al., 2013). The data and model output are available for scientific investigations upon request.
The supplement related to this article is available online at: https://doi.org/10.5194/acp-22-8221-2022-supplement.
Author contributions
ZC and JL designed the study and performed the research, with contributions
from all co-authors. YS, XC, ZC, and XL collected the observations and
analyzed the data. XQ and RJ run the field campaign of the Shandong Triggering
Lightning Experiment (SHATLE), and contributed to the backward trajectory
analysis of tracers. ZC and JL wrote and revised the paper, with input from
XC and MY. All authors commented on drafts of the paper.
Competing interests
The contact author has declared that neither they nor their co-authors has any competing interests.
Disclaimer
Publisher’s note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Special issue statement
This article is part of the special issue “Atmospheric ozone and related species in the early 2020s: latest results and trends (ACP/AMT inter-journal SI)”. It is not associated with a conference.
Acknowledgements
The computing resources used in
this study were provided by Fujian Normal University High Performance
Computation Center (FNU-HPCC). Specifically, we thank Zongxiang Li for
maintaining the atmospheric composition instruments in the field campaign.
The authors would also like to thank the five anonymous reviewers for their
suggestions and comments, which improved the paper.
Financial support
This research has been supported by the National Natural Science Foundation of China (grant no. 42105079) and the Key Laboratory of Middle Atmosphere and Global Environmental Observation (grant no. LAGEO-2021-03).
Review statement
This paper was edited by Martin Dameris and reviewed by five anonymous referees.
ReferencesAkritidis, D., Pozzer, A., and Zanis, P.: On the impact of future climate change on tropopause folds and tropospheric ozone, Atmos. Chem. Phys., 19, 14387–14401, 10.5194/acp-19-14387-2019, 2019.Aliaga, D., Sinclair, V. A., Andrade, M., Artaxo, P., Carbone, S., Kadantsev, E., Laj, P., Wiedensohler, A., Krejci, R., and Bianchi, F.: Identifying source regions of air masses sampled at the tropical high-altitude site of Chacaltaya using WRF-FLEXPART and cluster analysis, Atmos. Chem. Phys., 21, 16453–16477, 10.5194/acp-21-16453-2021, 2021.Baray, J. L., Ancellet, G., Randriambelo, T., and Baldy, S.: Tropical
cyclone Marlene and stratosphere–troposphere exchange, J. Geophys.
Res., 104, 13953–13970, 10.1029/1999JD900028, 1999.Betts, A. K., Gatti, L. V., Cordova, A. M., Dias, M. A. S., and Fuentes, J. D.: Transport of ozone to the surface by convective downdrafts at night, J. Geophys. Res.-Atmos., 107, LBA 13-1–LBA 13-6, 10.1029/2000JD000158, 2002.Brioude, J., Cooper, O. R., Trainer, M., Ryerson, T. B., Holloway, J. S., Baynard, T., Peischl, J., Warneke, C., Neuman, J. A., De Gouw, J., Stohl, A., Eckhardt, S., Frost, G. J., McKeen, S. A., Hsie, E.-Y., Fehsenfeld, F. C., and Nédélec, P.: Mixing between a stratospheric intrusion and a biomass burning plume, Atmos. Chem. Phys., 7, 4229–4235, 10.5194/acp-7-4229-2007, 2007.Brioude, J., Arnold, D., Stohl, A., Cassiani, M., Morton, D., Seibert, P., Angevine, W., Evan, S., Dingwell, A., Fast, J. D., Easter, R. C., Pisso, I., Burkhart, J., and Wotawa, G.: The Lagrangian particle dispersion model FLEXPART-WRF version 3.1, Geosci. Model Dev., 6, 1889–1904, 10.5194/gmd-6-1889-2013, 2013 (data available at: https://www.flexpart.eu/wiki/FpLimitedareaWrf, last access: 20 June 2022).Chan, C. Y., Chan, L. Y., Harris, J. M., Oltmans, S. J., Blake, D. R., Qin,
Y., Zheng, Y. G., and Zheng, X. D.: Characteristic of biomass burning
emission sources, transport, and chemical speciation in enhanced springtime
tropospheric ozone profile over Hong Kong, J. Geophys. Res., 108, 4015,
10.1029/2001JD001555, 2003.Chen, F. and Dudhia J.: Coupling an advanced land surface – hydrology model
with the Penn State – NCAR MM5 modeling system, Part I: Model implementation
and sensitivity, Mon. Wea. Rev., 129, 569–585,
10.1175/1520-0493(2001)129<0569:CAALSH>2.0.CO;2, 2001.Chen, L., Zhang, Y., Lu, W., Zheng, D., Zhang, Y., Chen, S., and Huang, Z.:
Performance evaluation for a lightning location system based on observations
of artificially triggered lightning and natural lightning flashes, J. Atmos.
Ocean. Tech., 29, 1835–1844, 10.1175/JTECH-D-12-00028.1,
2012.Chen, Z., Liu, J., Cheng, X., Yang, M., and Wang, H.: Positive and negative influences of typhoons on tropospheric ozone over southern China, Atmos. Chem. Phys., 21, 16911–16923, 10.5194/acp-21-16911-2021, 2021.Cooper, O. R., Trainer, M., Thompson, A. M., Witte, J. C., Oltmans, S. J.,
Morris, G., Pickering, K. E., Crawford, J. H., Chen, G., Cohen, R. C.,
Bertram, T. H., Wooldridge, P., Perring, A., Brune, W. H., Merrill, J.,
Moody, J. L., Tarasick, D., Nédélec, P., Forbes, G., Newchurch, M.
J., Schmidlin, F. J., Johnson, B. J., Turquety, S., Baughcum, S. L., Ren,
X., Fehsenfeld, F. C., Meagher, J. F., Spichtinger, N., Brown, C. C.,
McKeen, S. A., McDermid, I. S., and Leblanc, T.: Large upper tropospheric
ozone enhancements above midlatitude North America during summer: In situ
evidence from the IONS and MOZAIC ozone measurement network, J. Geophys.
Res.-Atmos., 111, D24S05, 10.1029/2006JD007306, 2006.Davies, T. and Schuepbach, E.: Episodes of high ozone concentrations at the
earth's surface resulting from transport down from the upper
troposphere/lower stratosphere: a review and case studies, Atmos. Environ.,
28, 53–68, 1994.Del Genio, A. D., Yao, M. S., and Jonas, J.: Will moist convection be
stronger in a warmer climate?, Geophys. Res. Lett., 34, L16703,
10.1029/2007GL030525, 2007.Dickerson, R. R., Huffman, G. L., Luke, W. T., Nunnermacker, L. J.,
Pickering, K. E., Leslie, A. C., Lindsey, C. G., Slinn, W. G. N., Kelly, T.
J., Daum, P. H., Delany, A. C., Greenberg, J. P., Zimmerman, P. R., Boatman,
J. F., Ray, J. D., and Stedman, D. H.: Thunderstorms-An important mechanism
in the transport of air pollutants, Science, 235, 460–464,
10.1126/science.235.4787.460, 1987.Dreessen, J.: A sea level stratospheric ozone intrusion event induced
within a thunderstorm gust front, B. Am. Meteorol. Soc., 100,
1259–1275, 10.1175/BAMS-D-18-0113.1, 2019.Dudhia, J.: Numerical study of convection observed during the winter monsoon
experiment using a mesoscale two-dimensional model, J. Atmos. Sci., 46,
3077–3107, 10.1175/1520-0469(1989)046<3077:NSOCOD>2.0.CO;2, 1989.Elbern, H., Kowol, J., Sladkovic, R., and Ebel A.: Deep stratospheric
intrusions: A statistical assessment with model guided analyses, Atmos.
Environ., 31, 3207–3226, 10.1016/S1352-2310(97)00063-0,
1997.French, A. J. and Parker, M. D.: Numerical simulations of bow echo
formation following a squall line-supercell merger, Mon. Wea. Rev., 142,
4791–4822, 10.1175/MWR-D-13-00356.1, 2014.Fu, D., Kulawik, S. S., Miyazaki, K., Bowman, K. W., Worden, J. R., Eldering, A., Livesey, N. J., Teixeira, J., Irion, F. W., Herman, R. L., Osterman, G. B., Liu, X., Levelt, P. F., Thompson, A. M., and Luo, M.: Retrievals of tropospheric ozone profiles from the synergism of AIRS and OMI: methodology and validation, Atmos. Meas. Tech., 11, 5587–5605, 10.5194/amt-11-5587-2018, 2018 (data available at: https://tes.jpl.nasa.gov/tropess/products/o3/, last access: 20 June 2022).Gelaro, R., McCarty, W., Suarez, M. J., Todling, R., Molod, A., Takacs, L., Randles, C. A., Darmenov, A., Bosilovich, M. G., Reichle, R., Wargan, K., Coy, L., Cullather, R., Draper, C., Akella, S., Buchard, V., Conaty, A., da Silva, A. M., Gu, W., Kim, G. K., Koster, R., Lucchesi, R., Merkova, D., Nielsen, J. E., Partyka, G., Pawson, S., Putman, W., Rienecker, M., Schubert, S. D., Sienkiewicz, M., and Zhao, B.: The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2), J. Climate, 30, 5419–5454, 10.1175/jcli-d-16-0758.1, 2017 (data available at: https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2, last access: 20 June 2022).Gerken, T., Wei, D., Chase, R., Fuentes, J., Schumacher, C., Machado, L.,
Andreoli, R., Chamecki, M., Ferreira de Souza, R., Freire, L., Jardine, A.,
Manzi, A., Nascimento dos Santos, R., von Randow, C., dos Santos Costa, P.,
Stoy, P., Tóta, J., and Trowbridge, A.: Downward transport of ozone rich
air and implications for atmospheric chemistry in the Amazon rainforest,
Atmos. Environ., 124, 64–76, 10.1016/j.atmosenv.2015.11.014,
2016.Grant, D. D., Fuentes, J. D., DeLonge, M. S., Chan, S.,Joseph, E., Kucera,
P., Ndiaye, S. A., and Gaye, A. T.: Ozone transport by mesoscale convective
storms in western Senegal, Atmos. Environ., 42, 7104–7114,
10.1016/j.atmosenv.2008.05.044, 2008.Han, H., Liu, J., Shu, L., Wang, T., and Yuan, H.: Local and synoptic meteorological influences on daily variability in summertime surface ozone in eastern China, Atmos. Chem. Phys., 20, 203–222, 10.5194/acp-20-203-2020, 2020.Hartmann, D. L., Moy, L. A., and Fu, Q.: Tropical convection and the energy
balance at the top of the atmosphere, J. Climate, 14, 4495–4511,
10.1175/1520-0442(2001)014<4495:TCATEB>2.0.CO;2, 2001.Holton, J. R., Haynes, P. H., McIntyre, M. E., Douglass, A. R., Rood, R. B.,
and Pfister, L.: Stratosphere-troposphere exchange, Rev. Geophys., 33,
403–439, 10.1029/95RG02097, 1995.Hong, S., Noh, Y., and Dudhia, J.: A new vertical diffusion package with an
explicit treatment of entrainment processes, Mon. Wea. Rev., 134,
2318–2341, 10.1175/MWR3199.1, 2006.Hu, X. M., Fuentes, J. D., and Zhang, F. Q.: Downward transport and
modification of tropospheric ozone through moist convection, J. Atmos.
Chem., 65, 13–35, 10.1007/s10874-010-9179-5, 2010.Jiang, R., Qie, X., Wang, C., and Yang, J.: Propagating features of upward
positive leaders in the initial stage of rocket-triggered lightning, Atmos.
Res., 129, 90–96, 10.1016/j.atmosres.2012.09.005, 2013.Jiang, Y. C., Zhao, T. L., Liu, J., Xu, X. D., Tan, C. H., Cheng, X. H., Bi, X. Y., Gan, J. B., You, J. F., and Zhao, S. Z.: Why does surface ozone peak before a typhoon landing in southeast China?, Atmos. Chem. Phys., 15, 13331–13338, 10.5194/acp-15-13331-2015, 2015.Kain, J. and Fritsch, J.: Convective parameterization for mesoscale models:
The Kain-Fritsch scheme, in: The Representation of Cumulus Covection in
Numerical Models, 46 edn., edited by: Emanuel, K. A. and Raymond, D. J., Meteorological Monographs, American Meteorological Society, Boston, MA, 165–170, 10.1007/978-1-935704-13-3_16, 1993.Keene, K. M. and Schumacher, R. S.: The bow and arrow mesoscale convective
structure, Mon. Wea. Rev., 141, 1648–1672,
10.1175/MWR-D-12-00172.1, 2013.Knowland, E., Ott, E., Duncan, N., and Wargan, K.: Stratospheric
intrusion-influenced ozone air quality exceedances investigated in the NASA
MERRA-2 reanalysis, Geophys. Res. Lett., 44, 10691–10701,
10.1002/2017GL074532, 2017.Lelieveld, J. and Crutzen, P. J.: Role of deep cloud convection in the
ozone budget of the troposphere, Science, 264, 1759–1761,
10.1126/science.264.5166.1759, 1994.Li, D. and Bian, J. C.: Observation of a summer tropopause fold by
ozonesonde at Changchun, China: Comparison with reanalysis and model
simulation, Adv. Atmos. Sci., 32, 1354–1364,
10.1007/s00376-015-5022-x, 2015a.Li, D., Bian, J. C., and Fan, Q. J.: A deep stratospheric intrusion
associated with an intense cut-off low event over East Asia, Science China:
Earth Sciences, 58, 116–128, 10.1007/s11430-014-4977-2,
2015b.Li, D., Vogel, B., Müller, R., Bian, J., Günther, G., Ploeger, F., Li, Q., Zhang, J., Bai, Z., Vömel, H., and Riese, M.: Dehydration and low ozone in the tropopause layer over the Asian monsoon caused by tropical cyclones: Lagrangian transport calculations using ERA-Interim and ERA5 reanalysis data, Atmos. Chem. Phys., 20, 4133–4152, 10.5194/acp-20-4133-2020, 2020.Li, K., Jacob, D. J., Liao, H., Shen, L., Zhang, Q., and Bates, K. H.:
Anthropogenic drivers of 2013–2017 trends in summer surface ozone in China,
P. Natl. Acad. Sci. USA, 116, 422, 10.1073/pnas.1812168116,
2019.Li, K., Jacob, D. J., Shen, L., Lu, X., De Smedt, I., and Liao, H.: Increases in surface ozone pollution in China from 2013 to 2019: anthropogenic and meteorological influences, Atmos. Chem. Phys., 20, 11423–11433, 10.5194/acp-20-11423-2020, 2020.Lin, Y.-C., Hsu, S.-C., Lin, C.-Y., Lin, S.-H., Huang, Y.-T., Chang, Y., and Zhang, Y.-L.: Enhancements of airborne particulate arsenic over the subtropical free troposphere: impact of southern Asian biomass burning, Atmos. Chem. Phys., 18, 13865–13879, 10.5194/acp-18-13865-2018, 2018.Li, Y., Pickering, K. E., Allen, D. J., Barth, M. C., Bela, M. M., Cummings,
K. A., Carey, L. D., Mecikalski, R. M., Fierro, A. O., Campos, T. L.,
Weinheimer, A. J., Diskin, G. S., and Biggerstaff, M. I.: Evaluation of deep
convective transport in storms from different convective regimes during the
DC3 field campaign using WRF-Chem with lightning data assimilation, J.
Geophys. Res.-Atmos., 122, 7140–7163, 10.1002/2017JD026461,
2017.Lu, X., Hong, J., Zhang, L., Cooper, O. R., Schultz, M. G., Xu, X., Wang,
T., Gao, M., Zhao, Y., and Zhang, Y.: Severe surface ozone pollution in
China: A global perspective, Environ. Sci. Technol. Lett., 5, 487–494,
10.1021/acs.estlett.8b00366, 2018.Melo, A. M., Dias-Junior, C. Q., Cohen, J. C., Sá, L. D., Cattanio, J.
H., and Kuhn, P. A.: Ozone transport and thermodynamics during the passage
of squall line in Central Amazon, Atmos. Environ., 206, 132–143,
10.1016/j.atmosenv.2019.02.018, 2019.Meng, K., Zhao, T., Xu, X., Hu, Y., Zhao, Y., Zhang, L., Pang, Y., Ma, X.,
Bai, Y., Zhao, Y., and Zhen, S.: Anomalous surface O3 changes in North
China Plain during the northwestward movement of a landing typhoon, Sci.
Total Environ., 820, 153196,
10.1016/j.scitotenv.2022.153196, 2022.Meul, S., Langematz, U., Kröger, P., Oberländer-Hayn, S., and Jöckel, P.: Future changes in the stratosphere-to-troposphere ozone mass flux and the contribution from climate change and ozone recovery, Atmos. Chem. Phys., 18, 7721–7738, 10.5194/acp-18-7721-2018, 2018.Mlawer, E., Taubman, S., Brown, P., Iacono, M., and Clough, S.: Radiative
transfer for inhomogeneous atmosphere: RRTM, a validated correlated-k model
for the long-wave. J. Geophys. Res., 102, 16663–16682, 10.1029/97JD00237, 1997.Morrison, H., Thompson, G., and Tatarskii, V.: Impact of cloud microphysics
on the development of trailing stratiform precipitation in a simulated
squall line: Comparison of one- and two-moment schemes, Mon. Wea. Rev., 137,
991–1007, 10.1175/2008MWR2556.1, 2009.Nathan, B., Kremser, S., Mikaloff-Fletcher, S., Bodeker, G., Bird, L., Dale, E., Lin, D., Olivares, G., and Somervell, E.: The MAPM (Mapping Air Pollution eMissions) method for inferring particulate matter emissions maps at city scale from in situ concentration measurements: description and demonstration of capability, Atmos. Chem. Phys., 21, 14089–14108, 10.5194/acp-21-14089-2021, 2021.Pan, L. L., Homeyer, C. R., Honomochi, S., Ridley, B. A., Weisman, M., Barth, M. C., Hair, J. W., Fenn, M. A., Butler, C., Diskin, G. S., Crawford, J. H., Ryerson, T. B., Pollack, I., Peischl, J., and Huntrieser, H.: Thunderstorms enhance tropospheric ozone by wrapping and shedding stratospheric air, Geophys. Res. Lett., 41, 7785–7790, 10.1002/2014GL061921, 2014a.Pan, L. L., Paulik, L. C., Honomichl, S. B., Munchak, L. A., Bian, J.,
Selkirk, H. B., and Vömel, H.: Identification of the tropical tropopause
transition layer using the ozone-water vapour relationship, J. Geophys.
Res.-Atmos., 119, 3586–3599, 10.1002/2013JD020558, 2014b.Pan, L. L., Honomichl, S. B., Bui, T. V., Thornberry, T., Rollins, A.,
Hintsa, E., and Jensen, E. J.: Lapse rate or cold point: the tropical
tropopause identified by in situ trace gas measurements, Geophys. Res.
Lett., 45, 10756–10763, 10.1029/2018GL079573, 2018.Phoenix, D. and Homeyer, C.: Simulated impacts of tropopause-overshooting
convection on the chemical composition of the Upper troposphere and lower
stratosphere, J. Geophys. Res., 126, 21,
10.1029/2021JD034568, 2021.Phoenix, D. B., Homeyer, C. R., Barth, M. C., and Trier, S. B.: Mechanisms Responsible for Stratosphere-to-Troposphere Transport Around a Mesoscale Convective System Anvil, J. Geophys. Res.-Atmos., 125, e2019JD032016, 10.1029/2019JD032016, 2020.Pickering, J. E., Thompson, A. M., Scala, J. R., Tao, W.-K., Simpson, J.,
and Garstang, M.: Photochemical ozone production in tropical squall line
convection during NASA/GTE/ABLE 2A, J.Geophys. Res., 96, 3099–3114,
10.1029/90JD02284, 1991.Pickering, K. E., Thompson, A. M., Scala, J. R. Tao, W.-K., and Simpson, J.:
Ozone production potential following convective redistribution of biomass
burning emissions, J. Atmos. Chem., 14, 297–313,
10.1007/BF00115241, 1992.Pochanart, P., Akimoto, H., Kajii, Y., and Sukasem, P.: Carbon monoxide,
regional-scale, and biomass burning in tropical continental Southeast Asia:
Observations in rural Thailand, J. Geophys. Res.-Atmos., 108, 4552,
10.1029/2002JD003360, 2003.Poulida, O., Dickerson, R. R., and Heymsfield, A.: Stratosphere troposphere
exchange in a midlatitude mesoscale convective complex, J. Geophys. Res.,
101, 6823–6836, 10.1029/95JD03523, 1996.Preston, A., Fuelberg, H., and Barth., M.: Simulation of chemical transport
by Typhoon Mireille (1991), J. Geophys. Res.-Atmos., 124, 11614–11639,
10.1029/2019JD030446, 2019.Qie, K., Qie, X., and Tian, W.: Increasing trend of lightning activity in
the South Asia region, Sci. Bull., 66, 78–84,
10.1016/j.scib.2020.08.033, 2021.Qie, X., Zhao, Y., Zhang, Q., Yang, J., Feng, G., Kong X., Zhou, Y., Zhang,
T., Zhang, G., Zhang T., Wang, D., Cui H., Zhao Z., and Wu, S.:
Characteristics of triggered lightning during Shandong artificial triggering
lightning experiment (SHATLE), Atmos. Res., 91, 310–315,
10.1016/j.atmosres.2008.08.007, 2009.Raupach, T. H., Martius, O., Allen, J. T., Kunz, M., Trapp, S., Mohr, S.,
Rasmussen, K., Trapp, R., and Zhang, Q. H.: The effects of climate change on
hailstorms, Nat. Rev. Earth. Environ., 2, 213–226,
10.1038/s43017-020-00133-9, 2021.Reichler, T., Damerisand, M., and Sausen, R.: Determining the tropopause
height from gridded data, Geophys. Res. Lett., 30, 2042,
10.1029/2003GL018240, 2003.Roebber, P. J.: Visualizing multiple measures of forecast quality, Wea.
Forecasting, 24, 601–608, 10.1175/2008WAF2222159.1, 2009.Sahu, L. K. and Lal, S.: Changes in surface ozone levels due to convective
downdrafts over the Bay of Bengal, Geophys. Res. Lett., 33, L10807,
10.1029/2006gl025994, 2006.Schumann, U. and Huntrieser, H.: The global lightning-induced nitrogen oxides source, Atmos. Chem. Phys., 7, 3823–3907, 10.5194/acp-7-3823-2007, 2007.Skamarock, W. C., Klemp, J. B., Dudhia, J., Gill, D. O., Barker, D. M., Duda, G. M., Huang, X.-Y., Wang, W., and Powers, J. G.: A description of the advanced
research WRF version 3, NCAR, Tech. Note, NCAR/TN-475þSTR, p. 113,
10.5065/D68S4MVH, 2008 (data available at: https://www2.mmm.ucar.edu/wrf/users/download/get_source.html, last access: 20 June 2022).Stenchikov, G., Dickerson, R., Pickering, K., Ellis, W., Doddridge, B.,
Kondragunta, S., Poulida, O., Scala, L., and Tao, W. K.:
Stratosphere-troposphere exchange in a midlatitude mesoscale convective
complex: 2. Numerical simulations, J. Geophys. Res., 101, 6837–6851,
10.1029/95JD02468, 1996.Stohl, A., Spichtinger-Rakowsky, N., Bonasoni, P., Feldmann, H.,
Memmesheimer, M., Scheel, H., Trickl, T., Hübener, S., Ringer, W., and
Mandl, M.: The influence of stratospheric intrusions on alpine ozone
concentrations, Atmos. Environ., 34, 1323–1354,
10.1016/S1352-2310(99)00320-9, 2000.Stohl, A., Bonasoni, P., Cristofanelli, P., Collins, W., Feichter, J.,
Frank, A., Forster, C., Gerasopoulos, E., Gaggeler, H., James, P.,
Kentarchos, T., Kromp-Kolb, H., Kruger, B., Land, C., Meloen, J.,
Papayannis, A., Priller, A., Seibert, P., Sprenger, M., Roelofs, G. J.,
Scheell, H., E. Schnabel, C., Siegmund, P., Tobler, L., Trickl, T., Wernli,
H., Wirth, V., Zanis, P., and Zerefos, C.: Stratosphere-troposphere
exchange: A review, and what we have learned from STACCATO, J. Geophys.
Res.-Atmos., 108, 8516, 10.1029/2002JD002490, 2003.Stohl, A., Forster, C., Frank, A., Seibert, P., and Wotawa, G.: Technical note: The Lagrangian particle dispersion model FLEXPART version 6.2, Atmos. Chem. Phys., 5, 2461–2474, 10.5194/acp-5-2461-2005, 2005.Tarasick, D. W., Carey-Smith, T. K., Hocking, W. K., Moeini, O., He, H.,
Liu, J., Osman, M. K., Thompson, A. M., Johnson, B. J., Oltmans, S. J., and
Merrill, J. T.: Quantifying stratosphere-troposphere transport of ozone
using balloon-borne ozonesondes, radar windprofilers and trajectory models,
Atmos. Environ., 198, 496–509,
10.1016/j.atmosenv.2018.10.040, 2019.
Verstraeten, W. W., Boersma, K. F., Zörner, J., Allaart, M. A. F., Bowman, K. W., and Worden, J. R.: Validation of six years of TES tropospheric ozone retrievals with ozonesonde measurements: implications for spatial patterns and temporal stability in the bias, Atmos. Meas. Tech., 6, 1413–1423, 10.5194/amt-6-1413-2013, 2013 (data available at: https://tes.jpl.nasa.gov/tropess/products/o3/, last access: 20 June 2022).Wang, X. L.: Historical air quality data in China, Hourly surface concentrations of ozone and CO in China [data set], https://quotsoft.net/air, last access: 21 January 2022.Wirth, V.: Diabatic heating in an axisymmetric cut-off cyclone and related
stratosphere-troposphere exchange, Q. J. Roy. Meteor. Soc., 121, 127–147,
10.1002/qj.49712152107, 1995.Wirth, V.: Static stability in the extratropical tropopause region, J.
Atmos. Sci., 60, 1395–1409,
10.1175/1520-0469(2003)060<1395:SSITET>2.0.CO;2, 2003.Zanis, P., Trickl, T., Stohl, A., Wernli, H., Cooper, O., Zerefos, C., Gaeggeler, H., Schnabel, C., Tobler, L., Kubik, P. W., Priller, A., Scheel, H. E., Kanter, H. J., Cristofanelli, P., Forster, C., James, P., Gerasopoulos, E., Delcloo, A., Papayannis, A., and Claude, H.: Forecast, observation and modelling of a deep stratospheric intrusion event over Europe, Atmos. Chem. Phys., 3, 763–777, 10.5194/acp-3-763-2003, 2003.