A 3 d episode of anomalously low ozone
concentrations in the stratosphere over northern Europe occurred on 3–5 November 2018. A reduction of the total ozone column down to ∼ 200–210 Dobson units was predicted by the global forecasts of the System for
Integrated modeLling of Atmospheric coMposition (SILAM) driven by the
weather forecast of the Integrated Forecasting System (IFS) of the European Centre
for Medium-Range Weather Forecasts (ECMWF). The reduction down to 210–215 DU was subsequently observed by satellite instruments, such as the Ozone
Monitoring Instrument (OMI) and Ozone Mapping Profile Suite (OMPS). The
episode was caused by an intrusion of tropospheric air, which was
initially uplifted by a storm in the northern Atlantic, south-east of Greenland.
Subsequent transport towards the east and further uplift over the Scandinavian
ridge of this humid and low-ozone air brought it to ∼25 km
altitude, causing ∼30 % reduction of the ozone layer
thickness over northern Europe. The low-ozone air was further transported
eastwards and diluted over Siberia, so that the ozone concentrations were
restored a few days later. Comparison of the model predictions with OMI,
OMPS, and MLS (Microwave Limb Sounder) satellites demonstrated the high
accuracy of the 5 d forecast of the IFS–SILAM system: the ozone anomaly
was predicted within ∼10 DU accuracy and positioned within a
couple of hundreds of kilometres. This episode showed the importance of the
stratospheric composition dynamics and the possibility of its short-term
forecasting, including such rare events.
Introduction
Quick variations (hours to days) in the ozone abundance in the lower
stratosphere and the upper troposphere are primarily associated with the
stratosphere–troposphere exchange. Its main mechanism in extratropical
regions is associated with synoptic-scale processes, in particular,
extratropical cyclones (Jaeglé
et al., 2017; Stohl, 2003). Attention is usually paid to intrusions of the
stratospheric air into the troposphere along the descending dry-intrusion
air streams of the cyclonic structure (Ebel
et al., 1991; Jaeglé et al., 2017; Reutter et al., 2015; Stohl, 2001,
2003). These intrusions are estimated to be responsible for 450–500 Tg of
annual ozone import in the troposphere, which is about 10 % of the ozone
chemical production in the troposphere (Edwards and Evans,
2017; Olsen et al., 2013; Roelofs and Lelieveld, 2000). The uplift of the
tropospheric air occurs along the ascending warm conveyor belt (WCB) of the
cyclonic structure (Stohl, 2001). The
dry intrusion–WCB mechanism is responsible for 40 %–60 % of the
intrusions in the middle latitudes over the Atlantic Ocean
(Reutter et al., 2015). It has
been suggested that these intrusions are quite shallow, i.e. most of the
plumes do not penetrate significantly beyond the UTLS
(upper troposphere–lower stratosphere) interface. For the
stratosphere-to-troposphere (STT) intrusions, in particular, the fraction of
streams reaching the middle troposphere is suggested to be just 15 %
(Jaeglé et al., 2017).
In the above works, as well as in earlier studies (see references in the
reviews of Stohl, 2003, and
Jaeglé et al., 2017), a dominant proposition is that the intrusions
related to the troposphere-to-stratosphere transport (TST) do not reach high
altitudes, predominantly staying within the UTLS layer where their impact on
the ozone concentrations is comparatively small. Exceptions are the moist
deep-convective updraughts in the tropics reaching up to 50 hPa (20 km
altitude) and pollution injection up to 80–100 hPa (17–19 km) by the Asian
monsoon (Orbe et al., 2015). The deep penetration
of the tropospheric air into the stratosphere leads to the corresponding
reduction of the ozone column. However, outside of the tropical regions and the
areas affected by the Asian monsoon the TST events are practically not
considered.
The TST intrusions are generally less studied in the literature compared to
the STT ones, which have a profound impact on the surface ozone
concentrations and the tropospheric ozone budget. However,
Stohl (2003) pointed out that the effect of
deep intrusions may be significant, and
Reutter et al. (2015) estimated
that just 34 % more mass is exchanged near North Atlantic cyclones for STT
than for TST, average over all seasons for 1979–2011.
Several other mechanisms can induce significant TST fluxes in extra-tropical
regions. Powerful intrusions regularly occur along the folded tropopause at
mid-latitudes. One of the early modelling efforts on this topic dates back
to the 1990s when the tropospheric chemistry-transport model EURAD was applied
to such an event and reproduced its main features under a simple assumption of
a linear relationship between ozone concentration and potential vorticity
(Ebel et al., 1991). A more recent diagnostic study
of Pan et al. (2009) pointed out that the association of
the ozone and the thermal structures demonstrates the physical significance
of the subtropical tropopause break and the secondary tropopause. However,
the core of such intrusions is generally under 15 km.
This short note analyses an unusual event that took place at the
beginning of November 2018 and initially looked like a typical extratropical
cyclone with sea-level pressure in the centre being just under 960 hPa.
However, the WCB plume was eventually uplifted to 20–25 km and significantly
affected the stratospheric ozone layer over northern Fennoscandia (60–70∘ N)
2 d later, causing its intermittent reduction by as much as 30 %. The
episode was predicted by the SILAM model (System for Integrated modeLling of
Atmospheric coMposition) 5 d in advance and subsequently observed by the
ozone-monitoring satellites.
In the following section, we present the SILAM model and outline the
satellite information, which was used to confirm the event and to validate
the forecasts retrospectively. The Results section presents the episode's
development and evaluation of the model predictions against the satellite
data. Finally, the Discussion section includes a short overview of similar historical
events and evaluates the significance of the current episode from the
large-scale standpoint.
Forecasting model and observational dataSILAM v.5.6 model and input data
System for Integrated modeLling of Atmospheric coMposition (SILAM,
http://silam.fmi.fi, last access: 24 January 2020; Sofiev et al., 2015) is an offline
chemistry-transport model covering the troposphere and the stratosphere.
Daily operational forecasts with SILAM v.5.6 provide global and
regional predictions up to 5 d ahead for concentrations and deposition of
113 species. The model chemistry transformation scheme consists of (i) the
modified CBM4 mechanism (Gery et al., 1989) with
updated chemistry rates, (ii) the heterogeneous inorganic chemistry of
(Sofiev, 2000) expanded with marine boundary
layer nitrate formation, (iii) the volatility basis set for the secondary
organic aerosols, (iv) the polar stratospheric cloud (PSC) formation
generally following Carslaw et al. (1995) for supercooled
ternary solutions of HNO3+H2SO4 and the formulations of the
FinROSE model (Damski et al., 2007) for nitric acid
trihydrate (NAT) and ice aerosols, and (v) the gas-phase chemistry
transformations in the stratosphere of FinROSE with an extended set of
halogenated species and an updated and extended set of photolytic reactions.
Input meteorological data for the SILAM forecast are taken from the
Integrated Forecasting System (IFS) of the European Centre for Medium-Range
Weather Forecasts (ECMWF, http://www.ecmwf.int, last access:
10 December 2019). The data are used in longitude–latitude projection with horizontal
resolution of 0.2∘× 0.2∘× 3 h and
135 vertical levels reaching up to ∼4 Pa.
Emission data are compiled from several sources. The main anthropogenic
emission dataset is MACCity (Granier et al., 2011)
with shipping excluded. It is complemented with the shipping emission
inventory produced with the STEAM model (Jalkanen
et al., 2009, 2016; Sofiev et al., 2018). Biomass burning emission and its
injection profile are calculated in real time by IS4FIRES (http://is4fires.fmi.fi, last access: 10 December 2019, Sofiev
et al., 2009, 2013) for aerosols and taken from the GFAS dataset
(Kaiser et al., 2009) for gases. Biogenic emission
is taken from the MEGAN computations (Sindelarova et
al., 2014). Supplementary datasets include RETRO-aircraft (Lee et al., 2009), GEIA NOx from lightning (Price et al.,
1997) and GEIA reactive chlorine compounds (Lobert et al.,
1999), and chlorofluorocarbon (CFC) (Cunnold et
al., 1994) emissions. The emissions of sea salt, wind-blown dust, and dimethylsulfide (DMS) are
computed online by SILAM (Sofiev et al., 2011). Finally, the
compensating emission of N2O was estimated from the global mass budget
conservation requirement and is introduced as a homogeneous constant flux
from the land areas, except for Antarctica.
The SILAM forecast is run daily, 5 d ahead, with the global horizontal
resolution of 0.2∘× 0.2∘ and 29 vertical
levels reaching up to 5.25 Pa (midpoint of the last layer). The model does
not use data assimilation and the initial conditions are taken from the
previous-day forecast. Hourly averaged 3-D fields of concentrations and 2-D
fields of dry and wet deposition as well as aerosol column optical
thickness constitute the model output presented on the model website
http://silam.fmi.fi (last access: 10 December 2019) in both graphical and
numerical forms.
Satellite observations
The current study used three sets of satellite data. The total-column
observations were taken from the Ozone Monitoring Instrument (OMI; https://aura.gsfc.nasa.gov/omi.html, last access: 10 April 2019,
Levelt et al., 2006, 2018) and the Ozone
Mapping Profiler Suite (OMPS, https://www.jpss.noaa.gov/mission_and_instruments.html, last access: 10 April 2019,
Flynn et al., 2006). Both satellites observe total
ozone column over cloud-free areas and stratospheric ozone column above the
clouds. Below, we present the Level 2 OMI total ozone column data with
removed row anomaly (the OMPS observations show very similar patterns). The
vertical ozone profile evaluation was based on the retrievals of the Microwave
Limb Sounder v4.2 (MLS, https://mls.jpl.nasa.gov/, last access:
10 April 2019, Waters et al., 2006). We used
the MLS data from the HARMonized dataset of OZone profiles (HARMOZ;
Sofieva et al., 2013) developed within
the Climate Change Initiative of the European Space Agency.
For the evaluation, the following processing has been applied to the
satellite data and the SILAM results. A full space and time collocation
was applied at the hourly level; i.e. we used only those grid cells of the SILAM
forecasts for which the satellite data were available during the specific
hour. The OMI–OMPS spatial resolution is higher than that of SILAM;
therefore the informative satellite pixels that fell into the same SILAM
grid cell were averaged. Since the columns were taken over the northern Atlantic
and Scandinavia where the contribution of the lower-troposphere ozone to the
total column is low, no averaging kernel was applied to the SILAM vertical
ozone profile. For comparison with MLS–HARMOZ, the vertical profiles of
SILAM were picked at the corresponding locations and reprojected to the
HARMOZ vertical using log-interpolation in pressure coordinate.
ResultsPredicted evolution of the low-ozone area
According to the SILAM forecasts, the episode was started at the beginning
of November 2018 in the Atlantic Ocean south-east of Greenland by a strong storm
(Figs. 1a and S1–S7 in the Supplement),
which created a powerful updraught reaching up to nearly 15 km of altitude.
Already then, this intrusion started affecting the stratospheric ozone
concentrations over the south-west of Norway but the reduction was just 10–15 DU
(Fig. 2a). The air masses were subsequently
transported to the north-east and further lifted over the Scandinavian ridge,
gradually mixing with the ozone layer at 20–25 km altitude
(Figs. 1b, 2a, b).
As a result, the area with an anomalously thin ozone column (∼ 200–210 DU) was formed over central and northern Finland
(Fig. 2b). In the following days, the eastward
transport continued and the low-ozone air masses were transported towards
Russia, gradually dissolving over Siberia (Fig. 2c, d). The episode practically ended on 7 November 2018 but the ozone layer
thickness remained somewhat low over Eurasia (230–240 DU) for a few days
after (Fig. 2d and the Supplement).
In the peak of the episode, on 4 November 2018, the ozone column over
Finland was 30 %–35 % thinner than the level of 300–350 DU outside the
depletion area (Fig. 2).
(a) Mean sea level (MSL) pressure (colour shades, hPa) and wind at
∼ 1830 m a.s.l. (eighth hybrid model level, vectors, m s-1) at
12:00 UTC on 2 November 2018; (b) vertical ozone concentration profiles (µmol m-3) at latitude 62∘ N at 12:00 on 4 November 2018.
Midday (UTC time) total ozone column in DU (Dobson units) for
3–6 November 2018 as predicted by the SILAM model on 1 November 2018. Forecast lengths
were from +59 for (a) until +131 h for (d).
Evaluation of the SILAM predictions
Evaluation of the above model predictions was performed against OMI and OMPS
satellite retrievals of the ozone total column, as well as against
MLS–HARMOZ vertical ozone profiles. Due to very similar patterns shown by
both nadir satellites, below we discuss the OMI-based comparison. The focus
was on the model ability to reproduce the absolute level of the ozone column
load, as well as on accurate location of the depletion area in space and
time.
The model predictions, namely the shape and evolution of the low-ozone area
over Scandinavia, were confirmed (Fig. 3 for
4 November 2018 and Figs. S8–S13 for the whole period). The
only issue revealed by the comparison was a quite homogeneous
underestimation of the total ozone column by SILAM – within 10–20 DU over
the bulk of the domain (Fig. 3). This bias was
also stable in time and practically did not vary throughout the episode (see
the Supplement); i.e. the anomaly of the ozone column was
predicted with <10 DU error, its location was accurate within
∼100 km, and timeliness was captured with <1 d
accuracy. Accounting for this bias, the actual ozone load was about 210–215 DU at the peak of the episode (whereas SILAM suggested it down to 200 DU),
compared to ∼ 310–320 DU of a zonal-mean level between 60
and 80∘ N excluding the depletion area (the corresponding SILAM mean was about
300 DU).
Daily-composite ozone column (DU) for 4 November 2018 observed by OMI
DOAS (a) and predicted by SILAM (b). Only grid cells
corresponding to valid OMI observations were retained in the SILAM forecast.
(c) Difference of modelled minus observed ozone column (DU).
Considering the S1–S7 and the corresponding S8–S13 figures, one can
notice that the underestimation of the ozone column load was somewhat
stronger in the tropics than in the northern regions. This has been traced
to the very low lightning emission of NO2 in the input files and too
intense scavenging of tropospheric ozone precursors. These resulted in low
tropospheric ozone concentrations in the tropical regions, thus adding
∼5 DU of the underestimation of the total column. However,
these effects do not concern the current case and have been rectified in the
new SILAM v.5.7 that will be put in operation in 2020.
The vertical distribution of the ozone loss on 4 November 2018 was predicted to
span up to 25 km and beyond (Fig. 1b). A similar
effect is also seen in the MLS retrievals (Fig. 4),
which show that the highest ozone concentrations during the episode were
predicted and observed at 22–23 km instead of the usual 17–18 km. The absolute
concentrations at that altitude however changed just a bit going slightly
below 7 µmol m-3 (Fig. 4b) instead of 7.5 µmol m-3 as
the median level over the latitude belt outside the depletion area. One can
also see that the bulk of ozone reduction occurred between the 5 and 23 km altitude levels, but even above the 25 km level the concentrations were in
the lower quartile of the 60–80∘ N belt. This is well in agreement with the
SILAM forecasts (Fig. 4) and confirms an unusually
strong penetration of the tropospheric air into the stratosphere. The only
noticeable disagreement between SILAM and MLS was around 15–18 km altitude,
where SILAM predicted concentrations about half a micromole per cubic metre lower
than reported by MLS, i.e. underestimated by ∼25 %.
However, the uncertainty of this bias is 2 times larger than its absolute
value, which might be explained by MLS approaching the lower end of the
observed altitude range. The altitude of 10 km was reached by only few MLS
profiles, which nevertheless showed very good agreement.
(a) Locations of the MLS ozone profiles on 4 November 2018; the
latitude belt 59–74∘ N and the longitudinal range 20–40∘ E (low-O3 area)
are highlighted. (b) SILAM O3 vertical profiles predicted within
and outside of the low-O3 area; (c) MLS and SILAM ozone vertical
profiles and their difference in the low-O3 area; (d) same as (c) but for rest of the latitude belt excluding the low-O3 area.
SILAM boxes in (c) and (d) are shifted upwards by 0.4 km in order to
prevent overlapping pictures.
As mentioned in the methodological Sect. 2, the
SILAM global forecasts are performed without observational data
assimilation; i.e. the next forecast is started from the appropriate time
step of the previous one. At a price of certain worsening of the formal
scores, such as the model bias at some altitudes, this approach ensures
well-balanced simulations: the quality of the forecast deteriorates only
slightly over the whole predicted period (see the Supplement).
The connection to reality is ensured by the meteorological driver IFS, which
assimilates the meteorological observations at the start of each forecast.
Discussion
Looking into history of the OMI observations, the current episode was quite
extreme, although not record setting. In its depth on 4 November 2018, it
corresponded to the 0.5th percentile of the ozone distribution in November
north of 60∘ N observed by OMI over the 12-year period of operations
(2005–2017). Its strength was a result of coincidence of otherwise normal
phenomena: storm in the northern Atlantic creating the initial WCB uplift,
eastwards air mass transport over the Scandinavian ridge with additional
rise, and low solar radiation in November delaying the ozone recovery.
Only three episodes, also in November (the month with the lowest ozone load
in the northern subpolar areas), during these 12 years were stronger. The
deepest decline in the subpolar region in November was in 2009 (the observed
column load was below 180 DU) followed by 2008 with minimum observed column
just over 180 DU, also spanning a large area (Fig. S14).
An interesting month was also November of 2012 when the median level of
column load was at 300 DU instead of the usual 320 DU. No evident trend in the
median or minimum column loads in November in northern subpolar latitudes
was found over these years.
The overall impact of the considered episode on the large-scale atmospheric
processes was small due to its intermittent limited-area character. The
reduction of the ozone amount at 12:00 4 November 2018 in comparison with the
“unperturbed” level was 1.3 Tg, which is almost 30 % of the layer over
Finland but just 0.6 % of the total ozone amount in the 60–80∘ N belt (205 Tg, as predicted by SILAM). However, one has to keep in mind that during the
stormy autumn–winter months quite a few cyclones have the capacity to create
such depletion events.
From a health prospective, the low UV level in November in northern
latitudes precluded any significant impact. For the future, the projected
increase in the strength of storms can potentially make the tropospheric
intrusions more significant players than the current episode.
Climate change will probably increase the strength and frequency of such
events but quantitative assessment is difficult. Indeed, as shown above,
such episodes are started by strong storms. Numerous studies summarized in
IPCC Assessment Report AR5 and the special report “Global
Warming of 1.5∘” showed that there is a general tendency of a decreasing global number
of tropical cyclones and accumulated cyclonic energy (e.g.
Elsner et al., 2008; Knutson et al., 2010; Hoegh-Guldberg et al., 2018,
and references therein). The phenomenon has also been understood from
theoretical point of view (Kang and Elsner, 2015). According to
these findings and future-climate projections, further decrease in cyclonic
activity is likely. However, IPCC assigned low confidence to this conclusion
due to several studies reporting contradicting trends. At the same time, the
number and intensity of severe cyclones and storms has increased and will
probably increase further (also with low confidence according to IPCC)
(Knutson et al., 2013). The latter expectation is
supported by, for example, statistics of strong storms in the Atlantic (includes the
whole of the Atlantic), which shows that the number of major named storms has
grown from seven per year in the 1850s to 13 in the 2010s (http://www.stormfax.com/huryear.htm, last access: 16 August 2019). The sharp growth
started around 1990, adding almost 30 % within the last 30 years. Since the
intermittent ozone holes will be associated with strong storms, one can
expect an increase in both frequency and strength of such events in the
future.
Conclusions
An episode of a strong tropospheric intrusion into the UTLS and to the
middle stratosphere was predicted by the SILAM model and subsequently
observed by the ozone monitoring satellites at the beginning of November 2018. According to the model predictions, the intrusion resulted in a short
(∼ 3 d) but significant (30 %, from >300
down to ∼200 DU) regional reduction of the total ozone
column. The most-significant reduction occurred over northern Scandinavia,
owing to an additional enforcement of the intrusion by the lift-up over the
Scandinavian ridge.
Satellite observations of the total ozone column (OMI and OMPS) and ozone
profiles (MLS) confirmed both the temporal development (within <1 d, which corresponds to frequency of the satellite overpasses) and the
spatial location of the depletion event. Absolute level of the total ozone
column has been homogeneously underestimated by ∼20 DU, both
within and outside of the depletion area, partially due to the very low
NO2 emission of lightning and somewhat too strong scavenging of ozone
precursors in the troposphere. Prediction of the ozone column anomaly was
within ∼10 DU.
The episode corresponded to the 0.5th percentile of the OMI observations over
the period 2005–2017 for the latitude belt 60–80∘ N in November (the month
with the lowest ozone concentration in the northern subpolar stratosphere).
Despite the comparatively extreme character of the episode, its impact on
the large-scale atmospheric processes and UV index at the surface was small
due to the intermittent character of the ozone reduction and the low level of UV
radiation in northern Europe in November. However, significance of the
phenomenon can grow in the future due to an increasing number of strong storms
in the northern Atlantic.
High accuracy of the episode prediction 5 d in advance by the IFS–SILAM
system shows the possibility of prediction of details of stratospheric
composition and its short-term dynamics, including such rare events.
Code and data availability
The SILAM forecasts are openly available from http://silam.fmi.fi/aqforecast.html (Sofiev et al., 2020) as a week-long rolling archive. Due to large size
(>2 TB d-1), only a subset of the forecasts is archived over
the long term. That information is available on request from the authors of
the paper.
SILAM is an open-code system and can be obtained from the GitHub open
repository (https://github.com/fmidev/silam-model, Kouznetsov and Delgado, 2020) or from the authors of the paper.
The supplement related to this article is available online at: https://doi.org/10.5194/acp-20-1839-2020-supplement.
Author contributions
MS performed the analysis of the operational forecasts and wrote the paper;
RK configured the operational forecasts and participated in the analysis and
writing; RH developed the new chemistry transformation scheme and
participated in writing; VFS performed the satellite data analysis and
participated in writing.
Competing interests
The authors declare that they have no conflict of interest.
Acknowledgements
The SILAM stratospheric modules were developed within the Finnish Academy ASTREX
project (grant no. 139126). The work has been performed within the GLORIA
project of the Academy of Finland (grant no. 310373). Support from the ESA SUNLIT and
H2020 AirQast (grant no. 776361) projects is kindly appreciated.
Financial support
This research has been supported by the Academy of Finland (grant nos. 310373 and 139126), the European Space Agency (SUNLIT project), and the Horizon 2020 Framework Programme (AirQast (grant no. 776361)).
Review statement
This paper was edited by Michel Van Roozendael and reviewed by three anonymous referees.
ReferencesCarslaw, K. S., Luo, B., and Peter, T.: An analytic expression for the
composition of aqueous HNO3-H2SO4 stratospheric aerosols including gas phase
removal of HNO3, Geophys. Res. Lett., 22, 1877–1880, 1995.Cunnold, D. M., Fraser, P. J., Weiss, R. F., Prinn, R. G., Simmonds, P. G.,
Miller, B. R., Alyea, F. N., and Crawford, A. J.: Global trends and annual
releases of CCl3F and CCl2F2 estimated from ALE/GAGE and
other measurements from July 1978 to June 1991, J. Geophys. Res., 99,
1107, 10.1029/93JD02715, 1994.
Damski, J., Thölix, L., Backman, L., Taalas, P., and Kulmala, M.:
FinROSE: middle atmospheric chemistry transport model, Boreal Environ. Res.,
12, 535–550, 2007.Ebel, A., Hass, H., Jakobs, H., Laube, M., Memmesheimer, M., Oberreuter, A.,
Geiss, H., and Kuo, Y.-H.: Simulation of ozone intrusion caused by tropopause
fold and COL, Atmos. Environ. A-Gen., 25, 2131–2144,
10.1016/0960-1686(91)90089-P, 1991.Edwards, P. M. and Evans, M. J.: A new diagnostic for tropospheric ozone production, Atmos. Chem. Phys., 17, 13669–13680, 10.5194/acp-17-13669-2017, 2017.Elsner, J. B., Kossin, J. P., and Jagger, T. H.: The increasing intensity of
the strongest tropical cyclones, Nat. Clim. Change, 455, 2–5,
10.1038/nature07234, 2008.
Flynn, L. E., Seftor, C. J., Larsen, J. C., and Xu, P.: The Ozone Mapping and
Profiler Suite, in: Earth Science Satellite Remote Sensing: Vol. 1: Science
and Instruments, edited by: Qu, J. J., Gao, W., Kafatos, M., Murphy, R. E., and
Salomonson, V. V., 279–296, Springer Berlin Heidelberg, Berlin,
Heidelberg, 2006.
Gery, M. W., Whitten, G. Z., Killus, J. P., and Dodge, M. C.: A photochemical
kinetics mechanism for urban and regional scale computer modeling, J.
Geophys. Res., 94, 12925–12956, 1989.Granier, C., Bessagnet, B., Bond, T., D'Angiola, A., Denier van der Gon, H.,
Frost, G. J., Heil, A., Kaiser, J. W., Kinne, S., Klimont, Z., Kloster, S.,
Lamarque, J.-F., Liousse, C., Masui, T., Meleux, F., Mieville, A., Ohara,
T., Raut, J.-C., Riahi, K., Schultz, M. G., Smith, S. J., Thompson, A.,
Aardenne, J., Werf, G. R., and Vuuren, D. P.: Evolution of anthropogenic and
biomass burning emissions of air pollutants at global and regional scales
during the 1980–2010 period, Climatic Change, 109, 163–190,
10.1007/s10584-011-0154-1, 2011.Hoegh-Guldberg, O., Jacob, D., Taylor, M., Bindi, M., Brown, S., Camilloni,
I., Diedhiou, A., Djalante, R., Ebi, K. L., Engelbrecht, F., Guiot, J.,
Hijioka, Y., Mehrotra, S., Payne, A., Seneviratne, S. I., Thomas, A.,
Warren, R., and Zhou, G.: Impacts of 1.5 ∘C Global Warming on Natural and
Human Systems, in: Global Warming of 1.5 ∘C, IPCC Special
Report on the impacts of global warming of 1.5 ∘C above
pre-industrial levels and related global greenhouse gas emission pathways,
in the context of strengthening the global response to the threat of climate
change, sustainable development, p. 138, IPCC, Switzerland, 2018.Jaeglé, L., Wood, R., and Wargan, K.: Multiyear Composite View of Ozone
Enhancements and Stratosphere-to-Troposphere Transport in Dry Intrusions of
Northern Hemisphere Extratropical Cyclones, J. Geophys. Res.-Atmos.,
122, 13436–13457, 10.1002/2017JD027656, 2017.Jalkanen, J.-P., Brink, A., Kalli, J., Pettersson, H., Kukkonen, J., and Stipa, T.: A modelling system for the exhaust emissions of marine traffic and its application in the Baltic Sea area, Atmos. Chem. Phys., 9, 9209–9223, 10.5194/acp-9-9209-2009, 2009.Jalkanen, J.-P., Johansson, L., and Kukkonen, J.: A comprehensive inventory of ship traffic exhaust emissions in the European sea areas in 2011, Atmos. Chem. Phys., 16, 71–84, 10.5194/acp-16-71-2016, 2016.Kaiser, J. W., Suttie, M., Flemming, J., Morcrette, J.-J., Boucher, O.,
Schultz, M. G., Nakajima, T., and Yamasoe, M. A.: Global Real-time Fire
Emission Estimates Based on Space-borne Fire Radiative Power Observations,
AIP Conf. Proc., 1100, 645–648, 10.1063/1.3117069, 2009.Kang, N. and Elsner, J. B.: Trade-o between intensity and frequency of
global tropical cyclones, Nat. Clim. Change, 5, 661–664,
10.1038/NCLIMATE2646, 2015.Knutson, T. R., McBride, J. L., Chan, J., Emanuel, K., Holland, G., Landsea,
C., Held, I., Kossin, J. P., Srivastava, A. K., and Sugi, M.: Tropical
cyclones and climate change, Nat. Geosci., 3, 157–163, 10.1038/ngeo779, 2010.Knutson, T. R., Sirutis, J. J., Vecchi, G. A., Garner, S., Zhao, M., Kim,
H.-S., Bender, M., Tuleya, R. E., Held, I. M., and Villarini, G.: Dynamical
Downscaling Projections of Twenty-First-Century Atlantic Hurricane
Activity?: CMIP3 and CMIP5 Model-Based Scenarios, J. Climate, 26, 6591–6617,
10.1175/JCLI-D-12-00539.1, 2013.Kouznetsov, R. and Delgado, R.: SILAM open code at GitHub, available at: https://github.com/fmidev/silam-model, last access: 10 February 2020.Lee, D. S., Pitari, G., Grewe, V., Gierens, K., Penner, J. E., Pet-zold, A., Prather, M. J., Schumann, U., Bais, A., Berntsen, T., Iachetti, D., Lim, L. L., and Sausen, R.: Transport impacts onatmosphere and climate: aviation, Atmos. Environ., 44, 4678–4734, 10.1016/j.atmosenv.2009.06.005, 2009Levelt, P. F., van den Oord, G. H. J., Dobver, M. R., Mälkki, A.,
Visser, H., de Vries, J., Stammes, P., Lundell, J. O. V., and Saari, H.: The
ozone monitoring instrument, IEEE T. Geosci. Remote Sens., 44,
1093–1101, 10.1109/TGRS.2006.872333, 2006.Levelt, P. F., Joiner, J., Tamminen, J., Veefkind, J. P., Bhartia, P. K., Stein Zweers, D. C., Duncan, B. N., Streets, D. G., Eskes, H., van der A, R., McLinden, C., Fioletov, V., Carn, S., de Laat, J., DeLand, M., Marchenko, S., McPeters, R., Ziemke, J., Fu, D., Liu, X., Pickering, K., Apituley, A., González Abad, G., Arola, A., Boersma, F., Chan Miller, C., Chance, K., de Graaf, M., Hakkarainen, J., Hassinen, S., Ialongo, I., Kleipool, Q., Krotkov, N., Li, C., Lamsal, L., Newman, P., Nowlan, C., Suleiman, R., Tilstra, L. G., Torres, O., Wang, H., and Wargan, K.: The Ozone Monitoring Instrument: overview of 14 years in space, Atmos. Chem. Phys., 18, 5699–5745, 10.5194/acp-18-5699-2018, 2018.
Lobert, J. M., Keene, W. C., Logan, J. A., and Yevich, R.: Global chlorine
emissions from biomass burning?: Reactive Chlorine Emissions Inventory, J.
Geophys. Res., 104, 8373–8389, 1999.Olsen, M. A., Douglass, A. R., and Kaplan, T. B.: Variability of
extratropical ozone stratosphere–troposphere exchange using microwave limb
sounder observations, J. Geophys. Res.-Atmos., 118, 1090–1099,
10.1029/2012JD018465, 2013.Orbe, C., Waugh, D. W., and Newman, P. A.: Air-mass origin in the tropical
lower stratosphere: The influence of Asian boundary layer air, Geophys. Res.
Lett., 42, 4240–4248, 10.1002/2015GL063937, 2015.Pan, L. L., Randel, W. J., Gille, J. C., Hall, W. D., Nardi, B., Massie, S.,
Yudin, V., Khosravi, R., Konopka, P., and Tarasick, D.: Tropospheric
intrusions associated with the secondary tropopause, J. Geophys. Res.,
114, D10302, 10.1029/2008JD011374, 2009.Price, C., Penner, J., and Prather, M.: NOx from lightning: 1. Global
distribution based on lightning physics, J. Geophys. Res., 102, 5929,
10.1029/96JD03504, 1997.Reutter, P., Škerlak, B., Sprenger, M., and Wernli, H.: Stratosphere–troposphere exchange (STE) in the vicinity of North Atlantic cyclones, Atmos. Chem. Phys., 15, 10939–10953, 10.5194/acp-15-10939-2015, 2015.Roelofs, G. and Lelieveld, J.: Tropospheric ozone simulation with a
chemistry-general circulation model?: Influence of higher hydrocarbon
chemistry, J. Geophys. Res.-Atmos., 105, 22697–22712,
10.1029/2000JD900316, 2000.Sindelarova, K., Granier, C., Bouarar, I., Guenther, A., Tilmes, S., Stavrakou, T., Müller, J.-F., Kuhn, U., Stefani, P., and Knorr, W.: Global data set of biogenic VOC emissions calculated by the MEGAN model over the last 30 years, Atmos. Chem. Phys., 14, 9317–9341, 10.5194/acp-14-9317-2014, 2014.
Sofiev, M.: A model for the evaluation of long-term airborne pollution
transport at regional and continental scales, Atmos. Environ., 34,
2481–2493, 2000.Sofiev, M., Vankevich, R., Lotjonen, M., Prank, M., Petukhov, V., Ermakova, T., Koskinen, J., and Kukkonen, J.: An operational system for the assimilation of the satellite information on wild-land fires for the needs of air quality modelling and forecasting, Atmos. Chem. Phys., 9, 6833–6847, 10.5194/acp-9-6833-2009, 2009.Sofiev, M., Soares, J., Prank, M., Leeuw, G., and Kukkonen, J.: A
regional-to-global model of emission and transport of sea salt particles in
the atmosphere, J. Geophys. Res., 116, D21302, 10.1029/2010JD014713,
2011.Sofiev, M., Vankevich, R., Ermakova, T., and Hakkarainen, J.: Global mapping of maximum emission heights and resulting vertical profiles of wildfire emissions, Atmos. Chem. Phys., 13, 7039–7052, 10.5194/acp-13-7039-2013, 2013.Sofiev, M., Vira, J., Kouznetsov, R., Prank, M., Soares, J., and Genikhovich, E.: Construction of the SILAM Eulerian atmospheric dispersion model based on the advection algorithm of Michael Galperin, Geosci. Model Dev., 8, 3497–3522, 10.5194/gmd-8-3497-2015, 2015.Sofiev, M., Winebrake, J. J., Johansson, L., Carr, E. W., Prank, M., Soares,
J., Vira, J., Kouznetsov, R., Jalkanen, J.-P., and Corbett, J. J.: Cleaner
fuels for ships provide public health benefits with climate tradeoffs, Nat.
Commun., 9, 406, 10.1038/s41467-017-02774-9, 2018.Sofiev, M., Kouznetsov, R., Vira, J., Hanninen, R., Uppstu, A., and Braznov, T.: SILAM Web site, available at: http://silam.fmi.fi/aqforecast.html, last access: 13 February 2020.
Sofieva, V. F., Rahpoe, N., Tamminen, J., Kyrölä, E., Kalakoski, N., Weber, M., Rozanov, A., von Savigny, C., Laeng, A., von Clarmann, T., Stiller, G., Lossow, S., Degenstein, D., Bourassa, A., Adams, C., Roth, C., Lloyd, N., Bernath, P., Hargreaves, R. J., Urban, J., Murtagh, D., Hauchecorne, A., Dalaudier, F., van Roozendael, M., Kalb, N., and Zehner, C.: Harmonized dataset of ozone profiles from satellite limb and occultation measurements, Earth Syst. Sci. Data, 5, 349–363, 10.5194/essd-5-349-2013, 2013.Stohl, A.: A 1-year Lagrangian “climatology” of airstreams in the Northern
Hemisphere troposphere and lowermost stratosphere, J. Geophys. Res.-Atmos.,
106, 7263–7279, 10.1029/2000JD900570, 2001.Stohl, A.: Stratosphere-troposphere exchange: A review, and what we have
learned from STACCATO, J. Geophys. Res., 108, 8516, 10.1029/2002jd002490,
2003.Waters, J. W., Froidevaux, L., Harwood, R. S., Jarnot, R. F., Pickett, H.
M., Read, W. G., Siegel, P. H., Cofield, R. E., Filipiak, M. J., Flower, D.
A., Holden, J. R., Lau, G. K. K., Livesey, N. J., Manney, G. L., Pumphrey,
H. C., Santee, M. L., Wu, D. L., Cuddy, D. T., Lay, R. R., Loo, M. S.,
Perun, V. S., Schwartz, M. J., Stek, P. C., Thurstans, R. P., Boyles, M. A.,
Chandra, K. M., Chavez, M. C., Chen, G. S., Chudasama, B. V, Dodge, R.,
Fuller, R. A., Girard, M. A., Jiang, J. H., Jiang, Y. B., Knosp, B. W.,
LaBelle, R. C., Lam, J. C., Lee, K. A., Miller, D., Oswald, J. E., Patel, N.
C., Pukala, D. M., Quintero, O., Scaff, D. M., Van Snyder, W., Tope, M. C.,
Wagner, P. A., and Walch, M. J.: The Earth Observing System Microwave Limb
Sounder (EOS MLS) on the Aura satellite, IEEE T. Geosci. Remote Sens.,
44, 1075–1092, 10.1109/TGRS.2006.873771, 2006.