Articles | Volume 21, issue 20
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Technical note: Uncertainties in eddy covariance CO2 fluxes in a semiarid sagebrush ecosystem caused by gap-filling approaches
Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, China
Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA
School of Atmospheric Sciences, Sun Yat-sen University, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China
Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA
Department of Atmospheric and Oceanic Sciences & Institute of Atmospheric Sciences, Fudan University, Shanghai, China
No articles found.
Honglin Pan, Jianping Huang, Jiming Li, Zhongwei Huang, Tian Zhou, and Kanike Raghavendra Kumar
Earth Syst. Sci. Data Discuss.,
Preprint under review for ESSDShort summary
We applied several correction procedures and rigorously checked for data quality constraints during the long observation period spanning almost 14 years (2007–2020). Nevertheless, some uncertainties remain mainly due to technical constraints, as well as limited documentation of the measurements. Even though not completely accurate, this strategy is expected to at least reduce the inaccuracy of the computed characteristic value of aerosol optical parameters.
Shikuan Jin, Yingying Ma, Zhongwei Huang, Jianping Huang, Wei Gong, Boming Liu, Weiyan Wang, Ruonan Fan, and Hui Li
Atmos. Chem. Phys., 23, 8187–8210,Short summary
To better understand the Asian aerosol environment, we studied distributions and trends of aerosol with different sizes and types. Over the past 2 decades, dust, sulfate, and sea salt aerosol decreased by 5.51 %, 3.07 %, and 9.80 %, whereas organic carbon and black carbon aerosol increased by 17.09 % and 6.23 %, respectively. The increase in carbonaceous aerosols was a feature of Asia. An exception is found in East Asia, where the carbonaceous aerosols reduced, owing largely to China's efforts.
Yuxin Zhao, Jiming Li, Lijie Zhang, Cong Deng, Yarong Li, Bida Jian, and Jianping Huang
Atmos. Chem. Phys., 23, 743–769,Short summary
Diurnal variations of clouds play an important role in the radiative budget and precipitation. Based on satellite observations, reanalysis, and CMIP6 outputs, the diurnal variations in total cloud cover and cloud vertical distribution over the Tibetan Plateau are explored. The diurnal cycle of cirrus is a key focus and found to have different characteristics from those found in the tropics. The relationship between the diurnal cycle of cirrus and meteorological factors is also discussed.
Bida Jian, Jiming Li, Guoyin Wang, Yuxin Zhao, Yarong Li, Jing Wang, Min Zhang, and Jianping Huang
Atmos. Chem. Phys., 21, 9809–9828,Short summary
We evaluate the performance of the AMIP6 model in simulating cloud albedo over marine subtropical regions and the impacts of different aerosol types and meteorological factors on the cloud albedo based on multiple satellite datasets and reanalysis data. The results show that AMIP6 demonstrates moderate improvement over AMIP5 in simulating the monthly variation in cloud albedo, and changes in different aerosol types and meteorological factors can explain ~65 % of the changes in the cloud albedo.
Xiaoyu Hu, Jinming Ge, Jiajing Du, Qinghao Li, Jianping Huang, and Qiang Fu
Atmos. Meas. Tech., 14, 1743–1759,Short summary
Cloud radars are powerful instruments that can probe detailed cloud structures. However, radar echoes in the lower atmosphere are always contaminated by clutter. We proposed a multi-dimensional probability distribution function that can effectively discriminate low-level clouds from clutter by considering their different features in several variables. We applied this method to the radar observations at the SACOL site and found the results have good agreement with lidar detection.
Zhiyuan Hu, Jianping Huang, Chun Zhao, Qinjian Jin, Yuanyuan Ma, and Ben Yang
Atmos. Chem. Phys., 20, 1507–1529,Short summary
This study investigates intercontinental transport of dust plums and distribution characteristics of dust at different altitudes over the Tibetan Plateau (TP). The results show that dust particles are emitted into atmosphere and then transport to the TP. The East Asian dust trasnports southward and is lifted up to the TP in northern slop, while the North Afican dust and Middle East dust transport eastward and concentrate in both northern and southern slops, then is lifted up to the TP.
Zhiyuan Hu, Jianping Huang, Chun Zhao, Yuanyuan Ma, Qinjian Jin, Yun Qian, L. Ruby Leung, Jianrong Bi, and Jianmin Ma
Atmos. Chem. Phys., 19, 12709–12730,Short summary
This study investigates aerosol chemical compositions and relative contributions to total aerosols in the western US. The results show that trans-Pacific aerosols have a maximum concentration in the boreal spring, with the greatest contribution from dust. Over western North America, the trans-Pacific aerosols dominate the column-integrated aerosol mass and number concentration. However, near the surface, aerosols mainly originated from local emissions.
Xiaoyue Liu, Jianping Huang, Jiping Huang, Changyu Li, and Lei Ding
Earth Syst. Sci. Data Discuss.,
Revised manuscript not acceptedShort summary
Atmospheric oxygen is crucial to life on earth. In this paper, we quantify oxygen consumption and production processes under the impact of human activities to build a dynamic global oxygen budget on a grid scale. Our result shows that the oxygen consumption related to human activities has risen significantly in recent decades while the oxygen production only displays a faint increase. Regionally, boreal forest and Tibetan plateau become the most important sources of atmospheric oxygen.
Kai Tang, Zhongwei Huang, Jianping Huang, Teruya Maki, Shuang Zhang, Atsushi Shimizu, Xiaojun Ma, Jinsen Shi, Jianrong Bi, Tian Zhou, Guoyin Wang, and Lei Zhang
Atmos. Chem. Phys., 18, 7131–7148,Short summary
To our knowledge, this is the first simultaneous field measurement of bioaerosols in dust events at four sites along the transport pathway of Asian dust. The samples were analyzed by means of fluorescence microscopy, scanning electron microscopy, and MiSeq sequencing analysis. The results indicate that dust clouds can carry many bacteria of various types into downwind regions, the alpha and beta diversity of which were investigated.
Zhijuan Zhang, Bin Chen, Jianping Huang, Jingjing Liu, Jianrong Bi, Tian Zhou, and Zhongwei Huang
Atmos. Chem. Phys. Discuss.,
Revised manuscript not acceptedShort summary
Environmental problems caused by aerosols such as dust aerosols are influencing people's lives and work. Due to different radiative effects of different types of aerosols, detection of the aerosol type is vital for improving our air quality. In this study, the optical properties of pure dust and transported anthropogenic dust are compared by using ground-based Lidar data. Based on our conclusion, detection of different dust aerosols will be more accurate using satellite-based Lidar.
Siyu Chen, Jianping Huang, Nanxuan Jiang, Zhou Zang, Xiaodan Guan, Xiaojun Ma, Zhuo Jia, Xiaorui Zhang, Yanting Zhang, Kangning Huang, Xiaocong Xu, Guolong Zhang, Jiming Li, Ran Yang, and Shujie Liao
Atmos. Chem. Phys. Discuss.,
Revised manuscript not accepted
Jinming Ge, Zeen Zhu, Chuang Zheng, Hailing Xie, Tian Zhou, Jianping Huang, and Qiang Fu
Atmos. Chem. Phys., 17, 9035–9047,Short summary
A modified method with a new noise reduction scheme that can reduce the noise distribution to a narrow range is proposed to distinguish clouds and other hydrometeors from noise and recognize more features with weak signal in cloud radar observations. It was found that our method has significant advantages in reducing the rates of both failed negative and false positive hydrometeor identifications in simulated clouds and recognizing clouds with weak signal from our cloud radar observations.
Jianrong Bi, Jianping Huang, Jinsen Shi, Zhiyuan Hu, Tian Zhou, Guolong Zhang, Zhongwei Huang, Xin Wang, and Hongchun Jin
Atmos. Chem. Phys., 17, 7775–7792,Short summary
We conducted a field campaign on exploring dust aerosol in Dunhuang farmland nearby Gobi deserts. The anthropogenic dust produced by agricultural cultivations exerted a significant superimposed effect on elevated dust loadings. Strong south wind in daytime scavenged the pollution and weak northeast wind at night favorably accumulated air pollutants near the surface. The local emissions remarkably modified the absorptive and optical characteristics of mineral dust in desert source region.
Ling Qi, Qinbin Li, Cenlin He, Xin Wang, and Jianping Huang
Atmos. Chem. Phys., 17, 7459–7479,Short summary
Black carbon (BC) is the second only to CO2 in heating the planet, but the simulation of BC is associated with large uncertainties. BC burden is largely underestimated over land and overestimated over ocean. Our study finds that a missing process in current Wegener–Bergeron–Findeisen models largely explains the discrepancy in BC simulation over land. We call for more observations of BC in mixed-phase clouds to understand this process and improve the simulation of global BC.
Siyu Chen, Jianping Huang, Litai Kang, Hao Wang, Xiaojun Ma, Yongli He, Tiangang Yuan, Ben Yang, Zhongwei Huang, and Guolong Zhang
Atmos. Chem. Phys., 17, 2401–2421,Short summary
Compared with the TD dust, the importance of the GD dust in eastern China, Japan, and Korea is always neglected. We focused primarily on the dynamic and thermodynamics mechanisms of dust emission and transport over TD and GD and further elucidate the influence of TD and GD dust on the entire East Asia based on a case study using WRF-Chem model in the study.
Jianrong Bi, Jianping Huang, Brent Holben, and Guolong Zhang
Atmos. Chem. Phys., 16, 15501–15516,Short summary
Dating absorptive capacity of Asian dust is still an outstanding issue. In this study, we identify two types of Asian dust: Pure Dust (PDU) and Transported Anthropogenic Dust (TDU). Overall average SSA, ASY, Re, and Ri at 550 nm for PDU are 0.935, 0.742, 1.526, and 0.00226, respectively, with 0.921, 0.723, 1.521, and 0.00364 for TDU. Our results promise to update and improve accuracy of Asian dust characteristics in present-day remote sensing applications and regional climate models.
Jin Ming Ge, Huayue Liu, Jianping Huang, and Qiang Fu
Atmos. Chem. Phys., 16, 7773–7783,Short summary
Nocturnal low-level jet (NLLJ), which refers to a narrow zone of strong winds, occurs frequently over the Taklimakan Desert. It is found that the NLLJ contains more momentum than without NLLJ, and the downward momentum transfer process is more intense and rapid in the warm season. The coincidence of the larger surface winds during NLLJ days with an enhancement of aerosol optical depth indicates that the NLLJ is an important mechanism for dust emission and transport over this region.
Zhiyuan Hu, Chun Zhao, Jianping Huang, L. Ruby Leung, Yun Qian, Hongbin Yu, Lei Huang, and Olga V. Kalashnikova
Geosci. Model Dev., 9, 1725–1746,Short summary
This study conducts the simulation of WRF-Chem with the quasi-global configuration for 2010–2014, and evaluates the simulation with multiple observation datasets for the first time. This study demonstrates that the WRF-Chem quasi-global simulation can be used for investigating trans-Pacific transport of aerosols and providing reasonable inflow chemical boundaries for the western USA to further understand the impact of transported pollutants on the regional air quality and climate.
Xiaodan Guan, Jianping Huang, Yanting Zhang, Yongkun Xie, and Jingjing Liu
Atmos. Chem. Phys., 16, 5159–5169,Short summary
An obvious peak in the total anthropogenic dust column, with much higher magnitude than those of wet regions, was observed in semi-arid regions. The anthropogenic dust column burden of semi-arid takes a positively correlated with the population and population change, indicating the production of anthropogenic dust in semi-arid regions is partly induced by human activities.
X. Guan, J. Huang, R. Guo, H. Yu, P. Lin, and Y. Zhang
Atmos. Chem. Phys., 15, 13777–13786,Short summary
Dynamical adjustment methodology has been applied to the raw surface air temperature and has successfully identified and separated the contribution of dynamically induced temperature (DIT) and radiatively forced temperature (RFT). It found that regional anthropogenic radiative forcing caused the enhanced warming in the semi-arid region, which may be closely associated with local human activities.
Y. Liu, Y. Sato, R. Jia, Y. Xie, J. Huang, and T. Nakajima
Atmos. Chem. Phys., 15, 12581–12594,Short summary
We firstly evaluated the Spectral Radiation-Transport Model for Aerosol Species combined with a non-hydrostatic regional model through comparing the simulation results and satellite observations, both in horizontal and vertical. The dust and anthropogenic aerosols in summer over the Tibetan Plateau are evaluated, and their distributions over the TP are presented. The transport of these aerosols over the Tibetan Plateau is also explored via combining the simulation results and reanalysis data.
J. P. Huang, J. J. Liu, B. Chen, and S. L. Nasiri
Atmos. Chem. Phys., 15, 11653–11665,Short summary
To understand the contribution of anthropogenic dust to the total global dust load, a new technique for distinguishing anthropogenic dust from natural dust is proposed by using CALIPSO dust measurements and PBL height retrievals along with a land use data set. Results reveal that local anthropogenic dust aerosol accounts for about 25% of the global continental dust load.
Q. Jin, J. Wei, Z.-L. Yang, B. Pu, and J. Huang
Atmos. Chem. Phys., 15, 9897–9915,Short summary
Satellite data show that Indian summer monsoon (ISM) rainfall is closely associated with Middle East dust aerosols. Numerical modeling shows that the increased ISM rainfall is related to the enhanced southwesterly flow and moisture transport from the Arabian Sea to the Indian subcontinent, associated with the development of an anomalous low-pressure system over the Iranian Plateau and the Arabian Sea due to dust-induced atmospheric heating.
R. Zhang, H. Wang, Y. Qian, P. J. Rasch, R. C. Easter, P.-L. Ma, B. Singh, J. Huang, and Q. Fu
Atmos. Chem. Phys., 15, 6205–6223,Short summary
We use the CAM5 model with a novel source-tagging technique to characterize the fate of BC particles emitted from various geographical regions and sectors and their transport pathways to the Himalayas and Tibetan Plateau (HTP). We show a comprehensive picture of the seasonal and regional dependence of BC source attributions, and find strong seasonal and spatial variations in BC-in-snow radiative forcing in the HTP that can be quantitatively attributed to the various regional/sectoral sources.
J. Li, J. Huang, K. Stamnes, T. Wang, Q. Lv, and H. Jin
Atmos. Chem. Phys., 15, 519–536,
C. Zhao, Z. Hu, Y. Qian, L. Ruby Leung, J. Huang, M. Huang, J. Jin, M. G. Flanner, R. Zhang, H. Wang, H. Yan, Z. Lu, and D. G. Streets
Atmos. Chem. Phys., 14, 11475–11491,
Hongru Yan, Zhanqing Li, Jianping Huang, Maureen Cribb, and Jianjun Liu
Atmos. Chem. Phys., 14, 7113–7124,
C. Zhao, S. Chen, L. R. Leung, Y. Qian, J. F. Kok, R. A. Zaveri, and J. Huang
Atmos. Chem. Phys., 13, 10733–10753,
R. Zhang, D. A. Hegg, J. Huang, and Q. Fu
Atmos. Chem. Phys., 13, 6091–6099,
Related subject area
Subject: Biosphere Interactions | Research Activity: Field Measurements | Altitude Range: Troposphere | Science Focus: Physics (physical properties and processes)Dynamics of aerosol, humidity, and clouds in air masses travelling over Fennoscandian boreal forestsResidence times of air in a mature forest: observational evidence from a free-air CO2 enrichment experimentEnergy and mass exchange at an urban site in mountainous terrain – the Alpine city of InnsbruckObservations of aerosol–vapor pressure deficit–evaporative fraction coupling over IndiaBiogeochemical and biophysical responses to episodes of wildfire smoke from natural ecosystems in southwestern British Columbia, CanadaTraces of urban forest in temperature and CO2 signals in monsoon East AsiaSimulating the spatiotemporal variations in aboveground biomass in Inner Mongolian grasslands under environmental changesConcentrations and biosphere–atmosphere fluxes of inorganic trace gases and associated ionic aerosol counterparts over the Amazon rainforestCharacterization of the radiative impact of aerosols on CO2 and energy fluxes in the Amazon deforestation arch using artificial neural networksNew particle formation events observed at the King Sejong Station, Antarctic Peninsula – Part 2: Link with the oceanic biological activitiesVertical observations of the atmospheric boundary layer structure over Beijing urban area during air pollution episodesCharacterisation of short-term extreme methane fluxes related to non-turbulent mixing above an Arctic permafrost ecosystemCharacterization of ozone deposition to a mixed oak–hornbeam forest – flux measurements at five levels above and inside the canopy and their interactions with nitric oxideDirect effect of aerosols on solar radiation and gross primary production in boreal and hemiboreal forestsThe monsoon effect on energy and carbon exchange processes over a highland lake in the southwest of ChinaTurbulent transport of energy across a forest and a semiarid shrublandStudy of the daily and seasonal atmospheric CH4 mixing ratio variability in a rural Spanish region using 222Rn tracerNighttime wind and scalar variability within and above an Amazonian canopyEstimating regional-scale methane flux and budgets using CARVE aircraft measurements over AlaskaCanopy uptake dominates nighttime carbonyl sulfide fluxes in a boreal forestNet ecosystem exchange and energy fluxes measured with the eddy covariance technique in a western Siberian bogBiophysical effects on the interannual variation in carbon dioxide exchange of an alpine meadow on the Tibetan PlateauQuantifying the contribution of land use change to surface temperature in the lower reaches of the Yangtze RiverOverview of mercury dry deposition, litterfall, and throughfall studiesScalar turbulent behavior in the roughness sublayer of an Amazonian forestSurface–atmosphere exchange of ammonia over peatland using QCL-based eddy-covariance measurements and inferential modelingCharacterization of total ecosystem-scale biogenic VOC exchange at a Mediterranean oak–hornbeam forestAre BVOC exchanges in agricultural ecosystems overestimated? Insights from fluxes measured in a maize field over a whole growing seasonStep changes in persistent organic pollutants over the Arctic and their implicationsEstimating surface fluxes using eddy covariance and numerical ogive optimizationNitrous oxide emissions from a commercial cornfield (Zea mays) measured using the eddy covariance techniqueObservations of the scale-dependent turbulence and evaluation of the flux–gradient relationship for sensible heat for a closed Douglas-fir canopy in very weak wind conditionsThe effect of atmospheric aerosol particles and clouds on net ecosystem exchange in the AmazonAcetaldehyde exchange above a managed temperate mountain grasslandSurface response to rain events throughout the West African monsoonThe role of vegetation in the CO2 flux from a tropical urban neighbourhoodAir-surface exchange measurements of gaseous elemental mercury over naturally enriched and background terrestrial landscapes in AustraliaFour-year (2006–2009) eddy covariance measurements of CO2 flux over an urban area in BeijingMomentum and scalar transport within a vegetation canopy following atmospheric stability and seasonal canopy changes: the CHATS experimentCoupling processes and exchange of energy and reactive and non-reactive trace gases at a forest site – results of the EGER experimentAbiotic and biotic control of methanol exchanges in a temperate mixed forestAnalysis of coherent structures and atmosphere-canopy coupling strength during the CABINEX field campaignMethane flux, vertical gradient and mixing ratio measurements in a tropical forestThe effects of clouds and aerosols on net ecosystem CO2 exchange over semi-arid Loess Plateau of Northwest ChinaSize-dependent aerosol deposition velocities during BEARPEX'07Day-time concentrations of biogenic volatile organic compounds in a boreal forest canopy and their relation to environmental and biological factors
Meri Räty, Larisa Sogacheva, Helmi-Marja Keskinen, Veli-Matti Kerminen, Tuomo Nieminen, Tuukka Petäjä, Ekaterina Ezhova, and Markku Kulmala
Atmos. Chem. Phys., 23, 3779–3798,Short summary
We utilised back trajectories to identify the source region of air masses arriving in Hyytiälä, Finland, and their travel time over forests. Combined with atmospheric observations, they revealed how air mass transport over the Fennoscandian boreal forest during the growing season produced an accumulation of cloud condensation nuclei and humidity, promoting cloudiness and precipitation. By 55 h of transport, air masses appeared to reach a balanced state with the forest environment.
Edward J. Bannister, Mike Jesson, Nicholas J. Harper, Kris M. Hart, Giulio Curioni, Xiaoming Cai, and A. Rob MacKenzie
Atmos. Chem. Phys., 23, 2145–2165,Short summary
In forests, the residence time of air influences canopy chemistry and atmospheric exchange. However, there have been few field observations. We use long-term open-air CO2 enrichment measurements to show median daytime residence times are twice as long when the trees are in leaf versus when they are not. Residence times increase with increasing atmospheric stability and scale inversely with turbulence. Robust parametrisations for large-scale models are available using common distributions.
Helen Claire Ward, Mathias Walter Rotach, Alexander Gohm, Martin Graus, Thomas Karl, Maren Haid, Lukas Umek, and Thomas Muschinski
Atmos. Chem. Phys., 22, 6559–6593,Short summary
This study examines how cities and their surroundings influence turbulent exchange processes responsible for weather and climate. Analysis of a 4-year observational dataset for the Alpine city of Innsbruck reveals several similarities with other (flat) city centre sites. However, the mountain setting leads to characteristic daily and seasonal flow patterns (valley winds) and downslope windstorms that have a marked effect on temperature, wind speed, turbulence and pollutant concentration.
Chandan Sarangi, TC Chakraborty, Sachchidanand Tripathi, Mithun Krishnan, Ross Morrison, Jonathan Evans, and Lina M. Mercado
Atmos. Chem. Phys., 22, 3615–3629,Short summary
Transpiration fluxes by vegetation are reduced under heat stress to conserve water. However, in situ observations over northern India show that the strength of the inverse association between transpiration and atmospheric vapor pressure deficit is weakening in the presence of heavy aerosol loading. This finding not only implicates the significant role of aerosols in modifying the evaporative fraction (EF) but also warrants an in-depth analysis of the aerosol–plant–temperature–EF continuum.
Sung-Ching Lee, Sara H. Knox, Ian McKendry, and T. Andrew Black
Atmos. Chem. Phys., 22, 2333–2349,Short summary
Wildfire smoke alters land–atmosphere exchange. Here, measurements in a forest and a wetland during four smoke episodes over four summers showed that impacts on radiation and heat budget were the greatest when smoke arrived in late summer. Both sites sequestered more CO2 under smoky days, partly due to diffuse light, but emitted CO2 when smoke was dense. This kind of field study is important for validating predictions of smoke–productivity feedbacks and has climate change implications.
Keunmin Lee, Je-Woo Hong, Jeongwon Kim, Sungsoo Jo, and Jinkyu Hong
Atmos. Chem. Phys., 21, 17833–17853,Short summary
This study examine two benefits of urban forest, thermal mitigation and carbon uptake. Our analysis indicates that the urban forest reduces both the warming trend and urban heat island intensity. Urban forest is a net CO2 source despite larger photosynthetic carbon uptake because of strong contribution of ecosystem respiration, which can be attributed to the substantial amount of soil organic carbon by intensive historical soil use and warm temperature in a city.
Guocheng Wang, Zhongkui Luo, Yao Huang, Wenjuan Sun, Yurong Wei, Liujun Xiao, Xi Deng, Jinhuan Zhu, Tingting Li, and Wen Zhang
Atmos. Chem. Phys., 21, 3059–3071,Short summary
We simulate the spatiotemporal dynamics of aboveground biomass (AGB) in Inner Mongolian grasslands using a machine-learning-based approach. Under climate change, on average, compared with the historical AGB (average of 1981–2019), the AGB at the end of this century (average of 2080–2100) would decrease by 14 % under RCP4.5 and 28 % under RCP8.5. The decrease in AGB might be mitigated or even reversed by positive carbon dioxide enrichment effects on plant growth.
Robbie Ramsay, Chiara F. Di Marco, Matthias Sörgel, Mathew R. Heal, Samara Carbone, Paulo Artaxo, Alessandro C. de Araùjo, Marta Sá, Christopher Pöhlker, Jost Lavric, Meinrat O. Andreae, and Eiko Nemitz
Atmos. Chem. Phys., 20, 15551–15584,Short summary
The Amazon rainforest is a unique
laboratoryto study the processes which govern the exchange of gases and aerosols to and from the atmosphere. This study investigated these processes by measuring the atmospheric concentrations of trace gases and particles at the Amazon Tall Tower Observatory. We found that the long-range transport of pollutants can affect the atmospheric composition above the Amazon rainforest and that the gases ammonia and nitrous acid can be emitted from the rainforest.
Renato Kerches Braghiere, Marcia Akemi Yamasoe, Nilton Manuel Évora do Rosário, Humberto Ribeiro da Rocha, José de Souza Nogueira, and Alessandro Carioca de Araújo
Atmos. Chem. Phys., 20, 3439–3458,Short summary
We evaluate how the interaction of smoke with sun light impacts the exchange of energy and mass between vegetation and the atmosphere using a machine learning technique. We found an effect of the smoke on CO2, energy, and water fluxes, linking the effects of smoke with temperature, humidity, and winds. CO2 exchange increased by up to 55 % in the presence of smoke. A decrease of 12 % was observed for a site with simpler vegetation. Energy fluxes were negatively impacted for all study sites.
Eunho Jang, Ki-Tae Park, Young Jun Yoon, Tae-Wook Kim, Sang-Bum Hong, Silvia Becagli, Rita Traversi, Jaeseok Kim, and Yeontae Gim
Atmos. Chem. Phys., 19, 7595–7608,Short summary
We reported long-term observations (from 2009 to 2016) of the nanoparticles measured at the Antarctic Peninsula (62.2° S, 58.8° W), and satellite-derived estimates of the biological characteristics were analyzed to identify the link between new particle formation and marine biota. The key finding from this research is that the formation of nanoparticles was strongly associated not only with the biomass of phytoplankton but, more importantly, also its taxonomic composition in the Antarctic Ocean.
Linlin Wang, Junkai Liu, Zhiqiu Gao, Yubin Li, Meng Huang, Sihui Fan, Xiaoye Zhang, Yuanjian Yang, Shiguang Miao, Han Zou, Yele Sun, Yong Chen, and Ting Yang
Atmos. Chem. Phys., 19, 6949–6967,Short summary
Urban boundary layer (UBL) affects the physical and chemical processes of the pollutants, and UBL structure can also be altered by pollutants. This paper presents the interactions between air pollution and the UBL structure by using the field data mainly collected from a 325 m meteorology tower, as well as from a Doppler wind lidar, during a severe heavy pollution event that occurred during 1–4 December 2016 in Beijing.
Carsten Schaller, Fanny Kittler, Thomas Foken, and Mathias Göckede
Atmos. Chem. Phys., 19, 4041–4059,Short summary
Methane emissions from biogenic sources, e.g. Arctic permafrost ecosystems, are associated with uncertainties due to the high variability of fluxes in both space and time. Besides the traditional eddy covariance method, we evaluated a method based on wavelet analysis, which does not require a stationary time series, to calculate fluxes. The occurrence of extreme methane flux events was strongly correlated with the soil temperature. They were triggered by atmospheric non-turbulent mixing.
Angelo Finco, Mhairi Coyle, Eiko Nemitz, Riccardo Marzuoli, Maria Chiesa, Benjamin Loubet, Silvano Fares, Eugenio Diaz-Pines, Rainer Gasche, and Giacomo Gerosa
Atmos. Chem. Phys., 18, 17945–17961,Short summary
A 1-month field campaign of ozone (O3) flux measurements along a five-level vertical profile of a mature broadleaf forest highlighted that the biosphere–atmosphere exchange of this pollutant is modulated by complex diel dynamics occurring within and below the canopy. The canopy removed nearly 80 % of the O3 deposited to the forest; only a minor part was removed by the soil and the understorey (2 %), while the remaining 18.2 % was removed by chemical reactions with NO mostly emitted from soil.
Ekaterina Ezhova, Ilona Ylivinkka, Joel Kuusk, Kaupo Komsaare, Marko Vana, Alisa Krasnova, Steffen Noe, Mikhail Arshinov, Boris Belan, Sung-Bin Park, Jošt Valentin Lavrič, Martin Heimann, Tuukka Petäjä, Timo Vesala, Ivan Mammarella, Pasi Kolari, Jaana Bäck, Üllar Rannik, Veli-Matti Kerminen, and Markku Kulmala
Atmos. Chem. Phys., 18, 17863–17881,Short summary
Understanding the connections between aerosols, solar radiation and photosynthesis in terrestrial ecosystems is important for estimates of the CO2 balance in the atmosphere. Atmospheric aerosols and clouds influence solar radiation. In this study, we quantify the aerosol effect on solar radiation in boreal forests and study forest ecosystems response to this change in the radiation conditions. The analysis is based on atmospheric observations from several remote stations in Eurasian forests.
Qun Du, Huizhi Liu, Lujun Xu, Yang Liu, and Lei Wang
Atmos. Chem. Phys., 18, 15087–15104,Short summary
Erhai Lake is a subtropical highland shallow lake on the southeast margin of the Tibetan Plateau, which is influenced by both South Asian and East Asian summer monsoons. The substantial difference in atmospheric properties during monsoon and non-monsoon periods has a large effect in regulating turbulent heat and carbon dioxide exchange processes over Erhai Lake. Large difference are found for the factors controlling sensible heat and carbon dioxide flux during monsoon and non-monsoon periods.
Tirtha Banerjee, Peter Brugger, Frederik De Roo, Konstantin Kröniger, Dan Yakir, Eyal Rotenberg, and Matthias Mauder
Atmos. Chem. Phys., 18, 10025–10038,Short summary
We studied the nature of turbulent transport over a well-defined surface heterogeneity (approximate scale 7 km) comprising a shrubland and a forest in the Yatir semiarid area in Israel. Using eddy covariance and Doppler lidar measurements, we studied the variations in the turbulent kinetic energy budget and turbulent fluxes, focusing especially on transport terms. We also confirmed the role of large-scale secondary circulations that transport energy between the shrubland and the forest.
Claudia Grossi, Felix R. Vogel, Roger Curcoll, Alba Àgueda, Arturo Vargas, Xavier Rodó, and Josep-Anton Morguí
Atmos. Chem. Phys., 18, 5847–5860,Short summary
To gain a full picture of the Spanish (and European) GHG balance, understanding of CH4 emissions in different regions is a critical challenge, as is the improvement of bottom-up inventories for all European regions. This study uses, among other elements, GHG, meteorological and 222Rn tracer data from a Spanish region to understand the main causes of temporal variability of GHG mixing ratios. The study can offer new insights into regional emissions by identifying the impacts of changing sources.
Pablo E. S. Oliveira, Otávio C. Acevedo, Matthias Sörgel, Anywhere Tsokankunku, Stefan Wolff, Alessandro C. Araújo, Rodrigo A. F. Souza, Marta O. Sá, Antônio O. Manzi, and Meinrat O. Andreae
Atmos. Chem. Phys., 18, 3083–3099,Short summary
Carbon dioxide and latent heat fluxes within the canopy are dominated by low-frequency (nonturbulent) processes. There is a striking contrast between fully turbulent and intermittent nights, such that turbulent processes dominate the total nighttime exchange during the former, while nonturbulent processes are more relevant in the latter. In very stable nights, during which intermittent exchange prevails, the stable boundary layer may be shallower than the highest observational level at 80 m.
Sean Hartery, Róisín Commane, Jakob Lindaas, Colm Sweeney, John Henderson, Marikate Mountain, Nicholas Steiner, Kyle McDonald, Steven J. Dinardo, Charles E. Miller, Steven C. Wofsy, and Rachel Y.-W. Chang
Atmos. Chem. Phys., 18, 185–202,Short summary
Methane is the second most important greenhouse gas but its emissions from northern regions are still poorly constrained. This study uses aircraft measurements of methane from Alaska to estimate surface emissions. We found that methane emission rates depend on the soil temperature at depths where its production was taking place, and that total emissions were similar between tundra and boreal regions. These results provide a simple way to predict methane emissions in this region.
Linda M. J. Kooijmans, Kadmiel Maseyk, Ulli Seibt, Wu Sun, Timo Vesala, Ivan Mammarella, Pasi Kolari, Juho Aalto, Alessandro Franchin, Roberta Vecchi, Gianluigi Valli, and Huilin Chen
Atmos. Chem. Phys., 17, 11453–11465,Short summary
Carbon cycle studies rely on the accuracy of models to estimate the amount of CO2 being taken up by vegetation. The gas carbonyl sulfide (COS) can serve as a tool to estimate the vegetative CO2 uptake by scaling the ecosystem uptake of COS to that of CO2. Here we investigate the nighttime fluxes of COS. The relationships found in this study will aid in implementing nighttime COS uptake in models, which is key to obtain accurate estimates of vegetative CO2 uptake with the use of COS.
Pavel Alekseychik, Ivan Mammarella, Dmitry Karpov, Sigrid Dengel, Irina Terentieva, Alexander Sabrekov, Mikhail Glagolev, and Elena Lapshina
Atmos. Chem. Phys., 17, 9333–9345,Short summary
West Siberian peatlands occupy a large fraction of land area in the region, and yet little is known about their interaction with the atmosphere. We took the first measurements of CO2 and energy surface balances over a typical bog of West Siberian middle taiga, in the vicinity of the Mukhrino field station (Khanty–Mansiysk). The May–August study in a wet year (2015) revealed a relatively large photosynthetic sink of CO2 that was close to the high end of estimates at bog sites elsewhere.
Lei Wang, Huizhi Liu, Jihua Sun, and Yaping Shao
Atmos. Chem. Phys., 17, 5119–5129,Short summary
This study found that the seasonal variation in CO2 exchange over an alpine meadow on the Tibetan Plateau was primarily affected by the seasonal pattern of air temperature, especially in spring and autumn. The annual net ecosystem exchange decreased with mean annual temperature, and then increased when the gross primary production became saturated. This study contributes to the response of the alpine meadow ecosystem to global warming.
Xueqian Wang, Weidong Guo, Bo Qiu, Ye Liu, Jianning Sun, and Aijun Ding
Atmos. Chem. Phys., 17, 4989–4996,Short summary
Land use or cover change is a fundamental anthropogenic forcing for climate change. Based on field observations, we quantified the contributions of different factors to surface temperature change and deepened the understanding of its mechanisms. We found evaporative cooling plays the most important role in the temperature change, while radiative forcing, which is traditionally emphasized, is not significant. This study provided firsthand evidence to verify the model results in IPCC AR5.
L. Paige Wright, Leiming Zhang, and Frank J. Marsik
Atmos. Chem. Phys., 16, 13399–13416,Short summary
The current knowledge concerning mercury dry deposition is reviewed, including dry deposition algorithms used in chemical transport models and at monitoring sites, measurement methods and studies for quantifying dry deposition of oxidized mercury, and measurement studies of litterfall and throughfall mercury. Over all the regions, dry deposition, estimated as the sum of litterfall and throughfall minus open-field wet deposition, is more dominant than wet deposition for Hg deposition.
Einara Zahn, Nelson L. Dias, Alessandro Araújo, Leonardo D. A. Sá, Matthias Sörgel, Ivonne Trebs, Stefan Wolff, and Antônio Manzi
Atmos. Chem. Phys., 16, 11349–11366,Short summary
Preliminary data from the ATTO project were analyzed to characterize the exchange of heat, water vapor, and CO2 between the Amazon forest and the atmosphere. The forest roughness makes estimation of their fluxes difficult, and even measurements at 42 m above the canopy show a lot of scatter. Still, measurements made around noon showed much better conformity with standard theories for the exchange of these quantities, opening the possibility of good flux estimates when the sun is high.
Undine Zöll, Christian Brümmer, Frederik Schrader, Christof Ammann, Andreas Ibrom, Christophe R. Flechard, David D. Nelson, Mark Zahniser, and Werner L. Kutsch
Atmos. Chem. Phys., 16, 11283–11299,Short summary
Accurate quantification of atmospheric ammonia concentration and exchange fluxes with the land surface has been a major metrological challenge. We demonstrate the applicability of a novel laser device to identify concentration and flux patterns over a peatland ecosystem influenced by nearby agricultural practices. Results help to strengthen air quality monitoring networks, lead to better understanding of ecosystem functionality and improve parameterizations in air chemistry and transport models.
Simon Schallhart, Pekka Rantala, Eiko Nemitz, Ditte Taipale, Ralf Tillmann, Thomas F. Mentel, Benjamin Loubet, Giacomo Gerosa, Angelo Finco, Janne Rinne, and Taina M. Ruuskanen
Atmos. Chem. Phys., 16, 7171–7194,Short summary
We present ecosystem exchange fluxes from a mixed oak–hornbeam forest in the Po Valley, Italy. Detectable fluxes were observed for 29 compounds, dominated by isoprene, which comprised over 60 % of the upward flux. Methanol seemed to be deposited to dew, as the deposition happened in the early morning. We estimated that up to 30 % of the upward flux of methyl vinyl ketone and methacrolein originated from atmospheric oxidation of isoprene.
Aurélie Bachy, Marc Aubinet, Niels Schoon, Crist Amelynck, Bernard Bodson, Christine Moureaux, and Bernard Heinesch
Atmos. Chem. Phys., 16, 5343–5356,Short summary
This research focuses on Biogenic Volatile Organic Compounds (BVOC) exchanges between a maize field and the atmosphere. Indeed, few BVOC studies have already investigated agricultural ecosystems. We found that the maize field emitted mainly methanol, that both soil and plants contributed to the net exchange, that exchanges were lower than in other studies and than considered by models. Our work tends thus to lower the impact of maize on terrestrial BVOC exchanges.
Y. Zhao, T. Huang, L. Wang, H. Gao, and J. Ma
Atmos. Chem. Phys., 15, 3479–3495,Short summary
After several decades of declining persistent organic pollutants in the arctic environment due to their global use restriction, some of these toxic chemicals increased in the mid-2000s and undertook statistically significant step changes which coincided with arctic sea ice melting. Results provide statistical evidence for the releasing of toxic chemicals from their reservoirs in the Arctic due to the rapid change in the arctic environment.
J. Sievers, T. Papakyriakou, S. E. Larsen, M. M. Jammet, S. Rysgaard, M. K. Sejr, and L. L. Sørensen
Atmos. Chem. Phys., 15, 2081–2103,
H. Huang, J. Wang, D. Hui, D. R. Miller, S. Bhattarai, S. Dennis, D. Smart, T. Sammis, and K. C. Reddy
Atmos. Chem. Phys., 14, 12839–12854,Short summary
An EC system was assembled with a sonic anemometer and a new fast-response N2O analyzer and applied in a cornfield during a growing season. This N2O EC system provided reliable N2O flux measurements. The average flux was about 63% higher during the daytime than during the nighttime. Seasonal fluxes were highly dependent on soil moisture rather than soil temperature.
D. Vickers and C. K. Thomas
Atmos. Chem. Phys., 14, 9665–9676,
G. G. Cirino, R. A. F. Souza, D. K. Adams, and P. Artaxo
Atmos. Chem. Phys., 14, 6523–6543,
L. Hörtnagl, I. Bamberger, M. Graus, T. M. Ruuskanen, R. Schnitzhofer, M. Walser, A. Unterberger, A. Hansel, and G. Wohlfahrt
Atmos. Chem. Phys., 14, 5369–5391,
F. Lohou, L. Kergoat, F. Guichard, A. Boone, B. Cappelaere, J.-M. Cohard, J. Demarty, S. Galle, M. Grippa, C. Peugeot, D. Ramier, C. M. Taylor, and F. Timouk
Atmos. Chem. Phys., 14, 3883–3898,
E. Velasco, M. Roth, S. H. Tan, M. Quak, S. D. A. Nabarro, and L. Norford
Atmos. Chem. Phys., 13, 10185–10202,
G. C. Edwards and D. A. Howard
Atmos. Chem. Phys., 13, 5325–5336,
H. Z. Liu, J. W. Feng, L. Järvi, and T. Vesala
Atmos. Chem. Phys., 12, 7881–7892,
S. Dupont and E. G. Patton
Atmos. Chem. Phys., 12, 5913–5935,
T. Foken, F. X. Meixner, E. Falge, C. Zetzsch, A. Serafimovich, A. Bargsten, T. Behrendt, T. Biermann, C. Breuninger, S. Dix, T. Gerken, M. Hunner, L. Lehmann-Pape, K. Hens, G. Jocher, J. Kesselmeier, J. Lüers, J.-C. Mayer, A. Moravek, D. Plake, M. Riederer, F. Rütz, M. Scheibe, L. Siebicke, M. Sörgel, K. Staudt, I. Trebs, A. Tsokankunku, M. Welling, V. Wolff, and Z. Zhu
Atmos. Chem. Phys., 12, 1923–1950,
Q. Laffineur, M. Aubinet, N. Schoon, C. Amelynck, J.-F. Müller, J. Dewulf, H. Van Langenhove, K. Steppe, and B. Heinesch
Atmos. Chem. Phys., 12, 577–590,
A. L. Steiner, S. N. Pressley, A. Botros, E. Jones, S. H. Chung, and S. L. Edburg
Atmos. Chem. Phys., 11, 11921–11936,
C. A. S. Querino, C. J. P. P. Smeets, I. Vigano, R. Holzinger, V. Moura, L. V. Gatti, A. Martinewski, A. O. Manzi, A. C. de Araújo, and T. Röckmann
Atmos. Chem. Phys., 11, 7943–7953,
X. Jing, J. Huang, G. Wang, K. Higuchi, J. Bi, Y. Sun, H. Yu, and T. Wang
Atmos. Chem. Phys., 10, 8205–8218,
R. J. Vong, I. J. Vong, D. Vickers, and D. S. Covert
Atmos. Chem. Phys., 10, 5749–5758,
H. K. Lappalainen, S. Sevanto, J. Bäck, T. M. Ruuskanen, P. Kolari, R. Taipale, J. Rinne, M. Kulmala, and P. Hari
Atmos. Chem. Phys., 9, 5447–5459,
Ahlström, A., Raupach, M. R., Schurgers, G., Smith, B., Arneth, A., Jung, M., Reichstein, M., Canadell, J. G., Friedlingstein, P., Jain, A. K., Kato, E., Poulter, B., Sitch, S., Stocker, B. D., Viovy, N., Wang, Y. P., Wiltshire, A., Zaehle, S., and Zeng, N.: The dominant role of semi-arid ecosystems in the trend and variability of the land CO2 sink, Science, 348, 895–899, https://doi.org/10.1126/science.aaa1668, 2015.
Aubinet, M., Vesala, T., and Papale, D. (Eds.): Eddy Covariance: A Practical Guide to Measurement and Data Analysis, Springer, Dordrecht, the Netherlands, 438 pp., https://doi.org/10.1007/978-94-007-2351-1, 2012.
Baldocchi, D. and Sturtevant, C.: Does day and night sampling reduce spurious correlation between canopy photosynthesis and ecosystem respiration?, Agr. Forest Meteorol., 207, 117–126, https://doi.org/10.1016/j.agrformet.2015.03.010, 2015.
Baldocchi, D. D.: Assessing the eddy covariance technique for evaluating carbon dioxide exchange rates of ecosystems: past, present and future, Glob. Change Biol., 9, 479–492, https://doi.org/10.1046/j.1365-2486.2003.00629.x, 2003.
Berg, A. and McColl, K. A.: No projected global drylands expansion under greenhouse warming, Nat. Clim. Chang., 11, 331–337, https://doi.org/10.1038/s41558-021-01007-8, 2021.
Biederman, J. A., Scott, R. L., Bell, T. W., Bowling, D. R., Dore, S., Garatuza-Payan, J., Kolb, T. E., Krishnan, P., Krofcheck, D. J., Litvak, M. E., Maurer, G. E., Meyers, T. P., OECHEL, W. C., Papuga, S. A., Ponce-Campos, G. E., Rodriguez, J. C., Smith, W. K., Vargas, R., Watts, C. J., Yepez, E. A., Goulden, M. L., Garatuza Payan, J., Kolb, T. E., Krishnan, P., Krofcheck, D. J., Litvak, M. E., Maurer, G. E., Meyers, T. P., OECHEL, W. C., Papuga, S. A., Ponce-Campos, G. E., Rodriguez, J. C., Smith, W. K., Vargas, R., Watts, C. J., Yepez, E. A., and Goulden, M. L.: CO2 exchange and evapotranspiration across dryland ecosystems of southwestern North America, Glob. Change Biol., 23, 4204–4221, https://doi.org/10.1111/gcb.13686, 2017.
Breiman, L.: Random forests, Mach. Learn., 45, 5–32, https://doi.org/10.1023/A:1010933404324, 2001.
Chen, Y. Y., Chu, C. R., and Li, M. H.: A gap-filling model for eddy covariance latent heat flux: Estimating evapotranspiration of a subtropical seasonal evergreen broad-leaved forest as an example, J. Hydrol., 468–469, 101–110, https://doi.org/10.1016/j.jhydrol.2012.08.026, 2012.
Chu, H., Luo, X., Ouyang, Z., Chan, W. S., Dengel, S., Biraud, S. C., Torn, M. S., Metzger, S., Kumar, J., Arain, M. A., Arkebauer, T. J., Baldocchi, D., Bernacchi, C., Billesbach, D., Black, T. A., Blanken, P. D., Bohrer, G., Bracho, R., Brown, S., Brunsell, N. A., Chen, J., Chen, X., Clark, K., Desai, A. R., Duman, T., Durden, D., Fares, S., Forbrich, I., Gamon, J. A., Gough, C. M., Griffis, T., Helbig, M., Hollinger, D., Humphreys, E., Ikawa, H., Iwata, H., Ju, Y., Knowles, J. F., Knox, S. H., Kobayashi, H., Kolb, T., Law, B., Lee, X., Litvak, M., Liu, H., Munger, J. W., Noormets, A., Novick, K., Oberbauer, S. F., Oechel, W., Oikawa, P., Papuga, S. A., Pendall, E., Prajapati, P., Prueger, J., Quinton, W. L., Richardson, A. D., Russell, E. S., Scott, R. L., Starr, G., Staebler, R., Stoy, P. C., Stuart-Haëntjens, E., Sonnentag, O., Sullivan, R. C., Suyker, A., Ueyama, M., Vargas, R., Wood, J. D., and Zona, D.: Representativeness of Eddy-Covariance flux footprints for areas surrounding AmeriFlux sites, Agr. Forest Meteorol., 301–302, 108350, https://doi.org/10.1016/J.AGRFORMET.2021.108350, 2021.
Cortes, C. and Vapnik, V.: Support-vector networks, Mach. Learn., 20, 273–297, https://doi.org/10.1007/bf00994018, 1995.
Delwiche, K. B., Knox, S. H., Malhotra, A., Fluet-Chouinard, E., McNicol, G., Feron, S., Ouyang, Z., Papale, D., Trotta, C., Canfora, E., Cheah, Y.-W., Christianson, D., Alberto, Ma. C. R., Alekseychik, P., Aurela, M., Baldocchi, D., Bansal, S., Billesbach, D. P., Bohrer, G., Bracho, R., Buchmann, N., Campbell, D. I., Celis, G., Chen, J., Chen, W., Chu, H., Dalmagro, H. J., Dengel, S., Desai, A. R., Detto, M., Dolman, H., Eichelmann, E., Euskirchen, E., Famulari, D., Fuchs, K., Goeckede, M., Gogo, S., Gondwe, M. J., Goodrich, J. P., Gottschalk, P., Graham, S. L., Heimann, M., Helbig, M., Helfter, C., Hemes, K. S., Hirano, T., Hollinger, D., Hörtnagl, L., Iwata, H., Jacotot, A., Jurasinski, G., Kang, M., Kasak, K., King, J., Klatt, J., Koebsch, F., Krauss, K. W., Lai, D. Y. F., Lohila, A., Mammarella, I., Belelli Marchesini, L., Manca, G., Matthes, J. H., Maximov, T., Merbold, L., Mitra, B., Morin, T. H., Nemitz, E., Nilsson, M. B., Niu, S., Oechel, W. C., Oikawa, P. Y., Ono, K., Peichl, M., Peltola, O., Reba, M. L., Richardson, A. D., Riley, W., Runkle, B. R. K., Ryu, Y., Sachs, T., Sakabe, A., Sanchez, C. R., Schuur, E. A., Schäfer, K. V. R., Sonnentag, O., Sparks, J. P., Stuart-Haëntjens, E., Sturtevant, C., Sullivan, R. C., Szutu, D. J., Thom, J. E., Torn, M. S., Tuittila, E.-S., Turner, J., Ueyama, M., Valach, A. C., Vargas, R., Varlagin, A., Vazquez-Lule, A., Verfaillie, J. G., Vesala, T., Vourlitis, G. L., Ward, E. J., Wille, C., Wohlfahrt, G., Wong, G. X., Zhang, Z., Zona, D., Windham-Myers, L., Poulter, B., and Jackson, R. B.: FLUXNET-CH4: a global, multi-ecosystem dataset and analysis of methane seasonality from freshwater wetlands, Earth Syst. Sci. Data, 13, 3607–3689, https://doi.org/10.5194/essd-13-3607-2021, 2021.
Dengel, S., Zona, D., Sachs, T., Aurela, M., Jammet, M., Parmentier, F. J. W., Oechel, W., and Vesala, T.: Testing the applicability of neural networks as a gap-filling method using CH4 flux data from high latitude wetlands, Biogeosciences, 10, 8185–8200, https://doi.org/10.5194/bg-10-8185-2013, 2013.
Didan, K.: MOD13Q1 MODIS/Terra Vegetation Indices 16-Day L3 Glob. 250m SIN Grid V006, NASA EOSDI [data set], https://doi.org/10.5067/MODIS/MOD13Q1.006, 2015.
Dragoni, D., Schmid, H. P., Grimmond, C. S. B., and Loescher, H. W.: Uncertainty of annual net ecosystem productivity estimated using eddy covariance flux measurements, J. Geophys. Res.-Atmos., 112, 17102, https://doi.org/10.1029/2006JD008149, 2007.
Falge, E., Baldocchi, D., Olson, R., Anthoni, P., Aubinet, M., Bernhofer, C., Burba, G., Ceulemans, R., Clement, R., Dolman, H., Granier, A., Gross, P., Grünwald, T., Hollinger, D., Jensen, N. O., Katul, G., Keronen, P., Kowalski, A., Lai, C. T., Law, B. E., Meyers, T., Moncrieff, J., Moors, E., Munger, J. W., Pilegaard, K., Rannik, Ü., Rebmann, C., Suyker, A., Tenhunen, J., Tu, K., Verma, S., Vesala, T., Wilson, K., and Wofsy, S.: Gap filling strategies for defensible annual sums of net ecosystem exchange, Agr. Forest Meteorol., 107, 43–69, https://doi.org/10.1016/S0168-1923(00)00225-2, 2001.
Feng, S. and Fu, Q.: Expansion of global drylands under a warming climate, Atmos. Chem. Phys., 13, 10081–10094, https://doi.org/10.5194/acp-13-10081-2013, 2013.
Finkelstein, P. L. and Sims, P. F.: Sampling error in eddy correlation flux measurements, J. Geophys. Res.-Atmos., 106, 3503–3509, https://doi.org/10.1029/2000JD900731, 2001.
Fix, E. and Hodges, J. L.: Discriminatory analysis. Nonparametric discrimination; consistency properties, Report Number 4, Project Number 21-49-004, USAF School of Aviation Medicine, Randolph Field, Texas, 1951.
Gao, Z., Russell, E. S., Missik, J. E. C., Huang, M., Chen, X., Strickland, C. E., Clayton, R., Arntzen, E., Ma, Y., and Liu, H.: A novel approach to evaluate soil heat flux calculation: An analytical review of nine methods, J. Geophys. Res., 122, 6934–6949, https://doi.org/10.1002/2017JD027160, 2017.
Gao, Z., Liu, H., Missik, J. E. C., Yao, J., Huang, M., Chen, X., Arntzen, E., and McFarland, D. P.: Mechanistic links between underestimated CO2 fluxes and non-closure of the surface energy balance in a semi-arid sagebrush ecosystem, Environ. Res. Lett., 14, 044016, https://doi.org/10.1088/1748-9326/ab082d, 2019.
Gao, Z., Liu, H., Chen, X., Huang, M., Missik, J. E. C. C., Yao, J., Arntzen, E., and Mcfarland, D. P.: Enlarged non-closure of surface energy balance with increasing atmospheric instabilities linked to changes in coherent structures, J. Geophys. Res.-Atmos., 125, e2020JD032889, https://doi.org/10.1029/2020jd032889, 2020a.
Gao, Z., Liu, H., Arntzen, E., Mcfarland, D. P., Chen, X., and Huang, M.: Uncertainties in Turbulent Statistics and Fluxes of CO2 Associated With Density Effect Corrections, Geophys. Res. Lett., 47, e2020GL088859, https://doi.org/10.1029/2020GL088859, 2020b.
Günther, F. and Fritsch, S.: Neuralnet: Training of neural networks, R Journal, 2, 30–38, https://doi.org/10.32614/rj-2010-006, 2010.
Huang, I.-H. and Hsieh, C.-I.: Gap-Filling of Surface Fluxes Using Machine Learning Algorithms in Various Ecosystems, Water, 12, 3415, https://doi.org/10.3390/w12123415, 2020.
Huang, J., Yu, H., Guan, X., Wang, G., and Guo, R.: Accelerated dryland expansion under climate change, Nat. Clim. Chang., 6, 166–171, https://doi.org/10.1038/nclimate2837, 2016.
Irvin, J., Zhou, S., McNicol, G., Lu, F., Liu, V., Fluet-Chouinard, E., Ouyang, Z., Knox, S. H., Lucas-Moffat, A., Trotta, C., Papale, D., Vitale, D., Mammarella, I., Alekseychik, P., Aurela, M., Avati, A., Baldocchi, D., Bansal, S., Bohrer, G., Campbell, D. I., Chen, J., Chu, H., Dalmagro, H. J., Delwiche, K. B., Desai, A. R., Euskirchen, E., Feron, S., Goeckede, M., Heimann, M., Helbig, M., Helfter, C., Hemes, K. S., Hirano, T., Iwata, H., Jurasinski, G., Kalhori, A., Kondrich, A., Lai, D. Y., Lohila, A., Malhotra, A., Merbold, L., Mitra, B., Ng, A., Nilsson, M. B., Noormets, A., Peichl, M., Rey-Sanchez, A. C., Richardson, A. D., Runkle, B. R., Schäfer, K. V., Sonnentag, O., Stuart-Haëntjens, E., Sturtevant, C., Ueyama, M., Valach, A. C., Vargas, R., Vourlitis, G. L., Ward, E. J., Wong, G. X., Zona, D., Alberto, M. C. R., Billesbach, D. P., Celis, G., Dolman, H., Friborg, T., Fuchs, K., Gogo, S., Gondwe, M. J., Goodrich, J. P., Gottschalk, P., Hörtnagl, L., Jacotot, A., Koebsch, F., Kasak, K., Maier, R., Morin, T. H., Nemitz, E., Oechel, W. C., Oikawa, P. Y., Ono, K., Sachs, T., Sakabe, A., Schuur, E. A., Shortt, R., Sullivan, R. C., Szutu, D. J., Tuittila, E. S., Varlagin, A., Verfaillie, J. G., Wille, C., Windham-Myers, L., Poulter, B., and Jackson, R. B.: Gap-filling eddy covariance methane fluxes: Comparison of machine learning model predictions and uncertainties at FLUXNET-CH4 wetlands, Agr. Forest Meteorol., 308–309, 108528, https://doi.org/10.1016/J.AGRFORMET.2021.108528, 2021
Jammet, M., Crill, P., Dengel, S., and Friborg, T.: Large methane emissions from a subarctic lake during spring thaw: Mechanisms and landscape significance, J. Geophys. Res.-Biogeo, 120, 2289–2305, https://doi.org/10.1002/2015JG003137, 2015.
Jung, M., Reichstein, M., Schwalm, C. R., Huntingford, C., Sitch, S., Ahlström, A., Arneth, A., Camps-Valls, G., Ciais, P., Friedlingstein, P., Gans, F., Ichii, K., Jain, A. K., Kato, E., Papale, D., Poulter, B., Raduly, B., Rödenbeck, C., Tramontana, G., Viovy, N., Wang, Y. P., Weber, U., Zaehle, S., and Zeng, N.: Compensatory water effects link yearly global land CO2 sink changes to temperature, Nature, 541, 516–520, https://doi.org/10.1038/nature20780, 2017.
Karatzoglou, A., Smola, A., Hornik, K., and Zeileis, A.: kernlab – An S4 Package for Kernel Methods in R, J. Stat. Softw., 11, 1–20, https://doi.org/10.18637/jss.v011.i09, 2004.
Kim, Y., Johnson, M. S., Knox, S. H., Black, T. A., Dalmagro, H. J., Kang, M., Kim, J., and Baldocchi, D.: Gap-filling approaches for eddy covariance methane fluxes: A comparison of three machine learning algorithms and a traditional method with principal component analysis, Glob. Chang. Biol., 26, 1499–1518, https://doi.org/10.1111/gcb.14845, 2020.
Knox, S. H., Matthes, J. H., Sturtevant, C., Oikawa, P. Y., Verfaillie, J., and Baldocchi, D.: Biophysical controls on interannual variability in ecosystem-scale CO2 and CH4 exchange in a California rice paddy, J. Geophys. Res.-Biogeo, 121, 978–1001, https://doi.org/10.1002/2015JG003247, 2016.
Kuhn, M., Wing, J., Weston, S., Williams, A., Keefer, C., Engelhardt, A., Cooper, T., Mayer, Z., Kenkel, B., Team, R. C., Benesty, M., Lescarbeau, R., Ziem, A., Scrucca, L., Tang, Y., Candan, C., and Hunt, T.: caret: Classification and Regression Training, cran [code], available at: https://cran.r-project.org/package=caret, last access: 15 April 2020.
Liaw, A. and Wiener, M.: Classification and Regression by randomForest, R News, 2, 18–22, 2002.
Mahabbati, A., Beringer, J., Leopold, M., McHugh, I., Cleverly, J., Isaac, P., and Izady, A.: A comparison of gap-filling algorithms for eddy covariance fluxes and their drivers, Geosci. Instrum. Method. Data Syst., 10, 123–140, https://doi.org/10.5194/gi-10-123-2021, 2021.
Ma, S., Baldocchi, D. D., Xu, L., and Hehn, T.: Inter-annual variability in carbon dioxide exchange of an oak/grass savanna and open grassland in California, Agr. Forest Meteorol., 147, 157–171, https://doi.org/10.1016/j.agrformet.2007.07.008, 2007.
Massman, W. J.: A simple method for estimating frequency response corrections for eddy covariance systems, Agr. Forest Meteorol., 104, 185–198, https://doi.org/10.1016/S0168-1923(00)00164-7, 2000.
Massman, W. J.: Reply to comment by Rannik on “A simple method for estimating frequency response corrections for eddy covariance systems, Agr. Forest Meteorol., 107, 247–251, https://doi.org/10.1016/S0168-1923(00)00237-9, 2001.
Mauder, M. and Foken, T.: Documentation and Instruction Manual of the Eddy Covariance Software Package TK2, 2004.
Metzger, S.: Surface-atmosphere exchange in a box: Making the control volume a suitable representation for in-situ observations, Agr. Forest Meteorol., 255, 68–80, https://doi.org/10.1016/J.AGRFORMET.2017.08.037, 2018.
Missik, J. E. C., Liu, H., Gao, Z., Huang, M., Chen, X., Arntzen, E., Mcfarland, D. P., Ren, H., Titzler, P. S., Thomle, J. N., and Goldman, A.: Groundwater-River Water Exchange Enhances Growing Season Evapotranspiration and Carbon Uptake in a Semiarid Riparian Ecosystem, J. Geophys. Res.-Biogeo., 124, 99–114, https://doi.org/10.1029/2018JG004666, 2019.
Missik, J. E. C., Liu, H., Gao, Z., Huang, M., Chen, X., Arntzen, E., Mcfarland, D. P., and Verbeke, B.: Groundwater Regulates Interannual Variations in Evapotranspiration in a Riparian Semiarid Ecosystem, J. Geophys. Res.-Atmos., 126, e2020JD033078, https://doi.org/10.1029/2020jd033078, 2021.
Moffat, A. M., Papale, D., Reichstein, M., Hollinger, D. Y., Richardson, A. D., Barr, A. G., Beckstein, C., Braswell, B. H., Churkina, G., Desai, A. R., Falge, E., Gove, J. H., Heimann, M., Hui, D., Jarvis, A. J., Kattge, J., Noormets, A., and Stauch, V. J.: Comprehensive comparison of gap-filling techniques for eddy covariance net carbon fluxes, Agr. Forest Meteorol., 147, 209–232, https://doi.org/10.1016/j.agrformet.2007.08.011, 2007.
Moncrieff, J., Clement, R., Finnigan, J., and Meyers, T.: Averaging, Detrending, and Filtering of Eddy Covariance Time Series, in: Handbook of Micrometeorology, edited by: Lee, X., Massman, W., and Law, B., Springer, Dordrecht, 7–31 pp., https://doi.org/10.1007/1-4020-2265-4, 2004.
Oncley, S., Foken, T., Vogt, R., Kohsiek, W., DeBruin, H. A. R., Bernhofer, C., Christen, A., Gorsel, E., Grantz, D., Feigenwinter, C., Lehner, I., Liebethal, C., Liu, H., Mauder, M., Pitacco, A., Ribeiro, L., and Weidinger, T.: The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance, Bound.-Lay. Meteorol., 123, 1–28, https://doi.org/10.1007/s10546-007-9161-1, 2007.
Papale, D. and Valentini, R.: A new assessment of European forests carbon exchanges by eddy fluxes and artificial neural network spatialization, Glob. Chang. Biol., 9, 525–535, https://doi.org/10.1046/j.1365-2486.2003.00609.x, 2003.
Pastorello, G., Trotta, C., Canfora, E. et al.: The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data, Sci. data, 7, 225, https://doi.org/10.1038/s41597-020-0534-3, 2020.
Reichstein, M., Falge, E., Baldocchi, D., Papale, D., Aubinet, M., Berbigier, P., Bernhofer, C., Buchmann, N., Gilmanov, T., Granier, A., Grünwald, T., Havránková, K., Ilvesniemi, H., Janous, D., Knohl, A., Laurila, T., Lohila, A., Loustau, D., Matteucci, G., Meyers, T., Miglietta, F., Ourcival, J. M., Pumpanen, J., Rambal, S., Rotenberg, E., Sanz, M., Tenhunen, J., Seufert, G., Vaccari, F., Vesala, T., Yakir, D., and Valentini, R.: On the separation of net ecosystem exchange into assimilation and ecosystem respiration: Review and improved algorithm, Glob. Chang. Biol., 11, 1424–1439, https://doi.org/10.1111/j.1365-2486.2005.001002.x, 2005.
Richardson, A. D. and Hollinger, D. Y.: A method to estimate the additional uncertainty in gap-filled NEE resulting from long gaps in the CO2 flux record, Agr. Forest Meteorol., 147, 199–208, https://doi.org/10.1016/j.agrformet.2007.06.004, 2007.
Richardson, A. D., Mahecha, M. D., Falge, E., Kattge, J., Moffat, A. M., Papale, D., Reichstein, M., Stauch, V. J., Braswell, B. H., Churkina, G., Kruijt, B., and Hollinger, D. Y.: Statistical properties of random CO2 flux measurement uncertainty inferred from model residuals, Agr. Forest Meteorol., 148, 38–50, https://doi.org/10.1016/J.AGRFORMET.2007.09.001, 2008.
Scott, R. L., Biederman, J. A., Hamerlynck, E. P., Barron Gafford, G. A., and Barron-Gafford, G. A.: The carbon balance pivot point of southwestern U.S. semiarid ecosystems: Insights from the 21st century drought, J. Geophys. Res.-Biogeo, 120, 2612–2624, https://doi.org/10.1002/2015JG003181, 2015.
Soloway, A. D., Amiro, B. D., Dunn, A. L., and Wofsy, S. C.: Carbon neutral or a sink? Uncertainty caused by gap-filling long-term flux measurements for an old-growth boreal black spruce forest, Agr. Forest Meteorol., 233, 110–121, https://doi.org/10.1016/j.agrformet.2016.11.005, 2017.
Stoy, P. C., Mauder, M., Foken, T., Marcolla, B., Boegh, E., Ibrom, A., Arain, M. A., Arneth, A., Aurela, M., Bernhofer, C., Cescatti, A., Dellwik, E., Duce, P., Gianelle, D., van Gorsel, E., Kiely, G., Knohl, A., Margolis, H., McCaughey, H., Merbold, L., Montagnani, L., Papale, D., Reichstein, M., Saunders, M., Serrano-Ortiz, P., Sottocornola, M., Spano, D., Vaccari, F., and Varlagin, A.: A data-driven analysis of energy balance closure across FLUXNET research sites: The role of landscape scale heterogeneity, Agr. Forest Meteorol., 171–172, 137–152, https://doi.org/10.1016/j.agrformet.2012.11.004, 2013.
Tramontana, G., Jung, M., Schwalm, C. R., Ichii, K., Camps-Valls, G., Ráduly, B., Reichstein, M., Arain, M. A., Cescatti, A., Kiely, G., Merbold, L., Serrano-Ortiz, P., Sickert, S., Wolf, S., and Papale, D.: Predicting carbon dioxide and energy fluxes across global FLUXNET sites with regression algorithms, Biogeosciences, 13, 4291–4313, https://doi.org/10.5194/bg-13-4291-2016, 2016.
Webb, E. K., Pearman, G. I., and Leuning, R.: Correction of flux measurements for density effects due to heat and water vapour transfer, Q. J. Roy. Meteorol. Soc., 106, 85–100, https://doi.org/10.1002/qj.49710644707, 1980.
Wilson, K., Goldstein, A., Falge, E., Aubinet, M., Baldocchi, D., Berbigier, P., Bernhofer, C., Ceulemans, R., Dolman, H., Field, C., Grelle, A., Ibrom, A., Law, B. E., Kowalski, A., Meyers, T., Moncrieff, J., Monson, R., Oechel, W., Tenhunen, J., Valentini, R., and Verma, S.: Energy balance closure at FLUXNET sites, Agr. Forest Meteorol., 113, 223–243, https://doi.org/10.1016/S0168-1923(02)00109-0, 2002.
Wutzler, T., Lucas-Moffat, A., Migliavacca, M., Knauer, J., Sickel, K., Šigut, L., Menzer, O., and Reichstein, M.: Basic and extensible post-processing of eddy covariance flux data with REddyProc, Biogeosciences, 15, 5015–5030, https://doi.org/10.5194/bg-15-5015-2018, 2018.
Xu, T., Guo, Z., Liu, S., He, X., Meng, Y., Xu, Z., Xia, Y., Xiao, J., Zhang, Y., Ma, Y., and Song, L.: Evaluating Different Machine Learning Methods for Upscaling Evapotranspiration from Flux Towers to the Regional Scale, J. Geophys. Res.-Atmos., 123, 8674–8690, https://doi.org/10.1029/2018JD028447, 2018.
Yao, J., Liu, H., Huang, J., Gao, Z., Wang, G., Li, D., Yu, H., and Chen, X.: Accelerated dryland expansion regulates future variability in dryland gross primary production, Nat. Commun., 11, 1665, https://doi.org/10.1038/s41467-020-15515-2, 2020.
Yao, J., Gao, Z., Huang, J., Liu, H., and Wang, G.: US-Hn1 flux and meteorological data, figshare [data set], https://doi.org/10.6084/m9.figshare.14747952, 2021.
Zeng, J., Matsunaga, T., Tan, Z. H., Saigusa, N., Shirai, T., Tang, Y., Peng, S., and Fukuda, Y.: Global terrestrial carbon fluxes of 1999–2019 estimated by upscaling eddy covariance data with a random forest, Sci. Data, 7, 1–11, https://doi.org/10.1038/s41597-020-00653-5, 2020.
Gap-filling usually accounts for a large source of uncertainties in the annual CO2 fluxes, though gap-filling CO2 fluxes is challenging at dryland sites due to small fluxes. Using data collected from a semiarid site, four machine learning methods are evaluated with different lengths of artificial gaps. The artificial neural network and random forest methods outperform the other methods. With these methods, uncertainties in the annual CO2 flux at this site are estimated to be within 16 g C m−2.
Gap-filling usually accounts for a large source of uncertainties in the annual CO2 fluxes,...