The 50 most-cited articles in Journal of Geophysical Research Atmospheres, 2022

Abstract Global‐scale changes in water vapor and responses to surface temperature variability since 1979 are evaluated across a range of satellite and ground‐based observations, a reanalysis (ERA5) and coupled and atmosphere‐only CMIP6 climate model simulations. Global‐mean column integrated water vapor increased by 1%/decade during 1988–2014 in observations and atmosphere‐only simulations. However, coupled simulations overestimate water vapor trends and this is partly explained by past studies showing that internal climate variability suppressed observed warming in this period. Decreases in low‐altitude tropical water vapor in ERA5 and ground‐based observations before around 1993 are considered suspect based on inconsistency with simulations and increased column integrated water vapor in microwave satellite data since 1979. Atmospheric Infra‐red Sounder satellite data does not capture the increased tropospheric water vapor since 2002 shown by other satellite, reanalysis, and model products. However, global water vapor responses to interannual surface temperature variability are…

Abstract We investigate the dependence of radiative feedback on the pattern of sea‐surface temperature (SST) change in 14 Atmospheric General Circulation Models (AGCMs) forced with observed variations in SST and sea‐ice over the historical record from 1871 to near‐present. We find that over 1871–1980, the Earth warmed with feedbacks largely consistent and strongly correlated with long‐term climate sensitivity feedbacks (diagnosed from corresponding atmosphere‐ocean GCM abrupt‐4xCO2 simulations). Post 1980, however, the Earth warmed with unusual trends in tropical Pacific SSTs (enhanced warming in the west, cooling in the east) and cooling in the Southern Ocean that drove climate feedback to be uncorrelated with—and indicating much lower climate sensitivity than—that expected for long‐term CO 2 increase. We show that these conclusions are not strongly dependent on the Atmospheric Model Intercomparison Project (AMIP) II SST data set used to force the AGCMs, though the magnitude of feedback post 1980 is generally smaller in nine AGCMs forced with alternative HadISST1 SST boundary…

Abstract The NOAA/NASA Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) experiment was a multi‐agency, inter‐disciplinary research effort to: (a) obtain detailed measurements of trace gas and aerosol emissions from wildfires and prescribed fires using aircraft, satellites and ground‐based instruments, (b) make extensive suborbital remote sensing measurements of fire dynamics, (c) assess local, regional, and global modeling of fires, and (d) strengthen connections to observables on the ground such as fuels and fuel consumption and satellite products such as burned area and fire radiative power. From Boise, ID western wildfires were studied with the NASA DC‐8 and two NOAA Twin Otter aircraft. The high‐altitude NASA ER‐2 was deployed from Palmdale, CA to observe some of these fires in conjunction with satellite overpasses and the other aircraft. Further research was conducted on three mobile laboratories and ground sites, and 17 different modeling forecast and analyses products for fire, fuels and air quality and climate implications. From Salina, KS the…

Abstract Atmospheric rivers, or long but narrow regions of enhanced water vapor transport, are an important component of the hydrologic cycle as they are responsible for much of the poleward transport of water vapor and result in precipitation, sometimes extreme in intensity. Despite their importance, much uncertainty remains in the detection of atmospheric rivers in large datasets such as reanalyses and century scale climate simulations. To understand this uncertainty, the Atmospheric River Tracking Method Intercomparison Project (ARTMIP) developed tiered experiments, including the Tier 2 Reanalysis Intercomparison that is presented here. Eleven detection algorithms submitted hourly tags‐‐binary fields indicating the presence or absence of atmospheric rivers‐‐of detected atmospheric rivers in the Modern Era Retrospective Analysis for Research and Applications, version 2 (MERRA‐2) and European Centre for Medium‐Range Weather Forecasts' Reanalysis Version 5 (ERA5) as well as six‐hourly tags in the Japanese 55‐year Reanalysis (JRA‐55). Due to a higher climatological mean for…

Abstract The persistent and growing spread in effective climate sensitivity (ECS) across global climate models necessitates rigorous evaluation of their cloud feedbacks. Here we evaluate several cloud feedback components simulated in 19 climate models against benchmark values determined via an expert synthesis of observational, theoretical, and high‐resolution modeling studies. We find that models with smallest feedback errors relative to these benchmark values generally have moderate total cloud feedbacks (0.4–0.6 W m −2 K −1 ) and ECS (3–4 K). Those with largest errors generally have total cloud feedback and ECS values that are too large or too small. Models tend to achieve large positive total cloud feedbacks by having several cloud feedback components that are systematically biased high rather than by having a single anomalously large component, and vice versa. In general, better simulation of mean‐state cloud properties leads to stronger but not necessarily better cloud feedbacks. The Python code base provided herein could be applied to developmental versions of models to…

Abstract We examine the thermal structure of the mesosphere and lower thermosphere (MLT) using observations from 2002 through 2021 from the SABER instrument on the NASA TIMED satellite. These observations show that the MLT has significantly cooled and contracted between the years 2002 and 2019 (the year of the most recent solar minimum) due to a combination of a decline in the intensity of the 11‐year solar cycle and increasing carbon dioxide (CO2.) During this time the thickness of atmosphere between the 1 and 10−4 hPa pressure surfaces (approximately 48 and 105 km) has contracted by 1,333 m, of which 342 m is attributed to increasing CO2. All other pressure surfaces in the MLT have similarly contracted. We further postulate that the MLT in the two most recent solar minima (2008–2009 and 2019–2020) was very likely the coldest and thinnest since the beginning of the Industrial Age. The sensitivity of the MLT to a doubling of CO2 is shown to be −7.5 K based on observed trends in temperature and growth rates of CO2. Colder temperatures observed at 10−4 hPa in 2019 than in the prior…

Abstract We analyze the effects of the diurnal cycle of fire emissions (DCFE) and plume rise on U.S. air quality using the MUSICAv0 (Multi‐Scale Infrastructure for Chemistry and Aerosols Version 0) model during the FIREX‐AQ (Fire Influence on Regional to Global Environments and Air Quality) and WE‐CAN (Western wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen) field campaigns. To include DCFE in the model, we employ two approaches: a DCFE climatology and DCFE derived from a satellite fire radiative power product. We also implemented two sets of plume‐rise climatologies, and two plume‐rise parameterizations. We evaluate the model performance with airborne measurements, U.S. EPA Air Quality System surface measurements, and satellite products. Overall, including plume rise improves model agreement with observations such as aircraft observations of CO and NOx for FIREX‐AQ and WE‐CAN. Applying DCFE also improves model performance, such as for surface PM2.5 in fire‐impacted regions. The impact of plume rise is larger than the impact of DCFE. Plume rise can greatly…

Abstract Afforestation is an appropriate approach to control soil erosion, but consumes extra water resources. It also exerts feedbacks on local precipitation, affecting the water availability for water‐limited areas. The Chinese Loess Plateau (LP) has implemented the world's largest afforestation program to mitigate severe soil erosion. However, it remains unclear how the atmospheric water cycle responds to large‐scale afforestation under climate change. Here we show that afforestation elevates precipitation in rainy season by intensifying the atmospheric water cycle over the LP. Results show the upward trend of vegetation coverage fraction increased by 3.15% decade−1 and climatological precipitation increased by 54.62 mm after launching the large‐scale afforestation in 1999. Such afforestation also enhanced evapotranspiration by 22.56 mm. We found the moisture inflow and outflow continuously decreased, but more atmospheric moisture was retained since the rate of decline of inflow was less than that of outflow. Using a dynamic precipitation recycling method, we explored changes in…

The amount of ice versus supercooled water in clouds is important for their radiative properties and role in climate feedbacks. Hence, knowledge of the concentration of ice-nucleating particles (INPs) is needed. Generally, the concentrations of INPs are found to be very low in remote marine locations allowing cloud water to persist in a supercooled state. We had expected the concentrations of INPs at the North Pole to be very low given the distance from open ocean and terrestrial sources coupled with effective wet scavenging processes. Here we show that during summer 2018 (August and September) high concentrations of biological INPs (active at >-20°C) were sporadically present at the North Pole. In fact, INP concentrations were sometimes as high as those recorded at mid-latitude locations strongly impacted by highly active biological INPs, in strong contrast to the Southern Ocean. Furthermore, using a balloon borne sampler we demonstrated that INP concentrations were often different at the surface versus higher in the boundary layer where clouds form. Back trajectory analysis…

Abstract Dynamical downscaling remains a powerful tool for studying regional climate processes, and the genesis of high‐resolution historical and future climate data. This technique is particularly important over areas of complex terrain, such as the western United States (WUS), where global models are especially limited in representing regional climate. After identifying a suite of WRF options that best simulate snow and precipitation for an average water year (2010) over the WUS, we evaluate the performance of the dynamically downscaled European Centre for Medium‐range Weather Forecasting's fifth Reanalysis (ERA5) from 1980 to 2020 on 45‐km, 9‐km, and two 3‐km grids. We find that by decreasing the horizontal grid spacing within WRF, improvements to Sierra Nevada and Northern Rocky Mountain snow, Santa Ana and Diablo winds, and coastal meteorology occur. For landfalling atmospheric rivers (ARs), the downscaled reanalysis simulates greater upstream integrated vapor transport (IVT) than ERA5. However, WRF skillfully simulates the positioning of the IVT and the timing and magnitude of…

Abstract Brown carbon (BrC) has been recognized as an important contributor to global warming due to its absorption of solar radiation with strong wavelength dependence. While early studies mostly consider biomass burning as a major emission source, a few recent studies have suggested coal combustion and vehicle exhaust as important contributors to BrC emissions. Considering dominant coal consumption, large residential biofuel usage, and the increasing number of vehicles, BrC pollution could result in remarkable regional climate effects in China. This study gives an overview of sources, chemical composition and absorption properties of BrC, focusing on BrC categorization and its absorption measurement techniques. The basic pollution features of BrC in China, including surface concentrations, column burden, sources and associated absorbing properties are then summarized and compared to other countries. BrC emissions as well as its optical emission at 365 nm from the primary sources in China are also summarized to provide a more straightforward understanding of the light‐absorbing…

Abstract Satellite, reanalysis, and ocean in situ data are analyzed to evaluate regional, hemispheric and global mean trends in Earth's energy fluxes during the first 20 years of the twenty‐first century. Regional trends in net top‐of‐atmosphere (TOA) radiation from the Clouds and the Earth's Radiant Energy System (CERES), ECMWF Reanalysis 5 (ERA5), and a model similar to ERA5 with prescribed sea surface temperature (SST) and sea ice differ markedly, particularly over the Eastern Pacific Ocean, where CERES observes large positive trends. Hemispheric and global mean net TOA flux trends for the two reanalyses are smaller than CERES, and their climatological means are half those of CERES in the southern hemisphere (SH) and more than nine times larger in the northern hemisphere (NH). The regional trend pattern of the divergence of total atmospheric energy transport (TEDIV) over ocean determined using ERA5 analyzed fields is similar to that inferred from the difference between TOA and surface fluxes from ERA5 short‐term forecasts. There is also agreement in the trend pattern over ocean…

Abstract Global trends in tropospheric nitrogen dioxide (NO2) have changed dramatically in the past decade. Here, we investigate tropospheric NO2 variabilities over United States, Europe, and E. China in 2005–2018 to explore the mechanisms governing the variation of this critical pollutant. We found large uncertainties in the trends of anthropogenic nitrogen oxides (NOx) emissions, for example, the reductions of NOx emissions, derived with different approaches and data sets, are in the range of 35%–50% over the United States and 15%–45% over Europe in 2005–2018. By contrast, the analysis in this work indicates declines of anthropogenic NOx emissions by about 40% and 25% over the United States and Europe, respectively, in 2005–2018, and about 20% over E. China in 2012–2018. However, the shift of major NOx sources from power generation to industrial and transportation sectors has led to noticeable diminishing effects in emission controls. Furthermore, satellite measurements exhibit the influence of NO2 background levels over the United States and Europe, which offset the impacts of…

Abstract Despite the necessity of Global Climate Models (GCMs) sub‐selection in downscaling studies, an objective approach for their selection is currently lacking. Building on the previously established concepts in GCMs evaluation frameworks, we develop a weighted averaging technique to remove the redundancy in the evaluation criteria and rank 37 GCMs from the sixth phase of the Coupled Models Intercomparison Project over the contiguous United States. GCMs are rated based on their average performance across 66 evaluation measures in the historical period (1981–2014) after each metric is weighted between zero and one, depending on its uniqueness. The robustness of the outcome is tested by repeating the process with the empirical orthogonal function analysis in which each GCM is ranked based on its sum of distances from the reference in the principal component space. The two methodologies work in contrasting ways to remove the metrics redundancy but eventually develop similar GCMs rankings. A disparity in GCMs' behavior related to their sensitivity to the size of the evaluation suite…

Abstract El Niño–Southern Oscillation is the strongest interannual variability in the tropical oceans and the major source of global climate predictability. In this work, we examine the evolution of oceanic and atmospheric anomalies in the tropical Pacific during 2020/2021 La Niña and compare it with the historical strong La Niña events since 1982, identify the contributions of different time scale components, and assess the predictions and the impact on extra‐tropical climate. 2020/2021 La Niña emerged in August 2020 and dissipated in May 2021. 2020/2021 La Niña was uniquely preceded by a borderline El Niño instead of an El Niño and a weak equatorial‐heat discharge process. That resulted in the weakest event among the strong La Niñas since 1982, although there were strong upwelling Kelvin wave activities. Moreover, compared with other strong La Niña events, the surface easterly wind anomalies and the warm pool extended further eastward in 2020/2021 La Niña, linking to a relatively weaker dipole‐like pattern of the subsurface ocean temperature anomalies. The strength of all the…

Abstract A multivariate bias correction based on N‐dimensional probability density function transform (MBCn) technique is applied to four different high‐resolution regional climate change simulations and key meteorological variables, namely precipitation, mean near‐surface air temperature, near‐surface maximum air temperature, near‐surface minimum air temperature, surface downwelling solar radiation, relative humidity, and wind speed. The impact of bias‐correction on the historical (1980–2005) period, the inter‐variable relationships, and the measures of spatio‐temporal consistency are investigated. The focus is on the discrepancies between the original and the bias‐corrected results over five agro‐ecological zones. We also evaluate relevant indices for agricultural applications such as climate extreme indices, under current and future (2020–2050) climate change conditions based on the RCP4.5. Results show that MBCn successfully corrects the seasonal biases in spatial patterns and intensities for all variables, their intervariable correlation, and the distributions of most of the…

Abstract Bowen ratio reflects the partitioning between sensible and latent heat fluxes and plays a crucial role in land–atmosphere interaction. In this study, the spatiotemporal variations of Bowen ratio among 12 vegetation types were analyzed using observations from 203 FLUXNET sites and compared against Community Land Model (CLM) simulations. Results showed that the annual mean Bowen ratio across all sites was 1.48 ± 1.20 (mean ± SD). Sites with Bowen ratios less than 1 were found across all continents, and the ones with a higher Bowen ratio appeared in dry and warm areas. Open shrublands showed the highest Bowen ratio (3.04 ± 0.58), whereas wetlands showed the lowest (0.74 ± 0.09). In terms of seasonality, Bowen ratio generally showed lower values in local summer and higher in spring and autumn in the northern hemisphere; the opposite occurred in the southern hemisphere. The spatiotemporal variations in Bowen ratio can be explained by climatic, geographical, and biological factors, with climate factors having the greatest impact. The spatial correlation analyses suggested Bowen…

Abstract Nitroaromatic compounds (NACs) are important light absorption contributors to atmospheric brown carbon; however, their formation pathways and the key influential factors in polluted urban atmospheres are largely unknown. Herein, we present the molecular characterization of atmospheric particulate NACs in urban Shanghai by applying ultra‐high‐performance liquid chromatography coupled to Orbitrap mass spectrometry, and investigated their seasonal and diel variations and formation pathways. The total number and abundance of NACs increased significantly during air pollution episodes, and these NACs exhibited the greatest relative abundance among CHON compounds. The 12 quantified NACs exhibited higher levels in winter (52.3 ± 29.1 ng m−3) than summer (7.83 ± 3.30 ng m−3), largely owing to air masses mostly passing through northern heating regions. Among NACs, 4‐nitrophenol and 4‐nitrocatechol were the most abundant species. Most of NACs were enhanced via photooxidation during the day in summer, while the day‐night variations in winter were not as obvious. Further analysis of…

Abstract Cirrus ice crystals are produced heterogeneously on ice‐nucleating particles (INPs) and homogeneously in supercooled liquid solution droplets. They grow by uptake of water molecules from the ice‐supersaturated vapor. The precursor particles, characterized by disparate ice nucleation abilities and number concentrations, compete for available vapor during ice formation events. We investigate cirrus formation events systematically in different temperature and updraft regimes, and for different INP number concentrations and time‐independent nucleation efficiencies. We consider vertical air motion variability due to mesoscale gravity waves and effects of supersaturation‐dependent deposition coefficients for water molecules on ice surfaces. We analyze ice crystal properties to better understand the dynamics of competing nucleation processes. We study the reduction of ice crystal numbers produced by homogeneous freezing due to INPs in both, individual simulations assuming constant updraft speeds and in ensemble simulations based on a stochastic representation of vertical wind…

Abstract Contrail ice nucleation and ice crystal loss during the vortex phase control ice crystal numbers in young contrails and can have a strong impact on the properties and the life cycle of contrail cirrus. For current soot number emissions, ice nucleation is controlled by the number of emitted soot particles and atmospheric conditions while the vortex phase loss depends predominantly on the nucleated ice crystal numbers and the ambient relative humidity. Initial ice crystal numbers after the vortex phase are close to the emitted soot particle number only for very low ambient temperatures (<210 K) and for highly ice‐supersaturated conditions. Higher temperatures and lower relative humidities lead to significantly decreased ice crystal numbers. Global climate model simulations show that initial contrail ice crystal numbers per fuel mass are on average 50%–65% decreased relative to the soot number emission index in the extratropics and more in tropics. In the extratropics, this is mainly caused by a high ice crystal loss during the vortex phase and in the (sub)tropics and at lower…

Abstract Isoprene is the dominant nonmethane organic compound emitted to the atmosphere, where it drives ozone and aerosol production, modulates atmospheric oxidation, and interacts with the global nitrogen cycle. Isoprene emissions are highly variable and uncertain, as is the nonlinear chemistry coupling isoprene and its primary sink, the hydroxyl radical. Space‐based isoprene measurements can help close the gap on these uncertainties, and when combined with concurrent formaldehyde data provide a new constraint on atmospheric oxidation regimes. Here, we present a next‐generation machine‐learning isoprene retrieval for the Cross‐track Infrared Sounder (CrIS) that provides improved sensitivity, lower noise, and thus higher space‐time resolution than earlier approaches. The Retrieval of Organics from CrIS Radiances (ROCR) isoprene measurements compare well with previous space‐based retrievals as well as with the first‐ever ground‐based isoprene column measurements, with 20%–50% discrepancies that reflect differing sources of systematic uncertainty. An ensemble of sensitivity tests…

Abstract Studying the spatiotemporal variations of the urban heat island (UHI) effect and its cause is important towards understanding urban climate change, planning and green development, and disaster mitigation. In this paper, by using surface observations and reanalysis data with objective classification of synoptic weather patterns (SWPs), we analyze the associations between canopy UHI intensity (CUHI) and SWPs in the planetary boundary layer (PBL) and their potential drivers during wintertime of the period 2012–2017. Six dominant types of SWP are identified as follows: In the case of Types 3, 4, and 6, weak high‐pressure systems exist to the south of Beijing, resulting in weak southerly winds with low PBL height, large cloud coverage and high relative humidity (RH). These conditions are generally conducive to a strengthening of the CUHII. In contrast, under Types 1, 2, and 5, high‐pressure systems are located to the northwest of Beijing, and the associated strong northwesterly flows of dry and cold air strengthen the boundary layer mixing process, resulting in large wind speed…

Abstract Previous studies have estimated that 25%–35% of Amazonian precipitation comes from evapotranspiration (ET) within the basin. However, due to simplifying assumptions of traditional models, these studies primarily focus on large spatial and temporal scales. This study is the first to analyze the moisture of Amazonian origin at the annual to daily timescale in four different subregions of the Amazon. We analyze the sources, sinks and stores of moisture that originates as Amazonian ET. To do this, we use the Weather Research and Forecast (WRF) regional meteorological model with the added capability of water vapor tracers to track this moisture. Moisture of Amazonian origin shows strong annual and semi‐annual signals, with contrasting behavior between the northern and southern parts of the basin. The tracers reveal a strong diurnal cycle of Amazonian water vapor which had not been previously reported. This signal is related to the diurnal cycle of ET, convective precipitation and advected moisture. ET's contribution to atmospheric moisture increases from early morning into the…

Abstract Simultaneous measurements of volatile organic compounds (VOCs) using two PTR‐TOF‐MS instruments were conducted at urban and suburban sites of New Delhi during the winter of 2018. The time series of VOC mixing ratios show substantial variations mainly influenced by local emissions and meteorological conditions. Mixing ratios of methanol (∼28 ppbv), acetaldehyde (7.7 ppbv), acetone (10.6 ppbv), isoprene (2.8 ppbv) and monoterpenes (0.84 ppbv) at the suburban site were higher than those at the urban site, while levels of aromatic VOCs were almost similar. The strong nighttime correlations of isoprene and monoterpenes with CO and benzene at the urban site indicate their predominant anthropogenic origin. Higher emission ratios of ∆VOCs/∆CO and ∆VOCs/∆benzene than those reported for vehicular exhaust suggest the contributions of other sources. In addition to vehicular emissions, episodes of biomass burning, industrial plumes and aged air strongly influenced the levels of VOCs at the suburban site. Despite the predominant primary anthropogenic emissions, the higher daytime…

Detailed knowledge of the physical and chemical properties and sources of particles that form clouds is especially important in pristine areas like the Arctic, where particle concentrations are often low and observations are sparse. Here, we present in situ cloud and aerosol measurements from the central Arctic Ocean in August-September 2018 combined with air parcel source analysis. We provide direct experimental evidence that Aitken mode particles (particles with diameters ≲70 nm) significantly contribute to cloud condensation nuclei (CCN) or cloud droplet residuals, especially after the freeze-up of the sea ice in the transition toward fall. These Aitken mode particles were associated with air that spent more time over the pack ice, while size distributions dominated by accumulation mode particles (particles with diameters ≳70 nm) showed a stronger contribution of oceanic air and slightly different source regions. This was accompanied by changes in the average chemical composition of the accumulation mode aerosol with an increased relative contribution of organic material toward…

Abstract Unexpectedly frequent severe haze episodes were observed in Beijing during February–March in 2021 after two phases of clean air action plan (2013–2020), yet the causes remained unclear. Here, we conducted real‐time fine particle (PM2.5) composition measurements during January–March in 2021 using a time‐of‐flight aerosol chemical speciation monitor and an aethalometer and compared with those during the coronavirus disease (COVID‐19) period in 2020. Our results showed ubiquitously elevated concentrations of chloride, black carbon (BC), and primary organic aerosol (POA) in 2021, suggesting increased primary emissions during the post‐COVID‐19 period. By using the machine learning‐based random forest (RF) algorithm, we found largely different responses of aerosol changes to meteorology in different months. After decoupling the effects of meteorology, the PM2.5 changes from 2020 to 2021 were reduced from −35.6% to −29.0% in January, −24.1% to −4.5% in February, and +92.6% to +34.2% in March, respectively. Our results demonstrate the dominant roles of stagnant meteorology and…

Abstract Previous studies have shown that Saharan dust can be transported thousands of miles, affecting regional climates, environments, and ecosystems. However, research on the long‐range transport of Saharan dust in Asia remains limited. We systematically investigated the long‐range transportation of Saharan dust over East Asia from 2007 to 2020 using WRF‐Chem model simulations, space‐borne CALIPSO lidar observations, NCEP/NCAR reanalysis data, as well as HYSPLIT trajectory analysis. The results show that one quarter (24.3 ± 6.2%) of dust events in East Asia during 2007–2020 originated from the Sahara Desert. Moreover, long‐range transported Saharan dust over East Asia was usually distributed in the upper troposphere. The average total amount of transported Saharan dust over East Asia between 2010 and 2015 was estimated at 33.05 ± 9.78 Tg/yr. Additionally, Saharan dust could be transported eastward all year and contributed about 35.8% of dust loading in the upper troposphere in Northern China in spring, which is almost the same amount of dust aerosols lifted up from East Asian…

Abstract From 17–22 July 2021, Henan Province experienced the most severe torrential rainfall event since 1975 with a maximum hourly precipitation of 201.9 mm appeared in Zhengzhou, which was the largest hourly rainfall thus far observed by meteorological observation stations over the Chinese Mainland. The appearance of a long‐lived (21‐hr) northwestward‐moving mesoscale convective vortex (MCV) and its interaction with its parent mesoscale convective system (MCS) was crucial to produce the extremely strong heavy rainfall in Zhengzhou. The backward trajectory analysis indicates that air particles in the lower troposphere beneath the MCS over Henan contributed mostly to the MCV's formation. These air particles experienced notable ascending motions and condensation with their strong cyclonic vorticity mostly produced 1‐hr before the MCV's formation. Vorticity budget denotes that strong upward transport of cyclonic vorticity and convergence‐related vertical stretching, both of which were mainly due to convection associated with the parent MCS, acted as dominant factors for the MCV's…

Abstract Strengthened land‐atmosphere coupling in the northeastern United States (NEUS), accompanied by a positive soil moisture‐rainfall feedback, may lead to more drought. Coupling between the land and atmosphere emerges when low soil moisture values limit surface latent heat flux, or evapotranspiration, so that a majority of absorbed solar radiation is emitted from the surface as sensible heat. In this study, the Weather Research and Forecasting model was run with four prescribed soil moisture levels across 7 years to elucidate the strength of land‐atmosphere coupling under potential, future soil moisture states in the NEUS. Under drier conditions, land‐atmosphere coupling strengthens, and a positive soil moisture‐precipitation feedback develops in all years despite differences in the amount of moisture advected into the study domain. As snowpack decreases and evaporative demand increases, soil conditions may become drier in future summers over the NEUS, resulting in the more frequent development of drought.

Abstract Fram Strait in the northern North Atlantic is a key region for marine cold air outbreaks (MCAOs), southward discharges of polar air under northerly air flow, which have a strong impact on air‐sea heat fluxes, boundary layer processes and severe weather. This study investigates climatologies and decadal trends of Fram Strait MCAOs of different intensity classes based on the ERA5 reanalysis product for 1979–2020. Among striking interannual variability, it is shown that the main MCAO season is December through March, when MCAOs occur around 2/3 of the time. We report on significant decadal MCAO decreases in December and January, and a significant increase in March. While the mid‐winter decrease is mainly related to the different paces of warming between the surface and the lower atmosphere, the increase in March can be related to changes in synoptic circulation patterns. As an explanation for the latter, a possible feedback between retreating Barents Sea sea ice, enhanced cyclonic activity and Fram Strait MCAOs is postulated. Exemplifying the trend toward stronger MCAOs during…

Abstract The complex morphology of soot aggregates is a major source of uncertainty in evaluating their warming effects in the atmosphere. Fractal dimension (D f ) is a key parameter in quantifying the morphology of soot particles. Previous studies are mostly based on manual identification of soot monomers in electron microscopic images and are hard to provide comparable results in determination of D f . Here we develop a novel image recognition technique to automatically determine the D f of individual soot aggregates from electron microscopy images. The novel method has been shown to be able to trace the small change of the soot D f from an urban tunnel (1.61 ± 0.19) to its exit (1.70 ± 0.15). By applying this new method, we show a substantial difference in average D f of soot particles emitted from vehicles (1.66 ± 0.17) than from biomass burning (1.75 ± 0.18) and coal burning (1.76 ± 0.18). Average D f of soot from an urban atmosphere (1.77 ± 0.18) is close to that from biomass and coal combustion but much lower than that from a rural atmosphere (1.85 ± 0.13). In summary, the…

Abstract Infrared aerosol spectra derived from Atmospheric Chemistry Experiment measurements following the June 2019 Raikoke volcanic eruption are used to evaluate the composition of stratospheric aerosols in the Arctic. A blanket of aerosols, spanning an altitude range from the tropopause (8–11 km) to 20 km, persisted in the stratosphere over northern latitudes for many months. The aerosols within this blanket were almost exclusively sulfates. The percentage of sulfuric acid in the aerosols decreased over time, dropping below 50% H2SO4 concentration at some altitudes by March 2020. Contrary to previous reports, the aerosol blanket was not comprised of smoke particles.

Abiotic and biotic releases of nitrous acid (HONO) from soils contribute substantially to the missing source of tropospheric HONO and hydroxyl radicals (OH). However, global and regional patterns of soil HONO emissions are rarely quantified, and the contributions of such emissions to atmospheric oxidization capacity are unclear. Here, we present that the best estimate of global soil HONO emissions in 2017 is 9.67 with a range of 7.36-11.99 Tg N yr⁻ 1 , where cropland soils accounted for ~ 79%. The analyses also indicate that regional soil HONO emissions enhanced ground OH concentrations by 10-60% and ozone concentrations by 0.5-1.5 ppb at daytime in the ambient area of Shanghai, China. The impact of soil HONO emissions on OH budgets were more important in rural than urban areas. These findings suggest that the global soil HONO emissions, especially from cropland, could quicken photochemical reactions and aggravate air pollution in rural areas.

Abstract Biomass burning (BB) events are occurring globally with increasing frequency, and their emissions are having more impacts on human health and climate. Large ash particles are recognized as a BB product with major influences on soil and water environments. However, fine‐ash particles, which have diameters smaller than several microns and characteristic morphologies and compositions (mainly Ca and Mg carbonates), have not yet been explicitly considered as a major BB aerosol component either in field observations or climate models. This study measured BB aerosol samples using transmission electron microscopy (TEM) and ion chromatography during the Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) campaign. We show that significant amounts of fine ash‐bearing particles are transported >100 km from their fire sources. Our environmental chamber experiments suggest that they can act as cloud condensation and ice nuclei. We also found considerable amounts of fine ash‐bearing particles in the TEM samples collected during previous campaigns (Biomass Burning…

Abstract Despite the implication of aerosols for the radiation budget, there are persistent differences in data for the aerosol optical depth ( τ ) for 1998–2019. This study presents a comprehensive evaluation of the large‐scale spatio‐temporal patterns of mid‐visible τ from modern data sets. In total, we assessed 94 different global data sets from eight satellite retrievals, four aerosol‐climate model ensembles, one operational ensemble product, two reanalyses, one climatology and one merged satellite product. We include the new satellite data SLSTR and aerosol‐climate simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and the Aerosol Comparisons between Observations and Models Phase 3 (AeroCom‐III). Our intercomparison highlights model differences and observational uncertainty. Spatial mean τ for 60°N – 60°S ranges from 0.124 to 0.164 for individual satellites, with a mean of 0.14. Averaged τ from aerosol‐climate model ensembles fall within this satellite range, but individual models do not. Our assessment suggests no systematic improvement compared to…

Abstract Land surface albedo plays a critical role in climate, hydrological and biogeochemical modeling, and weather forecasting. It is often assigned in models and satellite retrievals by albedo climatology look‐up tables using land cover type and other variables; however, there are considerable differences in albedo simulations among models, which partially result from uncertainty in obsolete albedo climatology. Therefore, this study introduces a new global 500 m daily blue‐sky land surface albedo climatology data set under both actual and snow‐free surface conditions utilizing 20‐year Moderate Resolution Imaging Spectroradiometer products from Google Earth Engine. In situ measurements from 38 long‐term‐maintained sites were utilized to validate the accuracies of different albedo climatology datasets. The root‐mean‐square error, bias, and correlation coefficient of the new climatology are 0.031, −0.003, and 0.96, respectively, which are more accurate than the Global Land Surface Satellite, GlobAlbedo, and 16 model datasets. Data intercomparison suggests that ERA5 exhibits better…

Abstract This study examines the overall performance of the Noah with multiparameterization (Noah‐MP) land surface model in simulating key land‐atmosphere variables at a global scale and explores the feasibility of running Noah‐MP with regionally different combinations of parameterization schemes. We conducted Noah‐MP ensemble simulations and evaluated the annual means and seasonal cycles of the simulated latent heat flux, net radiation (RN), runoff, soil moisture, snow water equivalent, land surface temperature (LST), leaf area index (LAI), and gross primary productivity (GPP) against a wide variety of global products. The results show that the global patterns of the modeled annual means of these variables generally agree with those of the reference data sets. By evaluating the best simulations in the ensemble, we show that Noah‐MP performs very well in simulating global LST and RN but produces biases in annual mean LAI and GPP by more than 40% in most herbaceous regions. Overall, the main disagreements between Noah‐MP and the reference data sets occurred in the tropical, polar,…

Abstract The formation of the Aralkum (Aral Desert), following the severe desiccation of the former Aral Sea since the 1960s, has created what may be regarded as one of the world's most significant anthropogenic dust sources. In this paper, focusing on dust emission and transport patterns from the Aralkum, the dust life‐cycle has been simulated over Central Asia using the aerosol transport model COSMO‐MUSCAT (COnsortium for Small‐scale MOdelling‐MUltiScale Chemistry Aerosol Transport Model), making use of the Global Surface Water data set to take into account the sensitivity to changes in surface water coverage over the region between the 1980s (the “past”) and the 2010s (the “present”). Over a case study 1‐year period, the simulated dust emissions from the Aralkum region increased from 14.3 to 27.1 Tg year −1 between the past and present, an increase driven solely by the changes in the surface water environment. Of these simulated modern emissions, 14.5 Tg are driven by westerly winds, indicating that regions downwind to the east may be worst affected by Aralkum dust. However a…

Abstract The Arctic stratospheric polar vortex is an important driver of winter weather and climate variability and predictability in North America and Eurasia, with a downward influence that on average projects onto the North Atlantic Oscillation (NAO). While tropospheric circulation anomalies accompanying anomalous vortex states display substantial case‐by‐case variability, understanding the full diversity of the surface signatures requires larger sample sizes than those available from reanalyses. Here, we first show that a large ensemble of seasonal hindcasts realistically reproduces the observed average surface signatures for weak and strong vortex winters and produces sufficient spread for single ensemble members to be considered as alternative realizations. We then use the ensemble to analyze the diversity of surface signatures during weak and strong vortex winters. Over Eurasia, relatively few weak vortex winters are associated with large‐scale cold conditions, suggesting that the strength of the observed cold signature could be inflated due to insufficient sampling. For both…

Abstract Projected changes in the Northern Hemisphere stratospheric polar vortex are analyzed using Climate Model Intercomparison Project Phase 6 experiments. Previous studies showed that projections of the wintertime zonally averaged polar vortex strength diverge widely between climate models with no agreement on the sign of change, and that this uncertainty contributes to the regional climate change uncertainty. Here, we show that there remains large uncertainty in the projected strength of the polar vortex in experiments with global warming levels ranging from moderate (SSP245 runs) to large (Abrupt‐4xCO2 runs), and that the uncertainty maximizes in winter. Partitioning of the uncertainty in wintertime polar vortex strength projections reveals that, by the end of the 21st century, model uncertainty contributes half of the total uncertainty, with scenario uncertainty contributing only 10%. Regression analysis shows that up to 20% of the intermodel spread in projected precipitation over the Iberian Peninsula and northwestern US, and 20%–30% in near‐surface temperature over western…

Abstract Diagnosing the vertical distributions of ozone formation sensitivities within the boundary layers is the prerequisite for formulating proper ozone control strategies. From 1 January 2020, to 20 August 2021, a multi‐function MAX‐DOAS instrument was set up in Guangzhou to detect the NO 2 and HCHO vertical profiles. The ozone formation sensitivities in different height layers were diagnosed using the FNR sec , which was defined as the ratio of secondary HCHO to NO 2 VMRs (HCHO sec /NO 2 ). The secondary sources in ambient HCHO participate in the photochemical reactions directly, and the FNR sec can indicate the ozone formation sensitivities more accurately. Therefore, the secondary source was separated from ambient HCHO via a multi‐linear regression method, and its relative contribution was approximately 66.9 ± 6.3%. The sensitivity thresholds of ozone formation were determined by the slope of the linear regression analysis for O 3 versus the normalized secondary HCHO or NO 2 mixing ratios for different FNR sec ranges, which were 0.22 and 0.36. For the ground layer, the…

Abstract HONO concentrations in Beijing (BJ) and Sanmenxia (SMX) were simultaneously measured in winter with a duration of 1 month, and the sources and sinks of HONO in the two cities were comparably analyzed. BJ and SMX had different pollution characteristics. Direct vehicle emission made a contribution to observed HONO of about 28% in BJ, whereas it contributed to HONO only about 12% in SMX. Additionally, direct emission from coal combustion in SMX also made a significant contribution to atmospheric HONO, which could achieve to be 13%. In BJ, nighttime NO2 conversion on the aerosol and ground surfaces contributed to HONO sources of 15% and 27%, respectively. In SMX, nighttime NO2 conversion on the aerosol and ground surfaces contributed to HONO sources of 40% and 30%, respectively. Daytime NO2 heterogeneous conversion (including photo‐enhanced conversion) on the aerosol and ground surfaces was important in SMX. Daytime NO3− photolysis contributed 9% HONO in SMX and 4% in BJ. The primary OH production rates from photolysis of daytime HONO in both BJ and SMX were three orders of…

Abrupt and large-scale climate changes have occurred repeatedly and within decades during the last glaciation. These events, where dramatic warming occurs over decades, are well represented in both Greenland ice core mineral dust and temperature records, suggesting a causal link. However, the feedbacks between atmospheric dust and climate change during these Dansgaard-Oeschger events are poorly known and the processes driving changes in atmospheric dust emission and transport remain elusive. Constraining dust provenance is key to resolving these gaps. Here, we present a multi-technique analysis of Greenland dust provenance using novel and established, source diagnostic isotopic tracers as well as results from a regional climate model including dust cycle simulations. We show that the existing dominant model for the provenance of Greenland dust as sourced from combined East Asian dust and Pacific volcanics is not supported. Rather, our clay mineralogical and Hf-Sr-Nd and D/H isotopic analyses from last glacial Greenland dust and an extensive range of Northern Hemisphere potential…

Abstract Aerosol emissions from spaceflight activities play a small but increasing role in the background stratospheric aerosol population. Rockets used by the global launch industry emit black carbon (BC) particles directly into the stratosphere where they accumulate, absorb solar radiation, and warm the surrounding air. We model the chemical and dynamical response of the atmosphere to northern mid‐latitude rocket BC emissions. We initially examine emissions at a rate of 10 Gg per year, which is an order of magnitude larger than current emissions, but consistent with extrapolations of space traffic growth several decades into the future. We also perform runs at 30 and 100 Gg per year in order to better delineate the atmosphere's response to rocket BC emissions. We show that a 10 Gg/yr rocket BC emission increases stratospheric temperatures by as much as 1.5 K in the stratosphere. Changes in global circulation also occur. For example, the annual subtropical jet wind speeds slow down by as much as 5 m/s, while a 10%–20% weakening of the overturning circulation occurs in the northern…

Abstract To improve our understanding of the impact of sea salt aerosols (SSA) on the Earth's climate, it is critical to understand the physical mechanisms which determine the size‐resolved SSA production flux. Of the factors affecting SSA emissions, seawater salinity has perhaps received the least attention in the literature and previous studies have produced conflicting results. Here, we present a series of laboratory experiments designed to investigate the role of salinity on aerosol production from artificial seawater using a continuous plunging jet. During these experiments, the aerosol and surface bubble size distributions were monitored while the salinity was decreased from 35 to 0 g kg−1. Three distinct salinity regimes were identified: (a) A high salinity regime, 10–35 g kg−1, where lower salinity resulted in only minor reductions in particle number flux but notable reductions in particle volume flux; (b) an intermediate salinity regime, 5–10 g kg−1, with a local maximum in particle number flux; (c) a low salinity regime, <5 g kg−1, characterized by a rapid decrease in…

Abstract This study classifies meteorological regimes in the southeastern Texas region to identify environmental conditions that favor sea‐breeze induced convection. The classification is accomplished using a Self‐Organizing Map (SOM) approach. We applied SOM to 10 years of 700‐hPa geopotential height anomalies during the summer months from reanalysis data to distinguish three dominant synoptic regimes, with a continuum of transitional states between those. The primary regimes include: (a) a pre‐trough regime associated with a synoptic trough, (b) a post‐trough regime with upper‐level northerly flow, and (c) an anticyclonic regime within the westward extent of the Bermuda High. We project the data from the Geostationary Operational Environmental Satellite and the Next Generation Weather Radar system onto each SOM node to investigate the characteristics of cloud and precipitation properties in different regimes. When southeastern Texas is positioned to the southwest quadrant of a maritime high pressure system, an increased cloud frequency is observed over the region during the…

Abstract The extreme rainfall from 19 to 21 July 2021, which caused massive flooding and loss of life, is the second heaviest rainfall that has occurred in Henan province, central China. To identify the key factors controlling this rainfall event, we conducted an ensemble‐based analysis using ECMWF operational global ensemble forecasts. The forecasts of extreme rainfall had a relatively large spread and there was a large bias in the ensemble mean precipitation, indicating uncertainties in the forecast. The extreme rainfall was closely related to the Huang‐Huai cyclone and the southerly and southeasterly flows. Although they had little influence on the southeasterly flow, the uncertainty and predictability of typhoons In‐fa and Cempaka probably caused the variation in the southerly flow and the maintenance of the Huang‐Huai cyclone, which determined the amount of precipitation for this extreme event in the ensemble forecast model. When typhoon In‐fa was located further northwest, the northeasterly airflow generated by the binary interaction between typhoons In‐fa and Cempaka weakened…

Abstract Intense snowfall sublimation was observed during a precipitation event over Davis in the Vestfold Hills, East Antarctica, from 08 to 10 January 2019. Radar observations and simulations from the Weather Research and Forecasting model revealed that orographic gravity waves (OGWs), generated by a north‐easterly flow impinging on the ice ridge upstream of Davis, were responsible for snowfall sublimation through a foehn effect. Despite the strong meridional moisture advection associated with an atmospheric river (AR) during this event, almost no precipitation reached the ground at Davis. We found that the direction of the synoptic flow with respect to the orography determined the intensity of OGWs over Davis, which in turn directly influenced the snowfall microphysics. We hypothesize that turbulence induced by the OGWs likely enhanced the aggregation process, as identified thanks to dual‐polarization and dual‐frequency radar observations. This study suggests that despite the intense AR, the precipitation distribution was determined by local processes tied to the orography. The…

Abstract Spatial and temporal distributions of Clear‐Air Turbulence (CAT) in the Northern Hemisphere were investigated using 41 years (1979–2019) of the European Centre for Medium‐range Weather Forecast Reanalysis version 5 (ERA5) data. We used two groups of CAT diagnostics to determine occurrence frequencies: (a) commonly used empirical turbulence indices (TI1, TI2, and TI3) and their components [vertical wind shear (VWS), deformation, ‐divergence, and divergence tendency], and (b) theoretical instability indicators [Richardson number (Ri), potential vorticity (PV), and Brunt‐Vӓisӓlӓ frequency]. The empirical indices showed high frequencies of moderate‐or‐greater (MOG)‐level CAT potential over the East Asian, Eastern Pacific, and Northwestern Atlantic regions in winter. Over East Asia, the entrance region of strong upper‐level jets showed the highest frequencies in TI1, TI2, and TI3 due mainly to strong VWS. The Eastern Pacific and Northwestern Atlantic areas near the exit region of jets had relatively high frequencies of these indices and also Ri. PV frequency was high on the…

Abstract This study evaluates the impact of land surface models (LSMs) and urban heterogeneity [using local climate zones (LCZs)] on air temperature simulated by the Weather Research and Forecasting model (WRF) during a regional extreme event. We simulated the 2017 heatwave over Europe considering four scenarios, using WRF coupled with two LSMs (i.e., Noah and Noah‐MP) with default land use/land cover (LULC) and with LCZs from the World Urban Database and Access Portal Tools (WUDAPT). The results showed that implementing the LCZs significantly improves the WRF simulations of the daily temperature regardless of the LSMs. Implementing the LCZs altered the surface energy balance partitioning in the simulations (i.e., the sensible heat flux was reduced and latent heat flux was increased) primarily due to a higher vegetation feedback in the LCZs. The changes in the surface flux translated into an increase in the simulated 2‐m relative humidity and 10‐m wind speed as well as changed air temperature within cities section and generated a temperature gradient that affected the temperatures…