Showing papers in "Journal Of Geophysical Research: Atmospheres in 2022"

Increases in Future AR Count and Size: Overview of the ARTMIP Tier 2 CMIP5/6 Experiment

Abstract: The Atmospheric River (AR) Tracking Method Intercomparison Project (ARTMIP) is a community effort to systematically assess how the uncertainties from AR detectors (ARDTs) impact our scientific understanding of ARs. This study describes the ARTMIP Tier 2 experimental design and initial results using the Coupled Model Intercomparison Project (CMIP) Phases 5 and 6 multi-model ensembles. We show that AR statistics from a given ARDT in CMIP5/6 historical simulations compare remarkably well with the MERRA-2 reanalysis. In CMIP5/6 future simulations, most ARDTs project a global increase in AR frequency, counts, and sizes, especially along the western coastlines of the Pacific and Atlantic oceans. We find that the choice of ARDT is the dominant contributor to the uncertainty in projected AR frequency when compared with model choice. These results imply that new projects investigating future changes in ARs should explicitly consider ARDT uncertainty as a core part of the experimental design.

A High‐Resolution Whole‐Atmosphere Model With Resolved Gravity Waves and Specified Large‐Scale Dynamics in the Troposphere and Stratosphere

Abstract: We present a new version of the HIgh Altitude Mechanistic general Circulation Model (HIAMCM) with specified dynamics. We utilize a spectral method that nudges only the large-scale flow to MERRA-2 reanalysis. The nudged HIAMCM simulates gravity waves (GWs) down to horizontal wavelengths of about 200 km from the troposphere to the thermosphere like the free-running model, including the generation of secondary and tertiary GWs. Case studies show that the simulated large-scale GWs are consistent with those in the reanalysis, while the medium-scale GWs compare well with observations in the northern winter 2016 stratosphere from the Atmospheric InfraRed Sounder (AIRS). GWs having wavelengths larger than about 1,350 km can be described with the nonlinear balance equation. The GWs relevant in the stratosphere, however, have smaller scales and require a different approach. We propose that the GW amplification due to kinetic energy transfer from the large-scale flow combined with GW potential energy flux convergence helps to identify the mesoscale GW sources due to spontaneous emission. The GW amplification is strongest in the region of maximum large-scale vertical wind shear in the mid-stratosphere. Maps of the time-averaged stratospheric GW activity simulated by the HIAMCM and computed from AIRS satellite data show a persistent hot spot over Europe during January 2016. At about 40 km, the average GW amplitudes are maximum in the region of fastest large-scale flow. We argue that refraction of GWs originating in the troposphere, as well as GWs from spontaneous emission in the stratosphere contribute to this effect.

Characterizing the Effect of Spatial Heterogeneity and the Deployment of Sampled Plots on the Uncertainty of Ground “Truth” on a Coarse Grid Scale: Case Study for Near‐Infrared (NIR) Surface Reflectance

Abstract: The quality of surface reflectance product is fundamentally important to ensure the information extracted from the downstream products can be trusted. However, ground validation of surface reflectance satellite products is challenging, because ground “truth” on a coarse grid scale based on sparse ground measurements is subject to uncertainty due to spatial heterogeneity. Based on a high-resolution numerical simulation, this study quantifies the influence of spatial heterogeneity on the uncertainty of surface reflectance ground “truth” in different sampling cases (i.e., the number and positions of sampled plots). The effect of spatial heterogeneity is very small and even negligible when optimal locations are identified. By contrast, for the averaged condition without optimal sampling, spatial heterogeneity is almost the only source of uncertainty of ground “truth,” with determination coefficients of 0.94, 0.99, and 1 for 1, 2, and 3 sampled plots, respectively. The response coefficients between them are about 0.77, 0.55, and 0.47 for 1, 2, and 3 sampled plots, respectively. Optimal sampling plays a more important role in reducing the uncertainty of ground “truth” than increasing the number of sampled plots. Particularly, the latter is not helpful in reducing the uncertainty when the worst locations are adopted. Furthermore, the thresholds of spatial heterogeneity of surface reflectance to meet a predefined uncertainty of 0.01 (about 3.5% for surface reflectance over the study area) were given for different sampling cases over northern China. This study provides important guidance to aid in situ network design for the validation of 1 km satellite surface reflectance products.

Performance Evaluation of the Meteorology and Air Quality Conditions From Multiscale WRF-CMAQ Simulations for the Long Island Sound Tropospheric Ozone Study (LISTOS)

Abstract: The Long Island Sound (LIS) Tropospheric Ozone Study was a multi‐agency collaborative field campaign conducted during the summer of 2018 to improve the understanding of ozone chemistry and transport from New York City to areas downstream, especially the LIS and adjacent Connecticut coastline. Measurements made during this campaign were leveraged to test and evaluate the coupled WRF‐CMAQ model at 12 km, 4 and 1.33 km horizontal grid spacing. Special attention was placed on the model's representation of sea breeze circulations, low level jets, and boundary layer evolution. The evaluation suggests using higher resolutions resulted in improved surface meteorology statistics throughout the whole summer, with temperature biases seeing the biggest statistical improvements when using 1.33‐km grid spacing, going from −0.12 to 0.08 K. Additionally, 4‐km grid spacing provided the biggest advantage when simulating ozone over the region of interest, with biases being reduced from 2.40 to 0.57 to 0.37 ppbV with increased resolution. Case studies of two high ozone concentration events (July 10 and August 6) revealed that sound breezes and low‐level jets had a critical role in transporting pollutant‐rich, shallow marine air masses from the LIS inland over the Connecticut coast. Modifications were made to the representation of sea surface temperatures, which subsequently improved the simulation of surface ozone predictions.

Modulation of Wintertime Canopy Urban Heat Island (CUHI) Intensity in Beijing by Synoptic Weather Pattern in Planetary Boundary Layer

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 and low RH. This is conducive to a weakening of the CUHII. In general, our work reveals the impacts of SWPs on the strength of CUHII mainly via the modulation of local weather conditions at diurnal and interannual scales, while spatial pattern of CUHII is largely dominated by local climate zones. Our findings have implications for CUHII forecasts, as well as impact assessments and policymaking in the context of UHI-related energy conservation in winter over high-density urban areas on the synoptic scale.

Global Changes in Water Vapor 1979–2020

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. AIRS 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 is consistent across datasets with increases of ∼4-5% near the surface and 10-15% at 300 hPa for each 1°C increase in global surface temperature. Global water vapor responses are explained by thermodynamic amplification of upper tropospheric temperature changes and the Clausius Clapeyron temperature dependence of saturation vapor pressure that are dominated by the tropical ocean responses. Upper tropospheric moistening is larger in climate model simulations with greater upper tropospheric warming.

Multivariate Bias‐Correction of High‐Resolution Regional Climate Change Simulations for West Africa: Performance and Climate Change Implications

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 analyzed variables. Relatively large bias reductions during the historical period give indication of possible benefits of MBCn when applied to future scenarios. Although the four regional climate models do not agree on the same positive/negative sign of the change of the seven climate variables for all grid points, the model ensemble mean shows a statistically significant change in rainfall, relative humidity in the Northern zone and wind speed in the Coastal zone of West Africa and increasing maximum summer temperature up to 2°C in the Sahara.

Observations of Inertia Gravity Waves in the Western Pacific and Their Characteristic in the 2015/2016 Quasi‐Biennial Oscillation Disruption

Abstract: The statistical characteristics of inertia-gravity waves (IGWs) in the troposphere (2-14 km) and lower stratosphere (18-28 km) are analyzed using daily radiosonde observations over six stations in the Western Pacific from 2013 to 2018. Stokes parameter method is used to extract the characteristic parameters of gravity waves (GWs), which are divided into upward and downward propagating waves, and compared with the results of hodograph analysis. In the stratosphere, due to the filtering effect of the background wind field, the IGWs generated in the troposphere mainly propagate eastward with lower frequency range. The tropospheric IGWs have obvious seasonal variation in spectral amplitude and energy, with the maximum in winter and the minimum in monsoon from 2013 to 2018. The stratospheric IGWs are enhanced during phase transition of the quasi-biennial oscillation, when the enhanced easterly wind appears in the lowest stratosphere, accompanied by enhanced wave energy in the troposphere. During the quasi-biennial oscillation disruption in late 2015 and early 2016, the tropospheric wave source excites more intense IGWs propagating upward. After reaching the stratosphere, IGWs with slower phase speed are absorbed by the mean flow, dissipating momentum to the lower stratosphere and generating additional enhanced westward forcing, which may have contributed to the development of the easterly wind within the westerly QBO phase. This article is protected by copyright. All rights reserved.

On the Evolution of a Long‐Lived Mesoscale Convective Vortex that Acted as a Crucial Condition for the Extremely Strong Hourly Precipitation in Zhengzhou

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 formation. After formation, the MCV first coupled with its parent MCS, during which its intensity, thickness, and precipitation were all maximized; then, it moved northwestward and decoupled from the MCS, during which it weakened rapidly and finally dissipated. Convection-related upward cyclonic vorticity transport and inward horizontal advection of cyclonic vorticity associated with an inverted trough over the Henan Province dominated the vortex's development/maintenance in the coupling stage; whereas outward horizontal advection of cyclonic vorticity dominated the MCV's dissipation after it completely decoupled from its parent MCS. These differ notably from the findings documented in previous MCV-related literature.

Highly Active Ice‐Nucleating Particles at the Summer North Pole

Abstract: 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 suggests strong sources of INPs near the Russian coast, possibly associated with wind-driven sea spray production, whereas the pack ice, open leads, and the marginal ice zone were not sources of highly active INPs. These findings suggest that primary ice production, and therefore Arctic climate, is sensitive to transport from locations such as the Russian coast that are already experiencing marked climate change.

Impact of COVID‐19 Pandemic Lockdown in Ambient Concentrations of Aromatic Volatile Organic Compounds in a Metropolitan City of Western India

Abstract: The real-time Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) concentrations were measured in a metropolitan city of India during January to May of 2020 and 2014-2015-2018 to assess the impact of emission reduction during the COVID-19 lockdown. The total BTEX (∑BTEX) concentrations were 11.5 ± 9.0, 15.7 ± 16, 5.3 ± 5.0, 2.9 ± 2.0, and 0.93 ± 1.2 ppbv in January-May 2020, respectively. The evening rush hour peaks of BTEX during lockdown decreased by 4-5 times from the same period of years 2014-2015-2018. A significant decline in background concentrations suggests a regional-scale reduction in anthropogenic emissions. The contributions of ∑TEX compounds to ∑BTEX increased from 42% to 59% in winter to 64%-75% during the lockdown under hot summer conditions. While emission reductions dominated during the lockdown period, the meteorological and photochemical factors may also have contributed. Meteorological influence on actual observed BTEX data was removed by normalizing with ventilation coefficient (VC). The actual ambient air reductions of 85%-90% and VC-normalized reductions of 54%-88% of the BTEX concentrations during lockdown were estimated compared to those during the same period of 2014-2015-2018. The estimated changes using nighttime data, which take into account BTEX photooxidation removal, are ∼8% lower than the VC-normalized estimates using all data. These significant reductions in BTEX concentrations are consistent with the change in people's movement as inferred from mobility data during the lockdown. Although enforced, the significant decline in ambient BTEX levels during lockdown was a good change for the air quality. The study suggests a need for more effective science-based policies that consider local and regional factors.

Moisture Sources for Precipitation Associated With Major Hurricanes During 2017 in the North Atlantic Basin

Abstract: The 2017 North Atlantic tropical cyclone season was among the most active in the last two decades, with 17 named storms, of which six reached the major hurricane (MH) intensity: Harvey, Irma, Jose, Lee, Maria, and Ophelia. In this study, the water vapor sources for precipitation for these six MHs were examined using a Lagrangian approach. The particle dispersion model, FLEXPART, was used to identify moisture sources. Overall, the North Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico were identified as the main moisture sources, supplying ∼75%–85% of the atmospheric humidity gained by tropical cyclones, which resulted in precipitation associated with the MHs. However, the South Atlantic Ocean also contributed considerable humidity (∼14%–20%), and the remaining ∼1%–5% originated from the tropical eastern Pacific Ocean. The accumulated moisture uptake higher than the 90th percentile generally appeared within approximately 3° to 5° of the TC trajectory.

Influence of Arctic Sea Ice Concentration on Extended‐Range Prediction of Strong and Long‐Lasting Ural Blocking Events in Winter

Abstract: It is traditionally considered that the predictability of atmosphere reaches approximately 2 weeks due to its chaotic features. Considering boundary conditions, the lead prediction time can exceed 2 weeks in certain cases. We find that the Arctic sea ice concentration (SIC) is crucial for extended-range prediction of strong and long-lasting Ural blocking (UB) formation. By applying the rotated empirical orthogonal function-based particle swarm optimization algorithm, the conditional nonlinear optimal perturbation is calculated with the Community Atmosphere Model, version 4, to identify the optimally growing boundary errors in extended-range prediction of strong and long-lasting UB formation. It is found that SIC perturbations in the Greenland Sea (GS), Barents Sea (BS), and Okhotsk Sea (OKS) are important for strong and long-lasting UB formation prediction in four pentads. Further analysis reveals that the SIC perturbations in these areas first influence the local temperature field through the diabatic heating process and further affect the temperature field in the Ural sector mainly by advection and convection processes. Moreover, the zonal winds in the Ural sector are adjusted by the thermal wind balance, thus affecting UB formation. The local characteristics of the SIC perturbations indicate that the GS, BS, and OKS may be sensitive areas in regard to extended-range prediction of strong and long-lasting UB formation, which can provide scientific support for the SIC target observations in the future.

Effects of Lake Nam Co and Surrounding Terrain on Extreme Precipitation Over Nam Co Basin, Tibetan Plateau: A Case Study

Abstract: Thousands of lakes and complex topography on Tibetan Plateau (TP) have important impacts on the local weather and climate, especially extreme weather events. In this study, the Weather Research and Forecasting model was adopted to quantify the impacts of Lake Nam Co (LNC) and surrounding topography on the extreme snowfall event over Nam Co basin on 24 October 2006 based on numerical experiments. The accumulated precipitation of 12 hr in this event is characterized by a maximum precipitation center with an intensity exceeding 20 mm over eastern LNC and downwind regions. Results show that the precipitation regionally averaged over eastern LNC and downstream regions can be reduced by 53%, 26%, and 68% when LNC, surrounding terrain, and both of them are absent, respectively, suggesting that LNC plays a dominant role in the formation of this event while the surrounding mountains further amplify the lake effect precipitation/snow over the downwind of LNC. Mechanism analysis indicates that the low-level convective instability and water vapor convergence induced by LNC are essential for the formation of this extreme snowfall event, while the wind deflection and topographic lifting further strengthen the precipitation over the downwind of LNC and shift the snow belt distribution. This study is not only important to deepen the understanding of the complex interactions between the lake and orography and their combined influences on regional extreme precipitation, but also helpful for further improving the refined forecasting of the extreme precipitation induced by the lake and surrounding terrain in other regions over TP.

Indirect Effects of Binary Typhoons on an Extreme Rainfall Event in Henan Province, China From 19 to 21 July 2021: 2. Numerical Study

Abstract: An extreme precipitation event over Henan province, China from 19 to 21 July 2021 led to flood disasters in this region and widespread concern about the subsequent loss of life and livelihoods. We conducted numerical simulations to examine the impacts of typhoons In-fa (2021) and Cempaka (2021) on this extreme rainfall event. The control simulation reasonably reproduced the motion of typhoons In-fa and Cempaka and the associated distribution and amount of extreme rainfall. Sensitivity experiments were conducted in which typhoon In-fa was artificially moved in both northerly and westerly directions in the initial conditions. The results indicated that the southerly flow between typhoon Cempaka and Henan, which determined the structure and distribution of the extreme rainfall event, was sensitive to the motion of typhoon In-fa. Numerical experiments that removed typhoon Cempaka confirmed that both the movement of In-fa and its interaction with Cempaka were closely associated with southerly flows and had a significant effect on the extreme precipitation event. In the absence of typhoon Cempaka, although typhoon In-fa still had a remote effect on precipitation, the effect was much smaller than in the presence of Cempaka. Our simulation of this extreme rainfall event in Henan and the associated sensitivity experiments are consistent with the results of previous studies of multiple tropical cyclones, which showed that interactions among multiple tropical cyclones can lead to changes in their outer circulation that affect extreme precipitation events.

Possible Dynamic Mechanisms of High‐ and Low‐Latitude Wave Trains Over Eurasia and Their Impacts on Air Pollution Over the North China Plain in Early Winter

Abstract: The Rossby wave train in boreal winter sometimes bifurcates into two branches near the Mediterranean, sometimes not. However, causes for bifurcating of the wave train are still being debated. Additionally, discussions about the differences in the deterioration ability of these wave trains on air pollution are also insufficient. This study uses the empirical orthogonal function (EOF) to obtain two dominant modes of the November-January season wave trains over Eurasia and discusses their different influences on air pollution over the North China Plain (NCP). From the EOF1 mode, bifurcation of the wave train appears to stem from the Rossby wave reflection near the Mediterranean because the Rossby wave source is located outside of a strong absolute vorticity gradient. From the EOF2 mode, the wave train propagates only along the subtropical westerly jet because the Rossby wave source is located inside of a strong absolute vorticity gradient, so that the wave train tends to be refracted near the Mediterranean. In addition, the wave train associated with the EOF1 is suggested to be related to the eastern Pacific El Niño. The eastern Pacific El Niño tends to force a wave train propagating into East Asia under the charger effect from positive feedback of air-sea coupling near the far eastern Atlantic and Mediterranean, while the wave train associated with the EOF2 is suggested to be mainly induced by natural internal variability. Furthermore, the results indicate that the bifurcation type wave train tends to cause higher PM2.5 concentrations over the NCP through a strengthened Northeast Asia anomalous anticyclone.

Ground‐Based Observation of a TGF Occurring Between Opposite Polarity Strokes of a Bipolar Cloud‐To‐Ground Lightning Flash

Abstract: We present the ground-based observation of a terrestrial gamma-ray flash (TGF) that occurred between positive (second) and negative (third) strokes of a five-stroke bipolar cloud-to-ground lightning flash. Those two strokes shared the same channel to ground at a distance of 200 m or so from the Lightning Observatory in Gainesville (LOG), Florida. Earlier TGF observations at ground level in Florida (a total of four) were either associated with the initial continuous current (ICC) of rocket-triggered lightning flashes or occurred during the relatively steady current following the return-stroke current peak in natural lightning flashes; that is, in the presence of current-carrying channel to ground. The TGF presented here occurred in a different context: at the early (in-cloud) stage of negative leader entering the remnants of the channel previously created by the positive stroke. The TGF had a duration of 35 μs and consisted of 18 pulses with amplitudes ranging from 114 to 912 keV. The overall flash context in which the TGF occurred was as follows. The first (143-kA) stroke was negative and terminated on ground 1.4 km from LOG, the second (12-kA) stroke was positive and forged a new path to ground about 200 m from LOG, and the third (28-kA) stroke (TGF producer) was negative and followed the path of the second (positive) stroke. The fourth (43-kA) stroke was negative and created a new termination on ground about 900 m from LOG, and the fifth (4.5-kA) stroke was also negative and followed the fourth-stroke channel.

Indirect Effects of Binary Typhoons on an Extreme Rainfall Event in Henan Province, China From 19 to 21 July 2021: 1. Ensemble‐Based Analysis

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 the intensity of the southerly flow, reduced the transport of water vapor to the rainstorm area and weakened the Huang-Huai cyclone, thus reducing precipitation in the control area. The results of this study indicate that ensemble-based analysis can improve our understanding and forecasting of extreme precipitation events under the influence of multiple remote tropical cyclones.

The Impact of Springtime‐Transported Air Pollutants on Local Air Quality With Satellite‐Constrained NO _x Emission Adjustments Over East Asia

Abstract: To quantify the impact of transported air pollutants on local air quality, this study applies an inverse modeling technique with tropospheric nitrogen dioxide column retrievals from TROPOspheric Monitoring Instrument, and the CMAQ-ISAM model, which computes source attribution over six regions of interest in spring 2019 over East Asia. Satellite-constrained nitrogen oxides (NOx) emissions successfully improve model performance by significantly reducing the normalized mean bias of concentrations of NOx, Ozone (O3), and PM2.5 from most regions in China and South Korea. Anticyclones over the Yellow Sea transport air pollutants and increase the contribution of emissions from adjacent regions to local air quality. Fluxes of air pollutants with posterior emissions showed notable enhancements in their magnitude by 3%–24% for NOy, O3, and PM2.5. The contributions of emissions from neighboring regions on local NOx and O3 budgets in the planetary boundary layer were 22.96%–35.24% and 24.23%–42.26%. The contribution of emissions from North Korea was notable despite its comparably lower emission rates. Regarding the impact of external influences on local air quality, the enhanced chemical loss of NOx compensated for increases by transport. Also, the increased vertical gradient of maximum daily 8-hr average O3 amplified vertical transport and dry deposition processes in the opposite direction along with slight changes in the chemical net O3 production rate. This study shows the nonlinear response of local air quality to changes in the transport of air pollutants, which could be further investigated concerning changes in emissions and climatological factors that would modify the inflow of air pollutants.

Cooling and Contraction of the Mesosphere and Lower Thermosphere From 2002 to 2021

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 solar minimum in 2009 may be due to a decrease of 5% in solar irradiance in the Schumann-Runge band spectral region (175-200 nm).

Evaluating Climate Models’ Cloud Feedbacks Against Expert Judgment

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 assess cloud feedbacks and cloud errors and place them in the context of other models and of expert judgment in real-time during model development.

Amazonian Moisture Recycling Revisited Using WRF With Water Vapor Tracers

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 afternoon. Some of this moisture is rained out through convective storms in the early evening. Later in the night and following morning, strong winds associated with the South American Low Level Jet advect moisture downwind. The beating pattern becomes apparent when visualizing the Amazonian water vapor as an animation.

Stratospheric Aerosol Composition Observed by the Atmospheric Chemistry Experiment Following the 2019 Raikoke Eruption

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.

High‐Resolution Aircraft Observations of Turbulence and Waves in the Free Atmosphere and Comparison With Global Model Predictions

Abstract: High-resolution flight data obtained from in situ measurements in the free atmosphere aboard the High Altitude and Long Range Research Aircraft (HALO) are used to determine eddy dissipation rates along extended flights during the recent Southern Hemisphere Transport, Dynamics, and Chemistry aircraft campaign (SOUTHTRAC) in the 2019 austral winter. These data are analyzed and correlated with quantities characterizing the ambient airflow and the magnitudes of vertical energy propagation through internal gravity waves. The observed turbulence events are strongly correlated with elevated shear values, and overturning gravity waves do not appear to play a role. A highlight of the analysis is the validation of a recently implemented Clear Air Turbulence (CAT) forecast index in the European Centre for Medium-Range Weather Forecast integrated forecast system. Here we find a slightly better correlation of the CAT prediction with the HALO research aircraft observations compared to those of commercial aircraft. The observed turbulence during SOUTHTRAC was never stronger than moderate, as EDR values remained below 0.3 m2/3 s−1. In general, light and light-to-moderate turbulence events were extremely rare, occurring in only about 5% of the flight time, and stronger events in less than 0.2%. These results are also reflected in the local atmospheric conditions, which were dominated by a thermally very stable airflow with low vertical shear and large Richardson numbers.

Physical and Chemical Properties of Cloud Droplet Residuals and Aerosol Particles During the Arctic Ocean 2018 Expedition

Abstract: 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 fall. Addition of aerosol mass due to aqueous-phase chemistry during in-cloud processing was probably small over the pack ice given the fact that we observed very similar particle size distributions in both the whole-air and cloud droplet residual data. These aerosol-cloud interaction observations provide valuable insight into the origin and physical and chemical properties of CCN over the pristine central Arctic Ocean.

Uncertainty in Aerosol Optical Depth From Modern Aerosol‐Climate Models, Reanalyses, and Satellite Products

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 CMIP5 and AeroCom-I. Although some regional biases have been reduced, τ from both CMIP6 and AeroCom-III are for instance substantially larger along extra-tropical storm tracks compared to the satellite products. The considerable uncertainty in observed τ implies that a model evaluation based on a single satellite product might draw biased conclusions. This underlines the need for continued efforts to improve both model and satellite estimates of τ, for example, through measurement campaigns in areas of particularly uncertain satellite estimates identified in this study, to facilitate a better understanding of aerosol effects in the Earth system.

Fine Ash‐Bearing Particles as a Major Aerosol Component in Biomass Burning Smoke

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 Observation Project and Megacity Initiative: Local and Global Research Observations). These ash particles are commonly mixed with organic matter and make up ∼8% and 5% of BB smoke by number and mass, respectively, in samples collected during the FIREX-AQ campaign. The measured ash-mass concentrations are approximately five times and six times greater than those of BB black carbon and potassium, respectively, scaling to an estimated global emission of 11.6 Tg yr−1 with a range of 8.8–16.3 Tg yr−1. Better characterization and constraints on these fine ash-bearing particles will improve BB aerosol measurements and strengthen assessments of BB impacts on human health and climate.

Evaluating Twenty‐Year Trends in Earth's Energy Flows From Observations and Reanalyses

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 for surface fluxes inferred as a residual between CERES net TOA flux and ERA5 analysis TEDIV and surface fluxes obtained directly from ERA5 forecasts. Robust trends are observed over the Gulf Stream associated with enhanced surface-to-atmosphere transfer of heat. Within the ocean, larger trends in ocean heating rate are found in the NH than the SH after 2005, but the magnitude of the trend varies greatly among datasets.

Global Evaluation of the Noah‐MP Land Surface Model and Suggestions for Selecting Parameterization Schemes

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, high-altitude, and hyperarid regions. This study also highlights the potential of land-cover-specific combinations of parameterization schemes to produce optimal modeling results over different land-cover types. In addition, we strongly suggest the use of multi-objective optimization of the key parameterizations and parameters to further improve the Noah-MP's overall performance.

Greenland Ice Core Record of Last Glacial Dust Sources and Atmospheric Circulation

Abstract: 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 dust sources reveal three most likely scenarios (in order of probability): direct dust sourcing from the Taklimakan Desert in western China, direct sourcing from European glacial sources, or a mix of dust originating from Europe and North Africa. Furthermore, our regional climate modeling demonstrates the plausibility of European or mixed European/North African sources for the first time. We suggest that the origin of dust to Greenland is potentially more complex than previously recognized, demonstrating more uncertainty in our understanding dust climate feedbacks during abrupt events than previously understood.