Simulation of dust aerosol and its regional feedbacks over East Asia using a regional climate model

International audienceThe ICTP regional climate model (RegCM3) coupled with a desert dust model is used to simulate the radiative forcing and related climate effects of dust aerosols over East Asia. Two sets of experiments encompassing the main dust producing months, February to May, for 10 years (1997?2006) are conducted and inter-compared, one without (Exp. 1) and one with (Exp. 2) the radiative effects of dust aerosols. The simulation results are evaluated against ground station and satellite data. The model captures the basic observed climatology over the area of interest. The spatial and temporal variations of near surface concentration, mass load, and emission of dust aerosols from the main source regions are reproduced by model, with the main model deficiency being an overestimate of dust amount over the source regions and underestimate downwind of these source areas. Both the top-of-the-atmosphere (TOA) and surface radiative fluxes are decreased by dust and this causes a surface cooling locally up to ?1°C. The inclusion of dust radiative forcing leads to a reduction of dust emission in the East Asia source regions, which is mainly caused by an increase in local stability and a corresponding decrease in dust lifting. Our results indicate that dust effects should be included in the assessment of climate change over East Asia

Optical properties and radiative forcing of urban aerosols in Nanjing, China

AbstractContinuous measurements of atmospheric aerosols were made in Nanjing, a megacity in China, from 18 January to 18 April, 2011 (Phase 1) and from 22 April 2011 to 21 April 2012 (Phase 2). Aerosol characteristics, optical properties, and direct radiative forcing (DRF) were studied through interpretations of these measurements. We found that during Phase 1, mean PM2.5, black carbon (BC), and aerosol scattering coefficient (Bsp) in Nanjing were 76.1 ± 59.3 μg m−3, 4.1 ± 2.2 μg m−3, and 170.9 ± 105.8 M m−1, respectively. High pollution episodes occurred during Spring and Lantern Festivals when hourly PM2.5 concentrations reached 440 μg m−3, possibly due to significant discharge of fireworks. Temporal variations of PM2.5, BC, and Bsp were similar to each other. It is estimated that inorganic scattering aerosols account for about 49 ± 8.6% of total aerosols while BC only accounted for 6.6 ± 2.9%, and nitrate was larger than sulfate. In Phase 2, optical properties of aerosols show great seasonality. High relative humidity (RH) in summer (June, July, August) likely attributed to large optical depth (AOD) and small Angstrom exponent (AE) of aerosols. Due to dust storms, AE of total aerosols was the smallest in spring (March, April, May). Annual mean 550-nm AOD and 675/440-nm AE were 0.6 ± 0.3 and 1.25 ± 0.29 for total aerosols, 0.04 ± 0.02 and 1.44 ± 0.50 for absorbing aerosols, 0.48 ± 0.29 and 1.64 ± 0.29 for fine aerosols, respectively. Annual single scattering albedo of aerosols ranged from 0.90 to 0.92. Real time wavelength-dependent surface albedo from the Moderate Resolution Imaging Spectroradiometer (MODIS) was used to assess aerosol DRFs. Both total and absorbing aerosol DRFs had significant seasonal variations in Nanjing and they were the strongest in summer. Annual mean clear sky TOA DRF (including daytime and nighttime) of total and absorbing aerosols was about −6.9 and +4.5 W m−2, respectively. Aerosol DRFs were found to be sensitive to surface albedo. Over brighter surfaces, solar radiation was more absorbed by absorbing aerosols and less scattered by scattering aerosols

Simulation of mineral dust aerosol with Piecewise Log-normal Approximation (PLA) in CanAM4-PAM

A new size-resolved dust scheme based on the numerical method of piecewise log-normal approximation (PLA) was developed and implemented in the fourth generation of the Canadian Atmospheric Global Climate Model with the PLA Aerosol Model (CanAM4-PAM). The total simulated annual global dust emission is 2500 Tg yr<sup>−1</sup>, and the dust mass load is 19.3 Tg for year 2000. Both are consistent with estimates from other models. Results from simulations are compared with multiple surface measurements near and away from dust source regions, validating the generation, transport and deposition of dust in the model. Most discrepancies between model results and surface measurements are due to unresolved aerosol processes. Biases in long-range transport are also contributing. Radiative properties of dust aerosol are derived from approximated parameters in two size modes using Mie theory. The simulated aerosol optical depth (AOD) is compared with satellite and surface remote sensing measurements and shows general agreement in terms of the dust distribution around sources. The model yields a dust AOD of 0.042 and dust aerosol direct radiative forcing (ADRF) of −1.24 W m<sup>−2</sup> respectively, which show good consistency with model estimates from other studies

Processes shaping the spatial pattern and seasonality of the surface air temperature response to anthropogenic forcing

In the period 1960-2010, the land surface air temperature (SAT) warmed more rapidly over some regions relative to the global mean. Using a set of time-slice experiments, we highlight how different physical processes shape the regional pattern of SAT warming. The results indicate an essential role of anthropogenic forcing in regional SAT changes from the 1970s to 2000s, and show that both surface-atmosphere interactions and large-scale atmospheric circulation changes can shape regional responses to forcing. Single forcing experiments show that an increase in greenhouse gases (GHG) can lead to regional changes in land surface warming in winter (DJF) due to snow-albedo feedbacks, and in summer (JJA) due to soil-moisture and cloud feedbacks. Changes in anthropogenic aerosol and precursor (AA) emissions induce large spatial variations in SAT, characterized by warming over western Europe, Eurasia, and Alaska. In western Europe, SAT warming is stronger in JJA than in DJF due to substantial increases in clear sky shortwave radiation over Europe, associated with decreases in local AA emissions since the 1980s. In Alaska, the amplified SAT warming in DJF is due to increased downward longwave radiation, which is related to increased water vapor and cloud cover. In this case, although the model was able to capture the regional pattern of SAT change, and the associated local processes, it did not simulate all processes and anomalies correctly. For the Alaskan warming, the model is seen to achieve the correct regional response in the context of a wider North Pacific anomaly that is not consistent with observations. This demonstrates the importance of model evaluation that goes beyond the target variable in detection and attribution studies

Numerical Simulation of the Direct Effects on Climate in East Asia Induced by Carbonaceous Aerosol

AbstractCarbonaceous aerosol is one of the main ingredients of the atmospheric aerosol, which includes black carbon and organic carbon. The numerical simulations from 1960 to 2000 are aimed at the direct radiative effects on climate induced by carbonaceous aerosol in East Asia using NCAR Community Atmospheric Model version 3.1 (CAM). The mean radiative forcing(RF) under all sky in Chinese mainland at TOA and surface are 0.38 and −5.31W/m2 respectively. This distinct RF leads to −0.1K surface temperature decrease in Chinese mainland, which includes −0.26K drop of daily maximum and 0.07K rise of minimum temperature. Air column temperature has also been increased 0.11K in Chinese mainland. Significant vapor and precipitation increase can be resulted from RF of carbonaceous aerosol in north China and the Yellow and Huai River basin, accompanied by the decrease in northeast China, far-east region, and Tibet Plateau

새로운 화학-기후 모델을 활용한 동아시아 지역 기후에 대한 에어로졸 효과 연구

학위논문(박사) -- 서울대학교대학원 : 자연과학대학 지구환경과학부, 2022. 8. 박록진.A new chemistry-climate model, the Global/Regional Integrated Model system Chemistry Climate Model (GRIMs-CCM), is developed by coupling the chemistry modules of the GEOS-Chem chemical transport model to the GRIMs general circulation model. The GRIMs-CCM is driven by meteorological variables simulated by the GRIMs and uses simulated gas and aerosol concentrations to calculate the radiative transfer equations at each time step. The model is evaluated by comparing ozone and aerosol concentrations with respective observations from the surface networks and the satellite datasets. It is found that the GRIMs-CCM successfully reproduces the observed spatial distributions of annual-mean aerosol optical depth and captures the seasonal and latitudinal variations of total column ozone. The evaluation of simulated aerosols in surface air against the observations reveals that the model reproduces the observed temporal and spatial variations but shows biases in soil dust aerosols. I also estimate the climatic impact of aerosols by conducting two sets of 10-year simulations for the preindustrial and present conditions. The GRIMs-CCM shows the aerosol radiative forcing of −0.30 W m-2 from the preindustrial to present-day climates, comparable to the values from other climate model intercomparison projects. These results suggest that the GRIMs-CCM is suitable for studying chemistry-climate interactions and their changes over time. I investigate the regional climatic impact of aerosols in East Asia by conducting sensitivity analyses using the GRIMs-CCM and Community Earth System Model (CESM). I conduct 20 ensembles of 7-year simulations prescribing a recently decreasing trend of aerosol optical depth in East Asia observed from the satellite measurements to the models. It is found that the ensemble means of GRIMs-CCM and CESM reproduce positive trends of recent wintertime surface temperature in East Asia shown in the ERA-Interim reanalysis data. Comparisons of model results with the sensitivity simulations with detrended aerosol optical depth show that the models with decreasing aerosol optical depth simulate stronger warming trends in surface temperature, which indicates that the recent reduction of aerosols in East Asia partly contributes to the positive trends in surface temperature in East Asia.GRIMs 전 지구 순환 모델과 GEOS-Chem 화학 수송 모델을 결합하여 새로운 화학-기후 모델인 Global/Regional Integrated Model system Chemistry Climate Model (GRIMs-CCM)을 개발하였다. GRIMs-CCM은 GRIMs에서 모의한 기상 변수들을 바탕으로 구동되며 화학 모듈에서 모의한 가스상 물질 및 에어로졸의 농도를 활용하여 복사 전달 방정식을 매 타임스텝 계산한다. 지상 네트워크에서 관측한 자료나 위성 관측 자료를 활용하여 모델의 오존 및 에어로졸 모의 성능을 검증하였다. 모델 검증 결과 GRIMs-CCM은 관측에서 나타난 연평균 에어로졸 광학두께의 전 지구적 공간분포를 성공적으로 모의하였고 연직 오존량의 계절적 변화와 위도에 따른 변화 또한 성공적으로 모의하였다. GRIMs-CCM에서 모의한 에어로졸 농도를 지상 관측 자료와 비교 검증한 결과 모델이 관측에서 나타난 에어로졸의 시공간 분포를 성공적으로 재현함을 확인하였으나 먼지 에어로졸의 농도를 관측보다 낮게 모의하였다. 또한 GRIMs-CCM을 활용하여 산업혁명 이전의 시기와 현재 시기의 10년 기후를 모의하고 그 차이를 비교함으로써 인간 활동에 따른 에어로졸 변화의 기후 효과를 산정하였다. GRIMs-CCM을 활용한 실험 결과에서는 산업혁명 이전의 시기부터 현재까지의 에어로졸 복사 강제력이 전구 평균 −0.30 W m-2로 산정되었으며, 이는 다른 여러 기후 모델을 활용한 실험 결과에서 산정된 값과 유사한 결과이다. 이러한 결과는 GRIMs-CCM을 화학-기후 상호 작용에 관한 연구에 적절하게 활용할 수 있음을 제시하고 있다. 또한 GRIMs-CCM과 Community Earth System Model (CESM)을 활용한 기후 민감도 분석을 수행함으로써 동아시아 에어로졸의 지역적 기후 효과에 대하여 연구하였다. 최근 동아시아에서 감소하고 있는 에어로졸 광학 두께를 모델에 처방하여 20개의 앙상블 실험을 수행하였을 때 그 앙상블 평균이 ERA-Interim 재분석 자료에서 나타난 동아시아 겨울철 기온의 상승 추세를 성공적으로 재현함을 확인하였다. 에어로졸 광학 두께의 감소를 반영하지 않은 실험 결과와 비교하였을 때 에어로졸 광학 두께가 감소하는 실험에서 동아시아 기온 상승이 더 강하게 나타났고, 이를 통해 최근 동아시아 에어로졸의 감소가 동아시아 기온 상승에 부분적으로 기여하고 있음을 확인하였다.1. Introduction 1 2. Model Description 7 2.1. Atmospheric General Circulation Model 7 2.2. Chemistry Modules 10 (a) Emissions 12 (b) Deposition 14 (c) Chemistry 15 (d) Transport 18 2.3. Coupling Chemical Processes to GRIMs 19 3. Model Evaluation 23 3.1. Aerosol Optical Depth 26 3.2. Ozone 38 3.3. Surface Particulate Matter (PM) 47 4. Aerosol Radiative Forcing 57 5. Effects of Aerosol Changes on Regional Climate 65 5.1 Recent Aerosol Changes in East Asia 65 5.2 Experiment Setup 72 5.3 Results and Discussions 74 6. Summary and Conclusions 83 Bibliography 87 국문 초록 119 감사의 글 123박

Aerosol-cloud-precipitation interaction based on remote sensing and cloud-resolving modeling over the Central Himalayas

The Central Himalayan region experiences pronounced orographic precipitation related to the South Asian summer monsoon, typically occurring from June to September. Atmospheric aerosols can influence regional and global climate through aerosol-radiation (ARI) and aerosol-cloud interactions (ACI). The study of the aerosol-precipitation relationship over the Central Himalayan region during the summer monsoon season is important due to extreme pollution over the upwind Indo-Gangetic Plains, enhanced moisture supply through monsoonal flow, and steep terrain of the Himalayas modulating the orographic forcing. This dissertation aims to study the impact of atmospheric aerosols, from natural and anthropogenic sources, in modulating the monsoonal precipitation, cloud processes, and freezing isotherm over the central Himalayas. The long-term (2002 – 2017) satellite-retrieved and reanalysis datasets showed regardless of the meteorological forcing, compared to relatively cleaner days, polluted days with higher aerosol optical depth is characterized by the invigorated clouds and enhanced precipitation over the southern slopes and foothills of the Himalayas. The mean freezing isotherm increased by 136.2 meters in a polluted environment, which can be crucial and significantly impact the hydroclimate of the Himalayas. Due to the limitations of satellite-retrieved observational data, these results underlined the need for state-of-the-art Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) in a cloud-resolving scale to better represent and study the impact of the aerosols from different sources through radiation and microphysics pathways over the complex terrain of the Central Himalayas. A cloud-resolving WRF-Chem simulation is performed to assess the impact of anthropogenic and remotely transported dust aerosols on the convective processes and elevation-dependent precipitation. Long-range transported dust aerosols significantly impacted cloud microphysical properties and enhanced the precipitation by 9.3% over the southern slopes of the Nepal Himalayas. The mid-elevation of the Central Himalayas, generally between 1000 and 3000 meters, acted as the region below and above which the diurnal variation and precipitation of various intensities (light, moderate, and heavy) responded differently for ARI, ACI, and the combined effect of aerosols. Due to the ARI effect of aerosols, the light precipitation is suppressed by 17% over the Central Himalayas. The ACI effect dominated and resulted in enhanced heavy precipitation by 12% below 2000 m ASL, which can potentially increase the risk for extreme events (floods and landslides). In contrast, above 2000 m ASL, the suppression of precipitation due to aerosols can be critical for the regional supply of water resources. The overview of the study suggests that the natural and anthropogenic aerosols significantly modulate the convective processes, monsoonal precipitation, and freezing isotherm over the Central Himalayan region, which could pose significant consequences to the changing Himalayan hydroclimate

Analyzing Meteorological Relationships to Aerosols in China

Meteorological conditions are influenced everyday by air-bound aerosols and pollution in the atmosphere, and understanding these processes from micro to synoptic scale, is essential for forecasting and creating high resolution weather models. In this study, three different experimental weather models are analysed to provide some understanding on how various meteorological parameters are influenced by modelling atmospheric aerosols. Conclusions surrounding relations between the individual parameters are drawn from the results and discussed with respect to previous studies and knowledge on meteorology and atmospheric chemistry. This analytic observation was made from data covering the Chinese Yangtze River Delta region over the months January and July 2010. This region holds the metropolitan city of Shanghai and experiences a relative subtropical monsoon climate. Examining how the direct and indirect climate effects influence weather parameters through the three simulated experimental models, attempting to draw conclusions connecting aerosol characteristics to the dynamics of the atmosphere. The primarily investigated parameters include surface temperature, cloud cover, precipitation in the form of rain, long and shortwave radiation measured near surface and at top of atmosphere. Differences in solid precipitation between the experiments are very small and will not be covered in this analytic study. Highlighting the relation between certain simulated parameters with respect to urban aerosols for additional observation concerning the climate effects. Furthermore, a modest investigation of a special case day scenario is analyzed to observe how short-term forecasting could be influenced by simulated aerosol modelling in hourly depict data.Ekonomin i Kina har blomstrat över de senaste tiotal åren, och tillsammans med det skyhöga antalet invånare, strävar landet nu efter att uppnå världens största medelklass. Men för att Kina och hela världen skall kunna upprätthålla en levnadsstandard likt den vi har i väst, så kommer vi göra det på stor bekostnad av klimatet. Huvudsakligen sker det på grund av den massiva förbränning av kol och fossila bränslen som släpps ut i luften, där Kina konsumerar nästan mer kol än resten av världen totalt. Uppemot 46% enligt The World Resources Institut. Denna massivt höjda koncentration av utsläppta partiklar i luften, även kallade aerosoler, är orsaken till att kinas städer t.o.m. anses som farliga att andas i, där folk bär masker över munnen för att undgå den smutsiga luften. Dessa extra partiklar, bestående till största delen av kol och sulfat, kan transporteras upp och runt i vår atmosfär av vindströmmar. Med ytterligare partiklar på alla höjder i atmosfären tillkommer även en del resulterande respons från klimatet och vårt väder. För oss meteorologer tillkommer nu utmaningen att implementera denna tillförsel av aerosoler i våra numeriska vädermodeller för att få fram en så noggrann prognos som möjligt. I vårt fall, för att specifikt approximera hur vädersituationen ser ut över Kina, kan vi simulera modeller som direkt beror på hur mycket utsläpp som sker under dagen, där vi troligtvis ser ett maximum under vardagarna. Tre fall av modeller simuleras för att undersöka situationen i Kina. Först ett referens-fall som är anpassad för europeiska förhållande av aerosoler, genom den så kallade HARMONIE modellen. Medans denna vädermodell i sig är okej, anses referensfallets beräknade koncentrationen av människoskapande aerosoler vara för låg, och ett ytterligare fall tilläggs där ytterligare tjocklek av aerosoler i atmosfären är approximerade. Denna nya experimentella modell ger oss simulerade väderparametrar så som det skulle vara med en signifikant ökning av utsläpp och ökning av ett så kallat optiskt djup på partiklarna. Detta optiska djup beskriver aerosolernas egenskap att uppfatta vågstrålning, och med en ökad ”tjocklek” på det optiska djupet kommer troligen en sådan atmosfär absorbera mer solljus som påföljd. Detta fenomen orsakat av aerosoler kallas för den direkta klimateffekten. Vi förväntar oss då att se en minskning av solstrålning som når jordens yta, och genom denna nya experimentella modell kan vi jämföra hur kortvågig solstrålning och alla andra simulerade meteorologiska fenomen beter sig p.g.a. nya aerosoler. Därmed kan vi försöka dra slutsatser kring förhållandet mellan Kinas väder och partiklarnas direkta klimateffekt. E Molnen kan vara något att observera för att få en uppfattning om vädersituationen i vårat fall, och här skapades ett tredje experimentellt fall för att iaktta hur de meteorologiska parametrarna förändras när även den indirekta klimateffekten tillsätts. Denna effekt förklarar hur ytterligare aerosoler av en viss typ (speciellt antropogen) skapar fler molndroppar och även moln som mer effektivt reflekterar solljus tillbaka ut i rymden. En speciell fredag i juli 2010 noterades ha stora skillnader mellan referensfallet och fallet med aerosolernas pålagda direkta klimateffekt över området YRD i Kina. Detta diskuteras i samband med hur den ökande uppvärmningen i atmosfären kan stabilisera den vertikala temperaturprofilen och därmed förhindra uppkomsten av väderscenarion, såsom den sydostasiatiska monsunen. Vilket skulle göra klimatet torrare med färre regnperioder. Vi observerar stora förändringar i molntäcket under denna dagen, även några anomaliteter i vissa regnskurar som vi misstänkte. I bilden kan man tydligt se betydelsen att väder-modellera med rätt aerosol statistik i åtanke, och med detta skapade vi en av de viktiga diskussionerna vi sökte för att jämföra Kinas meteorologiska befinnande mot de antropogena utsläppen

The aerosol-climate model ECHAM5-HAM

The aerosol-climate modelling system ECHAM5-HAM is introduced. It is based on a flexible microphysical approach and, as the number of externally imposed parameters is minimised, allows the application in a wide range of climate regimes. ECHAM5-HAM predicts the evolution of an ensemble of microphysically interacting internally- and externally-mixed aerosol populations as well as their size-distribution and composition. The size-distribution is represented by a superposition of log-normal modes. In the current setup, the major global aerosol compounds sulfate (SU), black carbon (BC), particulate organic matter (POM), sea salt (SS), and mineral dust (DU) are included. The simulated global annual mean aerosol burdens (lifetimes) for the year 2000 are for SU: 0.80 Tg(S) (3.9 days), for BC: 0.11 Tg (5.4 days), for POM: 0.99 Tg (5.4 days), for SS: 10.5 Tg (0.8 days), and for DU: 8.28 Tg (4.6 days). An extensive evaluation with in-situ and remote sensing measurements underscores that the model results are generally in good agreement with observations of the global aerosol system. The simulated global annual mean aerosol optical depth (AOD) is with 0.14 in excellent agreement with an estimate derived from AERONET measurements (0.14) and a composite derived from MODIS-MISR satellite retrievals (0.16). Regionally, the deviations are not negligible. However, the main patterns of AOD attributable to anthropogenic activity are reproduced