Pollutant emissions in China have significantly decreased over the past decade and are expected to continue declining in the future. Aerosols, as important pollutants and short-lived climate forcing agents, have significant but currently unclear climate impacts in East Asia as their concentrations decrease until mid-century. Here, we employ a well-developed regional climate model RegCM4 combined with future pollutant emission inventories, which are more representative of China to investigate changes in the concentrations and climate effects of major anthropogenic aerosols in East Asia under six different emission reduction scenarios (1.5 degrees C goals, Neutral-goals, 2 degrees C -goals, NDC-goals, Current-goals, and Baseline). By the 2060s, aerosol surface concentrations under these scenarios are projected to decrease by 89%, 87%, 84%, 73%, 65%, and 21%, respectively, compared with those in 2010-2020. Aerosol climate effect changes are associated with its loadings but not in a linear manner. The average effective radiative forcing at the surface in East Asia induced by aerosol-radiation-cloud interactions will diminish by 24% +/- 13% by the 2030s and 35% +/- 13% by the 2060s. These alternations caused by aerosol reductions lead to increases in near-surface temperatures and precipitations. Specifically, aerosol-induced temperature and precipitation responses in East Asia are estimated to change by -78% to -20% and -69% to 77%, respectively, under goals with different emission scenarios in the 2060s compared to 2010-2020. Therefore, the significant climate effects resulting from substantial reductions in anthropogenic aerosols need to be fully considered in the pathway toward carbon neutrality.

In the context of China's dual carbon goal, emissions of air pollutants are expected to significantly decrease in the future. Thus, the direct climate effects of black carbon (BC) aerosols in East Asia are investigated under this goal using an updated regional climate and chemistry model. The simulated annual average BC concentration over East Asia is approximately 1.29 mu g/m(3) in the last decade. Compared to those in 2010-2020, both the BC column burden and instantaneous direct radiative forcing in East Asia decrease by more than 55% and 80%, respectively, in the carbon peak year (2030s) and the carbon neutrality year (2060s). Conversely, the BC effective radiative forcing (ERF) and regional climate responses to BC exhibit substantial nonlinearity to emission reduction, possibly resulting from different adjustments of thermal-dynamic fields and clouds from BC-radiation interactions. The regional mean BC ERF at the tropopause over East Asia is approximately +1.11 W/m(2) in 2010-2020 while negative in the 2060s. BC-radiation interactions in the present-day impose a significant annual mean cooling of -0.2 to -0.5 K in central China but warming +0.3 K in the Tibetan Plateau. As China's BC emissions decline, surface temperature responses show a mixed picture compared to 2010-2020, with more cooling in eastern China and Tibet of -0.2 to -0.3 K in the 2030s, but more warming in central China of approximately +0.3 K by the 2060s. The Indian BC might play a more important role in East Asian climate with reduction of BC emissions in China.

The decadal variability of direct radiative effects of aerosols is investigated at Dibrugarh, a site in northeast India (NEI) at the eastern Himalayan foothills, primarily using multi-wavelength solar radiometer measurements spanning from October 2001 to February 2020. The ground-based aerosol observations are combined with satellite remote sensing, reanalysis data, and model simulations to study the change in atmospheric particle loading over the region. Observations indicate a statistically significant increase (similar to 0.015 yr(-1)) in Aerosol Optical Depth (AOD) during the last two decades in line with an increase in human activity. As compared to 2001-2007 (we call it as Stage I), the aerosol burden has grown rapidly during 2008 until 2020 (Stage II). AOD at 500 nm is found to increase by similar to 40% from Stage I to Stage II, resulting in an increase in the aerosol direct radiative forcing (DRF) at the top of the atmosphere (TOA) by similar to 43% during stage II (similar to-16.0 W m(-2)), from the base value of -11.2 W m(-2) in Stage I. Decreasing biomass burning activities, black carbon aerosol mass concentration, and high sulfate and organic aerosols are the primary factors responsible for the trend in TOA cooling by-0.46 W m(-2) yr(-1). This is further aided by the decrease in rainfall over NEI. MERRA-2 data analysis shows a similar enhancements in aerosol load over the entire NEI and the adjacent highly polluted Indo-Gangetic Plains (IGP). A similar feature is seen over the IGP, primarily driven by anthropogenic emissions, but precedes that in NEI by about a year. A simulation of the regional climate model (RegCM) over the south Asian domain quantifies the contribution of aerosol loading over NEI due to the aerosols carried from the IGP. In the highest aerosol loading period, about 12-30% of the aerosols, equivalent to 15-30% of atmospheric warming, are transported from the IGP to the NEI.

青藏高原积雪变化对陆面能量水分传输过程有重要影响。本文采用RegCM4.7-CLM4.5模式模拟了高原及其周边地区31年的积雪过程,通过对模拟结果的EOF分解,发现高原积雪的时空变化主要呈现为高原主体与高原东北部反相、东西反相以及南北反相3种模态,方差贡献率分别为30.05%,14.86%和8.48%。合成分析显示,高原积雪异常中心与高原的主要积雪区较为一致,积雪深度与积雪日数均有减小的气候倾向,高原东南部的"三江源区"减小趋势最明显,高原中北部积雪有略微增加的趋势。积雪与土壤水热参量的相关分析显示,多雪区积雪可以有效减少土壤中热量的流失,对土壤起到"保温"作用,积累和鼎盛阶段积雪与土壤温度、地表热通量同位相变化;积雪融水又可以增加土壤湿度,对土壤起到"增湿"作用,鼎盛阶段积雪与土壤含水量正相关,积雪日数对土壤湿度的影响要高于积雪深度。在多雪区,多雪年积累阶段、鼎盛阶段的土壤温度和土壤湿度也要高于少雪年。对整个高原而言,积雪偏多使得土壤冻结程度加大,土壤含水量减少。

青藏高原积雪变化对陆面能量水分传输过程有重要影响。本文采用RegCM4.7-CLM4.5模式模拟了高原及其周边地区31年的积雪过程,通过对模拟结果的EOF分解,发现高原积雪的时空变化主要呈现为高原主体与高原东北部反相、东西反相以及南北反相3种模态,方差贡献率分别为30.05%,14.86%和8.48%。合成分析显示,高原积雪异常中心与高原的主要积雪区较为一致,积雪深度与积雪日数均有减小的气候倾向,高原东南部的"三江源区"减小趋势最明显,高原中北部积雪有略微增加的趋势。积雪与土壤水热参量的相关分析显示,多雪区积雪可以有效减少土壤中热量的流失,对土壤起到"保温"作用,积累和鼎盛阶段积雪与土壤温度、地表热通量同位相变化;积雪融水又可以增加土壤湿度,对土壤起到"增湿"作用,鼎盛阶段积雪与土壤含水量正相关,积雪日数对土壤湿度的影响要高于积雪深度。在多雪区,多雪年积累阶段、鼎盛阶段的土壤温度和土壤湿度也要高于少雪年。对整个高原而言,积雪偏多使得土壤冻结程度加大,土壤含水量减少。

青藏高原积雪变化对陆面能量水分传输过程有重要影响。本文采用RegCM4.7-CLM4.5模式模拟了高原及其周边地区31年的积雪过程,通过对模拟结果的EOF分解,发现高原积雪的时空变化主要呈现为高原主体与高原东北部反相、东西反相以及南北反相3种模态,方差贡献率分别为30.05%,14.86%和8.48%。合成分析显示,高原积雪异常中心与高原的主要积雪区较为一致,积雪深度与积雪日数均有减小的气候倾向,高原东南部的"三江源区"减小趋势最明显,高原中北部积雪有略微增加的趋势。积雪与土壤水热参量的相关分析显示,多雪区积雪可以有效减少土壤中热量的流失,对土壤起到"保温"作用,积累和鼎盛阶段积雪与土壤温度、地表热通量同位相变化;积雪融水又可以增加土壤湿度,对土壤起到"增湿"作用,鼎盛阶段积雪与土壤含水量正相关,积雪日数对土壤湿度的影响要高于积雪深度。在多雪区,多雪年积累阶段、鼎盛阶段的土壤温度和土壤湿度也要高于少雪年。对整个高原而言,积雪偏多使得土壤冻结程度加大,土壤含水量减少。

利用耦合了陆面过程模式(CLM4.5)的区域气候模式(RegCM4)分别对青藏高原的一个多雪年和少雪年进行了数值模拟。通过对比模拟雪深与遥感雪深、土壤温湿度的模拟值与观测值、多雪年与少雪年的土壤温湿度模拟值,结果表明,RegCM4-CLM4.5可以有效模拟出高原的多雪年与少雪年特征,模拟雪深大值中心比遥感雪深高10～20 cm。土壤温度模拟效果要明显优于土壤湿度,模拟的土壤温度相关系数R为0.95～0.98,模拟的土壤湿度相关系数R为0.68～0.89。在冻结阶段(10月至次年1月),积雪的异常偏多,可以有效抑制地气间的热交换,从而使得多雪年土壤温度高于少雪年。在季节性冻土区的消融阶段(2-4月和6月),积雪对土壤还具有增湿作用,多雪年土壤湿度高于少雪年。土壤的冻结也会阻碍积雪融水的下渗,因此多雪年与少雪年土壤湿度的差异不超过±2%。在多年冻土区,积雪偏多,冻结深度加大,有利于冻土发育;而在季节性冻土区,积雪增加则不利于冻土发育。

利用耦合了陆面过程模式(CLM4.5)的区域气候模式(RegCM4)分别对青藏高原的一个多雪年和少雪年进行了数值模拟。通过对比模拟雪深与遥感雪深、土壤温湿度的模拟值与观测值、多雪年与少雪年的土壤温湿度模拟值,结果表明,RegCM4-CLM4.5可以有效模拟出高原的多雪年与少雪年特征,模拟雪深大值中心比遥感雪深高10～20 cm。土壤温度模拟效果要明显优于土壤湿度,模拟的土壤温度相关系数R为0.95～0.98,模拟的土壤湿度相关系数R为0.68～0.89。在冻结阶段(10月至次年1月),积雪的异常偏多,可以有效抑制地气间的热交换,从而使得多雪年土壤温度高于少雪年。在季节性冻土区的消融阶段(2-4月和6月),积雪对土壤还具有增湿作用,多雪年土壤湿度高于少雪年。土壤的冻结也会阻碍积雪融水的下渗,因此多雪年与少雪年土壤湿度的差异不超过±2%。在多年冻土区,积雪偏多,冻结深度加大,有利于冻土发育;而在季节性冻土区,积雪增加则不利于冻土发育。

利用耦合了陆面过程模式(CLM4.5)的区域气候模式(RegCM4)分别对青藏高原的一个多雪年和少雪年进行了数值模拟。通过对比模拟雪深与遥感雪深、土壤温湿度的模拟值与观测值、多雪年与少雪年的土壤温湿度模拟值,结果表明,RegCM4-CLM4.5可以有效模拟出高原的多雪年与少雪年特征,模拟雪深大值中心比遥感雪深高10～20 cm。土壤温度模拟效果要明显优于土壤湿度,模拟的土壤温度相关系数R为0.95～0.98,模拟的土壤湿度相关系数R为0.68～0.89。在冻结阶段(10月至次年1月),积雪的异常偏多,可以有效抑制地气间的热交换,从而使得多雪年土壤温度高于少雪年。在季节性冻土区的消融阶段(2-4月和6月),积雪对土壤还具有增湿作用,多雪年土壤湿度高于少雪年。土壤的冻结也会阻碍积雪融水的下渗,因此多雪年与少雪年土壤湿度的差异不超过±2%。在多年冻土区,积雪偏多,冻结深度加大,有利于冻土发育;而在季节性冻土区,积雪增加则不利于冻土发育。

Black carbon (BC) aerosol is a significant, short-lived climate forcing agent. To further understand the effects of BCs on the regional climate, the warming effects of BCs from residential, industrial, power and transportation emissions are investigated in Asian regions during summer using the state-of-the-art regional climate model RegCM4. BC emissions from these four sectors have very different rates and variations. Residential and industrial BCs account for approximately 85% of total BC emissions, while power BCs account for only approximately 0.19% in Asian regions during summer. An investigation suggests that both the BC aerosol optical depth (AOD) and direct radiative forcing (DRF) are highly dependent on emissions, while the climate effects show substantial nonlinearity to emissions. The total BCs AOD and clear-sky top of the atmosphere DRF averaged over East Asia (100-130 degrees E, 20-50 degrees N) are 0.02 and +1.34 W/m(2), respectively, during summer. Each sector's BC emissions may result in a warming effect over the region, leading to an enhanced summer monsoon circulation and a subsequent local decrease (e.g., northeast China) or increase (e.g., south China) in rainfall in China and its surrounding regions. The near surface air temperature increased by 0.2 K, and the precipitation decreased by approximately 0.01 mm/day in east China due to the total BC emissions. The regional responses to the BC warming effects are highly nonlinear to the emissions, which may be linked to the influences of the perturbed atmospheric circulations and climate feedback. The nonuniformity of the spatial distribution of BC emissions may also have significant influences on climate responses, especially in south and east China. The results of this study could aid us in better understanding BC effects under different emission conditions and provide a scientific reference for developing a better BC reduction strategy over Asian regions.