Assessment of aerosol effective radiative forcing and surface air temperature response over eastern China in CMIP5 models

气溶胶有效辐射强迫是评估气溶胶气候效应的有效指标。本文利用国际耦合模式比较计划(CMIP5)中7个模式的模拟结果,评估了模式对东亚地区气溶胶光学厚度和有效辐射强迫的模拟水平,并分析了东亚地区平均地表温度对局地人为气溶胶强迫的响应。研究结果显示,大部分模式低估了中国东部和西南部污染地区的气溶胶光学厚度,这可能与模式中气溶胶局地排放、化学过程以及模式分辨率有关;多模式平均的东亚地区气溶胶有效辐射强迫为.4.14 W m.2,气溶胶在东亚地区有明显的降温效应,1850–2005年气溶胶浓度增加使得东亚地区降温.1.05°C。

Simulation of the direct effects of dust aerosol on climate in East Asia

The results from some general circulation models show distinct radiative forcing （RF） by dust aerosol, which potentially has an effect on climate change. The direct RF and regional climatic effects of dust aerosol over the East Asian region are investigated in this study using NCAR＇s Community Atmospheric Model version 3.1. The negative RF at the top of the atmosphere （TOA） and the surface （SRF） has been revealed except for some high-albedo regions, which leads to a decrease in the surface air temperature and brings an increase of atmospheric radiative heating under both clear- and all-sky conditions. The decrease in the surface air temperature can be found over a wide region that includes the Indian peninsula and northwest China. It accompanies an increase in eastern China and the Korean peninsula, and temperature changes are not limited to regions with a large dust optical depth. A belt of vapor increase is revealed from the Indian peninsula extending east to northern China, while vapor content evidently deceases in southwest China. An increase in precipitation can also be found in the belt of increased vapor accompanying the reduction of precipitation across the regions to the south of 30~N. The pattern of rainfall change helps to offset the trend of increasing wetness in the south and increasing dryness in the north of China in recent years.

An Overview of Mineral Dust Modeling over East Asia

East Asian dust（EAD） exerts considerable impacts on the energy balance and climate/climate change of the earth system through its influence on solar and terrestrial radiation, cloud properties, and precipitation efficiency. Providing an accurate description of the life cycle and climate effects of EAD is therefore critical to better understanding of climate change and socioeconomic development in East Asia and even worldwide. Dust modeling has undergone substantial development since the late 1990 s, associated with improved understanding of the role of EAD in the earth system. Here, we review the achievements and progress made in recent decades in terms of dust modeling research,including dust emissions, long-range transport, radiative forcing（RF）, and climate effects of dust particles over East Asia. Numerous efforts in dust/EAD modeling have been directed towards furnishing more sophisticated physical and chemical processes into the models on higher spatial resolutions. Meanwhile, more systematic observations and more advanced retrieval methods for instruments that address EAD related science issues have made it possible to evaluate model results and quantify the role of EAD in the earth system, and to further reduce the uncertainties in EAD simulations. Though much progress has been made, large discrepancies and knowledge gaps still exist among EAD simulations. The deficiencies and limitations that pertain to the performance of the EAD simulations referred to in the present study are also discussed.

近10年东亚沙尘气溶胶辐射强迫与温度响应

利用一个耦合了在线沙尘模型的区域气候模式RegCM3,对2000-2009年东亚沙尘气溶胶辐射强迫及温度响应进行了数值模拟。结果表明:(1)东亚沙尘气溶胶分布具有明显的地理差异和季节差异,柱含量高值区主要位于塔克拉玛干沙漠和巴丹吉林沙漠,最大值均在1 000mg.m-2以上;从季节分布来看,春季最大,冬季次之,秋季最小。(2)沙尘气溶胶辐射强迫与分布具有较好的对应关系。东亚地区大气顶辐射强迫,春、秋季分别为-1.72W.m-2和-1.17W.m-2;而地表辐射强迫,春、秋季分别为-4.34W.m-2和-2.33W.m-2。(3)沙尘气溶胶使地表温度降低,东亚地区平均地表温度降低,春季为0.154℃,秋季为0.085℃。(4)沙尘气溶胶在不同高度对气温有不同的影响。在对流层下层,沙尘气溶胶使得气温降低,随高度增加,气温降幅逐渐减小;春季在300～400hPa出现升温区,而秋季升温区出现的高度东西差别较大。

沙尘气溶胶直接气候效应对东亚冬季风影响的模拟研究

利用东亚沙尘复折射指数数据和较新的植被分布对区域气候—沙尘耦合模式(Reg CM4-Dust)的沙尘光学特性和沙源区域进行了更新。在此基础上,研究了沙尘气溶胶直接辐射效应对东亚冬季风的影响。模拟结果表明,引入沙尘效应后,东亚大陆绝大部分季风区对流层低层冬季风环流增强。同时,对流层中、上层中低纬度纬向风增强而中高纬度纬向风减弱,导致中高—中低纬度之间纬向风经向切变加强,从而有利于中高纬度冷空气向南侵入,这是低层冬季风环流增强在中上层的反映。另外,沙尘气溶胶导致东亚绝大部分季风区降水明显减少,东北地区西南部、华北大部、黄土高原、黄淮以及长江中下游流域减少达10%以上,这是降水对冬季风增强的响应。沙尘气溶胶引起冬季东亚次大陆—西北太平洋之间温度梯度增大,进而导致海陆间湿静力能梯度增大,是导致东亚大陆冬季风增强的主要原因。

东亚沙尘气候效应对地面温度日较差影响的数值模拟

地面温度日较差(DTR)作为重要天气和气候指标,反映昼夜温差极值,比平均气温对地表辐射收支的变化更敏感,对环境变化和气候异常具有重要参考价值。沙尘气溶胶的气候效应是影响岩石圈-大气-海洋系统的重要因子,但目前的研究较少涉及沙尘气溶胶对DTR的影响机制。基于WRF-Chem模式(Weather Research and Forecasting coupled with Chemistry)揭示2002—2005年沙尘气溶胶气候效应对东亚地面温度日较差的影响。结果表明:WRF-Chem模式可以很好体现东亚气象场和沙尘气溶胶的时空分布特征。沙尘气候效应导致东亚大陆大部分地区DTR减小,沙尘直接辐射效应在其中起决定性作用。在白天,沙尘直接辐射强迫加热大气、冷却地表,减小地面总净辐射而降低日最高温度,导致DTR减小。在中国青藏高原和东北部地区,沙尘气溶胶间接效应占主导地位,导致青藏高原地区积雪覆盖减少,东北地区云水含量减小,间接导致DTR增大。