气溶胶对云宏微观特性和降水影响的研究进展

气溶胶—云—降水相互作用是当今大气科学研究的热点和前沿问题.概述性地回顾了气溶胶对云宏微观特性和降水影响的研究进展,分别讨论了气溶胶对层状云、对流云等典型云系的动力和微物理过程的影响,总结了国内外研究关于气溶胶对云宏微观特性影响的可能的物理解释.回顾外场观测及数值研究表明,气溶胶对云液态水含量、地面降水及光学厚度的影响...     

中国大气气溶胶辐射特性参数的观测与研究进展

长期系统的气溶胶辐射特性观测资料是定量研究气溶胶辐射和气候效应的重要基础.本文综合介绍中国大气气溶胶辐射特性观测与研究现状和成果,重点包括以下内容:地面太阳光度计联网观测气溶胶光学厚度、单次散射反照率、尺度谱;从全波段太阳辐射反演气溶胶光学厚度、单次散射反照率;浊度计和黑碳仪测量地面气溶胶散射系数和吸收系数;地基/星载激光雷达观测气溶胶(后向散射系数)垂直分布;极轨/静止卫星遥感反演气溶胶光学特性.     

华南气溶胶研究的回顾与展望

大气气溶胶的气候效应研究和环境效应研究都是当今国际科技界的热门研究话题,而研究大气气溶胶的气候效应和环境效应都必须充分细致地了解气溶胶的粒子谱分布、化学组成和辐射(光学)特性,其中大气气溶胶的辐射(光学)性质的直接观测研究是目前甚为紧迫的研究内容,其结果能直接为气溶胶强迫对气候变化的估计和预测的模式研究及其环境效应的研究提供必须的参数.     

人为源气溶胶的间接气候效应研究综述

气溶胶可以多种途径改变云特征来影响气候。作为凝结核,气溶胶可以增加暖云的云滴数和寿命,间接影响辐射和降水,即为气溶胶的第一间接效应和第二间接效应。观测(包括地面和卫星)和数值模拟是研究间接效应最主要的两种手段,目前这两种方法大多同时采用。本文介绍了气溶胶间接效应的原理及研究方法,并回顾国内一些研究和成果。      

气溶胶影响云和降水的机理和观测研究进展

气溶胶对云和降水的影响,对于气候系统、大气环境以及水循环至关重要。气溶胶粒子作为云凝结核和大气冰核影响云的微物理过程,进而影响雨、雪、雹和其他形式的降水。近年来,在理解气溶胶的化学成分,气溶胶微物理特性以及气溶胶作为云凝结核和大气冰核影响云降水等方面已取得重大进展。本文对于气溶胶的概念、来源以及气溶胶的直接和间接效应进行了简要概述,重点总结了国内外在气溶胶影响云和降水的机理研究方面的成果,回顾了近年来利用卫星、地面观测设备、机载探测设备等对气溶胶和云进行遥感观测和直接观测所获得的观测事实并讨论了其可能的物理机制,在总结前人研究成果的基础上对未来的研究方向进行了讨论。     

中国地区春季沙尘气溶胶短波辐射气候效应数值模拟研究

利用耦合了起沙模型(MEDM)的区域气候模式RegCM3,模拟研究了2000年春季中国地区沙尘气溶胶短波辐射气候效应。结果表明,春季中国沙尘气溶胶垂直负荷的大值区主要位于南疆盆地和阿拉善高原。引入沙尘气溶胶后,中国地区地表均出现负的辐射强迫,地面气温普遍降低,中低层(400 hPa层以下)大气温度则呈上升趋势。沙尘源区及其下游地区总云量及降水主要呈减少趋势,云量与降水的分布特征与空中流场的变化趋势一致性较好。     

自定义气溶胶模式下兰州及周边地区气溶胶光学厚度的反演

通过自定义气溶胶模式,选取类大陆型气溶胶,结合兰州大学半干旱气候与环境观测站(SACOL)气溶胶实测资料建立的气溶胶数谱模式,反演兰州市及周边地区100 km×100 km范围内的气溶胶光学厚度(AOD).结果表明,在不同气溶胶模式下,AOD分布表现出一些共同特征:在兰州市西固区(工业区域)存在一个AOD高值区,兴隆山、刘家峡水库地区AOD值较低,而在榆中县城、临夏市等城镇区也表现出AOD值高于周边地区.对比反演结果与地面实测资料,发现采用自定义气溶胶模型反演的精度有很大提高.     

中国沙尘气溶胶研究新进展

由于人类活动和气候变化的影响,沙尘气溶胶已成为一个重要的地球环境问题.近10年来,中国学者对沙尘气溶胶物理化学特性和气候效应的研究有了新的进展.前者偏重于对单次观测的研究,后者包括阳伞效应、冰核效应、铁肥料效应3个方面的研究,同时还开展了沙尘气溶胶的生态环境效应研究.上述研究虽取得一定成果,但由于沙尘气溶胶研究的极大不确定性,特别是缺乏对沙尘气溶胶长期、系统的观测,仍存在一些亟待解决的问题.     

东亚地区人为气溶胶直接辐射强迫及其气候效应的数值模拟

利用耦合化学过程的区域气候模式RegCM3,模拟研究3种主要人为排放气溶胶(硫酸盐、黑碳、有机碳)对东亚区域气候的影响.计算分析近20 a来3种气溶胶的时空分布、综合辐射强迫作用及其对地面气温和降水的影响.模拟结果表明:3种气溶胶冬夏季分布有所不同,冬季气溶胶大值区主要分布在南方地区,而夏季大值区北移;气溶胶短波辐射强迫在大气层顶和地面均为负值;气溶胶的加入对东亚地区地表气温有明显影响,冬季降温中心位于四川盆地,夏季降温大值区位于华北地区.气溶胶直接气候效应使得冬季东亚大部分地区降水减少,夏季东亚地区降水与中国南方地区夏季气溶胶浓度有较好的相关关系,中国东部雨带有南移趋势.     

大气气溶胶的卫星遥感及其在气候和环境研究中的应用

卫星遥感可以获得全球范围的大气气溶胶光学特性,目前国内外已有多颗卫星观测能够提供气溶胶特性的资料。本文综述性介绍国内外卫星遥感气溶胶特性方面的研究进展和成果,并讨论了卫星遥感资料在气候和环境研究领域中的应用。主要内容包括:极轨/静止卫星平台搭载的被动遥感传感器及其反演气溶胶特性的方法;星载激光雷达获取气溶胶光学特性的方法;国内外正在研发的新一代卫星主、被动气溶胶遥感探测器;卫星气溶胶产品在气溶胶辐射强迫、气候效应、大尺度污染输送、区域空气质量监测等研究中的应用。     

青藏高原-孟加拉湾大气热力差异与夏季暴雨

利用1979-2019年多年平均5-8月的逐日气象资料,采用EOF,MV-EOF、相关分析和合成分析等方法,对夏季青藏高原-孟加拉湾的大气热源与中国东部暴雨的时空演变特征及两者之间的联系进行探讨.研究结果表明:MV-EOF能够很好地表现不同要素的空间分布特征及其时间演变之间的联系.结果显示:在气候平均状态下,强降水事件...     

Assessing the Impacts of Initial Snow Conditions over the Tibetan Plateau on China Precipitation Prediction Using a Global Climate Model

Two ensemble experiments were conducted using a general atmospheric circulation model. These experiments were used to investigate the impacts of initial snow anomalies over the Tibetan Plateau（TP） on China precipitation prediction. In one of the experiments, the initial snow conditions over the TP were climatological values; while in the other experiment, the initial snow anomalies were snow depth estimates derived from the passive microwave remote-sensing data. In the current study, the difference between these two experiments was assessed to evaluate the impact of initial snow anomalies over the TP on simulated precipitation. The results indicated that the model simulation for precipitation over eastern China had certain improvements while applying a more realistic initial snow anomaly, especially for spring precipitation over Northeast China and North China and for summer precipitation over North China and Southeast China. The results suggest that seasonal prediction could be enhanced by using more realistic initial snow conditions over TP, and microwave remote-sensing snow data could be used to initialize climate models and improve the simulation of eastern China precipitation during spring and summer. Further analyses showed that higher snow anomalies over TP cooled the surface, resulting in lower near- surface air temperature over the TP in spring and summer. The surface cooling over TP weakened the Asian summer monsoon and brought more precipitation in South China in spring and more precipitation to Southeast China during summer.     

Estimation of the Aerosol Radiative Effect over the Tibetan Plateau Based on the Latest CALIPSO Product

Based on the CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation) Version 4.10 products released on 8 November 2016, the Level 2 (L2) aerosol product over the Tibetan Plateau (TP) is evaluated and the aerosol radiative effect is also estimated in this study. As there are still some missing aerosol data points in the daytime CALIPSO Version 4.10 L2 product, this study re-calculated the aerosol extinction coefficient to explore the aerosol radiative effect over the TP based on the CALIPSO Level 1 (L1) and CloudSat 2B-CLDCLASS-LIDAR products. The energy budget estimation obtained by using the AODs (aerosol optical depths) from calculated aerosol extinction coefficient as an input to a radiative transfer model shows better agreement with the Earth’s Radiant Energy System (CERES) and CloudSat 2B-FLXHR-LIDAR observations than that with the input of AODs from aerosol extinction coefficient from CALIPSO Version 4.10 L2 product. The radiative effect and heating rate of aerosols over the TP are further simulated by using the calculated aerosol extinction coefficient. The dust aerosols may heat the atmosphere by retaining the energy in the layer. The instantaneous heating rate can be as high as 5.5 K day^–1 depending on the density of the dust layers. Overall, the dust aerosols significantly affect the radiative energy budget and thermodynamic structure of the air over the TP, mainly by altering the shortwave radiation budget. The significant influence of dust aerosols over the TP on the radiation budget may have important implications for investigating the atmospheric circulation and future regional and global climate.     

Direct Radiative Forcing and Climatic Effects of Aerosols over East Asia by RegCM3

The authors used a high-resolution regional climate model(RegCM3) coupled with a chemistry/aerosol module to simulate East Asian climate in 2006 and to test the climatic impacts of aerosols on regionalscale climate.The direct radiative forcing and climatic effects of aerosols(dust,sulfate,black carbon,and organic carbon) were discussed.The results indicated that aerosols generally produced negative radiative forcing at the top-of-the-atmosphere(TOA) over most areas of East Asia.The radiative forcing induced by aerosols exhibited significant seasonal and regional variations,with the strongest forcing occurring in summer.The aerosol feedbacks on surface air temperature and precipitation were clear.Surface cooling dominated features over the East Asian continental areas,which varied in the approximate range of-0.5 to-2°C with the maximum up to-3-C in summer over the deserts of West China.The aerosols induced complicated variations of precipitation.Except in summer,the rainfall generally varied in the range of-1 to 1 mm d-1 over most areas of China.     

青藏高原西侧地区冬季降水的年际变率及其影响因子

基于全球降水气候中心（GPCC）和全球降水气候计划（GPCP）的降水数据及ERA-interim再分析资料,分析了1979~2012年冬季青藏高原（简称高原）西侧地区降水的基本特征及影响其年际变率的潜在因子。结果表明高原冬季降水主要发生在其西侧地区且为全区变化一致型,降水所需的水汽主要来自上游地区,从该区域的西边界输入。然而,高原西侧地区冬季降水的年际变率主要由水汽输送的动力过程所决定,表现为高原西侧的西南风异常。此外,高原西侧冬季降水的年际变率与其上游典型的大气内部变率北大西洋涛动和北极涛动相关性不强,而与赤道西印度洋和热带中东太平洋的海温显著相关。热带中东太平洋海温异常通过影响大气环流变化,在印度洋北部激发一个反气旋式的环流异常,使得高原西侧地区出现异常西南风,从而加强了水汽通量输送的动力作用。同时在赤道异常东风的作用下,暖水也向印度洋西部输送堆积。赤道中东太平洋海温的异常可进一步导致西风急流发生南北移动,从而也在一定程度上影响了高原西侧冬季水汽输送以及降水的年际变率。     

Recent Progress in the Impact of the Tibetan Plateau on Climate in China

Studies of the impacts of the Tibetan Plateau （TP） on climate in China in the last four years are reviewed. It is reported that temperature and precipitation over the TP have increased during recent decades. From satellite data analysis, it is demonstrated that most of the precipitation over the TP is from deep convection clouds. Moreover, the huge TP mechanical forcing and extraordinary elevated thermal forcing impose remarkable impacts upon local circulation and global climate. In winter and spring, stream flow is deflected by a large obstacle and appears as an asymmetric dipole, making East Asia much colder than mid Asia in winter and forming persistent rainfall in late winter and early spring over South China. In late spring, TP heating contributes to the establishment and intensification of the South Asian high and the abrupt seasonal transition of the surrounding circulations. In summer, TP heating in conjunction with the TP air pump cause the deviating stream field to resemble a cyclonic spiral, converging towards and rising over the TP. Therefore, the prominent Asian monsoon climate over East Asia and the dry climate over mid Asia in summer are forced by both TP local forcing and Eurasian continental forcing.
Due to the longer memory of snow and soil moisture, the TP thermal status both in summer and in late winter and spring can influence the variation of Eastern Asian summer rainfall. A combined index using both snow cover over the TP and the ENSO index in winter shows a better seasonal forecast.
On the other hand, strong sensible heating over the Tibetan Plateau in spring contributes significantly to anchor the earliest Asian monsoon being over the eastern Bay of Bengal （BOB） and the western Indochina peninsula. Qualitative prediction of the BOB monsoon onset was attempted by using the sign of meridional temperature gradient in March in the upper troposphere, or at 400 hPa over the TP. It is also demonstrated by a numerical experiment and theoretical study that the heating over the TP lea     

Greenhouse-gas versus aerosol forcing and African climate response

There are many indicators that human activity may change climate conditions all around the globe through emissions of greenhouse gases. In addition, aerosol particles are emitted from various natural and anthropogenic sources. One important source of aerosols arises from biomass burning, particularly in low latitudes where shifting cultivation and land degradation lead to enhanced aerosol burden. In this study the counteracting effects of greenhouse gases and aerosols on African climate are compared using climate model experiments with fully interactive aerosols from different sources. The consideration of aerosol emissions induces a remarkable decrease in short-wave solar irradiation near the surface, especially in winter and autumn in tropical West Africa and the Congo Basin where biomass burning is mainly prevailing. This directly leads to a modification of the surface energy budget with reduced sensible heat fluxes. As a consequence, temperature decreases, compensating the strong warming signal due to enhanced trace gas concentrations. While precipitation in tropical Africa is less sensitive to the greenhouse warming, it tends to decrease, if the effect of aerosols from biomass burning is taken into account. This is partly due to the local impact of enhanced aerosol burden and partly to modifications of the large-scale monsoon circulation in the lower troposphere, usually lagging behind the season with maximum aerosol emissions. In the model equilibrium experiments, the greenhouse gas impact on temperature stands out from internal variability at various time scales from daily to decadaland the same holds for precipitation under the additional aerosol forcing. Greenhouse gases and aerosols exhibit an opposite effect on daily temperature extremes, resulting in an compensation of the individual responses under the combined forcing. In terms of precipitation, daily extreme events tend to be reduced under aerosol forcing, particularly over the tropical Atlantic and the Congo basin. These results suggest that the simulation of the multiple aerosol effects from anthropogenic sources represents an important factor in tropical climate change, hence, requiring more attention in climate modelling attempts.     

夏季青藏高原大气热源准双周振荡及其传播途径

采用1979—2017年NCEP/NCAR逐日再分析资料估算大气热源,研究夏季青藏高原大气热源准双周振荡(Quasi-BiWeekly Oscillation,QBWO)的特征及传播途径。结果表明:青藏高原及其周边的大气热源QBWO的前两个主模态,即荷载中心在高原东南部的全区一致型和高原东南-西北反位相变化的偶极型,呈现了高原夏季大气热源QBWO自东向西传播过程中所处的两种不同状态。这主要是由于在中纬度地区对流层中上层,低频大气环流的活动表现为大的异常气旋和反气旋环流从我国东北经青藏高原至西亚的自东向西的传播,当移近高原时迅速增强,当西移离开高原时明显减弱。在此过程中,青藏高原及其周边、孟加拉湾以及印度半岛等地区的降水都发生了异常变化。     

青藏高原土壤湿度的变化特征及其对中国东部降水影响的研究进展

青藏高原土壤湿度受积雪与冻土的共同影响,能够记忆长时间的陆面干湿过程,是气候变化的重要因子,对随后的中国东部降水有预测意义。由于高原观测站点稀少,土壤湿度观测资料匮乏,致使现有相关研究大多是基于再分析资料、模式资料和卫星遥感资料(统称替代资料)进行的,且所得结论既有差异,也存在不确定性。因此本文首先综述了各种土壤湿度替代资料的适用性对比研究,进而讨论了青藏高原地区土壤湿度的变化特征及其对我国东部气候的影响。现有研究表明:1)资料对比研究指出,现有的各种替代资料对高原土壤湿度存在明显的高估或低估现象,且评估结论受评估指标和插值方法不同的影响。相对而言,SSM/I和风云3B的土壤湿度产品与实际观测资料相关性较好。2)高原土壤湿度具有多时间尺度变化特征和空间非均匀性,在年变化上具有显著的融冻特征,年代际变化趋势和年际特征呈现显著的区域性差异。SSM/I资料表明春季高原主体土壤湿度的年代际变化趋势呈现为增加的特征,与高原的增暖相一致;年际变率存在东、西两个高值区,与其相关的潜热、感热通量能共同激发遥相关波列影响我国长江流域降水;同时高原土壤湿度在垂直方向上具有一致性,在空间分布上具有南部边缘最大、由东南向西北递减的特征。3)前人对高原土壤湿度影响中国东部降水的结论各有不同,其可能原因之一是采用的替代资料及其适用性不同,其二是模式试验中忽略土壤湿度的空间差异性而带来的误差等。相关问题需要进一步深入研究。     

Simulations of the Impact of Lakes on Local and Regional Climate Over the Tibetan Plateau

ABSTRACT

Because of the high elevation and complex topography of the Tibetan Plateau (TP), the role of lakes in the climate system over the Tibetan Plateau is not well understood. For this study, we investigated the impact of lake processes on local and regional climate using the Weather Research and Forecasting (WRF) model, which includes a one-dimensional physically based lake model. The first simulation with the WRF model was performed for the TP over the 2000–2010 period, and the second was carried out during the same period but with the lakes filled with nearby land-use types. Results with the lake simulation show that the model captures the spatial and temporal patterns of annual mean precipitation and temperature well over the TP. Through comparison of the two simulations, we found that the TP lakes mainly cool the near-surface air, inducing a decreasing sensible heat flux for the entire year. Meanwhile, stronger evaporation produced by the lakes is found in the fall. During the summer, the cooling effect of the lakes decreases precipitation in the surrounding area and generates anomalous circulation patterns. In conclusion, the TP lakes cool the near-surface atmosphere most of the time, weaken the sensible heat flux, and strengthen the latent heat flux, resulting in changes in mesoscale precipitation and regional-scale circulation.