基于国际大气化学—气候模式比较计划模式数据评估中国沙尘气溶胶直接辐射强迫

目前气候模式对沙尘气溶胶直接辐射强迫模拟仍有很大不确定性,多模式对比有助于定量评估不确定范围。国际大气化学—气候模式比较计划(Atmospheric Chemistry and Climate Model Intercomparison Project,ACCMIP)旨在评估当前模式对短寿命大气成分辐射强迫和气候效应的模拟能力。基于7个ACCMIP模式模拟的中国地区沙尘气溶胶浓度,我们评估了中国区域沙尘气溶胶直接辐射强迫和不确定性范围。结果显示,中国区域沙尘气溶胶年排放总量为215±163 Tg a^(-1),区域年均地表浓度为41±27μg m^(-3),柱浓度为9±4 kg m^(-2),光学厚度为0.09±0.05。中国区域年均沙尘气溶胶产生的大气顶短波、长波和总辐射强迫分别为-1.3±0.8 W m^(-2)、0.7±0.4W m^(-2)和-0.5±0.7 W m-2;地表短波、长波和总的辐射强迫值为-1.5±1.0 W m^(-2)、1.8±0.9 W m^(-2)和0.2±0.2 W m^(-2)。沙尘气溶胶长波辐射强迫对沙尘浓度的垂直分布敏感。高层沙尘气溶胶浓度越大,其在大气顶产生更强的正值长波辐射强迫。然而,沙尘气溶胶短波辐射强迫主要受整层沙尘柱浓度控制,对沙尘浓度的垂直分布较不敏感。本文结果可为中国沙尘气溶胶的气候模拟提供参考。

冬夏季环流隔季相关的数值试验

利用海气耦合和大气气候模式研究东亚冬季风异常对夏季环流的影响,结果表明,东亚冬季风异常对于后期环流及海洋状态异常都起了很大的作用。一般情况下,强的冬季风与后期弱的东亚夏季风和较强的南海季风相对应。与强(弱)冬季风异常相关的风应力的改变可以使热带太平洋海温从冬季至夏季呈现LaNinna(ElNino)型异常分布。试验得到的由冬季风异常所产生的海洋及夏季环流的变化与实况是相当接近的。在异常的冬季风偏北风分量强迫下,西太平洋上形成的偏差气旋环流在夏季已不存在,这时东亚夏季风反而增强。而冬季赤道西风分量所产生的影响,则在西太平洋上形成显著的偏差气旋环流,使东亚副热带夏季风减弱,南海夏季风加强。对于东亚大气环流而言,与强弱冬季风对应的热带海洋海温异常强迫下,不仅是冬季,后期春季和夏季环流的特征都能得到很好的模拟。但是从分区看,西太平洋暖池区的海温异常比东太平洋更为重要。单纯的热带中东太平洋的海温异常对东亚大气环流的影响主要表现在冬季,对后期的影响并不十分清楚。整个热带海洋的异常型分布(不论是ElNino还是LaNina)型,对冬夏季风的影响是重要的,而单纯的某个地区的海温异常都比它的整体影响要小。从试验结果看,海温在大尺度冬夏季环流的隔季相关中起了十分重要的作用。

未来甲烷排放增加对平流层水汽和全球臭氧的影响

利用一个耦合的大气化学-气候模式(WACCM3)研究了地表甲烷排放增加对平流层水汽和全球臭氧变化的影响。结果表明,如果地表甲烷的排放量在2000年的基础上增加50%(达到政府间气候变化专门委员会A1B排放情景中2050年的值),平流层水汽体积分数将平均增加约0.8×10^(-6)。南半球平流层甲烷转化为水汽的效率比北半球高。在北半球平流层中,1 mol甲烷分子可以转化为约1.63 mol的水汽分子,而在南半球1 mol甲烷分子大概可以转化为约1.82 mol的水汽分子。甲烷排放增加50%将使全球中低纬度地区以及北半球高纬度地区的臭氧柱总量增加1%—3%,使南半球高纬度地区臭氧柱总量增加近8%,而秋季(南半球春季)南极地区臭氧柱总量增加幅度可高达20%,南极臭氧的这种显著增加主要是由于甲烷增加造成的化学反馈所致。在北半球中高纬度地区,甲烷增加引起的臭氧变化主要与甲烷氧化导致的水汽增加有关。研究还表明,未来甲烷排放增加对臭氧的恢复作用其实与溴化物排放的减少一样重要。

热带对流层顶层结构的变化特征和趋势

利用1989-2008年欧洲中期天气预报中心高时空分辨率的再分析资料以及1980~2019年的大气化学-气候模式模拟资料分析了热带对流层顶层（Tropical Tropopause Layer,TTL）结构的变化特征,并且预测了其未来变化趋势。结果表明,TTL结构存在明显的季节和空间变化。其厚度在北半球的春、秋两季比较薄,其季节变率在北半球的冬季最大;再分析资料表明1991年皮纳图博（Pinatubo）火山爆发导致对流层顶温度大幅升高,1992~1995年之间对流层顶温度明显下降。不考虑火山爆发的影响,1996年后对流层顶温度有所升高。近年来热带对流层顶层有抬升增暖的趋势,厚度有所减小,平流层水汽含量增多。大气化学气候模式资料预测的TTL的特征从1980~2019年也是同样的趋势。

Impact of European Black Carbon on East Asian Summer Climate

The remote response of the East Asian summer monsoon （EASM） to European black carbon （EUBC） aerosols was studied by using an ensemble of sensitivity experiments with the Geophysical Fluid Dynamics Laboratory （GFDL） atmospheric general circulation model （AGCM） Atmospheric Model version 2.1 （AM2.1）.The results show that EUBC causes an enhanced EASM.The resulted enhanced southwesterly brings more moisture supply from the Bay of Bengal,which causes an increase in precipitation over the Yangtze River valley,northeastem China,the eastern part of the Yellow River valley,and the Tibetan Plateau.Diagnostic examination suggests that EUBC induces enhanced tropospheric heating over most of the Eurasian Continent through a propagating wave train and horizontal air temperature advection.This phenomenon results in intensified thermal contrast between land and ocean,which accounts for the enhanced EASM.Moreover,reductions in EUBC emission in 1992 may have contributed to decadal weakening of the EASM in the early 1990s.

Coupling methods of global climate models and regional climate models

The future climate dynamical downscaling method is that output of general circulation models( GCMs) is employed to provide initial conditions,lateral boundary conditions,sea surface temperatures,and initial land surface conditions to regional climate models( RCMs). There are two methods of downscaling: offline coupling and online coupling. The two kinds of coupling methods are described in detail by coupling the Weather Research and Forecasting model( WRF) with the Institute of Atmospheric Physics of Chinese Academy of Sciences Atmospheric General Circulation Model Version 4. 0( IAP AGCM4. 0) in the study. And the extreme precipitation event over Beijing on July 212012 is simulated by using the two coupling methods. Results show that online coupling method is of great value in improving the model simulation. Furthermore,the data exchange frequency of online coupling has some effect on simulation result.

Impacts of Climate Change on Water Resources in Diyala River Basin, Iraq

Diyala River is the third largest tributary of the Tigris River running 445 km length and draining an area of 32,600 km2. The river is the major source of water supply for Diyala City for municipal, domestic, agriculture and other purposes. Diyala River Basin currently is suffering from water scarcity and contamination problems. Up-to-date studies have shown that blue and green waters of a basin have been demonstrating increasing variability contributing to more severe droughts and floods seemingly due to climate change. To obtain better understanding of the impacts of climate change on water resources in Diyala River Basin in near 2046-2064 and distant future 2080~2100, SWAT （soil and water assessment tool） was used. The model is first examined for its capability of capturing the basin characteristics, and then, projections from six GCMs （general circulation models） are incorporated to assess the impacts of climate change on water resources under three emission scenarios： A2, AIB and B1. The results showed deteriorating water resources regime into the future.

Effect of model errors in ambient air humidity on the aerosol optical depth obtained via aerosol hygroscopicity in eastern China in the Atmospheric Chemistry and Climate Model Intercomparison Project datasets

This analysis of the multi-model aerosol optical depth (AOD) in eastern China using the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) datasets shows that the global models underestimate the AOD by 33% and 44% in southern and northern China, respectively, and decrease the relative humidity (RH) of the air in the surface layer to 71%–80%, which is less than the RH of 77%–92% in reanalysis meteorological datasets. This indicates that the low biases in the RH partially account for the errors in the AOD. The AOD is recalculated based on the model aerosol concentrations and the reanalysis humidity data. Improving the mean value of the RH increases the multi-model annual mean AOD by 45% in southern China and by 33% in June–August in northern China. This method of improving the AOD is successful in most of the ACCMIP models, but it is unlikely to be successful in GISS-E2-R, in which the plot of its AOD efficiency against RH strongly deviates from the rest of the models. The effect of the improvement in the modeled RH on the AOD depends on the concentration of aerosols. The shape error in the frequency distribution of the RH is likely to be more important than the error in the mean value of the RH, but this requires further research.

Improved simulation of the East Asian winter monsoon interannual variation by IAP/LASG AGCMs

The simulation of the East Asian winter monsoon （EAWM） has been a challenge for climate models. In this study, the performances of two versions of the AGCM developed at the lAP, versions 1 and 2 of the Grid-point Atmospheric Model of the IAP/LASG （GAMIL1 and GAMIL2）, are evaluated in the context of mean state and interannual variation. Significant improvements are shown for GAMIL2 in comparison to GAMIL1. The simulated interannual variability of the EAWM, measured by the regional average of 1000 hPa meridional wind over East Asia, has evidently improved; the correlation coefficient with reanalysis data changes from 0.37 in GAMIL1 to 0.71 in GAMIL2. The associated interannual precipitation anomalies are also improved, in terms of both spatial pattern and magnitude. Analysis demonstrates that the improvements result from the better simulation of the El Nino-related Philippine Sea anticyclone （PSAC） in GAMIL2. The improved moist processes, including the stratiform condensation and evaporation in GAMIL2, lead to a reasonable atmospheric heating associated with El Nitro in the tropical Pacific, which further drives the PSAC as a Rossby- wave response.

Application of ANNs Model with the SDSM for the Hydrological Trend Prediction in the Sub-catchment of Kurau River, Malaysia

The paper describes the application of SDSM （statistical downscaling model） and ANNs （artificial neural networks） models for prediction of the hydrological trend due to the climate-change. The SDSM has been calibrated and generated for the possible future scenarios of meteorological variables, which are temperature and rainfall by using GCMs （global climate models）. The GCM used is SRES A2. The downscaled meteorological variables corresponding to SDSM were then used as input to the ANNs model calibrated with observed station data to simulate the corresponding future streamflow changes in the sub-catchment of Kurau River. This study has discovered the hydrological trend over the catchment. The projected monthly streamflow has shown a decreasing trend due to the increase in the, mean of temperature for overall months, except the month of August and November.

Assessing the Impacts of Eurasian Snow Conditions on Climate Predictability with a Global Climate Model

On the basis of two ensemble experiments conducted by a general atmospheric circulation model(Institute of Atmospheric Physics nine-level atmospheric general circulation model coupled with land surface model,hereinafter referred to as IAP9L_CoLM),the impacts of realistic Eurasian snow conditions on summer climate predictability were investigated.The predictive skill of sea level pressures(SLP)and middle and upper tropospheric geopotential heights at mid-high latitudes of Eurasia was enhanced when improved Eurasian snow conditions were introduced into the model.Furthermore,the model skill in reproducing the interannual variation and spatial distribution of the surface air temperature(SAT)anomalies over China was improved by applying realistic(prescribed)Eurasian snow conditions.The predictive skill of the summer precipitation in China was low;however,when realistic snow conditions were employed,the predictability increased,illustrating the effectiveness of the application of realistic Eurasian snow conditions.Overall,the results of the present study suggested that Eurasian snow conditions have a significant effect on dynamical seasonal prediction in China.When Eurasian snow conditions in the global climate model(GCM)can be more realistically represented,the predictability of summer climate over China increases.

Climate Change Impacts on Water Resources of Greater Zab River, Iraq

Greater Zab is the largest tributary of the Tigris River in lraq where the catchment area is currently being plagued by water scarcity and pollution problems. Contemporary studies have revealed that blue and green waters of the basin have been manifesting increasing variability contributing to more severe droughts and floods apparently due to climate change. In order to gain greater appreciation of the impacts of climate change on water resources in the study area in near and distant future, SWAT （Soil and Water Assessment Tool） has been used. The model is first tested for its suitability in capturing the basin characteristics, and then, forecasts from six GCMs （general circulation models） with about half-a-century lead time to 2046-2064 and one-century lead time to 2080-2100 are incorporated to evaluate the impacts of climate change on water resources under three emission scenarios： A 1 B, A2 and BI. The results showed worsening water resources regime into the future.

Impact of Different East Asian Summer Monsoon Circulations on Aerosol-Induced Climatic Effects

The different spatial distributions of aerosol-induced direct radiative forcing and climatic effects in a weak （2003） and a strong （2006） East Asian summer monsoon （EASM） circulation were simulated using a high-resolution regional climate model （RegCM3）.Results showed that the atmospheric circulations of summer monsoon have direct relations with transport of aerosols and their climatic effects.Both the top-of-the-atmosphere （TOA） and the surface-negative radiative forcing of aerosols were stronger in weak EASM circulations.The main difference in aerosol-induced negative forcing in two summers varied between 2 and 14 W m-2 from the Sichuan Basin to North China,where a maximum in aerosol-induced negative forcing was also noticed in the EASM-dominated areas.The spatial difference in the simulated aerosol optical depth （AOD） in two summers generally showed the similar pictures.Surface cooling effects induced by aerosols were spatially more uniform in weak EASM circulations and cooler by about 1-4.5℃.A preliminary analysis here indicated that a weaker low-level wind speed not conducive to the transport and diffusion of aerosols could make more contributions to the differences in the two circulations.

Changes of the tropical Pacific Walker circulation simulated by two versions of FGOALS model

Here we assessed the performances of IAP/LASG climate system model FGOALS-g2 and FGOAS-s2 in the simulation of the tropical Pacific Walker circulation （WC）. Both models reasonably reproduce the climatological spatial distribution features of the tropical Pacific WC. We also investigated the changes of WC simulated by two versions of FGOALS model and discussed the mechanism responsible for WC changes. Observed Indo-Pacific sea level pressure （SLP） reveals a reduction of WC during 1900-2004 and 1950-2004, and an enhancement of WC during 1982-2004. During the three different time spans, the WC in FGOALS-g2 shows a weakening trend. In FGOALS-s2, tropical Pacific atmospheric circulation shows no significant change over the past century, but the WC strengthens during 1950-2004 and 1982-2004. The simulated bias of the WC change may be related to the phase of the multi-decadal mode in coupled models, which is not in sync with that in the observations. The change of WC is explained by the hydrological cycle constraints that precipitation must be balanced with the moisture trans- porting from the atmospheric boundary layer to the free troposphere. In FGOALS-g2, the increasing amplitude of the relative variability of precipitation （AP/P） is smaller （larger） than the relative variability of moisture （Aq/q） over the tropical western （eastern） Pacific over the three time spans, and thus leads to a weakened WC. In FGOALS-s2, the convective mass exchange fluxes increase （decrease） over the tropical western （eastern） Pacific over the past 53 a （1950-2004） and the last 23 a （1982- 2004）, and thus leads to a strengthened WC. The distributions of sea surface temperature （SST） trends dominate the change of WC. Over the past 55 a and 23 a, tropical Pacific SST shows an E1 Nifto-like （a La Nifia-like） trend pattern in FGOALS-g2 （FGOALS-s2）, which drives the weakening （strengthening） of WC. Therefore, a successful simulation of the tropical Pacific SST change pattern is necessary for a reasonable simulation of WC change in climate system models. This idea is further sup- ported by the diagnosis of historical sea surface temperature driven AGCM-simulations.

AntarcticaLC2000：The new Antarctic land cover database for the year 2000

Antarctica plays a key role in global energy balance and sea level change.It has been conventionally viewed as a whole ice body with high albedo in General Circulation Models or Regional Climate Models and the differences of land cover has usually been overlooked.Land cover in Antarctica is one of the most important drivers of changes in the Earth system.Detailed land cover information over the Antarctic region is necessary as spatial resolution improves in land process models.However,there is a lack of complete Antarctic land cover dataset derived from a consistent data source.To fill this data gap,we have produced a database named Antarctic Land Cover Database for the Year 2000(AntarcticaLC2000) using Landsat Enhanced Thematic Mapper Plus(ETM+) data acquired around 2000 and Moderate Resolution Imaging Spectrometer(MODIS) images acquired in the austral summer of 2003/2004 according to the criteria for the 1:100000-scale.Three land cover types were included in this map,separately,ice-free rocks,blue ice,and snow/firn.This classification legend was determined based on a review of the land cover systems in Antarctica(LCCSA) and an analysis of different land surface types and the potential of satellite data.Image classification was conducted through a combined usage of computer-aided and manual interpretation methods.A total of 4067 validation sample units were collected through visual interpretation in a stratified random sampling manner.An overall accuracy of 92.3%and the Kappa coefficient of 0.836 were achieved.Results show that the areas and percentages of ice-free rocks,blue ice,and snow/firn are 73268.81 km2(0.537%),225937.26 km2(1.656%),and 13345460.41 km2(97.807%),respectively.The comparisons with other different data proved a higher accuracy of our product and a more advantageous data quality.These indicate that AntarcticaLC2000,the new land cover dataset for Antarctica entirely derived from satellite data,is a reliable product for a broad spectrum of applications.