Water vapor transport and cross-equatorial flow over the Asian-Australia monsoon region simulated by CMIP5 climate models

The summer mean water vapor transport (WVT) and cross-equatorial flow (CEF) over the Asian-Australian monsoon region simulated by 22 coupled atmospheric-oceanic general circulation models (AOGCMs) from the World Climate Research Programme’s Coupled Model Intercomparison Project Phase 5 (CMIP5) were evaluated. Based on climatology of the twentieth-century simulations, most of models have a reasonably realistic representation of summer monsoon WVT characterized by southeast water vapor conveyor belt over the South Indian Ocean and southwest belt from the Arabian Sea to the East Asian. The correlation coefficients between NCEP reanalysis and simulations of BCC-CSM1-1, BNU-ESM, CanESM2, FGOALS-s2, MIROC4h and MPI-ESM-LR are up to 0.8. The simulated CEF depicted by the meridional wind along the equator includes the Somali jet and eastern CEF in low atmosphere and the reverse circulation in upper atmosphere, which were generally consistent with NCEP reanalysis. Multi-model ensemble means (MME) can reproduce more reasonable climatological features in spatial distribution both of WVT and CEF. Ten models with more reasonable WVT simulations were selected for future projection studies, including BCC-CSM1-1, BNU-ESM, CanESM2, CCSM4, FGOALS-s2, FIO-ESM, GFDL-ESM2G, MRIOC5, MPI-ESM-LR and NorESM-1M. Analysis based on the future projection experiments in RCP (Representative Concentration Pathway) 2.6, RCP4.5, RCP6 and RCP8.5 show that the global warming forced by different RCP scenarios will results in enhanced WVT over the Indian area and the west Pacific and weaken WVT in the low latitudes of tropical Indian Ocean.     

Evaluation of spring persistent rainfall over East Asia in CMIP3/CMIP5 AGCM simulations

The progress made fi＇om Phase 3 to Phase 5 of the Coupled Model Intercomparison Project （CMIP3 to CMIP5） in simulating spring persistent rainfall （SPR） over East Asia was examined from the outputs of nine atmospheric general circulation models （AGCMs）. The majority of the models overestimated the precipitation over the SPR domain, with the mean latitude of the SPR belt shifting to the north. The overestimation was about 1mm d-1 in the CMIP3 ensemble, and the northward displacement was about 3°, while in the CMIP5 ensemble the overestimation was suppressed to 0.7 mm d-i and the northward shift decreased to 2.5°. The SPR features a northeast-southwest extended rain belt with a slope of 0.4°N/°E. The CMIP5 ensemble yielded a smaller slope （0.2°N/°E）, whereas the CMIP3 ensemble featured an unre- alistic zonally-distributed slope. The CMIP5 models also showed better skill in simulating the interannual variability of SPR. Previous studies have suggested that the zonal land-sea thermal contrast and sensible heat flux over the southeastern Tibetan Plateau are important for the existence of SPR. These two ther- mal factors were captured well in the CMIP5 ensemble, but underestimated in the CMIP3 ensemble. The variability of zonal land-sea thermal contrast is positively correlated with the rainfall amount over the main SPR center, but it was found that an overestimated thermal contrast between East Asia and South China Sea is a common problem in most of the CMIP3 and CMIP5 models. Simulation of the meridional thermal contrast is therefore important for the future improvement of current AGCMs.     

CAM5模式中两气溶胶模块的评估

公共大气模式 (CAM) 被广泛用于气候变化研究中,其5.0版中包含两个气溶胶模块MAM3和MOZART。利用AeroCom (2000年) 多模式中值、IMPROVE (1988—2005年) 和EMEP (2002—2008年) 站点资料对两模块进行了评估。结果表明:MAM3和MOZART模块都能很好地模拟硫酸盐气溶胶的季节变化, 与观测资料相比,模拟结果均在夏季偏高, 相关系数均在0.89左右,2倍误差内。两模块能较好地模拟黑碳气溶胶的时空分布特征, 与观测资料相比,模拟结果偏低,相关系数均在0.62左右, 排放源偏小而清除率偏大是造成黑碳气溶胶偏低的主要原因。两模块对有机碳气溶胶的模拟结果差别较大,大部分站点在3倍误差内,MAM3的结果偏高92.1%,MOZART则偏低58.1%;两模块一次有机碳的结果接近,差异主要源自对二次有机碳的模拟。两模块模拟的海盐气溶胶偏大,这主要是清除率偏小造成的。两模块采用相同的起沙机制,但起沙系数有差异, MAM3的沙尘源强偏大近两倍,模拟总量较大;MOZART的沙尘源强则偏低40%左右,模拟沙尘总量较低。即模式中气溶胶的输送和扩散过程偏弱,说明清除机制还有待改进。     

CMIP5气候模式对亚洲升温幅度的模拟与预估

基于新的全球表面温度数据集CMST(China merged surface temperature),全面评估了参加国际耦合模式比较计划第5阶段(CMIP5)的27个全球气候模式1900—2017年的气候模拟结果(1900—2005年为模式历史模拟,2006—2017年为不同典型浓度路径下的预估)。泰勒图及各种统计参数的对比表明,一些模式无论在历史模拟时段,还是在历史模拟和近期预估拼接时段,都稳定、较好地模拟出了观测序列的变化特征。利用筛选出模拟效果相对较优的9个模式,系统比较了其集合平均MT9(mean model top 9)与所有模式的集合平均MAM(mean all models)。分析结果表明:无论在哪种排放路径下,不管是时间变化,还是从空间分布方面,多数模式可能高估了亚洲区域增暖趋势,导致MAM过高估计了亚洲区域温度变化幅度与长期趋势,而优选的模式集合MT9明显比MAM更接近于观测值。进一步,采用了MT9的预估结果分析了2018—2099年的亚洲区域预估的地表升温幅度:到2099年,在RCP2.6浓度路径下,MT9预估亚洲地区的升温幅度较小,约为0.08℃;在RCP4.5浓度路径下,升温约为1.20℃;在RCP8.5浓度路径下,升温将达3.54℃,这些结果均略小于所有模式集合MAM的升温幅度,因而更加合理;同时还基于MT9预估分析了2018—2099年的温度距平的空间变化。     

SWDC-5倾斜摄影技术及其在国内的应用分析

文章简要介绍了SWDC-5数字航空倾斜摄影仪,重点分析了SWDC-5倾斜相机的各项关键技术,阐述了SWDC-5在国内的应用情况。以两个真实的工程项目为例,分析了该相机一贯的高精度优势,最后分析指出SWDC-5在国内倾斜摄影领域的引领作用以及倾斜摄影在国内必将取得快速发展的愿景。     

简化5级-CKF在SINS大失准角初始对准中的应用

针对大失准角情况下,利用3级-CKF进行SINS初始对准性能不高的问题,提出5级-CKF算法。在系统模型噪声和量测噪声均为加性噪声且量测方程为线性方程时,推导了简化5级-CKF算法,步骤需要在Kalman滤波的基础上利用5级容积采样点对非线性状态方程的状态及其方差进行预测。采用SINS静基座初始对准仿真实验验证算法的有效性,结果表明:简化5级-CKF对任意失准角都是有效的,失准角较小时,3级-CKF和简化5级-CKF的对准精度和收敛速度性能相近,但简化5级-CKF的数值稳定性更高;失准角较大时,简化5级-CKF较3级-CKF具有更高的收敛速度和对准精度。     

L5载波相位观测值的模拟分析

GPS现代化计划目前只在几颗卫星上加入了L5信号,第三频率观测数据尚不能进行组网数据处理.如何验证现有多频理论的有效性,以及进行更深入、更广泛的多频数据处理理论应用研究,L5数据的获取成为一个重要问题.文中结合载波相位观测值之间的物理相关性,模拟L5载波相位观测值,对L5载波相位观测值的精度进行了分析,取得了一些有益的结论.     

白令海Navarinsky海底峡谷地震剖面解译

第五次北极科学考察在北极区的白令海首次进行了高分辨率单道地震作业。Navarinsky峡谷头部测线BL11-12剖面中部识别出不对称沙波,陡的一面朝向陆架,波高约为9m、波长约为882m。结合站位U1345的沉积速率及站位U1344表层纵波速率推测沙波沉积可以追溯到中更新世(距今约0.258Ma),同时近陆架的洼地逐渐填平。将地层分为3个沉积层,分析沉积物变化情况,结合0.25Ma以来白令海海平面变化历史,推测最大海退事件对应的界面。结合沙波的地理位置及海平面变化情况,认为内波对沙波的形成起主要作用。