中尺度模式不同分辨率下大气多尺度特征模拟能力分析

Analysis of Mesoscale Numerical Model's Ability in Atmospheric Multi-Scale Characteristics Simulation for Different Resolutions

本文利用不同水平分辨率下的中尺度大气数值模式ARPS(Advanced Regional Prediction System)模拟我国内蒙古奈曼旗农牧交错带2001年7月23日18时至27日18时天气演变过程,以研究中尺度模式水平分辨率提高对多种时空尺度天气过程,尤其是更小时空尺度过程的模拟改进。为此,本文提取不同分辨率下u、v、w、θ、p气象要素的模拟结果进行分析。秩和检验和方差分析表明,模式分辨率提高对气象五要素的模拟具有一定的影响,但对不同要素的影响程度有所不同,其中,对p、θ、w影响最大,对u、v的影响次之,对流层下部和边界层对分辨率最为敏感,对流层中上部次之。谱分析和小波分析都表明分辨率的提高有利于再现大气运动的多尺度特征,但在不同大气分层和不同模式变量中又有所不同。总的来说,高层效果好于低层,具有强周期变化规律的变量效果好于周期性弱的变量。

Based on a Lagrangian dispersion model FLEXPART driven by the NCEP/NCAR global forecast system reanalysis data,the authors study the pathways and timescale of troposphere to stratosphere transport（TST） over the Asian monsoon regions during the summer of 2005 using the air parcels back trajectories,as well as the surface sources,defined in terms of the locations where each trajectory last left the atmospheric planetary boundary layer.The following conclusions are drawn in the paper：（1） The boundary layer sources are most located（approximately four fifths） vertically above two areas,one is the south of the Tibetan Plateau,the Indian Ocean,and the Bay of Bengal,and the other is the tropical western Pacific regions.These two areas correspond to those regions previously identified as sources for active deep convection.Even though the two regions make the same contribution to transportation from the PBL to the base of tropopause layer（about 16 km）,the transport from the tropopause layer to the stratosphere with a much smaller fraction（about 10%） arriving at the 20-22 km height is dominated by the former（approximately 75%）.These analysis results emphasize the importance of Asian monsoon regions in the TST,with the Tibetan Plateau,the Indian Ocean,and the Bay of Bengal being the dominant source of the stratospheric ＂overworld＇ air.（2） The analysis of trajectories reveals that the air parcels arrive at and cross the tropopause mainly over the south of Tibetan Plateau and its adjacent areas（25°N-35°N,90°E-110°E）.These pathways represent a regional pattern and are largely co-controlled by the South Asia high circulation in the upper troposphere,the northern hemispheric subtropical jet and the equatorial easterly jet.Then about at 150 hPa,the most air parcels are transported westward,the rest entered the South Asian monsoon regions.（3） The results also reveal that there are two main processes in the TST.One is a fast transport process related to the convection uplift which can bring the boundary layer mass into the stratosphere in 1-2 days and make a contribution about 10%-30% of the overall mass transport.The other is a slow transport process relatively which may be related to the large-scale vertical transport due to atmospheric radiative heating in the upper troposphere.Overall,a part of transport from the boundary layer to the lower stratosphere is so rapid that this can represent an important route by which very short-lived substances,emitted at the surface,can influence the lower stratospheric ozone and other tracer budget.