青藏高原低涡东移的数值试验

本文利用钱永甫的五层有地形的原始方程模式,模拟了一次高原低涡的东移过程。发现非绝热因子(辐射、积云对流、大尺度凝结潜热)只影响高原低涡的强度,其中辐射加热对高原低涡强度影响最大。当高原低涡西部有冷槽配合或高原北部45—55°N有高压脊存在时,有利于高原低涡东移。     

600hPa高原低涡生成机制的个例探讨

本文通过对１９８６年７月１６－１７日一次６００ｈＰａ高原低涡生成的数值试验得出，高原涡的生成与高原短波辐射加热密切相关，地面感热对高原涡的生成起主要作用，高原可减缓北部的冷空气向南运动，该冷空气与副高西侧的偏南气流相遇，在青藏高原特殊下垫面的影响下，极易产生对流性不稳定，低涡扰动与降水。     

湿有效能量与暴雨

本于从湿有效能量的局地方程出发,分析和比较了1979年6月21—26日梅雨期以及8209号登陆台风中的暴雨与湿有效能量的变化,从中找出湿有效能量在暴雨期的演变规律和湿有效能量的辐合、积累、释放对暴雨的作用。文中还讨论了台风环流与低压环流中湿有效能量释放项等特征。另外对湿有效能量的积累与释放以及低空急流的形成和发展也作了初步探讨。     

湿有效能量与暴雨

本于从湿有效能量的局地方程出发,分析和比较了1979年6月21-26日梅雨期以及8209号登陆台风中的暴雨与湿有效能量的变化,从中找出湿有效能量在暴雨期的演变规律和湿有效能量的辐合、积累、释放对暴雨的作用。文中还讨论了台风环流与低压环流中湿有效能量释放项等特征。另外对湿有效能量的积累与释放以及低空急流的形成和发展也作了初步探讨。     

盛夏长江上游不同暴雨落区天气形势对比及数值试验

通过对１９８１年７月１１－１４日川西暴雨和１９８２年７月２６－２９日川东暴雨的天气形势诊断分析和数值试验得出，盛夏川西暴雨多与高原低涡的加强有关。高原涡的东移与副热带高压的西南气流结合极易产生暴雨。川东出现暴雨时，高原上低值系统移动较快，东部多为西北气流控制。高原大地形影响着高原东部降水、低值系统的生成发展移动和副热带高压。１０５°Ｅ以东的地形对川东暴雨的影响较川西大。我国东部地形对高原降水有减弱     

一次江淮地区MCV过程的数值模拟分析

本文在前期统计工作的基础上,选取了一次典型的中尺度对流涡旋(MCV)个例,利用NCEP/NCAR再分析资料分析其背景场特征,并利用WRF数值模拟结果分析其成因及其触发"二次对流"的可能机制。结果表明:MCV发生前,江淮地区处于200 h Pa强辐散场中,高层抽吸作用明显,500 h Pa江淮西北部短波槽槽后不断有冷空气南下,加强该地区大气层结不稳定,850 h Pa湖北至安徽中部有切变线活动,这种高低层配置十分有利于MCV生成及对流发生;MCV生命史各阶段垂直输送项和涡管倾斜项呈反位相分布,而水平平流项和辐合辐散项的作用基本是相互抵消的,垂直输送项和辐合辐散项是MCV生成阶段中低层涡度的主要来源;MCV引发的"二次对流"出现在其生成阶段,且位于其南侧,MCV发展成熟后,对流迅速减弱;MCV的生成使南侧西南低空急流加强,伴随水平涡度的变化,"二次对流"的发生发展与水平涡度对应的垂直环流上升支有直接联系。     

热带扰动与远距离暴雨关系的统计分析与数值试验

对2006—2011年5—9月90~150°E、0°~50°N范围内远距离暴雨进行统计与合成分析,并选取典型个例进行诊断分析与数值试验,研究结果表明:1)在有利的大气背景下,强度较低的热带扰动也可以与中纬度系统共同作用引发远距离暴雨,对统计得出的21例依据水汽通道的类型分为3类:S型水汽通道、双水汽通道和西北向型水汽通道,其中S型水汽通道发生次数最多。2)低空急流合成分析表明,不论扰动强弱,热带扰动东侧的偏南低空急流是形成远距离暴雨的关键,是联系中低纬度系统的纽带和桥梁,对S型的个例进行诊断分析与数值试验也进一步显示,热带扰动东侧低空急流是中纬度暴雨区水汽输送的主要通道,偏南低空急流的强弱是影响远距离暴雨强度的主要因子之一。3)敏感性试验结果表明,热带扰动也可以引起Rossby波能量向东北方向传播,其强度与扰动强度成正比,从而改变远距离降水分布;去除热带扰动则无法形成波列,不利于能量的传播与远距离降水发展。     

STATISTICAL ANALYSIS OF SUMMER TROPICAL CYCLONE REMOTE PRECIPITATION EVENTS IN EAST ASIA FROM 2000 TO 2009 AND NUMERICAL SIMULATION

Using 1°×1° final analysis(FNL) data from the National Centers for Environmental Prediction(NCEP),precipitation data from the Tropical Rainfall Measuring Mission(TRMM) and the best-track tropical cyclone(TC)dataset provided by the Japan Meteorological Agency(JMA) for June-August of 2000-2009, we comprehensively consider the two factors low-level moisture channel and interaction between TCs and mid-latitude systems and implement a statistical analysis of remote precipitation in East Asia to the north of 0° and to the west of 150° E. 48 cases of remote precipitation occurred in this period, which are categorized into five classes. After a composite analysis of the different classes, the main systems at 850 h Pa and 500 h Pa that impact the remote precipitation are as follows:TC, mid-latitude trough, subtropical high and water vapor channel. In particular, the water vapor channel which usually connects with Indian monsoon has the most significant impact on remote heavy rainfall. Another important factor is the mid-latitude trough. The type of north trough/vortex-south TC remote precipitation events happen most frequently,accounting for 68.8% of the total incidence. Most remote precipitation events occur on the right side of the TC path(representing 71% of the total number). At 200 h Pa, the remote precipitation events usually occur on the right rear portion of a high-altitude jet stream, and there is an anti-cyclonic vortex to the east and west of the TCs. When there is no anti-cyclonic vortex to the east of the TC, the TC is relatively weak. When the remote precipitation occurs to the northwest of the TC and there is a trough in the northwest direction, the TC is relatively strong. Numerical experiments are carried out using Weather Research and Forecast(WRF) model. The results shows that the TC plays a main role in producing the heavy precipitation and results in the enhancement of precipitation by impacting the water vapor channel.     

RELATIONSHIP BETWEEN THE VARIATION IN HORIZONTAL VORTICITY AND HEAVY RAIN DURING THE PROCESS OF MCC TURNING INTO BANDED MCSS

Using real-time data and the WRF mesoscale model,a heavy rain event in the process of Mesoscale Convective Complex(MCC) turning into banded Mesoscale Convective Systems(MCSs) during 18-19 June 2010 is simulated and analyzed in this paper.The results indicated that the formation and maintenance of a southwest vortex and shear line at 850 h Pa was the mesoscale system that affected the production of this heavy rain.The low-vortex heavy rain mainly happened in the development stage of MCC,and the circular MCC turned into banded MCSs in the late stage with mainly shear line precipitation.In the vicinity of rainfall area,the intense horizontal vorticity due to the vertical shear of u and v caused the rotation,and in correspondence,the ascending branch of the vertical circulation triggered the formation of heavy rain.The different distributions of u and v in the vertical direction produced varying vertical circulations.The horizontal vorticity near the low-vortex and shear line had obvious differences which led to varying reasons for heavy rain formation.The low-vortex heavy rain was mainly caused by the vertical shear of v,and the shear line rainfall formed owing to the vertical shear of both u and v.In this process,the vertical shear of v constituted the EW-trending rain band along the shear line,and the latitudinal non-uniformity of the vertical shear in u caused the vertical motion,which was closely related to the generation and development of MCSs at the shear line and the formation of multiple rain clusters.There was also a similar difference in the positively-tilting term(conversion from horizontal vorticity to vertical positive vorticity) near the rainfall center between the low-vortex and the shear line.The conversion in the low vortex was mainly determined by бv/бp0,while that of the shear line by бu/бp0.The scale of the conversion from the horizontal vorticity to vertical vorticity was relatively small,and it was easily ignored in the averaged state.The twisting term was mainly conducive to the reinforcement of precipitation,whereas its contribution to the development of southwest vortex and shear line was relatively small.     

西太平洋大尺度环境场对TC生成初期的影响

利用NCEP/NCAR水平分辨率为1°×1°、逐6 h的分析资料,以及JTWC(美国联合台风预警中心,Joint Typhoon Warning Center)最佳TC路径资料,对2004—2010年5—9月北半球100°E~180°范围内,118例TC生成时刻周围系统辐散风的大小以及时间和空间分布特征进行了统计分析,根据作用系统的不同将TC分为7种类型,其中:1)越赤道气流型;2)越赤道气流和副高相当型;3)越赤道气流强,副高弱型;4)副高型,这4种类型最多,占总数的91.5%以上。以TC为中心,在新生TC闭合环流外500 km范围内,第Ⅰ象限为副高的影响,在第Ⅱ象限多为副高与大陆高压影响,第Ⅲ象限为越赤道气流影响,而在第Ⅳ象限多为越赤道气流影响,少数为副高影响。区域平均越赤道气流辐散风的影响强度在0.7~3.5 m·s~(-1)的范围内,副高辐散风的影响强度在0.6~1.5 m·s~(-1)的范围内。对0704号的控制试验和敏感性试验表明,去掉TC自身的作用后,仍然会在一段时间后生成新的TC,这也验证了周围系统对TC的生成有重要的作用。