LAND-SEA THERMAL CONTRAST OVER SOUTH ASIA AND ITS INFLUENCES ON TROPICAL MONSOON CIRCULATION

Based on the NCEP/NCAR reanalysis data, the thermodynamic features and the effect of spatially nonuniform heating on the circulation of the tropical monsoon area in South Asia due to the land- sea distribution have been analyzed, The influences of the subcontinent topography on the Asian tropical circulation are mostly characterized by its thermodynamic effects on low-level circulation, of which the strongest is observed in winter and spring but the relatively weak in summer, followed by the weakest in autumn. The thermodynamic difference between the lndo china Peninsula and Indian Peninsula and its influence on the circulation are regulated by the Tibetan Plateau. During the transitional period from spring to early summer, the Tibetan Plateau thermal forcing generates a large-scale cyclonic circulation in low latitudes in the lower troposphere. As a result, the southerlies/northerlies are increased to the east/west of the Bay of Bengal, Therefore latent heating of the atmosphere is strengthened and the surface sensible heating over the Indochina Peninsula is weakened. On the other hand the surface sensible heating over the Indian Peninsula is increased. It is shown that heating with various scales and different kinds can affect the tropical atmosphere in different ways, which lead to the unique characteristics of the tropical Asian circulation.     

IMPACTS OF DIFFERENT KINDS OF ENSO ON LANDFALLING TROPICAL CYCLONES IN CHINA

Interannual variability of landfalling tropical cyclones(TCs) in China during 1960-2010 is investigated.By using the method of partial least squares regression(PLS-regression),canonical ENSO and ENSO Modoki are identified to be the factors that contribute to the interannual variability of landfalling TCs.El Ni o Modoki years are associated with a greater-than-average frequency of landfalling TCs in China,but reversed in canonical El Ni o years.Significant difference in genesis locations of landfalling TCs in China for the two kinds of El Ni o phases occurs dominantly in the northern tropical western North Pacific(WNP).The patterns of low-level circulation anomalies and outgoing longwave radiation(OLR) anomalies associated with landfalling TC genesis with different types of El Ni o phases are examined.During canonical El Ni o years,a broad zonal band of positive OLR anomalies dominates the tropical WNP,while the circulation anomalies exhibit a meridionally symmetrical dipole pattern with an anticyclonic anomaly in the subtropics and a cyclonic anomaly near the tropics.In El Ni o Modoki years,a vast region of negative OLR anomalies,roughly to the south of 25°N with a strong large-scale cyclonic anomaly over the tropical WNP,provides a more favorable condition for landfalling TC genesis compared to its counterpart during canonical El Ni o years.For more landfalling TCs formed in the northern tropical WNP in El Ni o Modoki years,there are more TCs making landfall on the northern coast of China in El Ni o Modoki years than in canonical El Ni o years.The number of landfalling TCs is slightly above normal in canonical La Ni a years.Enhanced convection is found in the South China Sea(SCS) and the west of the tropical WNP,which results in landfalling TCs forming more westward in canonical La Ni a years.During La Ni a Modoki years,the landfalling TC frequency are below normal,owing to an unfavorable condition for TC genesis persisting in a broad zonal band from 5°N to 25°N.Since the western North Pacific subtropical high(WNPSH) in La Ni a Modoki years is located in the westernmost region,TCs mainly make landfall on the south coast of China.     

热带深对流云砧数值模拟及云凝结核数浓度对其影响的初步试验

利用中国科学院大气物理研究所发展的三维强风暴模式,对Egrett Microphysics Experiment with Radiation Lidar and Dynamics（EMERALD）试验期间的一次长寿命热带深对流个例进行对流产生、发展、消亡过程以及云砧的数值模拟,并与实测资料［包括C波段双线偏振雷达图像资料、机载云粒子成像仪（CPI）探测的云砧卷云微物理特性以及激光雷达探测的云砧宏观特性资料］进行了细致的对比,然后通过改变模式中最大云滴数浓度进行有关云凝结核数浓度影响云砧卷云冰晶含水量和数浓度的敏感性试验。模式较好地模拟出系统的一些重要宏观特征,如爆发性增长阶段、各高度雷达水平反射率因子的最大值、对流云主体移动方向、云砧底部和顶部高度。对云砧冰相粒子含水量、数浓度以及平均直径等微观特征的模拟结果与实测也比较接近。对于本文个例而言,异质核化为冰晶形成的最主要方式,其次为过冷云滴的均质核化。敏感性试验结果表明:当云凝结核数浓度增加时,爆发性增长阶段的垂直速度减小,使得对流云从中低层向高层的水物质输送量减少,从而使云砧卷云冰晶的数量减少。     

Technical note on a track-pattern-based model for predicting seasonal tropical cyclone activity over the western North Pacific

Recently, the National Typhoon Center (NTC) at the Korea Meteorological Administration launched a track-pattern-based model that predicts the horizontal distribution of tropical cyclone (TC) track density from June to October. This model is the first approach to target seasonal TC track clusters covering the entire western North Pacific (WNP) basin, and may represent a milestone for seasonal TC forecasting, using a simple statistical method that can be applied at weather operation centers. In this note, we describe the procedure of the track-pattern-based model with brief technical background to provide practical information on the use and operation of the model. The model comprises three major steps. First, long-term data of WNP TC tracks reveal seven climatological track clusters. Second, the TC counts for each cluster are predicted using a hybrid statistical-dynamical method, using the seasonal prediction of large-scale environments. Third, the final forecast map of track density is constructed by merging the spatial probabilities of the seven clusters and applying necessary bias corrections. Although the model is developed to issue the seasonal forecast in mid-May, it can be applied to alternative dates and target seasons following the procedure described in this note. Work continues on establishing an automatic system for this model at the NTC.     

ANALYSIS OF THE WESTWARD EXTENSION OFWESTERN PACIFIC SUBTROPICAL HIGH DURING A HEAVY RAIN PERIOD OVERSOUTHERN CHINA IN JUNE 2005

The NCEP/NCAR II daily mean reanalysis data and observed precipitation data are employed to investigate the westward extension of the western Pacific subtropical high (WPSH) during the heavy rain period over the southern China in June 2005. Results show that there may exist a relationship between the east-west shift of the WPSH and the process of a southern China heavy rain. The analysis indicates that the vertical motion in the WPSH area is mainly caused by the latent heat release of monsoon rain belts on its northern and southern sides. The vertical motion could cause the accumulation of air mass in the center and west of the WPSH, which leads to its strengthening. The appearance of the northern and southern monsoon rain belts could not only enhance the WPSH by strengthening the descending draft, but also excite the development of positive vorticity and restrict the WPSH’s movement in the north–south direction. Moreover, the Indian monsoon rainfall to the west of the WPSH may excite the development of anticyclonic vorticity on its eastern side, which leads to the westward extension of the WPSH.     

The kinetic energy budget of monsoon circulation over the Indian region during ISMEX-1973

A kinetic energy budget over the Indian region is computed for the period 4–9 July 1973, when a twin monsoon depression-one in the Bay of Bengal and another in the Arabian sea were the dominant synoptic features. The generation term caused by the cross-contour flow is a dominant source to the kinetic energy. The dissipation term is computed as a residual and is a major sink for the kinetic energy. The horizontal flux divergence is also a sink term but is much smaller in magnitude than other major source and sink terms. From the results it may be inferred that the generation term is the most important for the maintenance of monsoon disturbances.     

影响海南乐东热带气旋的气候特征分析

利用1971～2006年海南省气象台提供的热带气旋影响个例资料和乐东地面站人工观测风、雨实况资料,对影响海南乐东热带气旋的气候特征进行统计分析,以能为热带气旋的预报预测和防灾减灾起到一定的指导作用。结果表明：影响海南乐东的热带气旋频数年平均为3.47个;主要出现在7～9月,以8月出现频数最多;西太平洋移来和南海生成影响乐东的热带气旋频数大约各占一半。受海南岛和乐东地形及其所在位置的影响,来袭海南不同路径和强度的热带气旋对乐东的影响程度也不同,对县域内不同地区所造成的影响也有所差异,应区别应对及有针对性地开展防灾减灾工作。     

热带太平洋海表面高度特征及其与ENSO事件的关系分析

利用1980--2008年Godas的逐月海表面高度（SSH）资料,分析了热带太平洋不同季节海表面高度季节及年际变化特征,并初步探讨了海表面高度异常与ENSO事件的关系。结果表明：1）就赤道地区而言,东太平洋区域海表面最低,西北太平洋和西南太平洋海表面最高,中太平洋区域较低。2）西北太平洋和西南太平洋海表面高度年际异常大,赤道中东太平洋区域在秋季和冬季的异常较大。3）1、4、10月热带太平洋海表面高度年际异常与ENSO事件有良好的对应关系：在E1Nifio事件期问,热带太平洋东部海表面高度增加,西部和西南部减小,不同季节异常区略有区别;7月海表面高度异常与ENSO事件关系不密切。     

海口市人工催化热带对流云增雨降温的数值模拟

利用中国科学院大气物理研究所发展的具有火箭人工增雨催化功能的三维云分档数值模式(IAP2HBM),对2004年7月8日海南岛海口市区的一次热带对流云火箭人工增雨降温作业过程的宏、微观物理演变过程和人工增雨降温作业效果进行数值模拟。结果显示,人工催化播撒AgI后地面降水增加、地面气温下降的区域扩大、维持时间延长。催化导致云水含水量降低,雨水、冰晶、霰、雪含量增加,云中雨水的大量蒸发和冰晶、霰和冰雹粒子融化造成空气温度降低。     

1949～2005年海南岛登陆热带气旋的若干变化特征

利用热带气旋(TC)年鉴资料和海南岛逐日降水量资料,对海南岛57a登陆TC年频数、强度、登陆位置、活动时间、登陆维持时间、登陆TC降水量的变化特征进行了分析。结果表明:在全球气候变暖背景下,海南岛登陆TC年频数有显著减少趋势,但登陆时TC的平均强度和极端强度都有增强趋势,这主要归功于南海登陆海南岛的热带低压年频数的显著减少和强热带风暴的弱增加;登陆TC具有准3a的周期,而南海登陆海南岛的TC具有准3a、准5a的周期,西太平洋登陆海南岛的TC具有准13a和准3a的周期;海南岛登陆TC的登陆点位置有南移趋势,80年代中期以来在海南岛最南端地区登陆的TC频数明显增多;登陆TC的活动时间和登陆维持时间均有弱的缩短趋势;登陆TC暴雨与登陆时TC强度成显著负相关关系而和登陆维持时间有显著正相关关系,但登陆时TC强度对暴雨的影响强于登陆维持时间;登陆TC年降水量呈减少变化趋势,其中登陆风暴和强风暴的年降水量有增多趋势,登陆热带低压和登陆台风年降水量均有减少趋势。