RITC活跃年份的气候特征及个例研究

利用1981—2010年期间的热带气旋实况数据、ERA-Interim逐月和逐日的再分析资料及NOAA提供的向外长波辐射月数据,采用合成分析方法及天气学方法,对强度快速增强气旋活跃年份及不活跃年份的海温条件、向外长波辐射、垂直风切变、100 hPa位势高度距平场及季风槽进行了特征分析,结果表明:(1)RITC活跃年份-不活跃年份的海温距平场多表现为厄尔尼诺特征,即活跃年份的整个赤道中东太平洋海温较不活跃年份明显偏高;(2)RITC活跃年份所对应的赤道大部分地区(140°E以东)向外长波辐射值更低,表明对流活动明显东移;(3)RITC活跃年份的垂直风切变较小区域较不活跃年份总体偏东10～15个经度;(4)RITC活跃年份的南亚高压主体东端出现明显的扩展;(5)RITC活跃年份的季风槽为偏东型,不活跃年份的季风槽则为西北型。同时,对具有代表性的1983年第10号热带气旋"Forrest"的物理量场进行分析后发现:在该气旋强度快速增长阶段,气旋的整个中低层增暖增湿效果明显;表征积云对流发展的大范围的对流有效位温高值区存在于气旋及其周围,尤其是前进方向上;该阶段仍存在较强的垂直风切变,但强度及范围明显变弱、变小;各通道的水汽条件充沛。

Climatic charatistics of rapidly intensifying tropical cyclones and a case study

The multi-year (1981-2010) tropical cyclones, daily and monthly ERA Interim reanalysis, and monthly NOAA datasets are employed to examine the characteristics of sea surface temperature (SST) condition, outgoing longwave radiation (OLR), vertical wind shear, geopotential height anomaly at 100hPa and monsoon trough during the active and inactive years of rapidly intensifying tropical cyclones (RITC). It is found that, compared to those in inactive years, the SST is significantly higher in the central and eastern equatorial Pacific, the OLR in equatorial region east of 140oE is lower indicating the eastward extension of convective activities, the region with weak vertical wind shear is further eastward by 10-15 degrees in longitude, and the South Asia High expands further to the east in RITC active years. Moreover, the monsoon trough shows a by east pattern, while it is northwestern in inactive years. As shown by the physical quantity fields during the rapidly intensifying phase of tropical cyclone Forrest in 1983, the vertical wind share remained significant with decreased intensity and range, warming and humidifying effect was distinct within the lower atmosphere of the cyclone, higher value of the convective available potential energy (CAPE) located within and nearby the cyclone, and water vapor was abundant in all channels.