台风“莫拉菲”潜热的数值模拟研究

WRF天气研究和预报模式是新一代中尺度数值预报模式,本文采用最细2公里的网格距对台风“莫拉菲”内核的宏观、微观以及潜热过程进行数值模拟。通过对台风路径、风速大小、降水形态以及内核热力和动力结构的验证,证实了单向六参数WSM6方案的合理性。本文通过计算台风过程中的潜热加热率,揭示了总潜热主要来源于0℃层以下的凝结潜热和0℃层以上的凝华潜热。证实了与霰有关的云微物理过程是对总潜热贡献最重要的因子。除此之外,在本次台风“莫拉菲”的模拟中,其他重要的潜热贡献因子分别是水汽凝结成云水、云冰的凝华增长、雪的凝华增长、云冰的初始化、霰的凝华增长、云水被雪和霰收集、云水和雨水的蒸发、雪的升华、霰的升华、霰的融化以及云冰的升华。总体而言,本文模拟的潜热加热率廓线和TRMM卫星的廓线基本一致,尽管具体数值略有不同。     

DIAGNOSTIC ANALYSIS ON THE DISTRIBUTION OF RAINFALL ASSOCIATED WITH TYPHOON “MOLAVE” (0906)

This work examines the mechanism of rainfall associated with typhoon Molave(0906)in Guangdong province and Guangxi Zhuang Autonamous Region with rainfall observations,radar mosaics from China National Meteorological Center and the final analysis data of National Center of Environmental Prediction(FNL/NCEP,USA).The result shows that the mechanism is different for the rainfall in the these areas.The rainfall in eastern Guangdong is mainly associated with a convective line to the front-right of the typhoon.The convective line is about 200 km away from the typhoon center.The rainfall in western Guangdong and Guangxi appear ahead of or to the left of the typhoon and is very close to the typhoon center.Both rainfall moves forward with the typhoon anticlockwise.It was also found that the rainfall occurred in the boundary between unstable and low-level convergent areas and closer to the convergent area.The unstable area is located in the downstream of rainfall and ahead of the convective line.It is an important factor to the development and convection.Strong frontogenesis is observed in the backward or upstream convective area of rainfall and is thus an important lifting condition for the formation of rainfall.When the low-level convergent area moves to the unstable area ahead of it,the unstable energy is left behind and as a result the convection is strengthened.     

Lightning Activity and Precipitation Characteristics of Typhoon Molave （2009） Around Its Landfall

Cloud-to-ground （CG） lightning data,storm intensity and track data,and the data from a Doppler radar and the Tropical Rainfall Measuring Mission （TRMM） satellite,are used to analyze the temporal and spatial characteristics of lightning activity in Typhoon Molave （0906） during different periods of its landfall （pre-landfall,landfall,and post-landfall）.Parameters retrieved from the radar and the satellite are used to compare precipitation structures of the inner and outer rainbands of the typhoon,and to investigate possible causes of the different lightning characteristics.The results indicate that lightning activity was stronger in the outer rainbands than in the eyewall and inner rainbands.Lightning mainly occurred to the left （rather than ＂right＂ as in previous studies of US cases） of the moving typhoon,indicating a significant spatial asymmetry.The maximum lightning frequency in the tropical cyclone （TC） eyewall region was ahead of that in the whole TC region,and the outbreaks of eyewall lightning might indicate deepening of the cyclone.Stronger lightning in the outer rainbands is found to be associated with stronger updraft,higher concentrations of rain droplets and large ice particles at elevated mixed-phase levels,and the higher and broader convective clouds in the outer rainbands.Due to the contribution of large cloud nuclei,lightning intensity in the outer rainbands has a strong positive correlation with radar reflectivity.The ratio of positive CG lightning in the outer rainbands reached its maximum 1 h prior to occurrence of the maximum typhoon intensity at 2000 Beijing Time （BT） 18 July 2009.During the pre-landfall period （0300 BT 18 July-0050 BT 19 July）,the typhoon gradually weakened,but strong lightning still appeared.After the typhoon made landfall at 0050 BT 19 July,CG lightning density rapidly decreased,but the ratio of positive lightning increased.Notably,after the landfall of the outer rainbands at 2325 BT 18 July （approximately 1.5 h prior to the landfall of the TC）,significantly higher ice particle density derived from the TRMM data was observed in the outer rainbands,which,together with strengthened convection resulted from the local surface roughness effect,might have caused the enhanced lightning in the outer rainbands around the landfall of Molave.     

云分析系统在台风莫拉菲数值模拟中的应用

借鉴美国CAPS开发的中尺度ARPS模式的资料分析系统ADAS,设计了基于GRAPES_Meso的云分析系统,实现了地面云观测资料、卫星云图、多普勒雷达反射率资料在GRAPRS模式中的综合融合应用。通过对登陆台风莫拉菲 (0906) 数值模拟检验云分析系统的性能。结果表明:云分析系统通过地面云观测资料、卫星红外云图、可见光云图、多普勒雷达反射率的同化,能够反演出合理的三维云覆盖状况;在三维云覆盖的基础上结合云底云顶高度,进而反演出云水、云冰、雨水、雪、霰等云微物理量,并显著改善模式初始湿度场;在台风登陆过程的模拟中,虽然对台风路径的预报有所偏差,但对比控制试验,在台风登陆地点、台风强度、路径的预报中云分析发挥了正作用;通过对云分析后初始场反演的雷达回波进行检验,验证了云分析的可行性与正确性,对整体的降水预报效果也有明显改善。