基于CloudSat探测的西南低涡对流云垂直结构特征

基于CloudSat卫星数据,结合多源常规和遥感等气象资料,研究分析了2013年8月6~7日的一次受西南低涡向西北方向移动发展影响的强降水天气过程中,对流云发展的三维结构和演变特征,结果表明:西南低涡发展有利于受其影响的对流云团发展为深厚对流云。西南低涡发展和成熟阶段低涡中心与强对流中心均不一致,强对流中心位于低涡中心以南。西南低涡不同发展阶段对流云团发展均符合“撒播-供水”机制。低涡发展成熟阶段对流云内部存在高温高湿中心。

一次对流云团合并的卫星等综合观测分析

利用FY2C卫星观测反演得到的云物理特征参数,结合雷达、微波辐射计和地面雨量等资料,综合分析了2008年7月17日中国安徽一次强降水过程的云合并特征。结果表明:对流云团发展合并是这次强降水发生的主要原因,同一区域内FY2C卫星反演的云光学厚度、雷达回波以及地面降水的分布演变具有较好的一致性,强降水落区与云光学厚度大值区以及雷达强回波区基本对应;对流云团中的液水分布不均匀,以团块状结构为主,对流云团合并时,常先有云体上部(云顶)的合并,一旦云中不均匀的液水合并,合并部位的云光学厚度迅速增加,地面微波辐射计观测的整层液水含量跃增,地面将会出现强降水;一般降水增强之前云顶抬升,光学厚度增大;若云顶高但光学厚度较小时,地面降水一般不明显,光学厚度与降水的关系更密切;对流云团合并初期,云底由小粒子组成,T-re图上表现为深厚的凝结增长区域,合并时整层云粒子的有效半径增长明显,粒子相态达到混合相态区和冻结层的温度不断升高。

对流降水云中大气垂直运动反演及个例试验

为深入认识对流降水云结构及动力特征,基于降水频段调频连续波5520 MHz垂直指向雷达(VPR-CFMCW),使用地面至15 km高度的反射率因子及径向速度,建立对流降水云中大气垂直运动的反演方法,分析对流垂直结构及大气垂直运动随高度分布的演变特征。对在广东龙门测站探测的2019年4月20—22日前汛期4次对流降水进行反演试验发现,对流降水前大气上升运动对降水云反射率因子及地面降水有正贡献,深厚对流具有倾斜性,会导致垂直剖面在某些时刻呈分层结构;对流降水整层以下沉运动为主导,高层大气上升运动与下沉运动交替出现,低层大气下沉运动占比最高,大气上升运动在6 km高度以上占比有所增加;大气垂直速度在高层较大、在低层较小,超过10 m·s^(-1)的强上升运动与下沉运动多出现在6 km高度以上,4~6 km高度垂直运动变化较大,4 km高度以下的平均下沉运动小于5 m·s^(-1),上升运动约为2 m·s^(-1)。

Features of rainfall and latent heating structure simulated by two convective parameterization schemes

Using the latest version of SAMIL (Spectral Atmosphere Model of IAP LASG) developed by LASG/IAP,we evaluate the model performance by analyzing rainfall,latent heating structure and other basic fields with two different convective parameterization schemes:Manabe Scheme and Tiedtke Scheme.Results show that convective precipitation is excessively overestimated while stratiform precipitation is underestimated by Tiedtke scheme,thus causing less stratiform rainfall proportion compared with TRMM observation.In contrast,for Manabe scheme stratiform rainfall belt is well simulated,although precipitation center near Bay of Bengal (BOB) spreads eastward and northward associated with unrealistic strong rainfall downstream of the Tibet Plateau.The simulated latent heating structure indicates that Tiedtke scheme has an advantage over Manabe scheme,as the maximum convective latent heating near middle of troposphere is well reproduced.Moreover,the stratiform latent heating structure is also well simulated by Tiedtke scheme with warming above freezing level and cooling beneath freezing level.As for Manabe scheme,the simulated maximum convective latent heating lies near 700 hPa,lower than the observation.Additionally,the warming due to stratiform latent heating extends to the whole vertical levels,which is unreasonable compared with observation.Taylor diagram further indicates that Tiedtke scheme is superior to Manabe scheme as higher correlation between model output and observation data is achieved when Tiedtke scheme is employed,especially for the temperature near 200 hPa.Finally,a possible explanation is addressed for the unrealistic stratiform rainfall by Tiedtke scheme,which is due to the neglect of detrained cloud water and cloud ice during convective process.The speculation is verified through an established sensitivity experiment.