西南季风爆发前后大理近地层风场及湍流通量的变化特征

利用2008年4~5月大理国家气候观象台近地面层观测系统的梯度、涡动相关通量观测资料,结合背景场环流分析,分析了西南季风爆发前后大理近地面层的风速、风向变化特征、风速廓线和垂直切变变化特征以及动量、感热和潜热通量变化特征。结果显示:西南季风爆发前,大理近地层风向以东南风为主,平均风速较大;风速日变化的双峰型特征较显著,风速的垂直切变大,动量通量数值较大且日变化特征较明显。西南季风爆发后,大理近地层西北风频率显著增加,平均风速减小;风速日变化以单锋型为主,风速垂直切变较前期显著减小,动量通量数值减小而日变化特征较不显著。西南季风开始前后大理地气热量交换都以潜热为主,西南季风开始前一旬期间,潜热通量的逐日变化特点是随时间逐渐减少,感热通量逐渐增大,二者差值逐渐减小;西南季风开始后潜热通量的逐日变化为逐渐增大而感热通量逐渐减少,二者差值逐渐增大。就月平均值的日变化而言,潜热通量峰值变化不大,雨季略低于干季的4月;感热通量4~6月的月平均逐月降低。其原因既与雨季天气的变化有关,也与下垫面状况的改变相联系。

Characteristics of Wind Field and Turbulent Flux in the Surface Layer in Dali before and after the Southwestern Monsoon Burst in 2008

Observation data of the boundary-layer tower at the Dali National Climate Observatory from April to May 2008 were used to investigate the characteristics of wind speed, direction, profile, vertical shear, momentum flux, and sensible and latent heat flux in the surface layer before and after the southwestern monsoon burst in 2008. The results show that the main wind direction was southeast in April and northwest in May. The diurnal pattern of wind speed before and after the monsoon burst showed two peaks and one peak, respectively. After the monsoon burst, the wind speed, vertical shear, and momentum flux became lower. The latent heat flux was larger than the sensible heat flux throughout the entire period. The latent heat flux decreased (increased) before (after) the monsoon burst. The peak values of diurnal variation of monthly mean latent flux did not change significantly during the period, although the monthly mean values of sensible heat flux decreased monthly from April to June. The causes of the changed characteristics for wind and fluxes correlated with the weather and land surface conditions.