A Diagnostic Study of Interaction of Cumulus Updrafts and Downdraf is with Large-Scale Motions in GATE
A Diagnostic Study of Interaction of Cumulus Updrafts and Downdraf is with Large-Scale Motions in GATE
复制标题
积云上升气流和下降气流与GATE大范围运动相互作用的诊断研究
DOI：
10.2151/jmsj1965.56.4_232
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发表时间：
1978
影响因子：
3.1
通讯作者：
T. Nitta
中科院分区：
文献类型：
--
作者：
T. Nitta
在GATE第三阶段的A/ b尺度高空观测中，采用了积云上升气流和下降气流的诊断方法，研究了积云对流与大尺度运动的相互作用。第三阶段的平均结果表明，深层云和浅层云的质量通量大于对流层中层顶部云的质量通量，向下的质量通量相当于上升气流的40%*50%，对流质量通量是由积云下降气流完成的。计算了深、中、浅云团通量与大尺度垂直速度的相关系数，探讨了积云对大尺度强迫的响应。结果表明：深层云与各级大尺度垂直速度的相关性较高，中层云与大尺度垂直速度的相关性较低，浅层云仅与云底附近的垂直速度相关。深层云的最大活动几乎与高层最大大规模上升运动同时发生，但在最大低层辐合后约6小时。最强的下沉气流质量通量与最大的深云活动相对应。浅云质量通量与低层辐合呈负相关，表明低层辐合大时浅云活动弱。利用合成方法澄清了GATE观测到的积云对流与非洲波扰动之间的关系。深云质量通量最大的区域在波槽附近，大尺度垂直速度有峰值。这也是最大的下沉气流云团通量存在的区域。波槽附近浅云活动弱，波脊附近强。波扰动中云环境几乎到处都有微弱的下沉，幅度在几mb h-1左右，但在浅云团通量占主导地位的区域会出现稍大的下沉。
A diagnostic method including cumulus updrafts and downdrafts is applied to GATE A/B-scale upper-air observations for Phase III to study the interaction of the cumulus convection with large-scale motions. Average results for Phase III show that the mass fluxes for deep and shallow clouds are larger than those for clouds with tops in the middle troposphere and downward mass fluxes equivalent to 40%*50% of updrafts convective mass fluxes are accomplished by cumulus downdrafts. Correlation coefficients between deep, middle and shallow cloud mass fluxes and the large-scale vertical velocity are computed to examine the response of cumulus clouds to the large-scale forcing. The results show that deep clouds are highly correlated with the largescale vertical velocity at all levels, middle clouds have little correlations and shallow clouds are correlated only with the vertical velocity near cloud base. Maximum activity of deep clouds occurs nearly at the same time as maximum large-scale upward motion at higher levels but about 6 h after maximum low-level convergence. Strongest downdraft mass fluxes occur corresponding to maximum deep cloud activity. Shallow cloud mass fluxes have negative correlations with the low-level convergence indicating that shallow cloud activity is weak when the low-level convergence is large. A compositing method is used to clarify relationships between the cumulus convection and the African wave disturbance observed during GATE. Maximum deep cloud mass flux is found in the region near the wave trough where the large-scale vertical velocity has a peak. This is also the region where largest downdraft cloud mass fluxes exist. Shallow cloud activity is weak near the wave trough but strong near the wave ridge. Weak subsidence with amplitude of a few mb h-1 is present nearly everywhere in the environment of the clouds in the wave disturbance, but slightly larger subsidence occurs in the regions where shallow cloud mass fluxes dominate.