Subsynoptic convergence-rainfall relationships based upon 1971 south Florida data

Convergence-rainfall relationships are studied at subsynoptic scales of motion in relation to Florida convection. These relationships are based upon analyses of three selected thunderstorm cases. Analyses make use of radar and numerous surface wind and rainfall observations which were taken to the south of Lake Okeechobee, Florida, during the summer of 1971. The evolution of convergence, relative vorticity and rainfall is examined at the cloud-scale and at the meso-scale. Convergence-rainfall relationships at these two scales - together with those found for the Florida peninsula ("larger scale") - show the relation which links surface convergences and divergences at different scales with peak rainfall. Maximum surface convergence occurs first at the "larger scale" and it is followed by corresponding maxima at the meso-scale and then at the cloud-scale. After peak rainfall, maximum surface divergence occurs first at the cloud-scale and is followed by mesoscale and then by "larger scale" surface divergences. The findings of this study are discussed in relation to the parameterization and short-range forecasting of convective rainfall.

本研究针对佛罗里达对流活动，在次天气尺度（subsynoptic scales）运动范畴下探讨辐合-降雨的关联关系。该类关联基于3个精选雷暴个例的分析得到。分析采用了1971年夏季在佛罗里达州奥基乔比湖（Lake Okeechobee）以南采集的雷达观测数据与大量地面风场、降雨观测资料。研究分别在云尺度与中尺度维度下，考察了辐合、相对涡度与降雨的演变过程。上述两个尺度下的辐合-降雨关联，结合针对佛罗里达半岛（更大尺度）得到的关联结果，共同揭示了不同尺度下地面辐合与辐散和降雨峰值之间的关联机制。地面最大辐合首先出现在“更大尺度”，随后依次出现在中尺度与云尺度。降雨峰值出现后，地面最大辐散首先出现在云尺度，随后依次为中尺度与“更大尺度”的地面辐散。本研究的发现围绕对流降雨的参数化与短期预报展开了讨论。