Environmental Variability during TOGA COARE

Abstract

This study provides quantitative estimates of the thermodynamic and kinematic structures of the troposphere during various convective regimes observed during the Tropical Ocean Global Atmosphere Coupled Ocean?Atmosphere Response Experiment. The data source is the upper air soundings from six stations in the intensive flux array. A correction algorithm has been applied to the humidity data to remove biases between the stations. The data are analyzed using the nonhierarchical clustering method known as k means. Eleven thermodynamic clusters and 20 kinematic clusters are selected. The thermodynamic clusters are grouped into four general categories based on their midtropospheric equivalent potential temperature. Deep convective activity varies with the thermodynamic structure of the environment. When the ?dry intrusion? group is observed, convection is suppressed. The ?fair weather? category corresponds to undisturbed periods with light winds and small mesoscale convective systems (MCSs). The largest MCSs and the majority of the rainfall occur with the ?active? and ?convective recovery? categories. The kinematic clusters are also divided into four general categories based on the strength, direction, and depth of the low-level zonal flow. The timing of the clusters is related to the intraseasonal oscillation (ISO). Dry phases of the ISO are characterized by the ?low-level easterly? category. During transition periods between the easterly and westerly phases of the ISO, the ?calm? category is often seen. The ?moderate shear westerly? group is seen just before the strongest westerlies. The majority of the clusters fall into the ?strong shear westerly? group, associated with the peak westerly phase of the ISO.