The Vertical Structure of TOGA COARE Convection. Part II: Modulating Influences and Implications for Diabatic Heating

Abstract

The temporal variability of western Pacific warm pool convection, especially its vertical structure, is examined in this study. Distributions of convective echo top heights and 30-dBZ contour heights have been produced from shipboard radar data collected during Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). Elevation and suppression of convective heights was primarily influenced by the phase of the intraseasonal oscillation (ISO), with heights being suppressed during convectively inactive and westerly wind burst (WWB) phases of the ISO. Echo top heights were greatest during the convective phases and post-WWB phases of the ISO. However, at least some very deep convection was always present within the area observed by radar, indicating that local conditions were favorable for deep convection, even when the large-scale environment was not capable of supporting widespread deep convection. In addition to the ISO, echo top and 30-dBZ contour heights were also influenced over shorter timescales by intrusions of dry subtropical air into the COARE Intensive Flux Array (IFA). Periods of convective suppression were also accompanied by upper-tropospheric drying. Convective diabatic heating profiles, computed from a combination of surface radar and sounding data, reveal that the shape of the monthly mean heating profiles varied over the four-month intensive observing period. Maximum heating occurred at the highest elevations during the convectively inactive phases of the ISO, and at the lowest elevations during the convectively active phases of the ISO. These variations are qualitatively consistent with higher (lower) convective available potential energy values and higher (lower) 30-dBZ contour heights above the freezing level during the strong surface easterly (westerly) phase of the ISO. Factors leading to widespread convective suppression despite the presence of a high environmental CAPE are also discussed.