Interactions between Tropical Convection and the Environment: A View across Scales

Abstract

The interaction between moist convection and the environment that engenders it is a problem that spans multiple scales. In this study, the problem is approached using a suite of observational and modeling tools. The first approach was the development of an algorithm to estimate latent heating profiles from radar observations using a high-resolution version of the Weather Research and Forecasting Model (WRF). A lookup table was constructed from WRF output to statistically quantify the relationship between latent heating and three characteristics of radar-observed storms: size, mean height and mean intensity. A tight link between organization (characterized by the size of the system) and the intensity (as measured by latent heat release) was found. The algorithm was validated against field campaign observations and shows skill in replicating the short-term (less than daily) variability associated with tropical synoptic systems. The second approach was to analyze the relationship between convection and the environment via moisture modulation using the Tropical Rain Measuring Mission satellite and reanalysis data, with focus on the tropical precipitation-water vapor relationship (P-r curve) which is a power-law relationship, which at the convective time and space scales is characterized by a sharp increase in precipitation beyond a critical value of moisture (the pickup threshold). The convective and stratiform components of the P-r relationship were studied separately and it was found that the pickup in tropical precipitation mainly originates from a rapid pickup in the areal extent of stratiform precipitation. A survey of the P-r curve across the tropical world–both land and ocean–shows that the pickup threshold is much lower over tropical land than over the ocean and that convective precipitation picks up prior to stratiform precipitation. Finally, the implications of a precipitation-moisture relationship were explored for prominent forms of organized convection in the tropics, i.e, tropical waves and the Madden-Julian Oscillation. It was found that the different sources of column moisture (horizontal transport and convection) were influential in environments with different moisture levels. These relationships are also dependent on the time and space scale of analysis.