Thermal structure of intense convective clouds derived from GPS radio occultations

R Biondi,T Neubert,S.-P Ho,S Syndergaard,W J Randel

doi:10.5194/acp-12-5309-2012

Abstract

Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.

Highlights

Deep convective systems play a fundamental role in atmospheric circulation and climate
Biondi et al.: Thermal structure of intense convective clouds we study the thermal structure of deep convective systems using observations from Global Positioning System (GPS) radio occultation measurements
We focus on the period June 2006–July 2008, and selected 2157 cases of coincidences of Convective Clusters (CC) with GPS occultations, where the GPS measurements occur in a time window of 2 h and within the actual radius of the CC

Summary

Introduction

Deep convective systems play a fundamental role in atmospheric circulation and climate. Thunderstorms and mesoscale convective systems produce fast vertical transport, redistributing water vapor and chemical constituents and influencing the thermal structure of the Upper Troposphere and Lower Stratosphere (UTLS). Sherwood et al (2003) used regular radiosonde measurements stratified according to the intensity of nearby convection to identify convective influence, identifying middle tropospheric warming and cooling at altitudes near the tropopause (typically above the top of convection). Such cooling can result from convective overshooting, and from excitation of gravity or Kelvin waves by the convection (Garcia and Salby, 1987; Randel and Wu, 2005).

Objectives

Methods

Results

Conclusion