Convective Impact on Temperatures Observed near the Tropical Tropopause

Abstract

Observed temperature trends and interannual variations near the tropical tropopause suggest that temperatures up to the cold point are controlled by the troposphere, but some models indicate otherwise. Here, previous investigations of thermal anomalies and heating profiles associated with tropical convective outbreak are extended, by examining behavior near the tropopause. Observations show that active convective systems are locally associated with warm anomalies in the upper troposphere but cold anomalies in the lower troposphere and near the tropopause. Time-dependent solutions of Laplace's equations demonstrate that the cold anomaly below 100 hPa can be, at least partly, accounted for by adiabatic lofting associated with a transient heating pulse at lower levels. However, detailed examination of the cold-point tropopause in the data reveals that it moves against the lofting, downward toward higher pressure and colder potential temperatures, in response to convection. These variations qualitatively agree with longitudinal and ENSO-related variations in tropopause height and temperature reported in the literature, though seen here on hourly timescales. From this, local mesoscale diabatic cooling of several degrees kelvin per day close to the tropopause during active convection is inferred. This exceeds the likely contribution from cloud-top radiative cooling, suggesting a role for convective turbulence in refrigerating the tropopause.