Distribution and influence of convection in the tropical tropopause region

Abstract

A global analysis of convective cloud in the tropical tropopause region (12 - 17 km) is presented. The analysis is based on high-resolution global imagery of cloud brightness temperatures from satellites and from contemporaneous reanalysis temperatures. The coverage by deep convection decreases nearly exponentially with increasing altitude in the tropopause region. Convection is found at temperatures colder than the tropical cold point tropopause over ∼0.5% (±0.25%) of the tropics. Convection rarely penetrates more than 1.5 km above the tropopause. Large-scale relationships between cold tropopause temperatures and deep convection indicate that where the tropopause is coldest convection penetrates most frequently. Small-scale relationships show that the coldest diurnal tropopause temperatures occur after the diurnal peak in deep convection at tropopause levels over land. The coverage by deep convection is used to estimate the mass exchange or turnover time due to convection in the tropopause region. This turnover time is of the order of weeks at 12 km but increases to longer than a year at 18 km, with significant uncertainties in the tropopause region.