Impact of tropical land convection on the water vapour budget in the Tropical Tropopause Layer

Abstract

Abstract. The tropical deep overshooting convection is known to be most intense above continental areas such as South America, Africa and the maritime continent. However, its impact on the Tropical Tropopause Layer (TTL) at global scale remains debated. In our analysis, we use the 8 yr Microwave Limb Sounder (MLS) water vapour (H2O), cloud ice water content (IWC) and temperature datasets from 2005 to date, to highlight the interplays between these parameters and their role in the water vapour variability in the TTL, separately in the northern and southern tropics. The water vapour concentration is displaying a systematic diurnal cycle with a night-time peak in the tropical Upper Troposphere (pressure ≥146 hPa) and the opposite in the TTL (121 to 68 hPa) and the tropical Lower Stratosphere (pressure ≤56 hPa), of larger amplitude above continents than continental-oceanic areas such as the maritime continent or full oceanic areas such as the Western Pacific. In addition, the amplitude of the diurnal cycle is found systematically larger (5–10%) in the southern than in the northern tropics during their respective summer, indicative of a more vigorous convective intensity in the south. Using a regional scale approach, we investigate the geographical variations of mechanisms linked to the H2O variability. In summary, the MLS water vapour, ice water cloud and temperature observations are demonstrating a clear contribution of TTL and lower stratosphere moistening by ice crystals overshooting updrafts over land tropical regions and the much greater efficiency of the process in the Southern Hemisphere.