A statistical analysis of the influence of deep convection on water vapor variability in the tropical upper troposphere
- ISSN: 1680-7375
- DOI: 10.5194/acp-9-5847-2009
The factors that control the influence of deep convective detrainment on\nwater vapor in the tropical upper troposphere are examined using\nobservations from multiple satellites in conjunction with a trajectory\nmodel. Deep convection is confirmed to act primarily as a moisture\nsource to the upper troposphere, modulated by the ambient relative\nhumidity (RH). Convective detrainment provides strong moistening at low\nRH and offsets drying due to subsidence across a wide range of RH.\nStrong day-to-day moistening and drying takes place most frequently in\nrelatively dry transition zones, where between 0.01% and 0.1% of\nTropical Rainfall Measuring Mission Precipitation Radar observations\nindicate active convection. Many of these strong moistening events in\nthe tropics can be directly attributed to detrainment from recent\ntropical convection, while others in the subtropics appear to be related\nto stratosphere-troposphere exchange. The temporal and spatial limits of\nthe convective source are estimated to be about 36-48 h and 600-1500 km,\nrespectively, consistent with the lifetimes of detrainment cirrus\nclouds. Larger amounts of detrained ice are associated with enhanced\nupper tropospheric moistening in both absolute and relative terms. In\nparticular, an increase in ice water content of approximately 400%\ncorresponds to a 10-90% increase in the likelihood of moistening and a\n30-50% increase in the magnitude of moistening.