A statistical analysis of the influence of deep convection on water vapor variability in the tropical upper troposphere

  • Wright J
  • Fu R
  • Heymsfield A
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The factors that control the influence of deep convective detrainment on
water vapor in the tropical upper troposphere are examined using
observations from multiple satellites in conjunction with a trajectory
model. Deep convection is confirmed to act primarily as a moisture
source to the upper troposphere, modulated by the ambient relative
humidity (RH). Convective detrainment provides strong moistening at low
RH and offsets drying due to subsidence across a wide range of RH.
Strong day-to-day moistening and drying takes place most frequently in
relatively dry transition zones, where between 0.01% and 0.1% of
Tropical Rainfall Measuring Mission Precipitation Radar observations
indicate active convection. Many of these strong moistening events in
the tropics can be directly attributed to detrainment from recent
tropical convection, while others in the subtropics appear to be related
to stratosphere-troposphere exchange. The temporal and spatial limits of
the convective source are estimated to be about 36-48 h and 600-1500 km,
respectively, consistent with the lifetimes of detrainment cirrus
clouds. Larger amounts of detrained ice are associated with enhanced
upper tropospheric moistening in both absolute and relative terms. In
particular, an increase in ice water content of approximately 400%
corresponds to a 10-90% increase in the likelihood of moistening and a
30-50% increase in the magnitude of moistening.

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  • J S Wright

  • R Fu

  • A J Heymsfield

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