84th AMS Annual Meeting

Sunday, 11 January 2004
Using Radiosonde Data to Determine Statistical Properties of Convection
Room 608/609
Rebecca Chan, Plymouth State University, Randolph, MA
The outflow from deep convection influences the budgets of water vapor and other trace constituents in the upper troposphere. However, the processes that control the altitude of outflow are poorly understood at present. This study used radiosonde measurements of temperature and humidity to determine the statistical properties of subtropical and midlatitude convection. The near-surface equivalent potential temperature distribution, which can be used to determine the altitude of convective outflow, in the tropics was compared with that from the South Asian and North American continental regions. The results showed that South Asian monsoon convection has more air parcels with higher equivalent potential temperatures than convective systems in the tropical region; this implied that sufficient air parcels with high equivalent potential temperature were present in Southern Asia to generate deep convection with higher-altitude outflow than in the tropics. In contrast, the midlatitude distribution of equivalent potential temperature skewed toward lower values compared to the distribution of the tropics. Therefore, deep convective systems were less likely to occur at the midlatitudes and most convective outflow happened at an altitude of 10 km or lower. These results tentatively suggested that convective systems in the tropics are the primary means for transporting water vapor into the upper troposphere, possibly leading to ozone depletion and long term climate change as a result of radiative cooling. Meanwhile, midlatitude convection did not generate convection that was powerful enough to carry surface water vapor directly into the atmosphere.

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