8.5
Recent new evidences of troposphere-to-stratosphere transport by deep convective storms
Pao K. Wang, Univ. if Wisconsin, Madison, WI
Deep convective storms were not considered as an important contributor to the troposphere-to-stratosphere (TTS) transport even as recent as a few years ago. But recently evidences have been mounting that show that deep convective transport plays a highly important, perhaps even dominant, role in such a transport. This paper will summarize some recent findings related to this subject.
Satellite observations in the past two decades reveal that there are cloud features above anvils of some sever thunderstorms. These are now called anvil top plumes which are typically located at a few km above the anvil. Since the anvils of these severe storms were already at the tropopause level, the plumes must have been a feature in the stratosphere. We performed a cloud model study and showed that the water for the plume formation comes from the storm below. This implies that the deep convective storm serves as a conduit transporting water substance from the troposphere to the stratosphere. The same mechanism should also transport other trace chemicals from the troposphere to stratosphere. Model results show that this irreversible transport is a result of cloud top gravity wave breaking.
The same cloud model study also demonstrates that the so-called “jumping cirrus” phenomenon that occurred above the storm anvil as observed by Fujita in 1980s is exactly the result of gravity wave breaking. The sequence of occurrence, orientation and size of the jumping cirrus can be explained very satisfactorily by the wave breaking process.
Videos of model result animations and GOES satellite loops as well as a thunderstorm movie taken by a webcam in Zurich will be shown to illustrate this wave breaking process.
More recently, satellite and in-situ aircraft observations of the stratospheric HDO/H2O ratio indicate that this ratio is much higher than can be explained by the slow ascent model of water substance from the troposphere to the stratosphere. On the other hand, the high ratio can be explained by the very rapid vertical transport by deep convective storms' strong updraft. This again indicated that deep convective storms indeed play a very important role in the TTS transport. More details of the process and its implications will be discussed in the conference.
It has been observed that the lower stratospheric water vapor concentration has been increasing steadily in the last 50 years and the total increase may be as much as 50%. Given that water vapor is the source for making HOX that are highly effective in ozone depletion, the understanding of the deep convective transport should be an urgent research topic for stratospheric chemistry.
Session 8, Stratospheric Ozone and Tropospheric Weather-II
Thursday, 24 January 2008, 11:00 AM-12:15 PM, 230
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