Cross-Tropopause Convective Transport of Water Vapor: Model Study, Satellite Observation, and Implications
Pao K. Wang, Unversity of Wisconsin, Madison, WI
Water vapor not only plays a central role in weather and climate phenomena but in atmospheric chemical processes as well. This is especially true at the stratospheric level where water vapor serves as the source for strong oxidants such as OH and HOX radicals and, at the same time, strongly interacts with the infrared radiation. Recent observational studies indicate that there is an increasing trend of lower stratospheric water vapor in the midlatitudes in the last 30 years.
Nearly all previous studies about the transport of water vapor in the lower stratosphere focus on the isentropic diffusion. But recent observations of the plume phenomenon above some severe storms in midlatitudes point out the possibility of non-adiabatic cross-tropopause transport by the deep convective process.
This paper shows the simulation results of such a process using a 3-D cloud dynamical model with explicit microphysics. A few typical severe thunderstorms occurred in the US Midwest are used as the model storms for illustrating this penetrating plume phenomenon. Characteristics of the plumes from the model results and satellite observations show striking similarities and the agreement lends strong support for the proposed process. Analysis of the model results indicates that the transport is due to the breaking of cloud top gravity waves that sends water vapor from the overshooting dome shell into the stratosphere. Animation of the model results will be shown in the conference.
If water vapor can penetrate tropopause by this mechanism, so can other chemical species, such as dry aerosol particles and CFC’s that are even less susceptible to freeze-drying effect of the tropopause. This possibility is also confirmed by our model results of the inert tracer transport by these storms and animation of these results will also be presented. Implications of this process on the formation of the Junge Aerosol Layer will also be discussed.
Extended Abstract (196K)
Joint Session 4, Water Vapor Observations and Processes (Joint with 14th Symp. on Global Change and Climate Variations, 7th Symp. on IOS, Fifth Conf. on Atmospheric Chemistry, and Symp. on Observing and Understanding the Varability of Water in Weather and Climate)
Tuesday, 11 February 2003, 1:30 PM-5:30 PM
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