Numerical Study of the Cloud Top Dynamic and Thermodynamic Structures of Severe Thunderstorms in US: Numerical Study of the Cloud Top Dynamic and Thermodynamic Structures of Severe Thunderstorms in US Pao K. Wang Department of Atmospheric and Oceanic Sciences University of Wisconsin-Madison 1225 W. Dayton Street, Madison, WI 53706 GIMPAP review meeting 8/31/04


Objectives: Objectives Understand the mechanisms responsible for the satellite observed IR features such as the enhanced-V, cold-warm couplet, and distant warm areas, etc., atop some severe storms. Understand the dynamics of gravity waves atop severe storms. Explore potential applications of the above findings for satellite retrieval of atmospheric conditions. The tool for this study is a 3D nonhydrostatic cloud model WISCDYMM.


TAC Guidance from Last Year: TAC Guidance from Last Year Couple with radiative transfer model - Done Coordinate with L. Grasso of CIRA - Done, also with T. Greenwald of CIMSS Use more physical insight in design of model correlations; i.e., why should there be a correlation between vertical velocity and cloud top temperature? - In fact, we showed that there isn’t a correlation, so this is apparently based on a misunderstanding. Wrap up project in FY04 - A paper is in preparation summarizing major findings. More work could be done on retrieving cloud top winds. Consider possible continuation under GOES-R Risk Reduction


Progress-1: Progress-1 The study of the thermal structure of cloud top has been continued this year. The negative correlation between cloud top height and cloud top temperature field has been established. We have been working with Tom Greenwald and Louis Grasso to perform radiance calculations. We have also worked with Bob Rabin and Scott Bachmeier on satellite observations.We are summarizing the finding in this study in a paper: ·           Wang, P. K., et al., 2004: Physical mechanisms responsible for the satellite-observed IR features on top of some severe thunderstorms. (Under preparation). Since last year’s report contains similar charts, we will not repeat them here.


Progress-2: Progress-2 We have made studies on the gravity waves on top of some severe storms and found that the “jumping cirrus” phenomenon reported by Ted Fujita can actually occur. The cloud model simulates this phenomenon well. More details in the following slides.


Fujita’s descriptions on jumping cirrus: Fujita’s descriptions on jumping cirrus One of the most striking features seen repeatedly above the anvil top is the formation of cirrus cloud which jumps upward from behind the overshooting dome as it collapses violently into the anvil cloud”. (Fujita, 1982) Fountain cirrus – cirrus, which splashes up like a fountain, 1 to 2 min after an overshooting dome collapses into an anvil. This appears to be what mentioned in the quotation above. Flare cirrus – cirrus that jumps 1 to 3 km above the anvil surface and moves upwind like a flare. Geyser cirrus – cirrus that bursts up 3 to 4 km above the anvil surface like a geyser. (Fujita, 1989) Fujita, T. T., 1982: Principle of stereographic height computations and their application to stratospheric cirrus over severe thunderstorms, J. Meteor. Soc. Japan., 60, 355-368. Fujita, T. T., 1989: The Teton-Yellowstone tornado of 21 July 1987. Mon. Wea. Rev., 117, 1913-1940. How can cirrus move upwind?


Cloud Model Simulation : Cloud Model Simulation Wind


This is obviously a wave breaking phenomenon: This is obviously a wave breaking phenomenon Wave-breaking signature on the potential temperature contour.


The cause of wave breaking: The cause of wave breaking Wave breaks when the storm-relative wind speed becomes the same as the wave speed (so that breaking provides the dissipation mechanism). So, observation of jumping cirrus indicates that storm-relative wind = wave phase speed. Wave phase speed may be estimated from satellite observations (further studies necessary, but possible in principle). The wave speed then indicates cloud top wind.


Cloud top gravity wave signature: Cloud top gravity wave signature


Even the plumes atop storms are caused by wave breaking: Even the plumes atop storms are caused by wave breaking For more discussions, see: Wang, P. K., 2003: Moisture Plumes above Thunderstorm Anvils and Their Contributions to Cross Tropopause Transport of Water Vapor in Midlatitudes. J. Geophys. Res., 108(D6), 4194, doi: 10.1029/2003JD002581.


MODIS images (when available) can provide higher resolution data for verification and calibration purposes for GOES data. For example, the plume phenomenon can be seen in both kinds of satellite data.: MODIS images (when available) can provide higher resolution data for verification and calibration purposes for GOES data. For example, the plume phenomenon can be seen in both kinds of satellite data. MODIS Aqua visible 7-13-2004


Conclusions: Conclusions Both jumping cirrus and plumes are caused by gravity wave breaking. Wave breaking indicates that storm-relative winds ~ wave phase speed. Potentially useful for storm top wind retrieval. More details see:·           Wang, P. K., 2004: A Cloud Model Interpretation of Jumping Cirrus. Geophys. Res. Lett. (accepted)


Plans: Plans Further investigation of cloud top thermal structure to understand the dynamics. Analyze cloud top gravity waves to determine the wave characteristics. Test the sensitivity of wave characteristics to wind shear conditions including wave patterns and breaking mechanism and process.