ESRL/PSD Seminar Series
Momentum Transport in Mesoscale Convective Systems
UCAR VSP (Visiting Scientist Program)
Postdoctoral Fellow with PACE (Postdocs Applying Climate Expertise) Fellowship Program
Forecasting the motion and severe weather potential of mesoscale convective systems (MCSs) remains a challenge to both human forecasters and numerical models. The movement of observed MCSs is often the combined result of several physical processes that occur on different temporal and spatial scales, and the surface weather impact may be realized in the form of severe surface winds, flash flooding, hail, and tornadoes. The redistribution of momentum within MCSs has been examined by previous studies, mainly within the framework of feedbacks within the larger-scale environment and parameterization in large-scale numerical models. Fewer studies have focused on the downward-directed branch of momentum transport in MCSs, and the ways in which both convective- and mesoscale downdrafts may affect the lower-tropospheric wind field. If such transports substantially alter the low-level momentum field, it is conceivable that MCS speed and low-level winds may be affected, either by the advective effect of increasing the mean cloud-bearing wind, or the propagative effect of increasing winds within the cold pool itself. Therefore, this study seeks to investigate the following questions: (i) What influence does the vertical momentum transport (of both large-scale and perturbation winds) by an MCS have on the ground speed of the MCS itself?, and (ii) How sensitive is the significance of the momentum transport process to storm environment and model physics?
These questions are addressed within a quasi-idealized modeling framework, using the Weather Research and Forecasting (WRF) model to perform a number of diagnostic and sensitivity assessments. Implications for severe weather potential, forecasting and model representation of MCSs will also be discussed
Wednesday, 23 September 2009
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