Regional climate of hazardous convective weather through high-resolution dynamical downscaling
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We explore the use of high-resolution dynamical downscaling as a means to simulate the regional climatology and variability of hazardous convective-scale weather. Our basic approach differs from a traditional regional climate model application in that it involves a sequence of daily integrations. We use the weather research and forecasting (WRF) model, with global reanalysis data as initial and boundary conditions. Horizontal grid lengths of 4.25 km allow for explicit representation of deep convective storms and hence a compilation of their occurrence statistics over a large portion of the conterminous United States. The resultant 10-year sequence of WRF model integrations yields precipitation that, despite its positive bias, has a diurnal cycle consistent with observations, and otherwise has a realistic geographical distribution. Similarly, the occurrence frequency of short-duration, potentially flooding rainfall compares well to analyses of hourly rain gauge data. Finally, the climatological distribution of hazardous-thunderstorm occurrence is shown to be represented with some degree of skill through a model proxy that relates rotating convective updraft cores to the presence of hail, damaging surface winds, and tornadoes. The results suggest that the proxy occurrences, when coupled with information on the larger-scale atmosphere, could provide guidance on the reliability of trends in the observed occurrences.
KeywordsSevere thunderstorm Heavy rainfall Dynamical downscaling Reanalysis Weather research and forecasting model
This research was supported in part by NSF ATM-0756624 (RT, MB, ND, and ER), DOE DE-FG02-08ER64649 (ND), and benefitted from computing resources provided through the NCAR Accelerated Scientific Discovery program and by the Purdue University Rosen Center for Advanced Computing. Dr. David Ahijevych at NCAR provided helpful information regarding the Hovmöller diagrams. Comments made by the two anonymous reviewers helped us clarify and improve our discussion. This is PCCRC Paper #0920.
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