Trapp, R.J., B. A. Halvorson and N.S. Diffenbaugh

Telescoping, multi-model approaches to evaluate extreme convective weather under future climates

Journal of Geophysical Research-Atmospheres, 112, D20109, doi:10.1029/2006JD008345, 2007.

Understanding of the possible response of severe convective precipitating storms to elevated greenhouse gas concentrations remains elusive.  To address this problem, telescoping, multi-model approaches are proposed, which allow representation of a broad range of processes that could regulate convective storm behavior. Two telescoping approaches are considered.  In the Global-Cloud approach (G-C), the NCEP-NCAR Reanalysis Project (NNRP) global dataset provides initial and boundary conditions for short-term integrations of a mesoscale model and nested convective-cloud-permitting domain. In the Global-Regional-Cloud approach (G-R-C), the NNRP dataset provides initial and boundary conditions for long-term integrations of a regional climate model, which in turn forces short-term integrations of a mesoscale model and nested convective-cloud-permitting domain.  Upon applying these approaches to historical extreme convective storm events, it was found that the global-scale data could be dynamically downscaled to produce realistic convective-scale solutions.  In particular, tornado proxies computed from the model-simulated winds were shown to compare well in relative numbers to those of tornado observations on many of the days considered.  This supports the telescoping modeling concept as a viable means to address effects of elevated greenhouse gas concentrations on convective-scale phenomena.  In evaluation of the two approaches, it was also found that the solutions from the G-C were superior to those from the G-R-C.  Sensitivity of the convective-scale processes to details in the downscaled synoptic-scale flow, and to the placement of the mesoscale model domain within the regional climate model, reduced the effectiveness of the G-R-C.