The Response of Convective Precipitating Storms to Anthropogenically Enhanced Global Radiative Forcing

Funding Agency: National Science Foundation

Program: Physical and Dynamic Meteorology

Award #: 0756624

Duration: September 1, 2008 – August 31, 2011

Award Amount: $616,112

Other Principal Investigators: Robert Trapp, Michael Baldwin, Alexander Gluhovsky (Purdue University)

Abstract:

Convective precipitating storms (CPSs) and the associated hazards of hail, destructive surface winds, tornadoes, and flash floods pose serious risks to life and property. These hazardous phenomena are governed by the three-dimensional distributions of atmospheric moisture, temperature, and wind. Simple physical arguments suggest that changes in these state variables resulting from anthropogenic increases in greenhouse gas (GHG) concentrations will in turn affect the frequency and intensity of CPSs. In earlier work, the Principal Investigators (PIs) have shown that valuable insight about the dynamics of this local response can be gained using climate models in which convective processes are parameterized at subgrid scales. However, the limitations of this "indirect" approach highlight the importance of applying numerical models that explicitly resolve convective storms over large continental areas. In preliminary work, the PIs also established the basic viability of telescoping modeling strategies that consist of integrations of a convective-cloud-permitting model [the Weather Research and Forecasting (WRF) model] nested within a global model (the G-C strategy) and within a regional model that is itself nested within a global model (the G-R-C strategy). Building on the success of this pilot work, the PIs will utilize these strategies for the purpose of generating climatologies of CPSs and associated hazards over modern and future time periods. Some initial experiments using reanalyses as the global driver will be conducted, primarily to reveal model biases in the CPS statistics. The bulk of the experimentation will involve high-resolution integrations of the WRF model, driven by an ensemble of climate models forced by Intergovenmental Panel on Climate Change Special Report on Emissions Scenarios. This ensemble will help to quantify the sensitivity of the CPS dynamics to variations in the large-scale boundary conditions. Accompanying these experiments will be novel techniques to analyze the information-rich WRF model output. First, previously developed automated, object-oriented analysis procedures will be used to identify, characterize, and classify the precipitating systems. This will allow further consideration of attributes such as the areal extent of convective versus stratiform precipitation. Second, a proxy method will be adapted to provide a quantification of local-scale hazardous weather attendant with the CPSs. For example, tornado occurrence will be estimated using the storm-scale wind field in an empirical parameter. Similar parameters for damaging wind and hail will also be developed. Finally, a powerful resampling technique known as subsampling will be employed to compute statistical characteristics and their confidence intervals from observed and modeled time series, including means, variances, skewnesses, correlations, and parameters of extreme value distributions. The intellectual merit of this project is that it will provide an estimate of the potential response of convective precipitating storms and associated phenomena to the enhanced global radiative forcing associated with increases in GHG concentrations. This will be achieved through a novel scale-spanning modeling approach, and then through equally novel analysis techniques. One of the broader impacts of this project is that it will offer additional information that can be used to assess the potential impacts of anthropogenic climate change. The project will also affect graduate and undergraduate education at Purdue University. For example, a significant portion of the research will be performed by graduate students under the mentorship of faculty, thereby training the next generation of climate and weather scientists in cutting edge skills. To enhance this skill set, an annual workshop on climate modeling tools will be offered to Purdue students and faculty. In addition, components of the PIs' pilot project have already been incorporated into courses from the non-major, undergraduate level to the graduate level, including development of a graduate course on climate statistics. The PIs will continue (and expand) this incorporation into the graduate and undergraduate curriculum.