ABSTRACT

The dynamic and microphysical processes that govern the spatial and temporal variability of precipitation within extratropical cyclones remain poorly understood. Variability in the location, type, and intensity of precipitation is often determined by precipitation banding and/or embedded convection, particularly in the northwest and warm frontal quadrant in cyclones where frontal structures and associated frontal circulations are modified by deformation flow. The Principal Investigators will execute a comprehensive field campaign and numerical modeling study that will address outstanding scientific questions targeted at improving understanding of precipitation substructures in the northwest and warm frontal quadrants of continental extratropical cyclones. In the course of this study the following questions will be addressed: 1) What are the predominant spatial patterns of organized precipitation substructures, such as bands and generating cells and how do they evolve? 2) How do frontal scale systems above and within the boundary layer such as warm fronts, trowals, cold fronts aloft, and occluded fronts relate to these precipitation substructures? 3) What are the thermodynamic and kinematic structures of these frontal systems including the distribution of moisture and vertical motion? 4) What instabilities and types of mesoscale forcing control the generation and evolution of precipitation substructures? 5) How do microphysical processes vary between the different precipitation substructures and what are the consequences? 6) Is instability triggered in ice-saturated ascent critical in some of these instances and is it through the release of the latent heat of deposition that instabilities can persist?

The Principal Investigators will obtain and analyze detailed, high resolution observations of precipitation substructures using three mobile ground-based observing systems, the University of Alabama at Huntsville Mobile Integrated Profiling System, the Mobile Alabama X-band dual polarization radar, and the NSF/National Center for Atmospheric Research (NCAR) Mobile GPS Advanced Upper Air Sounding System, along with the NSF/NCAR C-130 Aircraft equipped with microphysical probes and the Wyoming Cloud Doppler Radar and Cloud Lidar. They will also simulate the precipitation substructures using the Weather Research and Forecasting Model at high horizontal and vertical resolution. The observations will provide the basis for the development of testable hypotheses that can be addressed systematically in the modeling studies. The field campaign (termed Profiling Of Winter Storms, or PlOWS) will have an education component, involving students from 9 universities with atmospheric science departments.

Intellectual merit: The combined dynamical/microphysical observational strategy in conjunction with high resolution numerical modeling, will provide the basis for answering key scientific questions in a more complete and definitive way than heretofore possible. The new observational capabilities that will be applied in this research will provide fundamentally new information about the structure, dynamic and physical properties of these storms on scales never before observed.

Broader impacts: Nationwide, nearly 7000 deaths, 600,000 injuries, and 1.4 million accidents per year are due to adverse road weather, mostly during winter, and costs associated with a single blizzard can range from $0.1M to $3.0B. The research will provide new insight concerning remote sensing of winter weather systems that can translate directly into better operational interpretation and observation strategies of winter weather mesoscale features. The research will contribute to a fundamental understanding of the relationship between the microphysical properties of clouds in winter cyclones and radar and lidar sensing of those properties. The modeling studies will determine if modeled precipitation substructures are consistent with observed features in winter storm systems and provide a better understanding of processes responsible for the occurrence of those substructures. Thus the findings will have direct application to forecasting. The education component, involving students from nine universities with atmospheric science departments, will contribute to undergraduate and graduate education and recruitment of new scientists into atmospheric field research.