This project examines variability in the mechanisms that produce both stratiform and convective precipitation over complex terrain. Previous work suggests that winter precipitation over the Southwestern U.S. comes from Pacific storms traversing the region from the west, and that precipitation amounts are strongly modulated by orography. Less understood is the variety of synoptic flow configurations that lead to heavy winter precipitation over the region and how the mesoscale distribution of precipitation varies for each synoptic type and with the properties of the upstream flow. A database has been assembled of the leading 100 precipitation producing winter storms over the southwest US (southern California, Arizona, and western New Mexico) between 1950 and 2008. Characteristic synoptic flow patterns accompanying heavy precipitation are identified by principal component analysis. Available gage data will be analyzed to identify the mesoscale distribution of precipitation from composites of each synoptic type. This work will also identify relationships between air mass properties and mesoscale rainfall distribution and test hypotheses that relate the distribution and intensity of precipitation to air flow orientation relative to terrain, upstream blocking, mountain wave activity, hydrometeor type, and cloud microphysics.
In addition, heavy warm-season convective precipitation and flash flood events are being investigated in the European Alps and other mountain ranges around the world. Despite the climatic variability between these various locations where orographically induced flash floods occur, there are striking similarities between these events in terms of the moisture profile, moist static instability, and low-level flow.
Initially, the modeling component of this work will determine the optimal configuration (resolution, microphysics parameterizations) of the Weather Research and Forecasting (WRF) model that best replicates observed precipitation and convective organization (radar and rain gage data) in complex orography. Then, the WRF model simulations will augment findings from the observational component of the research and diagnose the physical processes responsible for the observed characteristics of the convective systems.
Professor James developed a widely accepted software algorithm that corrects velocity aliasing errors in operational Doppler radar data.
Professor and Chair
Originally from New Zealand, Dr. Sinclair has worked as a weather forecaster and a research scientist, including field experience in Antarctica as part of the New Zealand Antarctic Research Program.