Recorded presentation12.3
A climatology of synoptic forcing for vertical motions over the western United States
Neil P. Lareau, University of Utah, Salt Lake City, UT; and J. Horel
The climatology and interannual variability of synoptic-scale ascending motion is examined over the Western United States. Using ERA-Interim reanalysis grids every 6 hours from 1 October- 30 April within the 20-year period from 1989-2008, several statistical measures are used to summarize the occurrence and variability of positive convergence of the quasi-geostrophic Q-vector at multiple pressure levels, which is assumed to represent forcing for synoptic scale upward vertical motion. Case studies are employed to present a more detailed examination of the temporal and spatial evolution of the convergent Q-vector field, revealing an inclusive range of structures and scales as well as the interaction of synoptic systems with the underlying terrain of the western United States. Year-to-year variability in the intensity of synoptic scale weather systems is represented by the standardized anomaly of accumulated positive Q-vector convergence, at each grid point, with respect to its long-term mean. This approach is in contrast to the more traditional use of the seasonal departure in mid-tropospheric heights from the long-term average. Subsequently, the linkage between interannual variations in precipitation and synoptic forcing is explored on the regional scale as well as over narrow mountain barriers in Northern Utah.
Session 12, Synoptic Climatologies in Complex Terrain
Thursday, 2 September 2010, 10:30 AM-12:00 PM, Alpine Ballroom A
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