HR: 0800h
AN: H41D-0427    [Abstracts]
TI: Interactions Between Surface Roughness and Orography in the Generation of Lake-Effect Precipitation
AU: * Lofgren, B M
EM: Brent.Lofgren@noaa.gov
AF: NOAA/Great Lakes Environmental Research Lab, 2205 Commonwealth Blvd, Ann Arbor, MI 48105 United States
AB: The lake effect produces large amounts of precipitation in certain regions bordering on large lakes, generally during the fall to early winter seasons. Among the affected regions are areas bordering the Laurentian Great Lakes of North America, with the primary lake-effect precipitation zones lying near the eastern edge of the lakes. Lake-effect precipitation is due to shallow convection, usually at the mesobeta scale. Factors that are prerequisite to lake-effect precipitation are: 1. plentiful evaporation of water from the lake, 2. an unstable boundary layer created by cold air overlying warmer water, and 3. uplift sufficient to trigger moist convection, via either low-level convergence due to boundary-layer friction or orographic uplift. Some aspects of the relative influence of these uplift mechanisms are examined in this paper. The direct effect of reducing the roughness length of land surfaces near the lakes might be expected to be a reduction in the uplift by frictional low-level convergence. However, in a comparison between RAMS-model simulations with higher and lower values of surface roughness length over land, the result was the opposite -- lower surface roughness length increased upward velocity and precipitation near the lee side of the lakes. The apparent mechanism is that the lower surface roughness length permits an overall higher wind speed in the boundary layer, resulting in greater orographic uplift as the wind reaches shore.
DE: 1632 Land cover change
DE: 1854 Precipitation (3354)
DE: 3322 Land/atmosphere interactions (1218, 1631, 1843)
DE: 9345 Large bodies of water (e.g., lakes and inland seas) (0746)
SC: Hydrology [H]
MN: Fall Meeting 2005