3.2
The Impact of SST on the Mid-level Troposphere
Qingtao Song, Oregon State University, Corvallis, OR; and D. B. Chelton
The mid-troposphere response to oceanic fronts is analyzed by using a combination of satellite observations and the wind fields of the ECMWF prediction model in conjunction with numerical simulations made with the Weather Research and Forecasting (WRF) mesoscale atmospheric model.
Analysis of vertically integrated cloud liquid water (CLW) measured by the AMSR reveals that CLW is strongly coupled to both SST and surface wind speed in regions of strong SST gradients. Results from analysis of 1-year averaged albedo show that the small-scale perturbations of the total albedo field are very strongly correlated with both SST and surface wind speed near the major ocean currents. Albedo is locally higher over warm water and the associated higher surface wind speed, and lower over cold water and the associated lower surface wind speed. Two-month averages of the horizontal divergence fields computed from the ECMWF winds at 850 hPa and 700 hPa are closely related to the oceanic fronts. It is speculated that perturbations of the divergence field at the surface propagate vertically and lead to complicated relationships between surface winds and horizontal divergence of the ECMWF model at discrete levels in the troposphere.
The above observational and modeling studies imply a possibly deep response of the troposphere to oceanic fronts. This hypothesis was tested with simulations made with the WRF modeling system in a two-dimensional (2D) configuration at 2-km horizontal grid spacing. The WRF simulations generate standing gravity waves near an oceanic front whose origins are tied directly to the interaction of the ambient air flow with strong SST gradients. Wave motions, induced by the SST front, propagate vertically and are evident in the vertical structure of the horizontal divergence and vertical velocity. The results of the experiments suggest that the generation of frontal gravity waves and their upward propagation can play an important role in the coupling between SST fronts, the marine atmospheric boundary layer (MABL), and the troposphere.
.Session 3, Atmosphere and Ocean Responses to Gradients in Sea Surface Temperature
Monday, 20 August 2007, 1:30 PM-3:00 PM, Broadway-Weidler-Halsey
Previous paper Next paper