| SABSOON : Air/Sea Interaction / Storm Events |
The SAB strongly influences the meteorology of the eastern seaboard. The paths of winter cyclones that impact the U.S. east coast cross the region. Also, many tropical storms and hurricanes pass through this area in summer and fall. As these systems come close to the eastern seaboard, predictions of storm development and landfall become critically important. Both types of storm systems derive their energy from the air- sea gradients in heat and humidity. The middle and outer shelf areas are relatively warm due to the proximity of the Gulf Stream and provide an important energy source for both of these systems. Present studies of these processes rely on extremely sparse coverage provided by ocean buoys and coastal stations. Since continuous mesoscale atmospheric observations from stable platforms near a large thermal sea gradient are rare, the tower platforms provide a unique opportunity to advance our understanding of how weather systems and the coastal ocean interact.
Six-minute average wind speed, air pressure, and significant wave height at tower R2 during the passage of Hurricane Irene in October 1999.Peak sustained winds exceeded 25 m/s, and peak wave heights reached 4.5 m.
Since July 1999, more than a dozen extreme wind events have been observed at 50 m height on R2 during the passage of squall lines. 6-minute averaged wind speeds of 40-60 m/s were associated with a rapid decrease in air temperature, high frequency fluctuations in barometric pressure, and downpours (April and Sept. squall line figures). A series of wind maxima at 50 m ht. (but not at 10 m ht.) usually occurred during such events. The R2 observations are consistent with "downburst" events (Fujita, 1985). On the Georgia shelf, this mechanism may transport continental air from aloft to the sea surface.
Oceanic heat budgets are important for understanding the Earth's climate and variability. The ocean absorbs solar radiation and stores heat in the upper layers, changes in heat storage result from local imbalances between heat input and output through the sea surface. The sum of the changes in heat fluxes into or out of a volume of water is the heat budget. The major terms of the heat budget include insolation (Qsw), back radiation (Qlw), sensible heat flux (Qsen) and latent heat flux (Qlat). The net heat flux (Qnet) is the sum of these terms. Shown in the figure below, a temperature prediction was made based on a simple mixed layer model, assuming that the net flux affects the entire water column.
Over the winter months the predicted temperature was a good estimate of observed ocean temperature, and departures from the prediction show a correlation with salinity variations. Since April 2000 the predicted temperature using observations from the primary meteorological package 50 m above the water is systematically lower than the observed temperatures. Replacing the air temperature and humidity readings with those from the secondary package 10 m above the water surface yields a better prediction. This method is preferable since the existing bulk formula cannot account for stratification in the marine boundary layer.