ATMOSPHERIC DISPERSION OVER CHESAPEAKE BAY

Abstract

Horizontal wind speed and direction range data range obtained during 300 hours of westerly winds on both the east and west shores of the Chesapeake Bay during the period December 1960 through May 1961. Measurements of air and water temperature were made at each shore as well as from a bridge tower in the bay. Standard deviations of the horizontal direction fluctuations (σΘ) were estimated from 5-minute direction range values for each shore. The east and west shore values of σΘ were then used to estimate the relative overwater-overland dispersive capacity of the atmosphere. It was found that, after the air had traveled for about 7 miles over the water, its direction fluctuations were always less than they had been before reaching the water. If the air was initially warmer than the water, and thus cooled from below during the overwater travel, the decrease in direction fluctuation was greater than occurred when the air was warmed from below. The wind speed usually increased as the air crossed the water. The increase was largest for warming from below and smallest for cooling from below. It was noted that frequently, when the air was cooled from below, the wind speed decreased as the air crossed the Bay. With the observed parameters it was possible to relate the overland to the overwater dispersive capacities of the atmosphere. The ratio of overland to overwater dispersive capacity, computed for a point 0.5 miles from a postulated source, varied from less than 5:1, for heating from below, to greater than 35:1 for cooling from below.