A STUDY OF THE SEA BREEZE AT ATLANTIC CITY, NEW JERSEY USING TETROONS AS LAGRANGIAN TRACERS

Abstract

During July 1964 more than 90 constant volume balloon (tetroon) flights were made from the area of Atlantic City, N.J., with the primary purpose of delineating the sea breeze regime at that locale. The transponder-equipped tetroons were ballasted to float at a height of 500 ft., and were tracked by the U.S. Weather Bureau WSR-57 radar at Atlantic City. The tetroon trajectories are compared with surface winds and with (surface) geostrophic winds derived from pressure readings at four nearby weather stations. On the average, the tetroon direction differs from the surface wind direction by only a few degrees, but the tetroon speed exceeds the surface wind speed by a factor of nearly two. During pronounced sea breeze regimes the tetroon moves toward low pressure at an average angle of 20° during the morning hours and nearly 90° during the early afternoon hours. Both sequential tetroon releases and individual tetroon trajectories indicate a veering of the sea breeze flow during late afternoon and evening. The ratio of tetroon speed and geostrophic speed averages about 0.60 on non-sea breeze days and 0.35 on sea breeze days, with a tendency for the ratio to be at maximum in the late afternoon. Tetroons released in the early morning into a gradient flow from the northwest exhibit a sharp turn to the north at the presumed position of the sea breeze front. On the basis of this turning it appears that the sea breeze front exists at sea prior to its arrival at the shore line, but the analysis is complicated by the fact that the tetroons are at some height above the surface. To the extent that tetroon trajectories represent air parcel trajectories, there is evidence that, frequently, sea breeze air is simply air from the land that has been modified by the sea surface. While the WSR-57 radar does not provide accurate tetroon-transponder height values, there is the suggestion of large vertical air motions near the sea breeze front and evidence that the sea air may, on occasion, override the land air so that the sea breeze frontal passage occurs first at some height above the ground. The atmospheric diffusion to be expected in both sea breeze and non-sea breeze regimes is investigated through the simultaneous and sequential release of tetroons. In the case of instantaneous-point-source (relative) diffusion, the data suggest that the lateral and longitudinal standard deviations increase in proportion to about the first power of the downwind distance out to distances of the order of 10 km., but thereafter increase in proportion to about the 0.5 power. In the case of continuous-point-source diffusion, the data suggest that, at downwind distances from about 10 to 50 km., the lateral standard deviation is proportional to nearly the 0.85 power of the distance, and proportional to about the 0.2 and 0.9 power of the tetroon release interval on sea breeze and non-sea breeze days, respectively.