Evaporation duct occurrences in the northeast Atlantic during late summer
Callahan, Thomas Edwin
Davidson, Kenneth L.
Schacher, Gordon E
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Analyses and interpretation of surface layer and synoptic-scale data obtained in the Northwest Atlantic were performed to obtain descriptions of the evaporation duct and associated atmospheric and oceanic synoptic features. The surface layer data were quite unique because they were obtained from high quality measurements from ships spatially separated in a fixed array. Magnitudes and horizontal homogeneity of duct heights were compared to air-mass trajectories and weather patterns. The mean duct height was 4-Sm and higher values (8-13m) occurred with North and Northwest trajectories. During times when the heights were 5-13m, horizontal homogeneity occurred 35% of the time with a maximum duration of 12 hours. This was established on the basis of a two hundred kilometer separation between locations of duct heights estimates. Significant features of the duct height and its temporal and spatial variations were related to synoptic scale descriptions. Satellite imagery used in conjunction with point observations appears to provide the most useful information in describing the intensity and areal distribution of the evaporation duct.
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