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Occurrence and Structure of Mesoscale Fronts and Cyclones near Icy Bay, Alaska

Michael ReynoldsNOAA/Pacific Marine Environmental Laboratory, Seattle, WA 98105

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Abstract

When synoptic-scale cyclones stagnate against the mountains of southeast Alaska, a trough extends to the northwest, along the southern Alaskan coast. A front between maritime and continental air masses develops along the coast. During early spring of 1977, two data buoys made surface meteorological measurements near the mouth of Icy Bay, 20 km and 60 km offshore, and on several occasions easterly winds were reported inshore while the offshore buoy showed westerlies. Synoptic analyses showed, that wind reversals occurred in association with the above coastal fronts. Shallow, mesoscale cyclones were observed to develop in the frontal region. In February 1977 a research aircraft made a detailed cross section of the boundary layer up to 1000 m during one of these reversal events. A 400 m deep front was observed in detail at ∼28 km offshore. Inland of the front, a shallow (∼200 m), northeasterly flow of cold air warmed and veered slowly to an easterly direction. At the discontinuity, a sudden jump in temperature, decrease in wind speed, veer to ∼220° and drop in humidity occurred. The data suggest that when cyclonic disturbances develop, they move along the coast to the southeast and occasionally move out to sea. In some cases they are significant enough to appear in the synoptic analysis though often they go undetected.

Abstract

When synoptic-scale cyclones stagnate against the mountains of southeast Alaska, a trough extends to the northwest, along the southern Alaskan coast. A front between maritime and continental air masses develops along the coast. During early spring of 1977, two data buoys made surface meteorological measurements near the mouth of Icy Bay, 20 km and 60 km offshore, and on several occasions easterly winds were reported inshore while the offshore buoy showed westerlies. Synoptic analyses showed, that wind reversals occurred in association with the above coastal fronts. Shallow, mesoscale cyclones were observed to develop in the frontal region. In February 1977 a research aircraft made a detailed cross section of the boundary layer up to 1000 m during one of these reversal events. A 400 m deep front was observed in detail at ∼28 km offshore. Inland of the front, a shallow (∼200 m), northeasterly flow of cold air warmed and veered slowly to an easterly direction. At the discontinuity, a sudden jump in temperature, decrease in wind speed, veer to ∼220° and drop in humidity occurred. The data suggest that when cyclonic disturbances develop, they move along the coast to the southeast and occasionally move out to sea. In some cases they are significant enough to appear in the synoptic analysis though often they go undetected.

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