The Structure and Evolution of Gap Outflow over the Gulf of Tehuantepec, Mexico

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Abstract
Mesoscale-model simulations are used to examine the structure and dynamics of a gap-outflow event over the Gulf of Tehuantepec, Mexico, that was associated with a surge of cold air along the eastern slopes of the Sierra Madre. The simulated gap-outflow winds emerged from Chivela Pass, reached a maximum speed of 25 m s−1, and turned anticyclonically as they fanned out over the gulf. Northerly winds were also able to ascend the mountains east, and to a lesser extent west, of Chivela Pass, indicating that the movement of cold air across the Sierra Madre was not confined to the pass. A mesoscale pressure ridge was aligned along the axis of the gap-outflow jet, which was flanked to the west by an anticyclonic eddy, and to the east by a weaker cyclonic eddy. A model-derived trajectory along the axis of the outflow jet traced an inertial path, with anticyclonic curvature produced primarily by the Coriolis acceleration. The cross-flow pressure-gradient acceleration along this trajectory was negligible be... Abstract Mesoscale-model simulations are used to examine the structure and dynamics of a gap-outflow event over the Gulf of Tehuantepec, Mexico, that was associated with a surge of cold air along the eastern slopes of the Sierra Madre. The simulated gap-outflow winds emerged from Chivela Pass, reached a maximum speed of 25 m s−1, and turned anticyclonically as they fanned out over the gulf. Northerly winds were also able to ascend the mountains east, and to a lesser extent west, of Chivela Pass, indicating that the movement of cold air across the Sierra Madre was not confined to the pass. A mesoscale pressure ridge was aligned along the axis of the gap-outflow jet, which was flanked to the west by an anticyclonic eddy, and to the east by a weaker cyclonic eddy. A model-derived trajectory along the axis of the outflow jet traced an inertial path, with anticyclonic curvature produced primarily by the Coriolis acceleration. The cross-flow pressure-gradient acceleration along this trajectory was negligible be...

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