The structure and evolution of gap outflow over the Gulf of Tehuantepec, Mexico

• Published in: Monthly weather review 1998-10, Vol.126 (10), p.2673-2691
• Main Authors: STEENBURGH, W. J, SCHULTZ, D. M, COLLE, B. A
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Marine; Meteorology; Winds and their effects
• ISSN: 0027-0644; 1520-0493
• DOI: 10.1175/1520-0493(1998)126<2673:tsaeog>2.0.co;2

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 super(-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 because it followed the axis of the mesoscale pressure ridge. Trajectories west (east) of the jet axis experienced stronger (weaker) anticyclonic curvature than expected from inertial balance because the cross-flow pressure-gradient acceleration produced by the mesoscale pressure ridge reinforced (opposed) the anticyclonic deflection by the Coriolis acceleration. As a result of these directional variations in the cross-flow pressure-gradient acceleration, a fanlike wind pattern was observed rather than a narrow jet. Because of the large changes in SST and surface roughness that are observed during these gap-outflow events, better representation of these effects might improve future mesoscale-model simulations. Such improvements could be accomplished through coupled atmosphere-ocean mesoscale modeling, which could also be used to advance understanding of the oceanography of the gulf.