Factors Influencing the Variability of Mountain Gap Wind Events over the Gulf of Tehuantepec

Friday, 19 December 2014
Emily Foshee and Udaysankar S Nair, University of Alabama in Huntsville, Huntsville, AL, United States
Mountain gap winds (MGW) are a low-level jet feature that results from the interaction between the large-scale flow and mountain gaps. The focus of this study is the MGW events that occur over the Gulf of Tehuantepec, originating from the Chivela Pass in the Sierra Madre mountain range. MGW at this location can attain speeds in excess of 25 meters per second and can extend for a long distance over the Gulf of Tehuantepec. The high winds and seas associated with an MGW event pose a hazard to both aviation and shipping industries within the area. In this context, it is important to understand processes that modulate the intensity of the jet, its diurnal variation, and the ability of numerical models to forecast these events. We utilized nested grid configuration of Weather Research and Forecasting (WRF) model over the Chivela Pass region to simulate the evolution of twelve different gap wind events. The case days considered includes gale, storm, and hurricane force events. Output from the 1km spacing inner most grid is compared against Cross-Calibrated, Multi-Platform (CCMP) ocean surface wind product. These events are also analyzed to determine processes that are most responsible for variability in jet intensity within and between the different event categories. Numerical simulations show distinct differences in the vertical structure of the jet as a function of the force categories. Distribution of pressure gradient in the vicinity of the Chivela Pass also shows substantial difference depending upon the force category. Intensity of the jet is also modulated by other factors including stability aloft and boundary layer evolution at the entrance and exit regions of the jet. The relationship of these factors to synoptic precursor patterns and the processes through which these factors impact the intensity of the jet will be discussed in context of conceptual models of mountain gap winds.