Impact of Terrain Induced Low-Level Jets on Tropical Cyclone Propagation and Intensity

Mountain gap winds are an intense, relatively small-scale wind phenomena that results from the interaction of flow with the surrounding topography. One location in which mountain gap winds are prevalent is the Chivela Pass within the Sierra Madre mountain range. Gap winds that originate from this location can extend hundreds of kilometers over the Gulf of Papagayo and can reach up to hurricane force. Previous studies have suggested that the presence of these gap winds over the Gulf of Papagayo affect tropical cyclogenesis in the eastern Pacific Ocean; where a large percentage of tropical cyclogenesis occurs. To investigate this further, the Weather Research and Forecast model is used to simulate numerous tropical cyclones that either originate near the Gulf of Papagayo or pass through the region. The tropical cyclone cases were chosen because a gap wind event that originated from the Chivela Pass either occurred simultaneously or just preceded the formation of the tropical cyclone, or a gap wind event is occurring when a tropical cyclone passes through the Gulf of Papagayo. Topography within WRF is modified during the pre-processing stages so that the elevations within the Chivela Pass are increased to remove the presence of the pass. The gap winds during the modified simulations are no longer present. The simulations are then compared to control runs in which the topography is left unchanged. Preliminary results from the WRF simulations show that while cyclone tracks between the control and modified runs are not significantly different, the presence of a gap wind over the Gulf of Papagayo leads to a change in both the precipitation patterns associated with the cyclone and the central pressure of the cyclone. More in-depth results about the impacts that the gap winds have on tropical cyclones will be shown. The mechanisms that govern the relationship between mountain gap winds and tropical cyclogenesis across the Eastern Pacific will also be discussed.