EAPSI: Understanding disturbances that initiate typhoons in the North West Pacific Ocean

Rydbeck Adam, Fort Collins CO

Investigators

Abstract

Several tropical cyclones develop over the globe each year, approximately a third of which originate in the northwest Pacific Ocean. Tropical cyclones always originate from precursor disturbances with sufficient vorticity (rotation) and deep convection (thunderstorms). This study will investigate the generation of precursor disturbances from particular atmospheric waves to help improve forecasts of tropical cyclone formation. The research will be performed in collaboration with Dr. Chung-Hsiung Sui, a highly regarded professor of tropical meteorology at National Taiwan University in Taipei, Taiwan. In particular this study will focus on the role of mixed Rossby-gravity (MRG) waves. MRG waves are not able to serve as precursor disturbances without first undergoing a transformation in which they are reduced in size, increased in vorticity, and coupled to convection. If such a transformation occurs, the transformed MRG waves are capable of initiating tropical cyclones. This study will use an atmospheric model to determine the frequency of such transformations. In the model, two simulations of the northwest Pacific atmosphere will be performed. The first simulation will be used to determine how well the model captures the features of MRG waves. In the second simulation, all MRG waves will be removed from the model. If the number of precursor disturbances is reduced in the second simulation compared to the first simulation, the results would suggest that MRG waves are an important source of precursor disturbances. If the number of precursor disturbances remains unchanged, the results would suggest that MRG waves are of little importance to the generation of precursor disturbances and thus tropical cyclones. In either case, atmospheric scientists will have an improved understanding of the genesis of tropical cyclones and the precursor disturbances responsible. This NSF EAPSI award is funded in collaboration with the National Science Council of Taiwan.