Extratropical impacts on variability and prediction of tropical cyclone activity

• Main Author: Chang, Chuan-Chieh
• Other Authors: Xiang, Baoqiang, Wang, Zhuo, Wuebbles, Donald, Sriver, Ryan, Cha, Eun Jeong
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Tropical cyclones; Extratropical Rossby wave breaking; Subpolar gyre sea surface temperature; Subtropical stationary waves; Air-sea coupled climate modes; Diabatic heating; Future projection of tropical cyclones; North Atlantic
• Online Access: http://hdl.handle.net/2142/113884

My PhD research focuses on the role of extratropical processes on the variability and prediction of tropical cyclone (TC) activity. In my first Ph.D. project, I examined the relative importance of local and remote forcing on TC frequency using the WRF model. I showed that the remote processes outside the North Atlantic, particularly extratropical Rossby wave breaking, play an important role in modulating the interannual variability of Atlantic TC frequency and that the remote impacts may exceed the direct impacts of local SST in some years. In my second project, I developed a skillful hybrid prediction scheme for multi-year variability of Atlantic TC activity. I employed a Poisson regression model and took SST indices averaged over the Atlantic main development region (MDR) and the Atlantic subpolar gyre region (SPG) from the CESM large-ensemble hindcasts as predictors. The model skillfully predicts various Atlantic TC indices (including landfalling TC frequency) during the past ~60 years. I found that the Atlantic SPG SST is a more important source of predictability than the Atlantic MDR SST on the multi-year time scale. I also explored the optimal ensemble size for skillful hybrid prediction and compared initialized CESM hindcasts with uninitialized ones to investigate the roles of internal variability and external forcing in TC prediction. My third research project focused on summertime stationary waves, which provide a unified dynamic framework integrating tropical and extratropical impacts on TC activity. I investigated the interannual variability of summertime subtropical stationary waves, their response to anthropogenic forcing, and the implications for regional TC projection. Through observational analysis, I found that the variability of the subtropical stationary waves can be largely explained by the longitudinal displacement of the zonal wavenumber-1 component and the intensity change of the zonal wavenumber-2 component. Both aspects are significantly correlated to the variability of TC activity over ...