Future Changes of the Monsoon Trough: Sensitivity to Sea Surface Temperature Gradient and Implications for Tropical Cyclone Activity

Most tropical cyclones (TCs) in the western North Pacific basin form, intensify, and move in the monsoon trough (MT), and its future changes have significant implications for TC activity. In this study, future changes in MT and its possible impacts on TC activity are investigated by using outputs from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and a downscaling system. The reliability of CMIP5 models is first examined by using their historical runs. Based on the constructed ensemble of 17 models with relatively high skill, the MT is found to intensify and extend eastward in the warming scenarios. This is also true for the ensemble mean of all of 36 available models. However, considerable intermodel uncertainty exists in the projection, which is related to the diversity in the projected sea surface temperature (SST) gradient over the equatorial North Pacific. The diversity in the SST pattern can generate different configurations of large‐scale circulations, and thus acts as an important source of uncertainty in projecting the TC activity in warming scenarios. The impacts of the MT change on TC activity are further explored by using a downscaling system. It is found that the intensification and eastward migration of the MT tend to shift TC formation locations eastward, increase TC influences in subtropical Asia, and decrease TC influences in south Asia. In addition, TCs intensify by a rate of 8.3% and 26.2% in terms of lifetime peak intensity and intense TC number for 1 K SST warming over the western North Pacific.