Examination of the combined effect of deep-layer vertical shear direction and lower-tropospheric mean flow on tropical cyclone intensity and size based on the ERA5 reanalysis

A way to further understand the VWS profile's effect is to examine the interaction between a TC and various shear-relative low-level mean flow (LMF) orientations. This study mainly uses the ERA5 reanalysis to verify that, consistent with idealized simulations, boundary layer processes associated with different shear-relative LMF orientations affect real-world TC's intensity and size.

Based on analyses of 720 TCs from multiple basins during 2004-16, a TC affected by an LMF directed toward downshear-left in the Northern Hemisphere favors intensification, whereas an LMF directed toward upshear-right is favorable for expansion. Furthermore, physical processes associated with shear-relative LMF orientation may also partly explain the relationship between the VWS direction and TC development, as there is a correlation between the two variables.