Impact of Vertical Wind Shear on Asymmetry of Stratospheric Gravity Waves Generated by Tropical Cyclones

Abstract This study focused on the impact of vertical wind shear (VWS) in the stratosphere on the asymmetry of stratospheric gravity waves (SGWs) generated by tropical cyclones (TCs), based on a set of numerical simulations of TC-SGWs completed under different stratospheric background wind conditions. Results showed that a constant background easterly wind leads to a slightly asymmetric distribution of TC-SGWs, with intense waves in the lower stratosphere located on the upwind side, attributable to the asymmetry in TC structure under the condition of the easterly wind. In contrast, VWS induces a notable asymmetric distribution of TC-SGWs through directional critical levels. Spectral and wavenumber–vector analyses revealed that the co-occurrence of radial and tangential propagation of TC-SGWs modifies the critical-level filtering effect, producing a final distribution with intense waves located mainly in the southeastern quadrant relative to a TC center and to a lesser extent in the northeastern and southwestern quadrants, rather than throughout the eastern quadrants as a whole.