Generation Mechanism for Stratospheric Gravity Waves by Unbalanced Flow in Tropical Cyclones

Abstract

AbstractThe generation mechanism of stratospheric gravity waves (SGWs) in tropical cyclones (TCs) is investigated with an idealized experiment using numerical model. The results show that there are two peaks of SGW amplitude during the mature period of TC, one above the eyewall and the other above the rainband. The SGWs can only exist in unbalanced flow, so a simplified balance equation suitable for the special structure of the TC is proposed to investigate the SGWs. Diagnosis of this equation shows there is significant unbalanced flow around the eyewall and rainband caused by the convection and the vertical shear between outflow and compensating inflow. Diagnosis of the source function indicates that diabatic heating and mechanical oscillations are the main mechanisms generating the SGWs above the eyewall and rainband. The Kelvin–Helmholtz instability induced by vertical shear also makes a non‐negligible contribution to the generation of SGWs above the rainband.