Influences of the Mid-Latitude Westerly Trough on Stratospheric Gravity Waves Generated by Typhoon Lekima (2019)

Characteristics of the gravity waves (GWs) in the lower stratosphere, produced by typhoon "Lekima" (2019) after its landfall, are studied using simulations with the high-resolution WRF-ARW4.2 model. In particular, the Characteristics and sources of the GWs are investigated. The results show that the GWs have a significant wavelength of 200-400 km and a significant period of 2.5-10 hr. The characteristics of stratospheric gravity wave induced by the typhoon after landing are affected by a westerly trough at mid-latitude. The GWs are reconstructed by Fourier inversion transform in the significant spectral region in order to reveal the source of waves inducing the stratospheric GWs. The frequency of reconstruction gravity waves varies with time, and the meridional wavenumber varies with latitude. The GW intensity (GWI) has two peak values during the interested period from 10 to 11 August 2019. The first peak in GWI is the result of the in-phase superposition of the GWs induced by the jet stream and the typhoon, when the two waves propagate almost in the same direction. The second intensity peak occurred when the trough moved away. The correlation between GWI and the typhoon and the trough are analyzed. It is found that the main factor affecting the changes of GWI is the northward movement of the trough. The location and strength of the typhoon and trough and their interaction are used to fit variations in GWI.