The Influencing Mechanism of a Mid-Latitude Westerly Trough on Stratospheric Gravity Waves Generated by Typhoon Lekima (2019)

The mechanism by which a mid-latitude trough influenced the gravity waves (GWs) generated by Typhoon Lekima (2019) was studied by changing the initial fields in a series of model experiments. A peak in GW intensity (GWI) develops as typhoons weaken. The vertical speed shows the patterns of GWs generated by the typhoon and trough are the same during this peak GWI period. The typhoon generates the main part of the GWs and the trough enhances their intensity. The phase speed spectra show intense GWs occur when the GWs generated by the typhoon and trough propagate at the same phase speed. The GWI generated by the trough and typhoon were calculated separately in the control experiment, and their sum shows the peak GWI was caused mainly by in-phase superposition. Finally, the model of the GWs superposition was proposed to quantitatively verify the existence of waves liner positive superposition.

Automated summary

This study investigates the influence of a mid-latitude trough on the gravity waves generated by Typhoon Lekima. It is found that the trough enhances the intensity of the gravity waves and they propagate in a similar pattern and phase speed as the waves generated by the typhoon. The peak intensity of the gravity waves is mainly caused by in-phase superposition.