Signature of two-step non-linear interactions associated to zonally symmetric waves during major sudden stratospheric warmings

Abstract

Atmospheric tides and associated dynamics during two major boreal sudden stratospheric warmings (SSWs) have been investigated. The evolutionary Lomb Scargle and wavelet spectral analysis of specular meteor radar (SMR)-derived hourly winds reveal evidence of non-linear interactions between the semidiurnal solar tide and the quasi-20-day wave (Q20dw) during SSWs. The zonal wavenumber (ZWN) diagnosis indicates possible non-linear interaction between the dominant semidiurnal migrating tide (SW2) and zonally symmetric 20-day wave (20dw0) component, producing the secondary waves. The non-linear interaction between the ZWN 2 component of stationary planetary wave (SPW2) and westward propagating 20-day wave (20dwW2) in the stratosphere seems crucial to produce the 20dw0. As observed in the SMR-derived wind spectra, the excited 20dw0 possibly interacts non-linearly with SW2 to generate secondary waves. Therefore, the present study provides the first observational evidence of a two-step non-linear interaction associated with zonally symmetric planetary waves during major SSWs.