Group seminar on 30. November, 14:15 CET
Linear and non-linear excitation mechanisms of mixed Rossby-gravity waves
Sándor István Mahó
The mixed Rossby-gravity wave is a fundamental component of tropical synoptic scale variability. Its presence in the upper troposphere and the stratosphere is well supported by evidence from wavenumber – frequency spectra of the symmetric component of the meridional wind averaged in the tropical region (Zangvil and Yanai, 1980). The mechanism that triggers the excitation in the troposphere is still under debate. In general, two competing theories are proposed: the lateral boundary forcing and the wave – CISK mechanism. The former one refers to the atmospheric response to a forcing exerted in the lateral boundary of the commonly used β-plane shallow water models. The latter one involves strong coupling between waves and convection. Another alternative excitation mechanism was proposed by Raupp and Silva Dias (2005) which suggests that non-linear wave interactions are important for the generation of these waves.
In this seminar, I will give an overview of the excitation theories concentrating on the “dry theories”: the lateral boundary forcing and the wave interaction mechanism. Furthermore, I will present the excitation mechanisms of mixed Rossby-gravity waves on the TIGAR model (Transient Inertia-Gravity And Rossby wave dynamics; Vasylkevych and Žagar, 2021). Here I will show how linear and non-linear processes generate these waves. Lastly, I will examine the mixed Rossby-gravity wave response in different background flows.