Abstract
The mechanical oscillator mechanism (MOM) for stratospheric gravity waves generated by convection is investigated with a dynamics model using the two-dimensional, nonhydrostatic and linear governing equations based on the Boussinesq approximation. The model is solved analytically with a fixed buoyancy oscillation (BO) at the tropopause as the boundary conditions. Results show that this BO is the source of stratospheric gravity waves and the MOM is the generation mechanism. The characteristics of the stratospheric gravity waves not only depend on the BO, but also rely on the stratospheric state, such as the background wind and the buoyancy frequency. When the vertical wavenumbers of the stratospheric gravity waves are close to those of the intrinsic characteristic waves (ICWs), which are the model solution without BO forcing at the tropopause, resonance occurs. Under the resonance conditions, the amplitudes of the stratospheric gravity waves increase significantly, even for low BO intensity. The background wind in the stratosphere has a large effect on wave resonance. Finally, numerical simulation results of a low-vortex system also verify that the MOM is the generation mechanism of stratospheric gravity waves generated by convection.
Highlights
As an important dynamic process in the stratosphere, the gravity waves play an important role in the transfer of energy and momentum in the stratosphere, and significantly affect general atmospheric circulation [1,2,3,4,5]
The mesoscale convection is a ubiquitous phenomenon in the troposphere, and convection is an important source of stratospheric gravity waves
To explore the mechanism of stratospheric gravity waves generated by convection is an important scientific problem
Summary
As an important dynamic process in the stratosphere, the gravity waves play an important role in the transfer of energy and momentum in the stratosphere, and significantly affect general atmospheric circulation [1,2,3,4,5]. The MOM was first proposed by Pierce and Coroniti [22], and developed and verified by Fovell et al [23], Alexander et al [24], and Lane et al [25,26] This mechanism asserts that the updraft within a convective system decelerates rapidly when it reaches the neutral buoyancy layer near the tropopause, where oscillations begin to occur [15,27,28]. Wang et al [15] investigated the generation, structure, and characteristics of mesoscale gravity waves in the Mei-Yu front systems in Asia by performing numerical simulations using the Weather Research and Forecasting (WRF) model, and found that gravity waves are generated during the development of moist convection, and, importantly, that these waves do not directly propagate into the stratosphere from the troposphere but are initiated by the MOM near the tropopause.
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