The Role of Stratified Turbulence in the Cold Summer Mesopause Region

Abstract

The summer mesopause at middle and high latitudes is the coldest place on Earth, and atmospheric gravity waves are responsible for the emergence of this extreme thermal phenomenon. Although the main physical mechanism behind the latter is understood, a deeper insight into it can be gained from the investigation of the mesoscale energy spectrum. In this work, we decompose the frequency spectra into divergent and rotational parts and find that their energy contributions are equipartitioned at high frequencies. This mesoscale energy equipartition is a feature of stratified turbulence and illustrates the complexity of the mesoscale dynamics in the summer mesopause region. We also analyze the power spectra of observed and simulated mesoscale zonal and meridional winds at middle latitudes in the southern hemisphere and show that stratified turbulence plays a role in the mesopause region during summer.

Dissipation Rates of Mesospheric Stratified Turbulence From Multistatic Meteor‐Radar Observations

“…During the summer maxima, the values are more localized and appear to have a maximum near the mesopause height. The seasonal pattern agrees well with the theory of how the zonal mean wind affects the altitudes where gravity wave drag is increased (Avsarkisov & Conte, 2023; Becker, 2012; Conte et al., 2018; Lindzen, 1981).…”

“…The framework of stratified turbulence (ST) predicts that for a vertically stratified fluid, the kinetic energy of a horizontal wind component cascades from large to small‐scale eddies in a manner similar to classical inertial subrange isotropic turbulence (Avsarkisov et al., 2022; Lindborg, 1999). In the case of the MLT region, kinetic energy enters the cascade via gravity waves and atmospheric tides on mesoscales (Avsarkisov & Conte, 2023). Below these scales, ɛ for stratified turbulence eddies is expected to be the same as the dissipation rate for the small‐scale isotropic turbulence (Avsarkisov, 2020), which removes the need for direct observation of inertial subrange to observe ɛ .…”