Observational evidence for temporary planetary wave forcing of the MLT during fall equinox

TL;DR

This study provides direct observational evidence that planetary waves temporarily influence the mesopause region during fall equinox, coinciding with minimal stratospheric winds and gravity wave filtering, leading to poleward wind perturbations and temperature rises.

Contribution

It offers the first direct observational evidence linking planetary wave activity to mesopause dynamics during fall equinox, highlighting a temporary forcing mechanism.

Findings

Planetary wave activity increases during fall equinox.

Mesopause temperatures rise temporarily during this period.

Meridional winds are perturbed poleward coinciding with planetary wave activity.

Abstract

We present direct observations of zonal wave numbers 1 and 2 planetary wave activity in the mesopause region derived from a longitudinal chain of high-latitude Northern Hemisphere (51-66$^{\circ}$N) Super Dual Auroral Radar Network radars. Over a 9 year period (2000-2008), the planetary wave activity observed shows a consistent increase around the fall equinox. This is shown to be coincident with a minimum in the magnitude of the stratospheric winds and consequently a minimum in the stratospheric gravity wave filtering and the subsequent momentum deposition in the mesopause region. Despite this, the observed meridional winds are shown to be perturbed poleward and mesopause temperatures rise temporarily, suggesting that westward momentum deposition from planetary waves temporarily becomes the dominant forcing on the mesopause region each fall equinox.