HF radar observations of a quasi-biennial oscillation in midlatitude mesospheric winds

Abstract

The equatorial quasi-biennial oscillation (QBO) is known to be an important source of interannual variability in the middle- and high-latitude stratosphere. The influence of the QBO on the stratospheric polar vortex in particular has been extensively studied. However, the impact of the QBO on the winds of the midlatitude mesosphere is much less clear. We have applied 13 years (2002-2014) of data from the Saskatoon Super Dual Auroral Radar Network HF radar to show that there is a strong QBO signature in the midlatitude mesospheric zonal winds during the late winter months. We find that the Saskatoon mesospheric winds are related to the winds of the equatorial QBO at 50 hPa such that the westerly mesospheric winds strengthen when QBO is easterly, and vice versa. We also consider the situation in the late winter Saskatoon stratosphere using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data set. We find that the Saskatoon stratospheric winds between 7 hPa and 70 hPa weaken when the equatorial QBO at 50 hPa is easterly, and vice versa. We speculate that gravity wave filtering from the QBO-modulated stratospheric winds and subsequent opposite momentum deposition in the mesosphere plays a major role in the appearance of the QBO signature in the late winter Saskatoon mesospheric winds, thereby coupling the equatorial stratosphere and the midlatitude mesosphere.