Is the stratospheric quasi-biennial oscillation affected by solar wind dynamic pressure via an annual cycle modulation?

Abstract

[1] In this study, statistical evidence of a possible modulation of the equatorial stratospheric quasi-biennial oscillation (QBO) by the solar wind dynamic pressure is provided. When solar wind dynamic pressure is high, the QBO at 30–70 hPa is found to be preferably more easterly during July–October. These lower stratospheric easterly anomalies are primarily linked to the high-frequency component of solar wind dynamic pressure with periods shorter than 3 years. In annually and seasonally aggregated daily averages, the signature of solar wind dynamic pressure in the equatorial zonal wind is characterized by a vertical three-cell anomaly pattern with westerly anomalies in both the troposphere and the upper stratosphere and easterly anomalies in the lower stratosphere. This anomalous behavior in tropical winds is accompanied by a downward propagation of positive temperature anomalies from the upper stratosphere to the lower stratosphere over a period of a year. These results suggest that the solar wind dynamic pressure exerts a seasonal change of the tropical upwelling that results in a systemic modulation of the annual cycle in the lower stratospheric temperature, which in turn affects the QBO during austral late winter and spring.