Is the stratospheric quasi-biennial oscillation affected by solar wind dynamic pressure via an annual cycle modulation?
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.
Authors: Lu, Hua ORCID record for Hua Lu, Jarvis, Martin J.