Cluster Hot Flow Anomaly Observations During Solar Cycle Minimum

TL;DR

This study analyzes hot flow anomalies during solar cycle minimum using Cluster spacecraft data, confirming that higher solar wind speeds are a key condition for HFA formation, independent of previous criteria.

Contribution

It demonstrates that higher solar wind speeds are a consistent condition for HFA formation during solar minimum, extending previous findings to a different solar cycle phase.

Findings

Higher solar wind speeds are necessary for HFA formation.

The condition is independent of Schwartz et al.'s criteria.

HFA occurrence during solar minimum confirms earlier results.

Abstract

Hot flow anomalies (HFAs) are studied using observations of the FGM magnetometer and the CIS plasma detector aboard the four Cluster spacecraft. Previously we studied several specific features of tangential discontinuities on the basis of Cluster measurements in February-April 2003 and discovered a new condition for forming HFAs that is the solar wind speed is higher than the average. However during the whole spring season of 2003, the solar wind speed was higher than average. In this study we analyse HFAs detected in 2007, the year of solar cycle minimum. Our earlier result was confirmed: the higher solar wind speed is a real condition for HFA formation; furthermore this constraint is independent of Schwartz et al. s condition for HFA formation.