On the Predictive Ability of Geomagnetic Disturbances from Solar Wind Measurements at Separated Solar Longitude

Abstract

In-situ solar wind measurement at a solar longitude separated from the earth in interplanetary space is expected to provide a great progress in practical space weather forecast, which has been confirmed by some recent studies. We introduce geoeffective solar wind conditions in correlation analysis between STEREO and ACE measurements. We sort solar wind data of ACE by using geomagnetic condition, and evaluate actual ability for predicting geoeffective solar wind arrival at ACE from STEREO-A and B solar wind measurement, by assuming simple corotating structures in interplanetary space. The results show that geomagnetic disturbances are more difficult to be predicted than quiet intervals, suggesting that the simple correlation method of solar wind measurement at separated solar longitude is not enough for accurately predicting geomagnetic disturbances, even though the correlation seems generally high. Although in-situ solar wind monitoring at a vantage point trailing behind the earth would definitely improve the prediction capability of solar wind structure arriving at the terrestrial plasma environment, we emphasize that the predictive ability of geoeffective disturbances would still remain low. We suggest that more sophisticated prediction schemes should be developed.