On the estimates of the ring current injection and decay

In the context of the space weather predictions, forecasting ring current strength (and of the Dst index) based on the solar wind upstream conditions is of specific interest for predicting the occurrence of geomagnetic storms. In the present paper, we have studied separately its two components: the Dst injection and decay. In particular, we have verified the validity of the Burton's equation for estimating the ring current energy balance using the equatorial electric merging field instead of the original parameter V Bs (V is the solar wind speed and Bs is the southward component of the Interplanetary Magnetic Field, IMF). Then, based on this equation, we have used the phasespace method to determine the best-fit approximations for the ring current injection and decay as functions of the equatorial merging electric field (Em). Results indicate that the interplanetary injection is statistically higher than in previous estimations using V Bs . Specifically, weak but not-null ring current injection can be observed even during northward IMF, when previous studies considered it to be always zero. Moreover, results about the ring current decay indicate that the rate of Dst decay is faster than its predictions derived by using V Bs . In addition, smaller quiet time ring current and solar wind pressure corrections are contributing to Dst estimates obtained by Em instead of V Bs . These effects are compensated, so that the statistical Dst predictions using the equatorial electric merging field or using V Bs are about equivalent.