Influence of the solar wind dynamic pressure on the decay and injection of the ring current

Abstract

The influence of the solar wind dynamic pressure on the decay and injection of the ring current is investigated empirically, on the basis of the solar wind and the geomagnetic index Dst of the OMNI database, for the period from January 1964 to July 2001. We found that when the position of the ring current is closer to the Earth for a higher solar wind dynamic pressure, the decay time of the ring current decreases. The decay time, in hours, varies as follows, τ = 8.70 exp(6.66/(6.04 + P)), for northward interplanetary magnetic fields (IMF), where P is the solar wind dynamic pressure in nanopascals. It is also found, by minimizing the root mean square errors of the hourly Dst difference between the calculated values and the measured ones, that the ring current injection rate is proportional to the solar wind dynamic pressure, with a power index equal to 0.2 during southward IMF. This implies that the ring current injection increases when the magnetosphere is more compressed by high solar wind dynamic pressure. On the basis of our new results we demonstrate that the predictions of Dst using O'Brien and McPherron's [2000a] model are improved, especially for intense geomagnetic storms when the influence of the solar wind dynamic pressure on the decay and injection of ring current is taken into consideration.