Quantitative Evaluation of Energy Coupling between Quasi-Periodic Substorms and High-Speed Coronal Streams

It has been known that high-speed solar wind streams associated with coronal holes lead to quasi-periodic substorms that occur approximately every 2˜4 hours. In this paper we examined 222 repetitive substorms that occurred during high-speed stream periods in July through December in 2003 to quantitatively determine a range of energy input from the solar wind into the magnetosphere between two consecutive substorms. For this study, we have used the Akasofu \varepsilon-parameter to time-integrate it for the interval between two consecutive substorms, and have applied this method to the 222 substorms. We find that the average amount of solar wind input energy between two adjacent substorms is 1.28×10^{14}J and about 85% out of the 222 substorms occur after an energy input of 2×10^{13}˜2.3×10^{14}J. Based on these results, we suggest that it is not practical to predict when a substorm will occur after a previous one occurs purely based on the solar wind-magnetosphere energy coupling. We provide discussion on several possible factors that may affect determining substorm onset times during high-speed streams.