Roles of interplanetary and geomagnetic parameters in ‘intense’ and ‘very intense’ magnetic storms generation and their geoeffectiveness

Abstract

This paper studies the probable roles of interplanetary and geomagnetic parameters in the generation of ‘intense’ and ‘very intense’ magnetic storms as well as the correlation between magnetic field B and flow speed V , southward turning of Bz ( Bs ) and Bs duration BT . 18 storm events were observed and for analysis were divided into two sections. This include 8 ‘intense’ magnetic storm (−250 nT ≤ peak Dst < −100 nT) events and 10 ‘Very intense’ storms (peak Dst < −250 nT); both spanning January 1976 until May 2005. From our analysis, it was observed that the interplanetary magnetic field Bz plays a prominent role alongside Dst in the generation of intense storms. So also is the interplanetary electric field associated with high-speed streams and the solar wind density Np in the ring current intensification. The result further shows that over 67% of the storm events under investigation are generated from magnetic clouds which are characterized by a low beta plasma, high IMF magnitude and large scale coherent field rotations often including large and steady north-south components.As regards the geoeffectiveness of the flow speed V , the Bs and Bs interval ( BT ) with the magnetic field B , it was observed that generally for all the selected storm events, the flow speed is the most correlated, showing a correlation coefficient of 50.9% with B, and hence the most geoeffective. However, the statistical significance of its correlation with B is not so directly implying a higher substorm occurrence during the faster solar wind, but that it is one of the causes of substorm occurrence at a value faster than 400 km/s. Furthermore, the result shows that ‘very intense’ storms whose main feature is a plasma flow speed greater than 550 km/s has a negligible or very low correlation between the flow speed and the magnetic field B ; whereas, ‘intense’ storms have a 58.7% correlation between the two parameters. Lastly, it could be argued that all ‘very intense’ storms are likely to have a plasma flow speed greater than 550 km/s within the storm interval, but not all flow speed greater than 550 km/s are ‘very intense’ storms.