ROLES OF INTERPLANETARY AND GEOMAGNETICPARAMETERS IN INTENSE AND VERY INTENSEMAGNETIC STORMS GENERATION AND THEIRGEOEFFECTIVENESS

摘要

This paper studies the probable roles of interplanetary and geomagnetic param-eters in the generation of intense and very intense magnetic storms as well as thecorrelation between magnetic field B and flow speed V, southward turning of Bz(Bs) and B duration BT. 18 storm events were observed and for analysis weredivided into two sections. This include 8 intense magnetic storm (-250 nT < peakDst < —100 nT) events and 10 'Very intense' storms (peak Dst < —250 nT); bothspanning January 1976 until May 2005. From our analysis, it was observed that theinterplanetary magnetic field Bs plays a prominent role alongside Dst in the gener-ation of intense storms. So also is the interplanetary electric field associated withhigh-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 aregenerated from magnetic clouds which are characterized by a low beta plasma, highIMF magnitude and large scale coherent field rotations often including large andsteady north-south components.As regards the geoeffectiveness of the flow speed 17, the B. and B, interval (Br)with the magnetic field B, it was observed that generally for all the selected stormevents, the flow speed is the most correlated, showing a correlation coefficient of50.9% with B, and hence the most geoeffective. However, the statistical significanceof its correlation with B is not so directly implying a higher substorm occurrenceduring the faster solar wind, but that it is one of the causes of substorm occurrenceat a value faster than 400 km/s. Furthermore, the result shows that very intensestorms whose main feature is a plasma flow speed greater than 550 km/s has anegligible or very low correlation between the flow speed and the magnetic fieldB; 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 plasmaflow speed greater than 550 km/s within the storm interval, but not all flow speedgreater than 550 km/s are very intense storms.