Abstract
Abstract This paper aims to clarify the effect of high-density plasma in interplanetary coronal mass ejection (ICME) observed during the May 2–3, 1998 geomagnetic storm. The examination is performed based on the estimation of Dst index, which is calculated with the observed solar wind parameters of the ICME. The estimated Dst index variation is compared with Dst index variation provided by the World Data Center for Geomagnetism, Kyoto (WDC, Kyoto). From this examination, we find that the trend of the estimated Dst is in good agreement with that of the provided Dst when the thresholds are taken into account for both the solar wind plasma density and the dawn-to-dusk solar wind electric field, as 30 #/cc and 0.49 mV/m, respectively. From the result, we can conclude that the effect of high-density plasma is important on the enhancement of geomagnetic storm as well as the effect of the other solar wind parameters, such as the interplanetary magnetic field (IMF) Bz and solar wind velocity. On the other hand, the solar source of the magnetic field of this ICME is examined. The magnetic field structure of the ICME is examined by fitting the flux rope model to the observed magnetic field and solar wind speed. The results are compared with the magnetic structure of the bases of coronal helmet streamers. From this comparison we can find that the magnetic structure of the interplanetary flux rope is in good agreement with that of the neutral line of the base of coronal helmet streamers. The result suggests that if we look for the causes of geomagnetic storm we should take into account both the plasma structure and the magnetic structure of the base of coronal helmet streamers.
Highlights
interplanetary coronal mass ejection (ICME) is frequently observed in association with enhanced magnetic field and high solar wind speed
We focus our attention to reveal the geomagnetic effect of high-density plasma in ICME
We examined the magnetic disturbance during the geomagnetic storm occurred on May 2–3, 1998 and estimated Dst index variation at the time of high density plasma observed in the magnetic cloud
Summary
ICME is frequently observed in association with enhanced magnetic field and high solar wind speed. A magnetic cloud is a kind of ICME characterized with enhanced magnetic field strength, smooth magnetic field rotation and low-temperature plasma (Burlaga et al, 1981, 1982). High-density plasma is frequently observed in association with ICME, which often yields large geomagnetic disturbances. It is well known that the dawn-to-dusk solar wind electric field plays an important role on the enhancement of geomagnetic storm. The geomagnetic effect of high-density plasma when it associates the southward Bz might be important. This has not yet been sufficiently examined
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