R P Lepping, A Szabo, F L Burlaga, K W Ogilvie and D
A Roberts
A J Lazarus and J T Steinberg
(Center for Space Research, MIT, Cambridge, MA 02139)
Two large (diameter = 1/4 AU) interplanetary magnetic clouds were observed in February and October 1995 in WIND magnetic field and plasma data. The present study concentrates on an aspect of these structures that has gotten little notice: the power spectral density (PSD) distributions of the fluctuations of the magnetic fields inside such clouds in comparison to those of the ambient fields. The 'quiet' regions inside magnetic clouds have low and sometimes unusually low plasma beta (~ 0.05), whereas in the solar wind outside of the cloud this quantity is typically >=1. If a sheath region exists between an interplanetary shock and the cloud, which was the case for the cloud on October 18 - 19, beta van be >>1. On February 8 a magnetic cloud whose axis was near the Y-GSE axis interacted with Earth's bow shock (BS) and magnetosphere causing the BS to be markedly displaced outward as observed by IMP 8. From preliminary PSD analyses of the fields from WIND measurements around the February event, carried out for the range of .001 to 2 Hz, we find that the spectral slope in the cloud became steeper above a certain frequency than a typical Kolmogorov spectrum (spectral index of 5/3) observed in the undistributed solar wind. When the magnetosheath was immersed in the cloud (IMP 8 observations), a spectral break exists very similar to what was observed in the solar wind cloud, except that the underlying spectrum appeared to be that of the undisturbed sheath, and the turnover point was at a lower frequency (between 0.2-0.7 Hz). Similar analyses will be done on the October magnetic cloud and its sheath, and various comparisons made.
Return to abstracts page
Last Modified:
(G.C.G.)