Magnetic flux in modeled magnetic clouds at 1 AU and some specific comparisons to associated photospheric flux

R. P. Lepping, A. Szabo, C. E. DeForest, and B. J. Thompson

Laboratory for Extraterrestrial Physics, NASA-Goddard Space Flight Center, Greenbelt, MD 20771


Interplanetary magnetic clouds are important because of their well-known dramatic effects on the Earth's magnetosphere. There are two parts to this study, which attempts to better understand the solar origins of magnetic clouds: (1) to obtain statistical distributions of the estimated axial magnetic flux of 30 magnetic clouds at 1 AU separated according to their occurrence during the solar cycle, and (2) to make a comparison of the magnetic flux of a magnetic cloud to the aggregate flux of apparently associated photospheric magnetic flux tubes, for some specific cases. The 30 magnetic clouds comprise 12 cases from WIND (mostly from solar min.) and the remainder (mostly from solar max.) from IMP-8, earlier IMP's, ISEE-3, and HELIOS. Employing a constant a (J = a B) cylindrical force-free flux rope model to determine the clouds' diameters (D o = 2 R o) and axial magnetic field strengths (B o), we are able to estimate the total magnetic flux (F o) along the cloud axis (i.e., F o = 1.39 B o R o 2). For the full set of events the average D o is 0.27 AU and the average B o is 17.7 nT, but the distributions of these quantities are skewed toward higher values for both solar max and solar min. The distribution of magnetic fluxes for the 30 clouds is shown to be in the form of a skewed gaussian, f(F o) ~ F oe-x, where X º (F o / 10.5x1020 Mx)2, and where the mode is 7.5(± 6.0) X 1020 Mx. For three specific cases, the relationship between the magnetic flux of a magnetic cloud at 1 AU (F o) and the flux in apparently associated photospheric flux tube(s) (F SUN) is presented in the form of F SUN = K F o. F SUN is based on SOHO/MDI measurements in coordination with SOHO/EIT and Yohkoh/SXT observations. For the two apparently successful cases of the three, the value of K is » 0.4.

Proceedings of the 31st ESLAB Symposium, 1997