WIND Magnetic Clouds for Years 1995 - 2003 : A Summary of Model-Fitted Parameters

Details WIND Magnetic Clouds for Years 1995 - 2003 : A Summary of Model-Fitted Parameters WIND Magnetic Clouds for Years 1995 - 2003 : A Summary of Model-Fitted Parameters

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsh31a1161l&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SH31A-1161

Physics

2100 Interplanetary Physics, 2134 Interplanetary Magnetic Fields

Scientific paper

Almost a decade's worth of WIND interplanetary magnetic clouds (MCs) has been identified, and their magnetic field structures have been parameter-fitted by a static force free cylindrically symmetric model [Lepping et al., 1990], with various levels of success, measured by an objective figure of quality. Quality (good, fair, or poor) is estimated from a quantitative consideration of a large set of parameters such as the chi-squared of the model fit, symmetry of the |B| profile, a comparison of the model-estimated radius vs. that from the duration of passage, etc. This paper summarizes various aspects of the results of the model fitting, including presenting of the estimated seven fit-parameter values for each of the 82 MCs that were discovered, their quality estimates, closest approach vector (in two coordinate frames), fit-parameter errors for the cases of acceptable quality (50 or 61%), axial magnetic fluxes, and axial current densities - as well as updated average MC profiles for various conditions. This set of MCs (called set 1) was initially identified by visual inspection of relevant field and plasma data. The resulting MC candidate is then "tested" through the use of the field model which also helps to better refine the boundary-times. Another, significantly larger, set of magnetic cloud-like (MCL) interplanetary structures (called set 2) are identified through an automated program whose criteria are based on MC plasma and field characteristics determined from the study of the earlier identified cases, set 1. Set 2 contains most of the set 1 cases, as expected, but in fact, its occurrence frequency of MCs better matches that of the sunspot cycle. However, cases in the difference-set (set 2 - set 1) are less intense (i.e., lower <|B|>) and have shorter durations than those in set 1, and almost never are they well represented as good flux ropes through force free parameter modeling. Nevertheless, many of the MCL structures are geoeffective often having long periods of negative BZ, somewhat similar to most MCs. We present a discussion of how a MC's front boundary is specifically identified in terms of multi-parameter considerations (i.e., any one or more of: increase in |B|, directional discontinuity, magnetic hole in |B|, drop in proton plasma beta, B-fluctuation level change, proton temperature drop, etc.), as well as through the application of the flux rope model. Also presented are examples of unusual MCs, including a case with a core and annulus in which the axial field changes polarity from the core to the annulus, as well as some commonly occurring relationships, such as the existence and frequency (about 1/2 of the time) of upstream interplanetary shocks, and less frequent internal shocks.
Ref: Lepping et al. (1990), J. Geophys. Res., 95, 1957.

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