Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh22d..09l&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SH22D-09
Other
7260 Theory And Modeling, 2111 Ejecta, Driver Gases, And Magnetic Clouds, 2134 Interplanetary Magnetic Fields
Scientific paper
This talk reviews our study of estimated errors in various output fit-parameters resulting from a specific cylindrically symmetric, force free, interplanetary magnetic cloud model [Lepping et al., 1990*], applied to appropriately noised-up fields of simulated clouds. This realistic input magnetic field noise was derived from actual clouds observed in WIND data over the years 1995 to 1998, inclusive; random noise, applied earlier to simulated flux ropes, was shown to give an underestimate of the complexity of a real magnetic cloud. A large number (N = 1824) of noised-up simulated clouds are produced for use in the same force free cloud model to study the spread in values for each of 7 model parameters, plus associated quantities, as a function of internal noise level. [Another source of error in estimating model parameters, the improper choice of boundaries, will be addressed here only very briefly.] The estimated model parameters are the field strength on the cloud's axis, the direction of the axis, the impact parameter (i.e., closest approach distance), degree of symmetry, handedness, and diameter. Four noise levels are used with standard deviations of 0.5, 2.0 (typical level), 3.0, and 4.0 nT per field component of input bias-free fluctuation fields. These are based on manipulation of difference-fields [B(obs) - B(model)] from 19 actual magnetic clouds. The averages and standard deviations of 240 output (model-fit) parameter-distributions are produced and discussed. A practical goal of the study is to determine how each model fit-parameter, and especially its distribution, varies as a function of the input noise levels and of the resulting least-squares (χ 2)1/2 values for various exact input parameters, such as the cloud's axial attitude and the closest-approach distance of the spacecraft. The importance of the degree of symmetry in the fit-solution is shown to be almost as important as the value of (χ 2)1/2 in judging the quality of the fit to the model. We will show that generally, of the seven fit-parameters, the impact parameter is the most poorly determined, and the axial direction is usually the most well determined, for similar levels of noise. The study was motivated by the desire (1) to better understand the capabilities of the cloud fitting model and (2) to provide a practical means of assigning uncertainties in model fit-parameters in future uses of the model. Can such error studies be fun? Generally, yes, but in any case it taught us a lot about the model. ................................................................... * Lepping, Jones, and Burlaga, J. Geophys. Res. 95, 11,957, 1990.
Berdichevsky Daniel B.
Ferguson James T.
Lepping Ronald P.
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