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Title:
Physics-based tests to identify the accuracy of solar wind ion measurements: A case study with the Wind Faraday Cups
Authors:
Kasper, J. C.; Lazarus, A. J.; Steinberg, J. T.; Ogilvie, K. W.; Szabo, A.
Affiliation:
AA(MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA); AB(MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA); AC(Los Alamos National Laboratory, Los Alamos, New Mexico, USA); AD(NASA Goddard Space Flight Center, Greenbelt, Maryland, USA); AE(NASA Goddard Space Flight Center, Greenbelt, Maryland, USA)
Publication:
Journal of Geophysical Research, Volume 111, Issue A3, CiteID A03105 (JGRA Homepage)
Publication Date:
03/2006
Origin:
AGU
AGU Keywords:
Interplanetary Physics: Solar wind plasma, Interplanetary Physics: Instruments and techniques, Interplanetary Physics: Interplanetary shocks, Interplanetary Physics: MHD waves and turbulence (2752, 6050, 7836)
Abstract Copyright:
(c) 2006: American Geophysical Union
DOI:
10.1029/2005JA011442
Bibliographic Code:
2006JGRA..11103105K

Abstract

We present techniques for comparing measurements of velocity, temperature, and density with constraints imposed by the plasma physics of magnetized bi-Maxwellian ions. Deviations from these physics-based constraints are interpreted as arising from measurement errors. Two million ion spectra from the Solar Wind Experiment Faraday Cup instruments on the Wind spacecraft are used as a case study. The accuracy of velocity measurements is determined by the fact that differential flow between hydrogen and helium should be aligned with the ambient magnetic field. Modeling the breakdown of field alignment suggests velocity uncertainties are less than 0.16% in magnitude and 3° in direction. Temperature uncertainty is found by examining the distribution of observed temperature anisotropies in high-beta solar wind intervals where the firehose, mirror, and cyclotron microinstabilities should drive the distribution to isotropy. The presence of a finite anisotropy at high beta suggests overall temperature uncertainties of 8%. Hydrogen and helium number densities are compared with the electron density inferred from observations of the local electron plasma frequency as a function of solar wind speed and year. We find that after accounting for the contribution of minor ions, the results are consistent with a systematic offset between the two instruments of 3-4%. The temperature and density methods are sensitive to non-Maxwellian features such as heat flux and proton beams and as a result are more suited to slow solar wind where these features are rare. These procedures are of general use in identifying the accuracy of observations from any solar wind ion instrument.
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