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The relationship between interplanetary quantities and Birkeland current densities
Author(s) -
Iijima T.,
Potemra T. A.
Publication year - 1982
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl009i004p00442
Subject(s) - physics , interplanetary magnetic field , solar wind , polar , morning , astrophysics , magnetic field , atmospheric sciences , astronomy , quantum mechanics
We have examined the relationship between hourly values of solar wind density, speed and the interplanetary magnetic field and the densities of Region 1 Birkeland currents. Magnetic field observations acquired by the TRIAD satellite were used to determine the Birkeland current densities. Data acquired from 51 passes in the morning sector (0800 to 1300 MLT) during IMF B y > 0 and 74 passes in the afternoon sector (1100 to 1600 MLT) during IMF B y < 0 were used in this study. This separation of data by polarity of IMF B y was done to avoid the complicated Birkeland current patterns related to the cusp region. To avoid further complications involving the seasonal dependence of Birkeland currents (c.f. Fujii et al., 1981), north polar data were selected during the period from May to August in 1973, 1974, 1976, and 1977. Correlation coefficients were computed for the morning and afternoon Region 1 densities (J m and J a , respectively) related to a variety of combinations of solar wind density (N), speed (V), and IMF B y and B z . The current densities show good correlation with negative values of B z (R = 0.39 for J m and R = 0.56 for J a ), but relatively poor correlation with positive values of B z (R = 0.07 for J m and R = 0.1 for J a ). Relating J m and J a with B T = (B y ² + B z ²) ½ provides correlation coefficients of 0.50 and 0.48; with B T sin ( θ /2), where θ is measured from the positive z axis, provides coefficients of 0.56 and 0.68; with the Akasofu “ϵ” parameter provides coefficients of 0.39 and 0.67; with VB T sin ( θ /2) gives 0.52 and 0.74; with [N ½ VB T sin ( θ /2)] ½ = (NVV A ) ½ gives 0.66 and 0.75. The dominant factor in these correlations appears to involve the magnitude of the IMF in the y‐z plane (B T ) and its orientation with respect to the geomagnetic field, sin ( θ /2). This suggests that magnetic reconnection may play an important role in determining the strength of Region 1 Birkeland currents. Substantial current densities (1 to 2 µ A/m²) exist at the origin of these plots (i.e. for θ = 0). These persistent Birkeland currents may be related to the convective flow (and associated electric fields) which prevail during periods of northward IMF.