B{sub x} control of polar cap potential for northward interplanetary magnetic field

Journal Article · Sun Oct 01 04:00:00 EDT 1995 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/95JA01085· OSTI ID:227134

Taguchi, S; Hoffman, R A ^[1]

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1. NASA Goddard Space Flight Center, Greenbelt, MD (United States)

The authors have examined how the magnitude of the polar cap potential for northward interplanetary magnetic field (IMF) changes with the angle of the field in the B{sub x}/B{sub z} plane. From the dawn-dusk passes (November-December 1981, May-June 1982, and November-December 1982) of the Dynamics Explorer 2 satellite, they selected 363 passes by requiring the IMF hourly value B{sub z} {le} 1 nT for the preceding 2-hour interval. Of these, 72 cases displayed a reverse convection pattern in the electric field data, i.e., sunward at the highest latitudes and antisunward at lower latitudes. The potential difference across the region of sunward convection correlates well with various functions that consist of all or some of the IMF parameters, B{sub z}, B{sub y}, the B{sub y}/B{sub z} angle, and the solar wind velocity. The authors {open_quotes}normalize{close_quotes} the potential, using these functions. To test for a B{sub x} dependence while eliminating dipole tilt effects, they introduce {phi}{sub h}{sup *}, the angle between the IMF vector projected to the X-Z meridian and the Earth dipole axis. The normalized potential F for the northern hemisphere is the largest when {phi}{sub h}{sup *}, measured from the northern dipole axis toward the Sun, is negative and large ({approximately}{minus}100{degrees}), and decreases as {phi}{sub h}{sup *} approaches zero and turns positive. An approximate equation for this relation is F({phi}{sub h}{sup *})=a+b/({phi}{sub h}{sup *}+125{degrees}), where the values for a and b lie between 0.0086 and 0.015 and between 1.6 and 1.9, respectively. This relation can be interpreted in terms of a model of magnetosheath field line motion which predicts that the reconnection belt on the magnetopause poleward of the cusp becomes longer as the magnetosheath field lines tilt toward the tail lobe. 19 refs., 9 figs., 1 tab.

• OSTI ID: 227134
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A10 Vol. 100; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ELECTRIC POTENTIAL
INTERPLANETARY MAGNETIC FIELDS
IONOSPHERE
PARAMETRIC ANALYSIS
POLAR REGIONS
SOLAR WIND