I. Non-Thermal Continuum Confinement to Low Latitudes

Green, J. L., S. A. Boardsen, and S. F. Fung, Confinement of non-thermal continuum radiation to low latitudes submitted to Geophys. Res. Letts., September, 1996.

Four years of Hawkeye plasma wave observations at 31.1 kHz were combined to form a plasma wave intensity map of the non-thermal continuum radiation. From the resulting wave image the source region for the non-thermal continuum radiation is located outside the plasmasphere in the dawn local time region. The continuum radiation emanating from the identified source region is clearly beamed in the outward direction. The ray tracing calculations model the observed angular distribution of the non-thermal continuum radiation and illustrate the importance of the near equatorial region as the location where trapped continuum radiation is preferentially seen. The Hawkeye observations presented and supported by the ray tracing analysis clearly demonstrates that the non-thermal continuum radiation has a distinct angular distribution where the source region is observed at low latitudes on the morning side of the magnetosphere, and that the resultant radiation pattern is such that it does not completely fill the magnetospheric cavity as previously believed.

II. High Latitude Reconnection Discovered

Kessel, R. L., S.-H. Chen, J. L. Green, S. F. Fung, S. Boardsen, L. Tan, T. Eastman, J. Craven, and L. A. Frank, Evidence of high-latitude reconnection during northward IMF: Hawkeye observations, Geophys. Res. Letts., 23 5, 583-586, 1996.

Reconnection is accepted as an important process for driving the solar wind/magnetospheric interaction although it is not fully understood. In particular, reconnection for northward interplanetary magnetic field (IMF) at high-latitudes tailward of the cusp, has received little attention in comparison with equatorial reconnection for southward IMF. Using Hawkeye data we present the first direct observations of reconnection at the high-latitude magnetopause (75 deg) during northward IMF in the form of sunward flowing protons. This flow is nearly field aligned, approximately Alfvenic, and roughly obeys tangential momentum balance. The magnetic field shear is large at the magnetopause and there is a non-zero Bn component suggesting the existence of a rotational discontinuity and reconnection. The Hawkeye observations support several recent simulations at least qualitatively in terms of flow directions expected for high-latitude reconnection during northward IMF. Even though its data are nearly two decades old, Hawkeye clearly remains a key data source for high-latitude magnetosphere observations.

III. Exterior and Interior Polar Cusps

Chen, S.-H., S. A. Boardsen, S. F. Fung, J. L. Green, R. L. Kessel, L. C. Tan, T. E. Eastman, and J. D. Craven, The exterior and interior polar cusps: Observations from Hawkeye, J. Geophys. Res., in press, March, 1997.

Hawkeye plasma, magnetic field, and plasma wave instruments directly sampled the throat of the northern polar cusp as the orientation of the interplanetary magnetic field (IMF) changed from southward to northward on July 3, 1974. Two distinct regions in the polar cusp were identified based on magnetic field, plasma flow and magnetic and electric noise: the interior and exterior cusps. The observations show highly variable flows in the exterior portion of the cusp and constantly strong dawn-dusk flows in the interior portion during periods of strong IMF By component. Results of a minimum variance analysis of the magnetic field at each cusp interface crossing provides evidence that the magnetopause surface normal deviated highly from empirical models. During intervals of relatively steady solar wind dynamic pressure, the motion of the cusp relative to the slow moving spacecraft was modulated by the varying IMF clock angle as observed by IMP 8 in the upstream solar wind. The motion did not show a correlation with internal processes monitored by the AE index. We propose that observed plasma flow patterns and cusp motion are results of reconnection between the IMF and the magnetospheric magnetic field. Flow velocity observed in the interior cusp is consistent with stress balance for a reconnection process. This unique interval provides an opportunity for detailed studies of the plasma, magnetic field, and plasma wave properties in both the exterior and interior cusp.

James L. Green,

Last updated on December 27, 1996 by Sean Chen