SM32C-04 1415h

The Generalized Walen Tests througout the May 4, 1998 Magnetopause Traverses

Jack D. Scudder1 (319-335-0804; jds@hydra.physics.uiowa.edu)
Pamela Puhl-Quinn1
Forrest S. Mozer2
John Wygant3
Christopher T. Russell4

1 University of Iowa, Jefferson at Dubuque St., Iowa City, IA 52242, United States

2 UC Berkeley, Centennial Dr. at Grizzly Peak Blvd., Berkeley, CA 94720, United States

3 University of Minnesota, Minneapolis, MN, United States

4 UCLA, IGPP, Los Angeles, CA, United States

The recently developed Generalized Walen tests (Scudder et al., 1999) are applied at the suite of directional discontinuities encountered during the strong compressions of the magnetosphere on May 4, 1998. In this complicated ensemble of events, the sense of matter flux in the frame of these directional changes is uniquely signaled by successful Generalized Walen tests performed with electron flow velocity measurements. These directions show a complicated set of alternations that will be discussed in conjunction with other spectral and moment indicators of plasma regime. The success of these tests forms a framework for suggesting that the various Hydra electron detectors are sufficiently balanced and intercalibrated to determine the vectorial correlation of flow velocity with the magnetic field and its correlation coefficient, consistent with the Hall MHD picture of the current carrying layer. When the bow shock swept over the spacecraft into the solar wind the electron flow velocity compares favorably with other known samples of its size as in for example, the three axis electric and magnetic field measurements. Noting that neither E nor the flow velocity are interchangeable, the comparison of flow velocities transverse to the magnetic field is favorable. The highly compressed magnetosheath and the high beta of the plasma adjoining the magnetopause significantly increase the difficulty of accurate electron flow measurements in this regime relative to the cooler examples of May 29, 1996. Nevertheless a large number of crossing are certified as meeting the Generalized Walen condition, indicative of an "open" magnetopause being traversed. A subset of the Walen certified structures would be more consistent with Alfven surface waves, having transverse magnetic signatures that are small compared to the mean field. The constraints on the magnetohydrodynamic regimes by the remaining Walen tests that accompany small components of B normal to the magnetopause will be discussed.