Bow Shock, Magnetopause, and Cusp II Posters
Presiding: D Sibeck, NASA Goddard Space Flight Center; Q Zong, Boston University
SM23A-01 1330h
Multiple Cusps Observed by Cluster and DMSP Spacecraft
On March 21- 22, 2001, four cusp-like regions were observed consecutively in about five and half hours by all four Cluster Spacecraft when interplanetary magnetic field (IMF) is northward with a significant By component. The multiple cusps were surrounded by the dayside magnetosphere rather than the magnetopause. Observational evidence showed that the observed multiple cusps were probably a temporal sequence. The boundary normal, velocity and timing analysis for six clear boundaries of the cusps obtained by all four spacecraft indicate that the observed cusps oscillated back and forth. The Cluster spacecraft were oscillating between the dayside magnetosphere and the cusp region. The normal velocities vn at boundary interfaces (exit from the cusp) are found to be almost three times as larger as that at boundary interfaces (entry into the cusp). There exists clear interfaces between the cusp and the dayside magnetosphere during northward IMF instead of a turbulent entry layer as proposed by Hhaerende. The observations made in this paper suggest the shape and location of the cusp may rarely be static but is often changing as a result of dynamic processes in the high latitude regions.
SM23A-02 1330h
Interball-1 Observations of Mantle FTEs
We present the results of a survey of Interball-1 magnetometer observations of flux transfer events on the high latitude dayside magnetopause during the period from launch in 1995 through 1999. Interball-1s highly elliptical orbit had an apogee of 31.4 RE, inclination of 62.8°, and period of 92 hours. We use a merged file of MIF-M and FM-3I magnetometer observations with 6s time resolution to identify transient events marked by bipolar magnetic field signatures normal to the nominal magnetopause and compressions in the total magnetic field strength. Consistent with past work, direct events predominate north of the geomagnetic equatoer, while reverse events predominate south of the equator. However, signatures with the opposite sense are sometimes observed in both the high-latitude magnetosheath and magnetosphere. Our survey reveals that such events invariably occur poleward of the cusps. Simultaneous observations by Wind, IMP-8, and Geotail indicate that the events can occur for a variety of IMF orientations, including strongly northward. Taken together, the observations indicate that bursty merging on the high-latitude magnetopause generates the events observed poleward of the cusps.
SM23A-03 1330h
Structure of Cusp Diamagnetic Cavities
While in the cusp region, POLAR regularly observes large (up to 6 RE) cavities characterized by depressed magnetic field and increased plasma pressure. The frequent occurance and apparent stability of these structures implies a pressure balance between the plasma inside and the field outside. We investigate this balance, using pressures derived from the HYDRA and MFE instruments and composition information from CAMMICE MICS, for multiple crossings of the cusp. Our results suggest that small-scale physics drives the structure of these regions.
SM23A-04 1330h
Source-Surface Approach to Modeling an Arbitrarily Shaped Magnetopause
The source surface method is used to compute the Chapman-Ferraro currents for an arbitrarily shaped magnetopause confining a number of large-scale current systems. The model caclulates the magnetic field within the specified boundary from a scalar potential expanded in a set of general basis functions. The normal component of the total magnetic field due to all current systems within the source surface is minimized by the least squares method. This method proves to be a flexible approach to handle irregular magnetopause shapes, such as those that may be produced under extreme solar wind driving conditions.