TABLE OF CONTENTS

THE GALILEO MISSION

The Galileo mission placed a well-instrumented spacecraft into orbit around Jupiter for the first time ever. The science objective of the Galileo orbiter is to investigate and monitor the space environment of Jupiter, its atmosphere, its magnetosphere, and its satellites. Prior to the start of primary data acquisition at Jupiter (orbit insertion was on December 7, 1995), the Galileo spacecraft returned a wealth of data from Venus, the Earth and the asteroids Gaspra and Ida. Magnetic field rotations were observed at both Gaspra and Ida were interpreted as an interaction between the solar wind and the asteroids. In attempts to understand the asteroid data, M. Kivelson and Zhi Wang analyzed how a plasma interacts with a body whose dimensions are small compared with the ion gyroradius using both theory and computer simulations. The interesting features is that perturbations cannot be understood from the usual magnetized fluid (MHD) model that describes the interactions of the solar wind with planets. The actual interactions are mediated by whistler mode waves which propagate close to the direction of the background magnetic field. This changes greatly both the spatial form of the disturbed region that surrounds the body and the nature of the disturbance. Two preliminary papers on this work appeared in Advances in Space Research. In one, the theory was examined. In the second, the argument was made that the signature at Gaspra was most likely caused by the interaction between the solar wind and a magnetized asteroid. The situation at Ida is more complex and the team is not yet certain whether a magnetized Ida is the most probable explanation. A more complete report on this work including various new simulations developed by Dr. Z. Wang was published in the Journal of Geophysical Research. References to all papers mentioned are given in the bibliography of Galileo Magnetometer Results From Jupiter's Magnetosphere.

The data from the Earth flybys have proved rich in interesting scientific phenomena. M. Kivelson,. K. Khurana, and R. Walker used the remarkably complete data taken as the spacecraft encountered two highly twisted magnetic structures referred to as flux ropes to obtain insight into the properties of these structures that are ubiquitous in space plasmas. Initially, the data were analyzed and reported. Then a mathematical model that describes not only the flux rope but also the plasma and field in which it is embedded was developed and found to add insight into the significance of the observations. These works are published in the Journal of Geophysical Research and in Geophysical Research Letters. Signatures of flux ropes can be related to flux ropes found in an MHD simulation. This work is a first attempt to understand the global structure and remote current patterns produced by these twisted fields. This work has been reported at meetings and submitted for publication.

Using data from the second Galileo flyby of Earth, the team reported on observation of the Earth's bow shock at unexpectedly large downtail distances. The work was initated by Khurana and Kivelson working with a visiting student, A. Prevost from Orsay University near Paris and continued by L. Bennett. A report was published in the Journal of Geophysical Research.

THE CLUSTER MISSION

The Cluster mission is an ESA (the European Space Agency) mission co-sponsored by NASA. The purpose is to place four spacecraft into closely-coordinated orbits about the Earth. Members of this Group (Kivelson, Khurana, and Kepko) are associated with the Cluster FGM magnetometer team (P.I. Andre Balogh of Imperial College, London) which includes representatives of seven countries from ten different institutions. The Group at UCLA developed techniques for intercalibrating the magnetometer instruments on the different spacecraft. Assuring that measurements from independent instruments on different spacecraft are highly accurate is central to the success of the mission which will provide direct measurements of physically significant vector gradients for the first time. Errors in the vector magnetic field that are considered negligibly small for a single spacecraft measurement yield spurious signatures of electrical currents comparable with those of physical importance. Innovative solutions to the intercalibration problem, which also led to development of an extremely efficient approach to the calibration of individual magnetometer instruments, have been submitted for publication. The team has begun new efforts directed to developing purpose-built tools for the analysis of data from several closely-spaced spacecraft. The launch orignally planned for late 1995, was postponed to late 1996 dues to delays in the development of Ariane 5 launch vehicle. Problems with the guidance system of the Ariane 5 resulted in the catastrophic destruction of all four spacecraft. Fortunately ESA/NASA will sponsor a Cluster II mission with a launch to occur in the next millenium. The UCLA group expects to participate in the data analysis.

THE POLAR MISSION

The Polar spacecraft was launched in January 1996 into a near polar orbit at high altitudes. The direct involvement of this group is with the energetic particle investigation (CEPPAD) on which Margaret Kivelson is a Co-I. Particular attention is being be directed to correlations of energetic particles and fluctuating magnetic fields (wave-particle interactions) which we are critical to some energy transport processes in the magnetosphere.

MHD SIMULATIONS

Dr. Walker, working with Dr. T. Ogino of Nagoya University, has used a global magnetohydrodynamic (MHD) model to study the response of the magnetosphere to an interplanetary magnetic field (IMF) with ßz <0 and ßy not equal to 0 in order to study the origin and evolution of magnetic flux ropes in the magnetotail. The southward IMF leads to dayside magnetic reconnection followed by reconnection on closed plasma sheet field lines. in a simulation run initiated with no IMF ßy the plasma sheet, tail reconnection led to the formation of a plasmoid with a quasi-two dimensional closed magnetic loop structure when the effects of a dawnward-oriented IMF ßy reached the equatorial region of the plasma sheet, the quasi-two dimensional plasmoid became a magnetic flux rope that extended from the southern dusk ionosphere across the plasma sheet and closed in the northern dawn ionosphere. In a simulation initiated with effects of IMF ßy not equal to 0 present in the plasma sheet, the reconnection immediately led to the formation of a flux rope structure. flux ropes in the magnetotail contain both closed, open and imf field lines. The open and IMF field lines in the flux rope become attached to the IMF when closed field lines in the flux rope reconnect with imf field lines at the flank magnetopause. Flux ropes can move tailward before all of the closed field lines have reconnected. this is primarily caused by the tension on IMF field lines which drape over the flux rope when tail lobe field lines reconnect. In the simulation, closed flux rope lines are found more than 60 Re down the tail. A paper appeareed in the Journal of Geomagnetism and Geoelectricity. Visiting student M. Stellmacher examined the effects of using difference equations to model the coupling between compressional and fast mode waves in a dipole magnetosphere. Noting that the simulation leads to periodic transfer of energy density from resonant localized perturbations to compressional power throughout the cavity on a time scale related to the discrete steps in resonant frequency near the resonant field lines, he confirmed that the mechanism of this coupling which would not be a feature of a fully continuous model.

THEORY & PHENOMENOLOGICAL MODELING

Theoretical activities have in recent years included a reconciliation of two apparently different theories that explained how the magnetosheath plasma adjusts to magnetopause boundary conditions and work on wave-particle interactions. Southwood and Kivelson demonstrated that the low density "depletion layer" that forms upstream of the dayside magnetopause when magnetic reconnection is not occurring nearby and the high density perturbations that appear a bit further upstream of the dayside magnetopause are both necessary to achieve the required boundry conditions at the magnetopause.

Kivelson and Southwood treated the non-linear mirror mode in a qualitative theory that accounts for the observed features of saturated mirror mode structures in space plasmas. Papers appeared in the Journal of Geophysical Research. They have also explained how ultra-low frequency standing waves in the earth's magnetospheric plasma can oscillate at particular frequency while also producing changes of field magnitude at twice the frequency (Journal of Geophysical Research).

DATA ACTIVITIES 1994 - 1995

Nine years ago NASA selected the Planetary Plasma Interactions (PPI) Node in IGPP to help the scientific community locate, access and preserve particles and fields data from planetary missions. nce planetary plasma data are varied and require expertise in many areas the PPI Node is distributed with an Outer Planets Subnode at the University of Iowa, a Radio Science Subnode at the Stanford University and an Inner Planets Subnode at UCLA. Dr. Walker heads the PPI Node while Professor Russell leads the Inner Planets Subnode. The PPI Node has worked with missions and individual scientists to secure the highest quality data possible and to thoroughly document it. They validate the data, place it on long lasting media and make certain it is properly archived for future use. As of October 1995, they have prepared over 2x10e11 bytes of data and have produced 219 CD-ROMs with peer reviewed data. During 1994 requests for approximately 1 terrabyte of data have been filled. In January 1995, NASA selected the PPI node at UCLA for a second five year funding period. The PPI team includes T. King, (Lead Programmer Analyst), E. Fried (Programmer Analyst), and J. Mafi (Data Processor). S. Joy is the Operations Manager of the PPI Node. Dr. Walker continues to serve as PDS Project Scientist.

The PPI Node was challenged to provide data access to users in a form which was independent of computer, operating system, data type and data format. They conceived an approach for managing data inventories called DITDOS (Distributed Inventory Tracking and Data Ordering Specifications). The system using DITDOS to manage planetary data is scalable so that the same software which is used to manage and access the data from the entire PPI Node can be used by individual investigators to manage the data on a single CDROM thereby greatly reducing the software development effort for both the PPI Node and users. DITDOS was conceived and developed by T. King and colleagues. A paper on the PPI node of PDS and the DITDOS approach has been accepted for publication in Planetary and Space Science.

NASA's most recent data effort is the Space Physics Data System (SPDS). It has been charged with preserving space physics data and providing space physicists with access to it. Professor R. McPherron has been chosen to head the SPDS which is starting a program to restore data which is in danger of being lost. Dr. Walker serves as a member of the SPDS Management Council.

Last Update: July 23, 1998