TABLE OF CONTENTS
The Space Physics Group (SPG) studies the chain of energy transport from the surface of the sun to eventual arrival in planetary stratospheres. It is using interplanetary measurements to investigate the structure of coronal mass ejections and their evolution in space. It is using Galileo observations to understand energy and mass transport in the jovian magnetosphere. It is using Polar observations in the high altitude magnetosphere to understand how the solar wind couples to the Earth's magnetosphere. It is using measurements from the FAST mission to determine how the magnetosphere couples to the ionosphere. It is studying magnetic pulsations both to determine their origin and to use them as diagnoses of the state of the magnetosphere and it is using numerical simulations both as an extrapolation of localized data and as a tool to investigate magnetospheric behavior. It also uses the data from the FORTE and Alexis missions to study terrestrial lightning. The Space Physics Group also plays a vital role in the community in disseminating the observations from space missions, maintaining communications within the field, educating students of space physics through textbooks and software, interacting with visitors and training students. In the sections below we discuss the achievements of the SPG over the period July 1997 to July 1998 in the areas of instrumentation, research, dissemination of data, communication, education, visiting scientists and students.
The SPG has developed an inexpensive, high precision and accurately timed magnetometer for terrestrial ground based studies. These magnetometers have been deployed in four different "arrays". The first array is the Sino Magnetic Array at Low Latitudes that will ultimately consist of 16 or more magnetometers in a 2-D array across China. In the last year six more (for a total of eight) magnetometers were sent to China as the first segment of that array. The second array is a chain of seven magnetometers that are being installed by M. Moldwin along the eastern seaboard of the U.S. in the MEASURE array. Six of the seven magnetometers have been delivered for these sites. The seventh magnetometer awaits a decision as to whether it will be installed. The third array is the IGPP/LANL array that is intended to ultimately cover the western U.S. At present there are five operating stations in San Gabriel, CA; Los Alamos, NM; the Air Force Academy; Colorado Springs, CO; Boulder, CO; and outside New Orleans, LA. The latter site has a less sensitive magnetometer that will be replaced later. Finally there is a loose-knit global array with sites in Jicamarca, Peru; Mexico City, Mexico; and Crete, Greece. Most of these magnetometers were switched on for the first time in 1997/98 and some have not yet been installed at their final sites. Thus only preliminary science results are available at present.
We have built an analog magnetometer for the Brazilian microsatellite SACI-1 that is scheduled for launch on a Long March rocket in 1999. The Brazilian principal investigator Nalin Trivedi has taken care of the analog to digital conversion and the testing and integration of the investigation. The orbit for SACI-1 will be circular polar at an altitude of about 800 km.
The Australian government is planning to launch a microsatellite to celebrate their 100th anniversary and to demonstrate their scientific and technical prowess. Brian Fraser, the principal investigator for the magnetometer has approached us for assistance with this project. The mission will be launched into an 800 km orbit as well.
The availability of magnetometer data from the NEAR mission on its way to the asteroid 433 Eros has permitted us to study the structure and evolution of interplanetary coronal mass ejections. These structures are the evolutionary products of the expulsion of massive ejections of magnetized plasma from the corona. We find that the magnetic structure varies on a scale size of about 10o in longitude but simultaneous events can be seen over angular separations of over 30o. Thus these eruptions on the sun must have a global component that exceeds that of the magnetic scale of the features seen at 1 AU. We also have found evidence for both expansion of the features as they propagate radially and decelerations in the radial velocity.
The Space Physics Group is presently involved in two planetary magnetospheric missions: Galileo that has been in orbit about Jupiter since December 1995 and Cassini on its way to Saturn for an arrival in 2004. The NEAR mission, with which we are also involved, will attempt to determine if the asteroid 433 Eros has an intrinsic magnetic field, but a strong magnetic field capable of producing a magnetosphere is not expected to be present. The activities associated with the Cassini and NEAR missions consisted principally of software development and mission planning. The Galileo activities, however, resulted in major increases in our understanding of the jovian magnetosphere. In a series of papers we were able to show that the mass addition of Io leads to a radial outward flow of plasma that moves slowly outward at first but then accelerates as it moves outward. Signatures seen near Europa indicate that the flow is moving at close to 500 m/s there. At about 25 jovian radii this has increased to about 10 km/s and at 50 radii about 50 km/s. The plasma then flows down the magnetotail but does not take the magnetic flux with it because reconnection takes place episodically. These reconnection events create magnetic islands that transport no net magnetic flux but do transport ions. The ions on these islands are lost from the tail of the magnetosphere and the emptied magnetic flux tubes return to the inner magnetosphere. They appear to move inward because they are buoyant, being empty, and centrifugal force pulls the heavier full flux tubes outward. These empty flux tubes appear also to be small and to move inward relatively rapidly.
The study of the terrestrial magnetosphere is centered principally around the POLAR mission with some retrospective studies of ISEE measurements. On POLAR we have concentrated on understanding the formation of the polar cusp and how the polar cusp is controlled by the conditions in the solar wind. This region forms in the vicinity of the bifurcation of the magnetic field where field lines go either toward the nose or toward the tail of the magnetosphere. We find that we can explain the observed behavior of the cusp in terms of a variable location of the reconnection site. When the interplanetary magnetic field is due southward it reconnects with the terrestrial magnetic field near the subsolar point. When it is northward it reconnects at high latitudes behind the cusp region. When the IMF is at an intermediate direction the reconnection site moves off the noon midnight meridian and is found at an intermediate latitude as well. These results explain both the behavior seen at the POLAR spacecraft at high altitudes and that seen at low altitudes by other spacecraft.
Using Polar data, we have also examined effects of the equatorial ring current and the magnetopause current in the magnetic field observations in the low-altitude polar magnetosphere. The magnetic field in the region of the low altitude magnetosphere is dominated by the Earth's internal field. The average magnetic field strength due to external sources (the residual of the observed magnetic field strength minus that from the newest IGRF 95 internal field model) is typically a few tens of nT, or a few tenths of one percent of the total magnetic field over the polar cap at the altitude of the POLAR spacecraft. We have demonstrated that the magnetic field associated with the ring current can explain totally the residual of the field strength observed in the low-altitude polar region. Thus, measurements from low-altitude polar orbiting spacecraft are potentially useful as monitors of the ring current and Dst index when they cross the polar cap.
Our study of magnetosphere using data from ISEE mission is centered on the understanding of internal structure of flux transfer events at the magnetopause. We have studied the interior structure of flux transfer events by examining high resolution magnetic field and plasma distribution functions from the ISEE spacecraft. The sampling time and cadence of these data are more than adequate to resolve the rapidly changing plasma regimes and to avoid spatial aliasing. We have confirmed the existence of two distinct regions within an FTE: a central core and a field draping region; and these two regions have been found within FTEs observed both on the magnetosheath side and the magnetospheric side of the magnetopause. The boundaries between the two regions are apparent in both the field and the plasma data. The plasma signatures within FTEs unambiguously show the reconnection of the interplanetary magnetic field and the Earth s magnetic field and indicate that the magnetic field lines within the central core region are open allowing the inflow of cold magnetosheath plasma and the outflow of hot magnetospheric plasma through the open flux tube. The reconnection picture is further supported by the observation of separate electron and ion edges at the trailing boundary of a northward moving flux tube, expected as time-of-flight effects on newly reconnected field lines. Thus, our observations are consistent with the reconnected open flux tube interpretation for FTEs.
The Space Physics Group has continued to analyze the particles and fields data from the Fast Auroral Snapshot (FAST) Explorer. Our research efforts have encompassed two quite diverse topics. The first is the investigation of the stresses applied to the polar ionosphere, as evidenced by the deviations in the Earth's magnetic field. These "delta-B's" indicate, for example, where reconnection at the Earth's magnetopause and the tailward transport of high latitude field lines cause the polar cap field-lines to also bend tailward. The second topic under investigation is the generation of Auroral Kilometric Radiation (AKR). We have shown that AKR is generated in deep density cavities, where the energetic electrons dominate the wave dispersion. Furthermore, the effect of the acceleration by parallel electric fields and the magnetic mirror force results in a "horseshoe"-shaped electron distribution, which can generate AKR quite efficiently.
Research on magnetic pulsations emphasizes two major directions. The first is to examine the spatial and temporal structure of the pulsations in the magnetosphere by using the data from ground magnetometer arrays. This is also one of the major scientific objectives for the establishment of a ground station network as described in the "Instrumentation" section. The cross-phase technique that has become popular in recent years using the data from multiple stations on the same magnetic meridian will be used to estimate the plasma density in the magnetosphere. However, we find that the cross-phase spectrum in literature was incorrectly interpreted by a model of two simple harmonic oscillators, and the correct interpretation should be the field line resonance theory modified by the ionospheric effects. The second direction is to understand the transport of pulsation energy in the magnetosphere from spacecraft observations. By using ISEE-1 observations, we find that the continuous pulsations (Pc) are in fact maintained by a series of pulses. Between the pulses we usually find a phase skip in the wave signals. Nevertheless, the propagation path of pulsations in the magnetosphere is still an open question. We are using the Polar data to investigate the high-latitude regions where there were very few spacecraft measurements. The initial results suggest that the cusp is not as important a conduit of Pc 3-4 wave energy as people expected.
Global simulations of Earth's magnetosphere and ionosphere are used to investigate basic magnetospheric processes, to supplement experimental studies, and to investigate the feasibility of magnetospheric multiprobe missions. Of particular interest are our studies of the development of the substorm current wedge and the magnetospheric topology under northward IMF conditions. For the latter case we found that previous global model predictions of a closing magnetosphere for northward IMF may be wrong due to numerical diffusion in the codes. Joint experimental-simulation studies center around Interball observations in the tail flanks and the GEM substorm challenge which we helped formulate. We are also active in the GEM GGCM (Global Geospace Circulation Model) phase 1 effort and are the first modeling group to offer access to global modeling results over the Web.
In collaboration with scientists at the Los Alamos National Laboratory the Space Physics Group has continued to analyze radio frequency (RF) signals observed by the ALEXIS spacecraft. The signals, known as Trans-Ionospheric Pulse Pairs (TIPPs), were originally thought to be generated by lightning. Our work has shown that TIPPs are generated by a specific type of lighting: intracloud lightning. Furthermore, TIPPs have the same general diurnal and geographic variation as lightning, although TIPPs appear to occur later in the day than normal lightning. We have also shown that TIPPs occur in pairs because of reflection from the ground, rather than being an intrinsically double-pulsed phenomenon. We have begun a follow-on investigation of TIPPs and other RF signatures of lightning using the FORTE spacecraft.
Due to our long involvement in Space Physics research, we have built a tremendous data base of measurements of the solar terrestrial system. As part of NSF's Global Environmental Measurement program and later in cooperation with the Space Physics Data System, we set up systems for the dissemination of those data to the community. We originally set up an on-line data base of IMP-8 data. We then developed a web-based distribution system for this effort. Now we have added POLAR magnetometer data to this system, and now provide on-line access to the ground-based magnetometer data obtained during the IMS (1977+) to the ISEE1 and 2 magnetometer data.
The Space Physics Group has taken the lead in fostering communication in the discipline as part of the NSF's Global Environment Modeling (GEM) program as well as for the American Geophysical Union's (AGU) Space Physics and Aeronomy section. Guan Le serves as editor for the electronic and hard copy newsletters, the GEM Messenger and the GEMstone. These appear about once a month and semiannually respectively. Guan Le also serves as the editor of AGU/SPA's electronic newsletter, SPA News, which appears twice a week on average. She has been the editor of the SPA web pages that provide access to information on meetings, publications and links to other members of the community. This year, Bob Strangeway was appointed the SPA editor for AGU's weekly newspaper EOS.
There are four major developments in education from the Space Physics Group. First there is its development of the interactive Space Physics educational software, also known as Xspace. We continue to update and distribute this package. Some of the exercises have been converted to JAVA and can now be used over the internet. Second, we continue to participate in the International Space Physics Education Consortium that is fostering and coordinating computer-based instruction in Space Physics. Third, C. T. Russell is the Director of UCLA's branch of the California Space Grant activities. Fourth, the book Introduction to Space Physics, edited by M. G. Kivelson and C. T. Russell continues to sell well. In fact, it is now in its third printing.
Hideaki (Hedi) Kawano finished his extended stay with our group in January 1998 to take up an assistant professorship in Kyushu University in Fukuoka Japan. Michael Gedalin from Ben Gurion University visited us for a two week period to continue his studies of the bow shock. Xochitl Blanco-Cano from UNAM visited for three two-week intervals as part of her joint UCMEXUS research effort with C. T. Russell to study the generation of ULF waves both in the solar wind and at Jupiter. Oleg Vaisberg visited twice to continue his studies of reconnection at the magnetopause. Other visitors for shorter periods included Vassilis Angelopoulos from U.C. Berkeley, Nalin Trivedi from INPE in Brazil, N. Tsyganeako from Goddard, Brian Fraser from Newcastle University in Australia, Uli Auster from the TUB in Germany and Hector Perez-de-Tejada from UNAM.
During the period 1997/98 there were five continuing PhD students: F. Kostantinidis, T. Mulligan, J. Newbury, X. M. Zhou and R. S. Zuelsdorf. One student, P. J. Chi, successfully completed his requirements for the PhD.
The SPG staff consists of students, engineering staff, programmers, computer operators and student assistants, clerical help and researchers. The researchers and graduate students have been listed above. The other staff members are as follows:
C. T. Russell and D. E. Huddleston, The interaction of Io with the Jovian magnetosphere, presented at the 8th Scientific Assembly of IAGA, Uppsala, Sweden, August 1997.
C. T. Russell, X-W. Zhou, G. Le, S. Fuselier, J. D. Scudder, F. Fenrich and J. G. Luhmann, The structure of the Polar cusp, presented at Fall AGU meeting (abstract) Eos. Trans. AGU, 78(46), Fall Meeting Suppl., F585, 1997.
R. E. Ergun, C. W. Carlson, J. P. McFadden, G. T. Delory and R. J. Strangeway, FAST Satellite Observations in the AKR Source Region, Eos. Trans. AGU, 79(45), Supplement, F700, American Geophysical Union Fall Meeting, San Francisco, 1998.
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