TABLE OF CONTENTS
The activities of the space physics group are divided into three principal areas of focus: scientific research, scientific programming and space flight instrumentation and is supervised by Professor C. T. Russell. A major part of the activity of the space physics group involves studies of the energy flow from the sun through the solar wind and into the terrestrial and planetary magnetospheres, both induced and intrinsic, and how this energy is dissipated within these magnetospheres. In the paragraphs below we summarize briefly the activity of the group in these areas over the last year.
In the modern paradigm of solar activity it is the coronal mass ejection that is both the source of solar activity and the driver of the largest geomagnetic disturbances. Janet Luhmann and graduate student Gretchen Lindsay have been studying the occurrence of coronal mass ejections and their effect of the solar wind. As part of their initial studies they have shown that CME's cause the majority of interplanetary shocks. Presently, Gretchen Lindsay is examining the geoeffectiveness of coronal mass ejections and stream-stream interactions. She is characterizing coronal mass ejections seen on the sun and later observed at Venus and Helios at right angles to the line of sight and she is using multispacecraft observations of CME to constrain their possible geometry. Debbie Huddleston has undertaken a study with Richard Woo of JPL to compare Doppler scintillation measurements with in-situ ISEE-3 observations and confirm the detection of broadened coronal streamers at 1 AU. The ISEE-3 results find that density fluctuation amplitudes do not scale exactly with the density, and therefore while enhanced scintillation is a useful detector of solar wind transients, it does not necessarily impy an equivalently enhanced density.
Before the solar wind interacts with the magnetosphere it passes through and is modified by the bow shock. Thus it is important to understand the process that occur in the bow shock and just upstream of it. Perhaps the most significant research in this area was the testing of the two fluid MHD theory originally developed by Stringer (1963) and later extended to high beta plasmas by Formisano and Kennel (1969). Much to the surprise of the two-fluid MHD community, graduate student Darius Orlowski working with Prof. Russell conclusively showed, by comparing both kinetic theory and MHD theory with observations of upstream waves, that the two fluid MHD theory was inappropriate for moderate and high beta applications. This same result was later found in a study of the magnetopause by D. Walthour of Dartmouth working with Prof. Russell. In other studies Darius Orlowski showed that the source of upstream whistlers at Venus was the bow shock and that two types of upstream particles were needed to explain upstream wave properties of Saturn. These particles were the specularly reflected particles and the leakage particles. In later work he examined the propagation and damping of upstream whistlers generated by the shock, answering conclusively that the source of these waves was indeed the shock front and not an instability of the upstream region. Joint work with T. Zhang of the Austrian Space Research Institute showed that the upstream plasma was decelerated in the region of upstream waves in front of the bow shock. Finally, Guan Le returned to studies of the wave frequency of upstream waves to examine what factors control this frequency.
At the bow shock itself an important first observation was made, the first switch-on shock, in which a tangential magnetic field suddenly appears with little or no tangential magnetic field upstream. This phenomenon occurs only for low Mach numbers at quasi-parallel shocks and had been predicted theoretically but never observed. Additionally, Michael Farris as part of his dissertation research under Prof. Russell completely characterized the magnetic structure of the low beta shock for all directions of the upstream magnetic field. Finally, and perhaps very surprisingly, despite 30 years of study there has been no model for the location of the bow shock under low Mach number conditions. In studies of Pioneer Venus data T. Zhang and C. T. Russell found that the shock moved far away from the planet at low Mach numbers. This is important because some researchers had been using distant bow shock crossings to infer that Mars had an intrinsic magnetic field. This study, in turn, inspired Michael Farris to develop a model for the location of the low Mach number bow shock. Graduate student, Jennifer Newbury, began a study of shock structure at higher Mach numbers and discovered a very thin shock with thickness of the order of the electron inertial length.
Downstream from the bow shock, the present hot topic is the identification of wave modes. Paul Song of HAO, working with C. T. Russell, has developed an "automatic" identification scheme using field and plasma cross-correlations and spectral comparisons. This model will enable us to better probe the physical processes occurring in this complex region. Closer to the magnetopause S. M. Petrinec as part of his dissertation research under Prof. C. T. Russell developed a model of the shape and size of both the dayside and nightside magnetopause. The development of the nightside model used an innovative approach in which the magnetopause position could be calculated without the spacecraft having to cross it. These studies are important because they illustrate that earlier models had serious flaws in both their pressure and magnetic field dependencies. Most importantly in the Earth's magnetosphere there seems to be no flux transfer from the dayside to the nightside of the magnetosphere when the IMF is northward. These results were reaffirmed in an independent study by visiting scientists Jih-Hong Shue and Jerry Chao working with C. T. Russell.
Reconnection of the magnetosheath and magnetospheric magnetic fields is now an accepted part of the solar wind coupling process but its form and effects are not fully understood. One of the controversial aspects of reconnection is its role in the formation of the phenomenon known as a flux transfer event. D. Walthour working with C. T. Russell showed that flux transfer events have the appearance of a long flux tube pressed into the boundary. Graduate student, Han Kuo examined the factors that control the occurrence rate of these events but principally reaffirmed the importance o the direction of the IMF in their origin. Paul Song together with C. T. Russell established the reasons why the phenomenology of flux transfer events were consistent with such a model and not with surface waves. Just inside the magnetopause boundary is the low latitude boundary layer. Paul Song, Zhi Wang and C. T. Russell have developed a reconnection-based model of the formation of this boundary layer. Even though this layer was originally thought to be a diffusion related feature, it now appears that reconnection at high latitudes is responsible. In two observational studies Guan Le confirmed the correctness of the northward reconnection model and add some refinements. In a separate study she examined the role of the ratio of thermal to magnetic pressure in determining the thickness of the magnetopause.
The currents on the magnetopause affect the field everywhere in the magnetosphere, including on the surface of the Earth. When the solar wind dynamic pressure suddenly increases the magnetic field strength on the surface of the Earth does too. Mary Ginskey and C. T. Russell have shown that when the interplanetary magnetic field is northward the change in field strength on the surface of the Earth is what is classically expected on the dayside but somewhat reduced at night. When the IMF is southward additional currents flow and the response is reduced on the dayside. At higher (subauroral) latitudes the response becomes even more complex responding to the overall compression of the magnetosphere waves propagating through the magnetosphere, the beading of the magnetopause and reconnection currents. Finally, Peter Chi as part of his dissertation research showed that pc 3,4 waves had little coherence across the magnetosphere even though they clearly showed evidence of a source in the solar wind. On the other hand, the amplitude envelope of these waves shows they are a global phenomenon that propagates through the system.
The Earth's tail is a vast energy reservoir for geomagnetic activity, and much of current magnetospheric research is devoted to determining how that energy reservoir is filled and is emptied. Z. Kaymaz working with Janet Luhmann showed how the interplanetary field controlled the magnetic structure of the tail and the current systems therein. C. T. Russell working with V. Angelopoulos, V. Sergeev and S. Ohtani over several different studies examined the structure and dynamics of the plasma and current sheets at both quiet and disturbed times. One of the important findings of these investigations was that the so-called bursty bulk flows were same fraction of the time caused by solar wind pressure increases. Most recently visiting scientist, Xiao Yan Zhou working with C. T. Russell has examined a period of great activity in the geomagnetic tail when there were three spacecraft in the tail at different radial distances. This study reveals the tail to be an extremely complex region, with waves, with flows, with thinning and thickening and with reconnection.
The magnetotails of the unmagnetized planets are also of great interest. Much of that interest involves whether the properties of the tails can be used to set limits on the intrinsic magnetic moment of the planet. C. T. Russell undertook joint studies of the Venus tail with O. Vaisberg, and the Mars tail with undergraduate T. Mulligan, and also with T. Zhang. The results of these studies indicate that the tails of Venus and Mars behave quite similarly in their response to the solar wind, and that there is no evidence in this behavior for an intrinsic component of the magnetic field. Measurements deep in the ionosphere of Venus during the Pioneer Venus orbiter re-entry period also show evidence for a strongly magnetized ionosphere and no evidence for an intrinsic magnetic field. Debbie Huddleston has examined the night time Venus ionosphere as seen by the PVO magnetometer during the Galileo Flyby. She finds 5-10 minute delays of magnetic features from their appearance in the solar wind.
One of the outstanding issues addressed by the Space Physics Group concerns the evidence for lightning on Venus. C.-M. Ho's Doctoral thesis addresses this topic. In his thesis he analyzed the plasma wave data from low altitudes in the nightside ionosphere of Venus. He showed that many of the properties of the waves were consistent with a sub-ionospheric source. The burst rate was found to be largest at lowest altitudes, and furthermore the 100 Hz waves had properties consistent with whistler-mode propagation from below the ionosphere. In parallel with C.-M. Ho's efforts, R. J. Strangeway carried out an instability analysis showing that it is very difficult to generate whistler-mode waves in situ in the nightside ionosphere. He also showed that many of the properties of the signals are inconsistent with Doppler-shifted lower hybrid resonance waves generated by gradients within the plasma. Plasma waves are also observed above the dayside ionopause at both Venus and Mars. These waves appear to be associated with the presence of plasmas of both planetary and solar wind origin. It has been argued that the waves provide energy for heating the topside ionosphere at the unmagnetized planets. Recently, R. J. Strangeway and G. K. Crawford have argued instead that the waves are more likely to be a local phenomenon, acting to couple momentum and energy from the solar wind to plasma of planetary origin within the magnetosheath, rather than acting to provide energy to the topside ionosphere. Most recently K. Cole has argued that the Joule dissipation associated with waves coming from the atmosphere would heat the ionospheric electrons to levels far above that observed, and thus inferring that there must be no waves coming out of the atmosphere and hence no lightning. R. J. Strangeway has effectively countered this criticism and answered the paradox by showing that collisional cooling of the electrons maintain the observed temperatures in the presence of the observed lightning generated VLF waves.
The successful analysis of scientific data often requires sophisticated analysis tools. One such example is the separation of ambient signal from noise on the Pioneer Venus VLF experiment. Visiting scientist Tom Higuchi working with R. J. Strangeway developed a technique for this separation that has been vital to the continued analysis of this data set. More recently visiting scientist, H. Kawano, working with T. Higuchi has developed a bootstrap method for determining the orientation of the magnetopause.
In addition to the conduct of scientific studies, progress is fostered through communication and organization of scientific knowledge. We participated in this fostering through the editing of three books in the last year. Introduction to Space Physics (with M. G. Kivelson); The Global Geospace Mission; and The Physics of Collisionless Shocks. C. T. Russell also with Guan Le continued to help coordinate NSF's GEM program, principally aiding in the editing of an electronic and print newsletter. Guan Le also acted as editor of the AGU/SPA newsletter which appears several times each week.
C. T. Russell serves as the UCLA director of NASA Space Grant program. He also organized a two day workshop on Instructional Computing in Space Physics in March 1995. This workshop lead to the founding of ISPEC, the International Space Physics Educational Consortium, dedicated to fostering the development of resources for space physics education, especially over the Internet. One of our home grown products, a learning module running on Sun workstations, called Space- Physics had a very successful year. Not only was it distributed worldwide over a variety of platforms but it played a role in the awarding of a Computerworld-Smithsonian "Oscar" to the UCLA Learning Center.
Each week the teams meet to discuss issues of common concern and to plan the weeks activities. The programming team meets Mondays 1:30 to 3:00; the engineering team meets Fridays 2:00 to 3:00 and the research group Thursdays 4:00 to 6:00. The programming group consists of system manager C. T. Russell, Bryan Littlefield, interactive programming supervisor Sophie Wong, and data processing coordinator Bruce Rezin. Robert Strangeway and Debbie Huddleston participate in this activity. The engineering team consists of head engineer Joe Means, engineers Dave Pierce and Don Dearborn and technician William Greer together with Bob Snare the previous chief engineer of the group, now retired. The research effort is divided into four principal areas of concern: low altitude magnetospheric measurements, principally the FAST mission under R. J. Strangeway; high altitude magnetospheric measurements, principally ISEE and POLAR missions, under Guan Le; the solar wind and magnetized planets under Debbie Huddleston (Galileo and Cassini) and the unmagnetized planets under R. J. Strangeway (PVO)
The engineering group continues to prepare the POLAR magnetometer for launch, presently expected in December 1995. They also stand ready to support the launch of FAST that has now been delayed until the summer of 1996. They are also presently engaged in two development activities of great importance to the group, a new inexpensive but very accurate fluxgate magnetometer for ground-based studies and a new light-weight scalar magnetometer for low Earth orbit. The fluxgate magnetometer has been proposed to the NSF to be deployed at 20 sites in China in a joint Chinese-American study. We are also awaiting approval of funds to build a magnetometer for a small Brazilian satellite.
In addition to analyzing data from their old flight projects: ISEE 1 and 2 in Earth orbit; Pioneer Venus orbiting Venus and the interplanetary trajectory of Galileo the members of the Space Physics Group are readying themselves for the following upcoming activities: the orbital insertion of the Galileo spacecraft in December 1995; the launch of the Polar spacecraft in December 1995; the launch of the Near Earth Asteroid Mission in February 1996; the launch of the FAST spacecraft in mid 1996; the launch of the Mars 1996 mission and the launch of Cassini in 1997.
Debbie Huddleston arrived October 1, 1994. Debbie received her Ph.D from the University College London in 1990 under the supervision of A. Johnstone. She has most recently been studying cometary ion pickup and solar wind processes as an NRC post doctoral fellow with Marcia Neugebauer at JPL. At UCLA she will assist C. T. Russell undertake collaborative studies of the Galileo measurements of Venus, Earth and shortly Jupiter. Debbie has joined the Institute as an Assistant Research Geophysicist for an indefinite term of appointment.
Xiaoyan Zhou arrived October 12, 1994. Xiaoyan obtained her Ph.D from the Institute of Geophysics Chinese Academy of Sciences, Beijing, in 1991 under the supervision of Professor K. Tschu. She is presently the chief of the Geomagnetic Storm and Substorm Research Group of the Institute of Geophysics, Beijing. At UCLA she will pursue with C. T. Russell studies of the nature of the solar wind interaction with the magnetosphere. Dr. Zhou's stay is expected to extend through October 1995.
Hideaki (Hedi) Kawano arrived in August, 1994. Hedi obtained his Ph.D from the University of Tokyo in 1992 under the supervision of Professor S. Kokubun. He has most recently been studying data from the GEOTAIL mission. At UCLA he will continue his studies of GEOTAIL data, examine ISEE observations and participate in collaborative studies of GEOTAIL and POLAR, once the latter spacecraft is launched. Dr. Kawano's stay is expected to extend through February 1997.
Dr. Jerry Chao arrived on January 6, 1995. Dr. Chao received his Sc.D. Dr. Jerry Chao arrived on January 6, 1995. Dr. Chao received his Sc.D degree from MIT in 1970 under the supervision of Professor S. Olbert. He is presently a professor in Space Physics at Institute of Space Sciences, National Central University, Taiwan. His research interests include intermediate shock waves, structure of the Earth's magnetopause and bow shock, and waves in the magnetosheath. At UCLA, Dr. Chao will pursue with C. T. Russell these studies using ISEE data. His stay extended through April, 1995.
Jih-Hong Shue arrived on March 8, 1995. He received his Ph.D. from the University of Alaska, Fairbanks in 1993. He is currently a postdoctoral scientist at the National Central University in Taiwan. His research interests include structure of the magnetopause and waves in the magnetosheath. At UCLA he will pursue with C. T. Russell the compilation of magnetopause crossings using ISEE data. Dr. Shue's stay extended through April 20, 1995.
Wieslaw Macek arrived on May 6, 1995. He received his Ph.D degree from Warsaw University, Poland, in 1976 under the supervision of Prof. dr. G. Bialkowski. He is presently an associate professor at Space Research Center, Polish Academy of Sciences. His research interests include planetary bow shocks, planetary magnetotails, and the heliopause. At UCLA, he pursued with C. T. Russell studies of collisionless shocks and associated phenomena. Dr. Macek's stay extended through June 30, 1995.
Professor T. J. Odera arrived from Kenya on May 16, 1995. Tim received his Ph.D. from the University of Edinburgh in 1982 for his work on "The control and generation of magnetic pulsations on the ground and in interplanetary space by parameters of the solar wind". From 1983-1991 he was a member of the Physics Department, Kenya University, first as a senior lecturer and then as associate professor. Presently he is a professor of physics at Maseno University College, Kenya, having just finished a term as Dean of the Faculty of Science at Maseno. At UCLA Tim is pursuing with C. T. Russell studies of ULF waves in the magnetosphere. Prof. Odera's stay is expected to extend through December 1995.
The Space Physics Group also notes the welcome visits by: Ulli Auster (Berlin) March 27, 28, Carol Nairn (Kiruna) March 27-31, Malcolm Dunlop (London) March 30, 31, Werner Magnes (Graz) April 10-12, Andrey Fedorov (Moscow) April 10-15, Y. F. Gao, Y. T. Chen, X-Y Xu and S-F Yang, July 16-23, 1995.
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