TABLE OF CONTENTS
The Space Physics Group (SPG) studies the chain of energy transport from the surface of the sun to its eventual arrival in planetary stratospheres. It uses interplanetary measurements to investigate the structure of coronal mass ejections and their evolution in space. It uses Galileo observations to understand energy and mass transport in the jovian magnetosphere, and the secular variation of the jovian magnetic field. It studies the data received from the Cassini mission on its way to Saturn and the NEAR mission in orbit about the asteroid 433 Eros both to understand the physical process occurring at planetary bodies and to understand the structure and dynamics of the magnetized plasmas in interplanetary space. It uses Polar observations throughout the magnetosphere to understand how the solar wind couples to the Earth's magnetosphere and the magnetosphere couples to the ionosphere. It uses measurements from the FAST mission to determine the microprocess occurring in that coupling region. It studies magnetic pulsations both to determine their origin and to use them as diagnoses of the state of the magnetosphere and it uses numerical simulations both as an extrapolation of localized data and as a tool to investigate magnetospheric behavior. The SPG is also preparing the data dissemination system for the IMPACT investigation on the STEREO mission to be launched in 2005. The Space Physics Group plays a vital role in the community in disseminating the observations from current and past 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 2000 to July 2001 in the areas of instrumentation, research, dissemination of data, communication, education, visiting scientists and students.
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 asked us to build the magnetometer for this mission and we have done so. The engineering unit and flight unit have been assembled, tested and very shortly will be delivered to Australia and installed on the spacecraft.
The fifth project of the New Millennium Program is a three spacecraft mini-satellite mission in the Earth's magnetosphere. UCLA was selected to provide the magnetometers for this program. We have entered the design phase of this effort but the approval for completion of the project has not yet been given. This is an important project to the group because it enables us to improve and modernize our design and it will eventually provide good data for studying processes in the magnetosphere. Finally, it keeps our magentometer group competitive for future mission opportunities.
ST5 is one of the technology projects developed by NASA as part of its New Millenium Program. The magnetometers to be flown on ST5 take the classical fluxgate design as developed by the Space Physics Group, and apply new technology to the design to reduce the power, mass and size of the magnetometer. This effort includes building smaller (50 g) sensors, and moving much of the design out of the analog domain into the digital domain. This involves the use of "surface-mount" technologies, as well as flying new 20 bit analog/digital converters. As a result of the effort, UCLA will have built and flown the next generation flight-qualified fluxgate magnetometers that will in turn be the prime candidates for flight on missions such as the "Magnetospheric Constellation." Robert J. Strangeway is the Principal Investigator for this effort.
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 consists of 14 magnetometers in a 2-D array across China. 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. The third array is the IGPP/LANL array that is intended to ultimately cover the western U.S. At present there are six operating stations in San Gabriel, CA; Los Alamos, NM; the Air Force Academy; Colorado Springs, CO; Boulder, CO; Minneapolis, MN, and at Teoloyucan, Mexico. Finally there is a loose-knit global array with sites in Jicamarca, Peru; and Crete, Greece. These magnetometers have now been used in innumerable studies including sounding the density of the plasmasphere, sudden impulse propagation and Pi2 timing of substorms.
The SPG has also developed a sensitive searchcoil magnetometer that can measure both pulsations and lightning generated Schumann resonances. Ultimately these units will be time tagged with GPS timing.
The electronics laboratory acquired through a grant from the IGPP a vapor-phase soldering station. This device allows the fabrication of state of the art, low-mass instruments for flight on the microsatellite missions of the 21st century, and is presently being used to fabricate our various magnetometers.
Interplanetary Coronal Mass Ejections (ICMEs) are being studied using the solar cycle long data base obtained from Pioneer Venus and using multipoint datasets obtained from chance encounters of Pioneer Venus, ISEE, NEAR, Wind and ACE spacecraft. With a single spacecraft one can invert the structure of ICMEs using an assumed cylindrical symmetry but clearly ICMEs are not cylindrically symmetric. Thus we have altered our inversion routine to simultaneously fit ropes seen at two spacecraft. We find that an ICME can extend over 45 degrees in azimuthal but still retain its rope-like character, albeit it is much thinner along the Earth-Sun line than it is wide perpendicular to it. Other two satellite studies have enaabled us to measure the expansion of the ICMEs as they move radially and to determine the bend in the axis of the rope with distance along the axis of the rope. We have also shown that the orientation of the axis of the ropes (clock angle) is controlled by the neutral line on the magnetic source surface in the corona.
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, in orbit about the asteroid 433 Eros has examined if Eros has intrinsic magnetic field, and found none even upon landing. The activities associated with the Cassini mission consisted principally of software development and mission planning.
The Galileo activities 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.
In 1999 the Galileo spacecraft finally returned to Io again and in a series of passes mapped out the region of ion cyclotron wave growth. This pattern indicated that cross field transit by neutrals must play an important role in the emplacement of the ions of the Io torus. A simulation of this process has been developed that enables us to test assumptions about the mass addition process and determine their consequences. These observations also revealed the presence of SO and S as well as the previously detected SO2in the upper atmosphere of Io.
The orbit of Galileo also provides data useful for the study of the secular variation of the jovian magnetic field. Pioneer 11 provided an excellent baseline for the later Galileo data. The ability of a spacecraft to probe the magnetic field depends very critically on its orbit. The initial orbits of Galileo were appropriate for studies of the dipole field but not until orbit C22 did Galileo begin to resolve the quadrupole terms sufficiently accurately to determine if there had been any change in the field since the Pioneer 11 measurements. Galileo's advantage over previous missions is that it makes multiple passes through the magnetosphere and can smooth out statistical fluctuations in noise sources. Thus Galileo provides a much improved measurement over missions such as Voyager and Ulysses. Thus far Galileo has provided a new estimate for the rotating period of Jupiter, shown that there is a change in the tilt of the dipole magnetic moment and that the secular change in the quadrupolar field is similar to that on Earth.
The study of the terrestrial magnetosphere is centered principally around the POLAR and FAST missions 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, as the tilt of the Earth's dipole axis to the solar wind flow. We have shown that the pressure in the cusp plasma is directly controlled by the solar wind dynamic pressure incident along the normal to the surface of the cusp. When the solar wind pressure drops to low values the magnetosphere becomes dipolar and the fluctuations cease but the field aligned currents remain constant.
Using Polar data, we have also examined effects of the equatorial ring current and the magnetopause current in the magnetic field observations in the magnetosphere. A preliminary map of the depression in the magnetosphere field at varying Dst levels and as a function of radius and latitude and local time has been created from databases of ISEE, CCE and POLAR data. In a separate study we have examined the effect of pressure changes in the solar wind on the magnetosphere. We have found that the magnetic field does not increase everywhere but that near noon principally off the equator and on the dayside the magnetic field decreases when the solar wind compresses the magnetosphere. ULF waves are also frequently amplified when these compressions occur.
Most recently we have examined the strength of currents flowing into the auroral oval from the magnetosphere as a function of the interplanetary electric field and the solar illumination of the ionosphere. The currents do not depend on the interplanetary electric field if it is from dusk-to-dawn but they do vary proportional to the dawn-to-dusk field. Also currents are twice as strong into the dayside ionosphere as on the nightside.
The Fast Auroral Snapshot (FAST) small explorer spacecraft, which was launched in August 1996, continues to acquire data from the Earth's auroral zone. The magnetometers on board FAST include both fluxgate (DC) and search-coil (AC) magnetometers, and Robert J. Strangeway is the lead investigator at UCLA responsible for monitoring the health of these instruments for the FAST mission. As part of his efforts he also is actively involved in several research areas related to auroral processes. Primary of these is the generation of Auroral Kilometric Radiation (AKR). AKR is a fundamental radio-wave emission process, and understanding how AKR is generated has relevance to both planetary and astrophysical radio sources. FAST has demonstrated that AKR is directly related to the presence of parallel electric fields required so that field-aligned currents of sufficient density can flow along the terrestrial magnetic field. These currents are in turn driven by magnetospheric processes, such as the magnetic reconfiguration associated with a substorm, flow bursts, and other dynamical processes.
While FAST has demonstrated the basic instability mechanism for the generation of AKR, several issues remain. These include how the radio waves propagate in the auroral density cavity, and how the radiation escapes from the cavity to be observed at large distances from the planet. We are collaborating with Dr. P. L. Pritchett, Dept. of Physics, UCLA in investigating how AKR escapes from the source region. Dr. Strangeway is also collaborating with researchers outside of UCLA, for example, Prof. R. E. Ergun, of the University of Colorado, Boulder. Prof. Ergun is investigating the mechanisms by which the parallel electric fields observed by the FAST spacecraft are maintained on the auroral-zone field lines. Parallel electric fields appear to come in two "flavors." One is large scale, the other is much smaller, being only of the Debye lengths in scale. Included in the small-scale structures are electron solitary waves and the sheath that shields back-scattered auroral electrons from the higher altitude regions of the auroral flux-tube. Understanding the evolution and stability of these electric field structures is again of fundamental importance for understanding plasma physical processes in space plasmas.
Research on magnetic pulsations emphasizes two major directions: measuring the mass density of the plasma in the magnetosphere during storms and studying the propagation of sudden impulses through the magnetosphere. These are also two of the major scientific objectives for the establishment of a ground station network as described in the "Instrumentation" section.
Magnetic Pulsations for studying magnetic storms - We continued the analysis of the plasma mass density during the September 1998 magnetic storm by using the gradient technique of magnetic pulsations. Magnetometer data at middle and high latitudes (collected by the Canadian CANOPUS Project) show that more plasma was found in the trough region during the first two days of the storm, associated with the enhanced ion outflow from the ionosphere. Enhanced broadband ULF wave power was also found during the storm, enabling the gradient method to be applied on the magnetometer data at very low latitudes (collected by the Circum-pan Pacific Magnetometer Network), where we find that the phase change across the resonant shell has an opposite sense compared to what is found elsewhere in the magnetosphere. This implies that the frequency of field line resonance decreases with decreasing L-value due to the rapid increase of density toward the ionosphere.
Sudden Impulses - The Preliminary Impulses (PI) associated with the arrival of interplanetary shocks at the magnetospheric boundary has been known to occur almost simultaneously at high latitudes and at the equator. For many years the Earth-ionosphere waveguide model has been widely accepted for explaining such rapid propagation of signals. We analyzed the data from several magnetometer arrays to study the occurence time of the PI's associated with the Sudden Commencement on September 24, 1998. The high- resolution data with GPS accuracy in time enables us to identify the small time delays among the PI signatures seen at different stations. The results clearly indicate that the propagation of PI can in fact be interpreted by MHD wave propagation. Moreover, the density structure of the magnetosphere can be inferred from the arrival times of these waves much like seismic waves can tell us about the interior of the Earth.
Global simulations of Earth's magnetosphere, ionosphere, and thermosphere are performed by J. Raeder, graduate student Y. L. Wang and their collaborators outside of UCLA. These simulations are used to investigate basic magnetospheric processes, to supplement experimental studies, to investigate the feasibility of magnetospheric multiprobe missions, and as a precursor to operational space weather prediction models. In collaboration with Tim Fuller-Rowell (NOAA/SEC) our model has now been coupled with the NOAA Coupled Thermosphere Ionosphere Model and has thus become a General Geospace Circulation Model (GGCM) that covers Earth's space environment from the solar wind to the upper atmosphere. The coupling of the two models has resulted in much improved geomagnetic storm simulations.
Using the coupled model we studied the January 10/11 and Bastille day (July 14/15, 2000) geomagnetic storms. We could show that the model predicts ground magnetic perturbations and the entry of geostationary satellites into the magnetosheath with high fidelity. With these studies we also investigated the saturation of the cross polar cap potential during times when the driving electric field in the solar wind reaches very high values, such as those typical during a geomagnetic storm. We found that the combined compression and erosion of the dayside magnetosphere leads to a geometry of the dayside magnetopause that inhibits the convection towards the reconnection region and thus effectively choking dayside reconnection.
In collaboration with N. Maynard (Mission Research Corp.) we organized the the NSF/GEM substorm challenge which aimed at testing geospace models with a well documented substorm event (The event chosen occurred on November 24, 1996 at approximately 2230 UT). Besides us several other groups participated in this study which resulted in a collection of 8 JGR papers. Our simulation results showed that the tail breakup at the substorm expansion phase onset occurs between 10 and 25 RE from Earth, consistent with recent experimental estimates. The simulation also showed that no one single x-line forms at onset; instead there are multiple reconnection sites which lead to considerable fragmentation of the tail current sheet. Such fragmentation cannot be observed with single satellites, and the simulation makes it quite clear why it has been difficult and inconclusive to deduce the tail processes from statistical single satellite observations, despite 3 decades of effort.
With the inception of the National Space Weather Program global geospace models are now being considered a centerpiece of operational space weather forecasting. However, there are a number of obstacles that make the transition of models like ours into operations difficult, in particular the lack of metrics (i.e., measures that describe the models' fidelity), and the lack of resources both at the research and the operational end. NSF has now embarked on a metrics evaluation program in which we participate. The first metrics comparison used DMSP convection parameters from about 100 DMSP polar cap overpasses and compared them with model predictions. The results were somewhat mixed, both for our model and others. While the predictions for some DMSP passes were extraordinarily good, the predictions of other passes were sometimes dismal. However, this study gave us many clues as to where the model needs improvement. To address the resources problem a multi-agency Community Coordinated Modeling Center (CCMC, http://ccmc.gsfc.nasa.gov) was formed at Goddard Space Flight Center. The prime objective of the CCMC is to take science grade models, evaluate them, and help to transition models into operations. Our model was one of the first chosen by the CCMC. The CCMC has received our model recently and now offers "runs on demand" with our model for researchers in the scientific community who wish to make use of it. In parallel, the CCMC evaluates the possibility of transitioning our model to one of the operational space weather centers.
We continue to improve our model. We now collaborate with Frank Toffoletto (Rice University) to couple the Rice Convection Model (RCM) to our GGCM. The RCM provides a better physical description of the energetic plasma of the inner magnetosphere, i.e., the ring current and the radiation belts. By contrast, the RCM is limited to the regions of the magnetosphere where the field lines are closed. Thus, the RCM is not a global model but requires a number of inputs that drive the model. In coupling our GGCM with the RCM the latter model will receive these parameters directly from our GGCM, and the GGCM will receive field-aligned current, precipitation parameters, and inner magnetosphere pressure from the RCM. In parallel, we pursue algorithmic enhancements to our model, in particular the inclusion of adaptive mesh refinement (AMR) technology. We collaborate with LLNL researchers (R. Hornung, K. Chu) who have developed a software infrastructure (SAMRAI) that provides solutions to a number of AMR related issues.
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, as well as Wind and ACE magnetometer and solar wind data, and now provide on-line access to the ground-based magnetometer data obtained during the IMS (1977+) to the ISEE1 and 2 magnetometer data and also all the 1- second ground based data. We have been asked by the IMPACT team on the STEREO mission to provide this capability for them in the future.
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. While Guan Le has now left UCLA she still uses our computer resources for her various newletters. In 1998, Bob Strangeway was appointed the SPA editor for AGU's weekly newspaper EOS. His term expired in 2001.
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.
In the academic year 2000-2001 we were visited by C-C. Cheng on sabatical from his university in Taiwan. He chose to study the behavior of a particular class of Pi2 pulsations that occurred sequentially with a gap of about 20 min. These waves appear to arise from the onset of reconnection and from a rapid increase in that rate respectively. Furthermore the separation of the two pulsations appears to be controlled by the amount of reconnection occurring at the front of the magnetosphere. These results appear to be consistent with a substorm model in which the first onset is associated with the creation of the near-Earth neutral point in the plasma sheet and the second occurring when reconnection finally reaches the open flux of the tail.
During the period 2000/2001 there were seven continuing graduate students: S. Georgilas, G. J. Fowler, T. Mulligan, Y. L. Wang, Z. J. Yu, X. M. Zhou and L. Jensen. One student, X-W. Zhou, successfully completed her requirements for the PhD degree.
The SPG staff consists of students, engineering staff, programmers, computer operators and student assistants, clerical help and researchers. The graduate students have been listed above. The research staff are R. J. Strangeway, J. Raeder, P. J. Chi and T. S. Hsu. The other staff members are as follows:
C. T. Russell, Multscale coupling in planetary magnetospheres, presented at the 33rd COSPAR Scientific Assembly, Warsaw, July, 2000.
C. T. Russell, Reconnection in planetary magnetospheres, presented at the 33rd COSPAR Scientific Assembly, Warsaw, July, 2000.
C. T. Russell, F. R. Fenrich, X. W. Zhou and J. G. Luhmann, The accuracy of present models of the high altitude polar magnetosphere, presented at the 33rd COSPAR Scientific Assembly, Warsaw, July, 2000.
C. T. Russell and M. G. Kivelson, Identification of SO in Io's exosphere, presented at the 33rd COSPAR Scientific Assembly, Warsaw, July, 2000.
C. T. Russell, Io as a plasma source in the jovian system, presented at the AGU Fall Meeting (abstract), EOS, Trans., AGU, 81(48), F787, 2000.
C. T. Russell, The state of the magnetosphere on the threshold of Cluster, presented at European Geophysical Society meeting, Nice, March 2001.
C. T. Russell and M. G. Kivelson, A status report on the magnetic exploration of the planets, presented at the Spring National AGU meeting (abstract), EOS, Trans. AGU, 82(20), S123, 2001.
J. Raeder, T. Fuller-Rowell, and Y. Wang, Global geospace modeling - State-of-the-art and current developments Huntsville 2000: A new View of Geospace, Pine Mountain, GA, October 2000.
T. J. Fuller-Rowell, J. Raeder, and Y. Wang, Thermospheric effects on M-1 coupling, AGU Fall Meeting, San Francisco, EOS, 83, 2000.
J. Raeder, The Low-Latitude Boundary Layer in global simulations, AGU Chapman Conference: The Low- Latitude Boundary Layer and its Dynamic Interaction with the Solar Wind and Magnetosphere, New Orleans, Louisiana, April 2001.
J. Raeder, Recent Advances in First-Principles Modeling of Ionospheric Currents and Ground Perturbations, NOAA Space Weather Week, Boulder, CO, May 2001.
R. J. Strangeway, R. E. Ergun, and P. L. Pritchett, Particle and field observations in the source region of Auroral Kilometric Radiation: Implications for generation mechanisms, p. 280 (abstract), The First S-RAMP Conference, Sapporo, Japan, 2000.
R. J. Strangeway, The magnetospheric drivers of ionospheric outflows, p. 35 (abstract), The 7th Bi-annual Huntsville Workshop, Pine Mountain, 2000.
R. J. Strangeway, "Newton and Maxell in Space Plasmas: The Mechanical View of Magnetosphere-Ionosphere Coupling," Distinguished Researcher Lecturer, Institute of Geophysics and Planetary Physic, University of California, Los Angeles, May 2001.
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