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 is working with the University of Newcastle to investigate current systems and waves in the low altitude magnetosphere with the FedSat mission. 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 SPG has also been asked to provide the magnetometer for the Dawn mission to be launched in 2006 to Vesta and Ceres. The Dawn mission is led by C. T. Russell. 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 2001 to July 2002 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 magnetometer 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. Launch of ST-5 is currently scheduled for late 2004.
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 enabled 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. We continue to develop methods for diagnosing ICME properties.
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. Numerical Modeling of the Eros solar wind interaction and those of the asteroids, Gaspra and Ida, suggest that S-type asteroids do not intrinsic magnetic fields. 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 SO2 in the upper atmosphere of Io. These signals vary from pass to pass in a manner that suggests that the Io atmosphere itself is time varying.
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.
Robert J. Strangeway is continuing his collaboration with Dr. P. L. Pritchett, Dept. of Physics, UCLA in investigating how Auroral Kilometric Radiation (AKR) escapes from the source region. Dr. Strangeway provides the analysis of AKR wave forms acquired by the Fast Auroral Snapshot Explorer (FAST), with emphasis on the polarization of the wave fields. This allows us to determine the direction of propagation of the waves, which in turn can be compared with predictions from computer simulations carried out by Dr. Pritchett. The wave fields are found to be consistent with perpendicularly propagating waves. Furthermore, if any tendency in the perpendicular wave propagation direction is found it is along the auroral arc. Some theories have predicted that AKR should propagate across the arc, forming a standing wave structure, since the waves are reflected at the density gradients at the edge of the auroral cavity. The data are inconsistent with this model. The computer simulations also indicate a lack of standing wave structure. Instead, the waves appear to be freely propagating within the cavity.
A further complication to be investigated in more detail is the role of Alfven waves in enhancing soft electron precipitation.
Research on magnetic pulsations has been focused on two subjects: estimation of the density distribution of the magnetospheric plasma from the travel time of MHD waves, as well as analysis of the electromagnetic ion cyclotron (EMIC) waves observed by the Polar satellite, which has a distinctive advantage in covering high-latitude regions.
Travel-Time Magnetoseismology - We extended our analysis of the propagation time of sudden impulses further to the estimation of the mass density of the magnetospheric plasma from the observations of the signal travel time. The approach is very similar to the methodology of terrestrial seismology, in which the arrival time of seismic waves provides the knowledge of Earth’s interior structure. The "travel-time magnetoseismology" provides an alternative method to the normal-mode method that is based on field line resonance observations for monitoring the magnetospheric density from the ground. The establishment of the ground magnetometer network as described in the "Instrumentation" section will provide an important database to carry out this research.
Electromagnetic Ion Cyclotron (EMIC) Waves - The EMIC waves play an important role in the loss process of ring current ions and as a heating mechanism for thermal heavy ions. Placed in an 86-degree inclination orbit, the Polar satellite collects important observations of the properties of these waves at latitudes above the equatorial plane. The Polar Magnetic Field Experiment (MFE) data show that bursts of Pc 1 waves could occur as the spacecraft crossing different L-shells. The analysis of wave frequency and polarization at multiple latitudes suggest that these ion cyclotron waves are generated near the equator. The waves also suffer a polarization reversal as they travel toward higher latitudes, as predicted by the dispersion relation. Also observed are intensive structured Pc 1 waves in the recovery phase of magnetic storms. From the Poynting flux observed for these Pc 1 bursts, we confirm that these structured Pc 1’s are not bouncing wave packets. However, the cause of the periodicity of these wave bursts remains unclear and further research is needed.
Global simulations of Earth's magnetosphere, ionosphere, and thermosphere are performed by J. Raeder, graduate student Y. L. Wang, undergraduate student N. Myiake, 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. Efforts are now also underway to to couple the GGCM with the Rice Convection Model (RCM). The RCM is a model of the inner magnetosphere that accounts for all the drifts of energetic plasma, including gradient and curvature drifts while foregoing the inertial forces. It is expected that the RCM and the MHD part of the GGCM augment each other such that the combined model produces a realistic ring current population.
Graduate student Y. L. Wang is using the GGCM code to study the plasma depletion layer (PDL). The PDL is a layer of decreased plasma density and increased magnetic field just outside of the dayside magnetopause that is often observed during times of northward IMF. The PDL is difficult to study because the solar wind and IMF are rarely steady for a sufficiently long period during which a PDL observing satellite traverses the layer. Because the speed of PDL observing spacecraft is slow it is difficult to separate temporal variations imposed by the solar wind and the IMF from the true spatial structure of the PDL. Because of the few observational constraints models of the PDL are also poorly developed or tested. We have used high resolution GGCM model runs of two observed PDL crossings for which the solar wind and IMF were relatively stable and reliably observed. The model was driven with the observed solar wind and IMF values and the model output was directly compared with the in situ observations. The model reproduced the observed values very well. The differences between the model and the observations were in general less than the intrinsic variations of the observed plasma and field parameters. Thus, we proved two things: first, that the model is indeed capable of reproducing a mesoscale structure like the PDL in spite of intrinsic limitations like numerical diffusion, and second, that the PDL is a MHD structure that does not require pressure anisotropy or a kinetic description. The latter point is particularly important because it now allows us to treat the PDL as a MHD structure with confidence. The study also showed that most of the observed small scale variations that are typically superimposed on the parameters that define the PDL are temporal variations and have nothing to do with the intrinsic PDL structure. Although there have been previous simulation studies of the PDL, this one was to our knowledge the first that verified the simulation results against in situ measurements.
Recent observational, simulation, and theoretical studies have shown that the cross polar cap potential (CPCP) has a tendency to saturate during strong solar wind driving. It is not quite clear yet why this happens. If the solar wind driver is small (a few mV/m east-west interplanetary electric field (IEF)) a linear relationship between the IEF and the CPCP describes the correlation well. For substantially larger IEF values the CPCP saturates at about 300 kV.If one scales the linear relationship that is only valid for small IEF to the largest events one would predict CPCP values in excess of 1 MV. We have used the GGCM to further investigate the IEF-CPCP relation. We find that the large IEF values lead to substantial erosion of the magnetosphere. Thus the x-line shortens which should lead to a reduction of the CPCP. Since the length of the x-line is roughly proportional to the magnetopause standoff distance, which in case of the Bastille Day storm becomes as small as 4.9 RE, this effect is substantial. However, it is not quite large enough to explain the observed saturation values. If one considers at the same time the bulging of the lobes towards the dayside the combined effect may be sufficient to explain the saturation.
One of the goals of NSF's GEM program is the development of one or more Geospace General Circulation Model(s) (GGCMs) that can be used by the community for a variety of studies. The GGCM development is supposed to proceed in 3 phases. In phase 1 model results for a number of selected solar wind and IMF conditions are made available via the web for the community. We have been offering phase 1 results for several years now on a web page (link to http://www-ggcm.igpp.ucla.edu/gem-ggcm-phase1). During the current year we have received funding and started to build a website that will provide GGCM phase 2 products, that is, model runs on demand. On this web site anyone from the community will be able to conduct model runs with his/her choice of parameters and analyze the results. In order to perform these runs we will install a 16 node Beowulf cluster system.
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. The electronic newsletters for GEM and SPA were successfully run by Guan Le, a former member of SPG, and the editorship for both newsletters was passed on to Peter Chi since December 2002. In 1998, Bob Strangeway was appointed the SPA editor for AGU's weekly newspaper EOS. His term expired in 2001. Robert J. Strangeway was elected to serve a two year term (2002-2004) as the Space Physics and Aeronomy - Magnetospheric Physics Section Secretary of the American Geophysical Union.
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.
Beginning in April 2002 we were visited by Tom Takeuchi from Kyoto Univ. in Japan, who has been studying the solar wind interaction with the Earth, including the effects of interplanetary shocks. We were also visited by Xochitl Blanco-Cano who, for a shorter period in September 2002, investigated the magnetic signatures of asteroids Gaspra and Ida in the solar wind using the hybrid code.
During the period 2001/2002 there were six continuing graduate students: S. Georgilas, G. J. Fowler, T. Mulligan, Y. L. Wang, Z. J. Yu, and E. Jensen. One student, T. Mulligan, successfully completed her requirements for the PhD degree. Two undergraduate students were employed as research aides: M. Fleishman and A. Shinde.
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, and P. J. Chi. The other staff members are as follows:
Chi, P. J., and C. T. Russell, Magnetoseismology: Remote sensing of plasma density in the magnetosphere by ground magnetometer observations, presented at AGU Spring Meeting, May 2002.
Raeder, J., Global Geospace Modeling: Tutorial and Review, The Sixth International School for Space Plasma Simulations, Garching, Germany, September 2001.
Raeder, J., What does global modeling tell us about tail dynamics and its relation to the ionosphere? LANL/IGPP Conference on Magnetotail Dynamics, Yellowstone, Wyoming, October 2001.
Raeder, J., Magnetosphere-ionosphere Magnetic Field Connectivity, AGU Fall Meeting, San Francisco (EOS, vol. 82, no. 47), 2001.
Raeder, J., Polar cap potential saturation during geomagnetic storms Colloquium presentation, University of New Hampshire, February 2002.
Raeder, J., Polar cap potential saturation, Colloquium presentation, IGPP/UCLA, March 2002.
Russell, C. T., The magnetic field and magnetosphere of Mercury, presented at Mercury: Space Environment, Surface, and Interior, Chicago, October 2001.
Russell, C. T., The structure of the magnetopause, presented at EGS General Assembly, Nice, France, April 2002.
Strangeway, R. J., R. E. Ergun, and P. L. Pritchett, Auroral Kilometric Radiation as a diagnostic of the electron acceleration region, p. 218 (abstract H5-05), 2001 Asia-Pacific Radio Science Conference, Tokyo, Japan, August 2001.
Strangeway, R. J., Auroral Kilometric Radiation: A Fundamental Plasma Process, tutorial, Kanazawa Workshop on Waves in Plasmas, Kanazawa, Japan, August 2001.
Strangeway, R. J., Does Poynting Flux Control Ionospheric Outflow? Earth and Space Sciences Seminar, University of California, Los Angeles, October 2001.
Strangeway, R. J., Geomagnetic Storms: Sources and Sinks of the Terrestrial Ring Current, Physics Department Seminar, University of Texas, El Paso, October 2001.
Strangeway, R. J., Auroral Acceleration Processes and Their Role in Magnetosphere-Ionosphere Coupling, CEDAR 2002 Workshop, Longmont, June 2002.
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