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 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 2002 to July 2003 in the areas of instrumentation, research, dissemination of data, communication, education, visiting scientists and students.
In December 2002 the Australian government launched a microsatellite to celebrate their 100th anniversary and to demonstrate their scientific and technical prowess. The UCLA engineering team assembled, tested and delivered the magnetometer to Australia and helped install it on the spacecraft. The magnetometer continues to operate flawlessly.
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. In addition, a new effort named Mid-continent Magnetoseismic Chain (McMaC) has started to extend the observational coverage of IGPP/LANL magnetometers – northward to the Fort Churchill Line of CANOPUS Array and southward to the existing IGPP magnetometer station in Mexico. This 4-year project led by Peter Chi has been approved by NSF, and it will make use of the two methods of "magnetoseismology" on McMaC data to obtain the density distribution of the magnetosphere (see Magnetic Pulsations in RESEARCH).
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 has developed a protyping facility in the Geology Building basement. This facility allows ideas to be rapidly taken from concept to hardware.
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. We continue to develop methods for diagnosing ICME properties including examining plasma properties such as cool ion temperatures and declining velocity profiles indicative of flux rope expansion.
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. Prior to encounter the activities associated with the Cassini mission consist principally of software development and mission planning. A new effort in planetary magnetospheres began this year with N. Omidi of UCSD and X. Blanco-Cano of UNAM, using hybrid simulations to model solar wind-magnetosphere interactions of different scale sizes. The hybrid code follows ion motion but assumes the electrons act as a mass loss fluid. The simulations reveal that the magnetospheres through phase transitions and the processes change as the magnetosphere gets stronger.
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. Galileo is scheduled to cease operations by impacting Jupiter on September 21, 2003.
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 - Our previous analysis on the propagation of preliminary reverse impulse (PRI) to low-latitude regions clearly demonstrates that the signal propagates from the subsolar region of the magnetosphere to the ground mainly by means of MHD waves. Our results stimulated further discussion on JGR-Space Physics over the issue of the generation mechanism of ground signals of sudden impulses. Through the discussion it is clear that one of the critical drawbacks of the Earth-ionosphere waveguide model, previously considered as the standard interpretation of the ground signals of sudden impulses, is that it cannot interpret the discontinuity in the arrival time of PRI seen in observations. On the other hand, the arrival time predicted by the MHD wave model shows excellent agreement with the observations on the ground and in space.
After the shift in the understanding of sudden impulse propagation, we made one step further to infer the plasma density distribution in the magnetosphere from the observations of PRI arrival time. It is shown that the estimated density inferred by this method well agrees with that from the field line resonance observations. Both estimated densities are also consistent with the empirical model of magnetospheric density, such as the Carpenter-Anderson model. With the start of the new McMaC project (see Ground Magnetometers in INSTRUMENTATION), we will explore further on this new subject, now called "travel-time magnetoseismology", in addition to our continuous analysis using the field line resonance method to measure the mass density of the magnetospheric plasma.
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, J. Weygand, 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.
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. In the last year we used high resolution GGCM model runs of two observed PDL crossings for which the solar wind and IMF were relatively stable and reliably observed to show that the model is able to reproduce the PDL. Although that study showed a very good match between the in situ observations and the model results it was somewhat limited in that the observations were taken in the magnetosheath flanks which are not generally considered to be the key regions for the formation of the PDL. We have now extended the study by examining in detail the results of simulation runs with fixed solar wind conditions. These results show that the PDL is neither the result of flux tube squeezing as one model predicts (Zwan and Wolf, 1975), nor the result of a slow mode wave front as another model would predict (Southwood and Kivelson, 1995). Rather, the PDL is formed by a complex interplay of forces in the magnetosheath. While the force exerted by the magnetic pressure slows flux tubes down near the stagnation point (unlike the pressure gradient force as gas dynamic models would predict), the pressure gradient force parallel to the flux tubes accelerates plasma away from the subsolar point, thus depleting the flux tubes. The possible existence of a slow mode front is also tested. Slow mode fronts can exists, however, they seem not to be necessary for the PDL formation.
Flux transfer events (FTEs) have been known for more than 20 years now, yet their nature is still elusive. Although it is widely accepted that they are the result of some form of magnetic reconnection at the magnetopause it is not clear why reconnection at the dayside magnetopause is at times time dependent, like during FTEs, while at other times reconnection seems to proceed in a steady fashion for extended periods. With the unabated increase in computing power we are now able to push the resolution of our GGCM into an area where the study of meso-scale processes like FTEs becomes possible. We show that simply by increasing the grid resolution at the magnetopause from about 3000 km down to approximately 750 km a transition occurs where steady reconnection becomes unsteady and leads to the generation of flux ropes at the magnetopause. In the simulations with coarser resolution numerical diffusion overwhelms the formation of flux ropes; they simply diffuse away while they are forming. The coarse simulations also clearly exhibit a decoupling of the flow from the field on scales of a few RE which is clearly not physical. High resolution of the code is necessary for flux rope formation but not sufficient. One also needs to break the symmetry between the flow and the field. In the case of no dipole tilt and due southward IMF no FTEs form because the stagnation streamline coincides with the x-line. Either dipole tilt or a finite IMF By component break the symmetry and FTEs start to form. When FTEs form in the simulation their ‘spacecraft signatures’ are remarkably similar to those observed. In particular, we find a repetition period of about 8 minutes, bipolar normal field signatures, and strong core fields.
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). We are now developing our phase 2 product, that is, GGCM runs on demand with user supplied parameters. We installed and tested a 16 node Beowulf cluster. N. Myiake has developed a web based interface that allows users to submit runs, choose parameters, and to perform analysis of the simulation results. This interface is now in testing, and several users at UCLA are already taking advantage of it.
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 three 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. In the past year we also converted the program to work on a Linux-base platform and distributed the software to all participants at the GEM meeting in Snowmass. Second, C. T. Russell is the Director of UCLA's branch of the California Space Grant activities. Third, 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.
From April 2002 to April 2003 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 2002/2003 there were six continuing graduate students: M. Cowee, G. J. Fowler, Y. L. Wang, Z. J. Yu, E. Jensen, and R. Troy. One undergraduate student was employed as research aide: A. Shinde.
The SPG staff consists of students, engineering staff, programmers, computer operators and student assistants, clerical help and researchers. The student researchers have been listed above. The research staff are R. J. Strangeway, J. Raeder, and P. J. Chi. The other staff members are as follows:
Raeder, J., Global Modeling of Magnetospheric Flux Transfer Events, Colloquium presentation, NCAR/HAO, November 2002.
Raeder, J., Magnetospheric Flux Transfer Events, Colloquium presentation, University of New Hampshire, February 2003.
Fuller-Rowell, T., M. Codrescu, and J. Raeder, Future modeling challenges, 2003 Joint EGU/AGU Meeting, Nice, France, 2003.
Raeder, J., Small scale variability in the high-latitude ionosphere from global simulations, 2003 Joint EGU/AGU Meeting, Nice, France, 2003.
Russell, C. T., Outer planet magnetospheres: a Tutorial, presented at the 34th Scientific Assembly of COSPAR, Houston, Texas, October 2002.
Russell, C. T., Interaction of Galilean moons with their plasma environments, presented at EGS-AGU-EUG Joint Assembly, Nice, France, April 2003.
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