This page will give you a short biography of my research activities at JPL, and a bibliography of my limited contribution to the quasi-infinite expanse of the peer reviewed scientific literature. I am primarily a support person, specializing in scientific programming, algorithm development, and the analysis of observational data. As a result, I don't get my name on many papers. But I am happy to have accomplished this much.
I came to the Jet Propulsion Laboratory in January 1981, as part of the Radio Astronomy Group, which later changed its name to the Radio/Submillimeter Astronomy Group, in order to emphasize our transition into the newly available submillimeter wavelengths. Our main thrust in those days was to use observations characteristic of thermal emission, to probe the structure of the atmospheres of the gas giant planets: Jupiter, Saturn, Uranus, and Neptune. A number of papers had already come out of the group, on Jupiter and Saturn, before I joined. This paper was the first one I was to work on. Our group was the first to recognize the time variability of the Uranian microwave spectrum, and the first to suggest a cause.
Abstract: Radio astronomical observations of Uranus show that the radio emission spectrum is evolving in time. Ammonia vapor must be depleted in the Uranian atmosphere as Gulkis and his co-workers previously suggested. Since 1965, ammonia either has been decreasing in time or is a decreasing function of latitude, or both, provided that the radio emission is atmospheric in origin. If Uranus has an observable low-emissivity "surface," these trends may be reversed. The microwave observations made in 1965, at the time when the spin axis of Uranus was nearly perpendicular to the sun-Uranus line, are consistent with an atmospheric opacity profile that would be produced by saturated ammonia vapor in a predominately hydrogen atmosphere. At the present time, when the spin axis of Uranus is nearly aligned with the sun-Uranus line, the measurements require an opacity that would be produced by saturated water vapor. A large thermal gradient between the pole and equator is ruled out.
The other major project that I worked on was the Jupiter Patrol, a long term project of Mike Klein's that monitored the synchrotron emission from Jupiter at 2295 MHz, using the radio antennae of the Deep Space Network, for more than a full solar cycle. We were eventually able to draw direct correlations between the synchrotron emission, and the solar wind loading of the Jovian magnetosphere. This was a significant result, because we were monitoring emissions from deep within the Jovian magnetosphere. At the time, it was thought that low energy electrons from the solar wind could not diffuse into the inner magnetosphere on such short time scales as we were able to demonstrate. Scott Bolton eventually came up with a new theoretical model for electron diffusion that became his PhD thesis, and explained the observations nicely.
Abstract: A long-term observational program to monitor the time variations of the microwave emission from Jupiter has been in progress since April 1971. The measurements are made several times each month with the NASA Deep Space Network (DSN) antennas operating at 2295 MHz (13.1 cm). The data set, when combined with measurements by other observers, provides a record that extends over two 11-year solar cycles. The combined data set shows considerable variability that may be directly related to the high-energy electron population of the inner magnetosphere. Preliminary results of a study to search for plausible correlations between the Jovian synchrotron emission and solar-related phenomena reveal that a positive correlation may exist with the ion number density in the solar wind.
Abstract: It is generally believed that the strong magnetic field of Jupiter insulates the inner magnetosphere from fluctuations in the solar wind, and that the high energy electrons (>1Mev) responsible for the synchrotron radio emission from the planet are produced by inward diffusion of electrons from regions of weak to strong magnetic field intensity. Both the driving force for the diffusion process and the source of the relativistic electrons are presently unknown. It is widely believed that the diffusion process is driven by winds in Jupiter's ionosphere rather than fluctuations in the solar wind. Possible sources for the electrons include the Jovian satellites, in particular Io, Jupiter's ionosphere, and the solar wind. Thus far, no unambiguous connection between the solar wind properties and the relativistic inner belt electrons has been established. Such correlations, if they exist, could help to understand the physical processes that lead to the radiation belts. This paper reports on a study aimed at searching for correlations between Jovian decimetric radio emission and various solar wind parameters described below. Measures of correlations of the solar wind parameters with the decimetric radio emission will be presented.
The radio data used in our study are based primarily on a uniform set of observations carried out since April 1972 [sic] with the NASA Deep Space Network of antennas operating at 2295 MHz (13.1 cm) (Klein et al., 1972; Klein, 1976). This data set, when combined with measurements by other observers provides a record that extends over two 11-year solar cycles. The combined data set shows considerable variability that can be directly related to the high energy electron population (Hide and Stannard, 1976; Klein, 1976).
The data set of the solar wind parameters is composed of five quantities measured by numerous earth orbiting spacecraft along with Pioneer 10 and 11 and Voyager 1 and 2. These are 1) solar wind, 2) velocity, 3) proton density, 4) proton temperature, and the 5) strength and direction of the magnetic field. The data, provided by the NSSDC, encompasses the time frame from 1963 to 1985.
References
Hide, R. and D. Stennard, Jupiter's magnetism, observation and theory, Jupiter, ed. T. Gehrels, University of Arizona Press, Tucson, 767-787, 1976.
Klein, M.J., The variability of the total flux density and polarization of Jupiter's decimetric radio emission, Journal of Geophysical Research, 81, 3380-3382, 1976.
Klein, M.J., S. Gulkis, and C.T. Stelzreid, Jupiter: New evidence of long term variations of its decimetric flux density, Astrophysical Journal, 176, L85-L88, 1972.
Abstract: Results of a study comparing long-term time variations (years) in Jupiter's synchrotron radio emission with a variety of solar wind parameters and the 10.7-cm flux are reported. Data from 1963 through 1985 were analyzed, and the results suggest that many solar wind parameters are correlated with the intensity of the synchrotron emission produced by the relativistic electrons in the Jovian Van Allen radiation belts. Significant nonzero correlation coefficients appear to be associated with solar wind ion density, ram pressure, thermal pressure, flow velocity, momentum, and ion temperature. The highest correlation analysis suggests that the delay time between fluctuations in the solar wind and changes in the Jovian synchrotron emission is typically about 2 years. The delay time of the correlation places important constraints on the theoretical models describing the radiation belts. The implication of these results, if the correlations are real, is that the solar wind is influencing the supply and/or loss of electrons to Jupiter's inner magnetosphere. We note that the data for this work spans only about two periods of the solar activity cycle, and because of the long time scales of the observed variations, it is important to confirm these results with additional observations.
By this time the Radio Astronomy Group was heavily involved in the NASA SETI project, which began to grow rapidly in 1988. In 1992, on Columbus Day the NASA SETI project made its official start, amidst fanfare and publicity. Congress cancelled the program within a year. I left the Radio Astronomy Group at about that time as the money for astronomy and astrophysics became too scarce. However, we all received NASA Group Achievement Awards for what we were able to get done. All SETI is now in private hands, mostly The SETI Institute and The Planetary Society
I also had minor a minor support role in the COBE project. But one other intersting project, which unfortunately had little support, was a project we dubbed Argus. This was an attempt to monitor the Milky Way for supernova explosions, which are quite visible in the radio, but not optically, because of the heavy dust burden in the plane of the Galaxy. We collaborated with Woody Sullivan (who finally has a web page!), from the Astronomy Department at the University of Washington. Despite its scientific value, the program simply wasn't flashy enough to get funded over the long term.
After working in the radio astronomy group from 1981 to 1993, I spent a year as an assistant network administrator for the Science Computing Network, in the Earth & Space Sciences Division at JPL. It was a mixed network of mostly Sun workstations, along with Digital miniVAX, and a few Apple Macs, designed to supply computer support for the division scientists.
Early in 1994 I joined the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) project, where I worked on atmospheric radiative transfer models, image processing, data analysis, field work, and algorithm development. I was primarily involved with the thermal infrared surface radiance data product (AST09T). The field work included a trip to Venice, Italy, in April 2001, when none of the equipment we took with us worked right! See my Venice page, and my ASTER page for more about my work on this project.
In January, 2002, I joined the staff of the newly created Center for Long Wavelength Astrophysics, in the Earth & Space Sciences Division at JPL (which has since been renamed as simply The Science Division). I was initially involved in setting up the software for the center, supporting JPL astronomers in proposal preperation, and simulating data from the Space Infrared Telescope Facility (SIRTF), which was then expected to launch in January 2003. SIRTF eventually launched on August 25, 2003, and was renamed the Spitzer Space Telescope, in honor of Lyman Spitzer, Jr.. It was Spitzer who, in 1947, first pointed out the value of space based telescopes.
Since then I have been more heavily involved in super-resolution enhancement of Spitzer images. Spitzer makes observations by adding up individual frames that are dithered in half-pixel increments. That means there is information about structures smaller than one pixel in the collected images, and our software will extract that information, creating images that are enhanced in resolution by about a factor of 3. The first major result of this was the discovery of an asymmetry in the debris disk around the star Fomalhaut. Our resolution enhanced imagery was able to show that the observations were consistent with models which indicate that the asymmetry is caused by a planet embedded in the debris disk. Of course, this is only an indirect indication, but an exciting result, nonetheless. I was a member of the group which co-authored the paper. The disk models were created by Elizabeth Holmes, who sadly passed away in her office while working on her models. The paper is dedicated to her memory. The September 2004 issue of The Astrophysical Journal Supplement Series is exclusively devoted to the Spitzer Space Telescope. Our enhanced resolution capabilities were also reported in a poster presented at the 204th meeting of the American Astronomical Society, in Denver, Colorado, June 1, 2004.
A PDF preprint of this paper is avalable from the Spitzer Science Center page of publications for 2004.
Back to Tim Thompson's Home Page
