TRESPASS SPRING 1999 SCHEDULE

The Institute for Astrophysical Research

Walking down the 5th floor hallway past the Astronomy Department office,itis clear that something new is afoot. What is purpose of the new construction?What is all this one hears about a telescope in Flagstaff and a new Institute? Where have all the printers gone and where are the mailboxes? Will anything ever be the same again? Many of the answers to these questions involve a new unit which came into being on January 1st. Called the "Institute for AstrophysicalResearch," this new grouping will be to many of the astrophysicists in the AstronomyDepartment what the CSP is to the space physicists -- their research "home." TheInstitute, or "IAR," will help its members manage their research projects, actas a central clearing house for research infrastructure, manage our externaltelescope sites such as at Flagstaff and at the South Pole, and work tostrengthen the research and education components of our astrophysics groups.In this talk, I will introduce the Institute and its founding membersand try to convey a sense of how the Institute, the Center for Space Physics,and the Astronomy Department will be related. I will also try to summarize many of the current research projects being pursued within the IAR and make someguesses as to where the IAR might venture in the next few years.This is an exciting time for astrophysicists, both at Boston Universityand across the world. By banding together to form a new Institute, we are muchbetter poised to bring a higher fraction of the world-wide excitement inastrophysics to Boston University. We have built our new Institute onfoundations similar to those supporting the Center. We hope that with the IAR wecan reach some of the same levels of enhanced productivity and discovery whichhave characterized the first decade of operations of the CSP.

Multi-instrument observations of cusp/cleft dynamics related to solar wind-magnetosphere interactions.

According to existing models of the open magnetosphere, magneticstresses give rise to an initial east-west motion of magnetic flux tubes whichdepends on the IMF By polarity. Hence, an IMF By controlled prenoon-postnoonoccurrence asymmetry of auroral transients is expected to be a unique signatureof merging related activity testable from ground. Statistics on cusp data fromNy-Aalesund (Svalbard) during negative IMF Bz conditions, shows that the auroralevent occurrence distribution in the 1000-1400 MLT sector depends on IMF By,consistent with predictions of reconnection to within a 95% level of confidence.In this presentation the pattern of moving auroral forms around noon, i.e. fromDanmarkshavn (East-Greenland) and Ny-Aalesund, is investigated in more detail.This instrumentation offers a unique opportunity to study the auroral activityon either side of noon. Simultaneous ion drift observations by the EISCAT radarsas well as the Greenland magnetometer data allow us to study the spatial andtemporal relationships between the auroral activity and the ion convection. Thefocus is placed on the morphology of dayside cusp/cleft auroras, based onoccurrence, location, intensities, structures and direction of motions.

Searching for Life Elsewhere.

There have been a number of scientific revolutions in the last two decades thatchange our view of the potential for life elsewhere. These are driven by ourchanging views of the origin and evolution of life on Earth, the environmentsthat occur on planets and that might be conducive to life, and the discovery ofplanets orbiting around other stars. In particular, the rapid origin of life onEarth argues that life is likely to originate on any planet that meetsrelatively straightforward environmental requirements. In our solar system, twoplaces are generally thought to meet these requirements--Mars and Europa--andthe NASA exploration program is centered in large part on searching for evidenceof life. The discovery of life elsewhere (or of its absence) will haveimportant implications for understanding the nature of life and itsphilosophical significance. I'll discuss the history of life on Earth andimplications for the occurrence of life elsewhere, the potential for life toexist elsewhere in our solar system, and the possibility of life on planetsaround other stars. In addition, I'll discuss the philosophical implications ofthe search for life elsewhere and what it would mean to find (or not find) life.

Large-scale B- and E-field parameters derived from multi-point geostationary particle measurements

Charged particle drifts in the inner magnetosphere are determined by acombination of the magnetic field geometry (gradient and curvature) and themacroscopic electric field. Magnetic gradient and curvature drift velocitiesdepend linearly on the field aligned and field normal kinetic energy of theparticles and are in opposite directions for ions and electrons. In contrast,electric field drift velocities are the same for all species and energies. Ifone can measure the drift speed of particles as a function of species, energy,and pitch angle, it is possible to some extent to monitor separately thestrength of the macroscopic electric field and certain aspects of the magneticfield geometry. Average particle drift speeds can be measured by timing thearrival of spectral features at different spacecrafts. Thus the paramters can bemeasured on a size scale of the separation between the spacecrafts, and on atime scale of the drift time between spacecrafts. We are developing thistechnique with the Los Alamos MPA and SOPA instruments into what may ultimatelybe a routine and automated monitor of such global field parameters in thegeostationary region. The derived parameters may help in case studies inselecting global field models for the inner magnetosphere. The technique alsoprovides a good test and demonstration of the capabilities that we may expectfrom particle instruments on future many satellite constellation missions.

Exploring the Solar System Frontier: Heliospheric Interface from 1 AU

The interaction of our star, the sun, with the surrounding interstellar medium leads to formation of the heliosphere. How does this interaction occur? Where is the termination shock and what is its nature? Where is the heliopause, a boundary that separates the solar wind and galactic plasma of LISM? Is the interstellar wind subsonic or supersonic? These questions have not been answered, and direct experimental data on the heliospheric interface region are extremely scarce and ambiguous. We will discuss possibilities of experimental study of the heliospheric interface remotely, from 1 AU. Global heliosphere imaging in energetic neutral atom (ENA) fluxes would allow remote study of the termination shock. The technique is well understood and the instrumentation is mature. Another possible technique is mapping of the heliopause in extreme ultraviolet (EUV) that was recently proposed and may allow determination of the interstellar magnetic field.

Electron Phase-Space Tornados:Observations in Space, Simulations, and Animations

Four Earth orbiting satellites have recently measured streams of isolated electric field pulses traveling along the Earth's magnetic fields in regions as diverse as the auroral ionosphere, the Earth's bow-shock, and the magnetotail. These measurements result from stable electron density depletions and contain some of the highest electric field energy densities found in space plasmas. In 1D, these depletions result from "phase-space electron holes" where rotating trapped electron vortices in (X-Vx) phase space are contained by a strong positive potential. In 2D, electron holes form tornadoes when viewed in (X-Y-VX) phase space. This talk discusses the observations, theory and simulations of phase-space electron holes. Additionally, we will demonstrate simulated electron phase-space tornado behavior through use of computer animations.

An early autumn chill, in Uranus' upper atmosphere

Between 1977 and 1983, the Uranian system was the subject of intense monitoring by stellar occultations. An analysis of 23 occultation lightcurves showed an increase of the average temperature at 1 microbar of 8 K/year (Baron et al. 1989), from ~ 100 K in 1977 to ~ 170 K in 1983. No correlation with latitude was detected. All published stellar occultations of the Uranian atmosphere at 1 microbar occurred before Uranus' southern summer solstice in 1985, which raises the question: is the temperature increase tied to the seasons on Uranus? The current subsolar latitude is -34 degrees, more equatorial than the first Uranian occultation in 1977. If the temperature variation were tied strictly to season, we should expect a temperature slightly smaller than the first temperature detected. We observed a stellar occultation by Uranus from the Perkins telescope at Lowell Observatory and the IRTF at Mauna Kea on November 6, 1998, from which we measured the temperature at one location in the summer hemisphere and two in the winter. The derived temperature was ~ 80 K on the summer hemisphere, suggesting a correlation with season. In the winter hemisphere we derived a temperature of ~ 135 K, so the seasonal dependence of the temperatures in the winter hemisphere are unclear.

The Largest Wave: The Magnetospheric Response to Hot Flow Anomalies

The purpose of the talk was to demonstrate the close relationship between transients in the foreshock, magnetopause, magnetosheath, and dayside auroral ionosphere. Hot flow anomalies are tenuous hot cavities with strongly deflected flows observed upstream from the bow shock. They have their origins in kinetic effects associated with the passage of interplanetary magnetic field (IMF) tangential discontinuities. The study of these hot flow anomalies currently involves two major questions: are they rare, or are they only observable near the bow shock, and what are their effects upon the magnetosphere?

Proton Transport in the High Latitude Regions,One of the Processes at the Origin of Aurora

Originating in the magnetosphere, protons in the keV energy range precipitate down to the ionosphere of high latitude regions. They interact with the ambient neutrals through collisions: this interaction mainly leads to electron and ion productions and auroral emissions. The transport of protons in the atmosphere can be described by solvingthe Boltzmann equation. In the light of space/ground observations I will underline the key role protons can play in the ionospheric perturbations. I will then present results of 3D-in-space numerical simulations concerning the impact of protons on both the ionosphereand the thermosphere on a planetary scale. Finally I will discuss the relevance of H emissionobservations for proton precipitation study, and more generally for auroral issues.

The Non-Optical Aurora: Recent Radio and X-Ray Observations

The aurora is perhaps best known for its beautiful optical displays. However, energetic particles entering the Earth's atmosphere produce a variety of responses. These include not only photometric emissions, but radio emissions, ionization, bremsstrahlung x-rays, and absorption of radiowaves. In this talk, I will discuss some of the recent observations and underlying plasma physics associated with auroral x-rays, auroral radio emissions, as well as cosmic noise absorption.

High Latitude Ionospheric Electrodynamic Parameters During Auroral Substorms.

Substorms are the dominate feature of nightside magnetosphere. However, although they seem to control the majority of energy and mass flow, they are not well understood. One of the unknowns is the exact nature of the role of the ionosphere during a substorm. Critical to understanding this are the electrodynamic parameters, such as conductivity, which control they flow of currents in to, out of, and through the ionosphere. Comprehensive measurements of these parameters were presented in this talk. Data were used from the DE-1 and DE-2 (Dynamics Explorers 1 and 2) satellites to investigate substorm currrent systems. The standard view of a substorm is that a current wedge forms in the nightside magnetosphere which diverts the cross tail current, channeling it through the ionosphere. The two DE spacecraft were in orbits such that one, at high altitude, could measure visible emissions from the aurora (across the whole nightside ionosphere) while the second spacecraft, in a low altitude orbit, could measure the fields and particles associated with the substorm current system. The speaker presented a technique wherein observations were ordered by region of a "classic" or ideal substorm bulge. Data were sorted into catagories such as the east or west edge of the bulge or the bulge center. The size of the substorm region was also normalized to a standard "size" and "shape". Once this was done data from different substorms could be combined to provide statistics of a "standard" set of substorm electrodynamic parameters. The results indicate a substorm current wedge which has a longitudinally extended region of downward field-aligned currents in the midnight and early morning sectors and a more localized return current in the substorm surge region.

Are Small Comets Bombarding Earth?

In 1986, Louis Frank and colleagues from the University of Iowa astonished the geophysical community by proposing that Earth is being bombarded by house-sized comets at the rate of 20 per minute. The hypothesis was invoked to explain dark spots in far-ultraviolet images of the upper atmospheric airglow obtained with the Iowa instrument on the Dynamics Explorer 1 satellite. This idea was widely criticized because of the profound implications for the water budget of Earth's ionosphere, atmosphere, and ocean, for the water budgets of other planets, and for effects on a host of other solar system phenomena. The small comet controversy resurfaced in 1997 with the report by the same group of new observations of airglow dark spots, as well as new images of oxygen and OH features in emission, obtained with an ultraviolet camera on the POLAR satellite, launched in 1996. Following the latest reports, an NRL team used the world's most powerful radar in terms of sensitivity-solid angle product to search for small comets: the Naval Space Surveillance System radar. The radar routinely observes space objects with radar cross sections of order 0.1 square meters in low Earth orbit and 1 square meter at altitudes of 10,000 20,000 km. Thousands of small comets should have been detected in six weeks of data obtained during Fall, 1997. None were found. In this seminar, I will review the small comet hypothesis and the controversy, and will describe the radar search.

The Interactions of the Jupiter's Inner Magnetosphere with the Atmospheres and Ionospheres of the Galilean Satellites: Io and Europa

This talk will focus on HST observations of UV OI 1356/1304 A multiplet emissions obtained for Europa (Hall et al., 1995; 1998), STIS Io images of OI 1356A (Woodward et al., 1999), and MHD models of the magnetospheric-atmospheric interactions occurring at Io and Europa (Saur et al., 1998; 1999). After a review of the salient observational features, I will discuss the theoretical/numerical aspects of our MHD models of these magnetospheric-atmospheric interactions with an emphasis on the underlying physics. With this background I will then examine methods of remotely sensing and diagnosing the nature of these interactions.

The polar cusp and the low latitude boundary layer (LLBL)

A review of cusp and LLBL research is given, with an emphasis on low-altitude satellite observations. Progress in quantitative modeling of the cusp is stressed. A consideration of the reasons for believing the LLBL is partly closed and partly open are presented. It will be argued that magnetosheath plasma is introduced onto closed field lines in ways incompatible with merging alone; i.e., other means such as plasma instabilities or chaotic particle motion must be invoked to explain some LLBL observations.

The Role Of The Cusp As A Source For Magnetospheric Particles: A New Paradigm?

New observations from the NASA GGS POLAR satellite of cusp energetic particle [CEP] events indicate that there is a mechanism in the dayside cusp that accelerates the solar wind plasma to 100s and 1000s of kiloelectronvolts energies. The mechanism seems to be active much of the time but is impulsive in nature with an event having a lifetime of 10 to 60 minutes. This mechanism is capable of producing energetic particles that fill the cusp on a continual basis as well as a layer that straddles the magnetopause along the flanks of the magnetosphere. These energetic particles enter the magnetosphere as a result of gradients in the magnetic field and the resultant drifts they cause; ions entering along the dawn flank drifting to the west and electrons entering along the dusk flank drifting east will carry a current. Since these particles will drift to distances less than six earth radii in the nightside equatorial plane, their variations in time probably control the dynamics of the magnetosphere in the range 6 < L < 13 and these particles are probably the source of the plasma sheet energetic particle population. This result has the potential to be a new paradigm for the way we view the dynamics of the magnetosphere.