TRESPASS FALL 1995 SCHEDULE

DATE SPEAKER AFFILIATION TOPIC
8/31/95 Robert Sheldon University of Bern Observation And Theory Of Ring Current Ion Populations
9/7/95 V. K. Jordanova University of Michigan Kinetic Model Of The Terrestrial Ring Current
9/14/95 NO SEMINAR MEMORIAL SERVICE FOR PROFESSOR HERB BRIDGE (MIT)
9/21/95 Richard Lambour Phillips Lab Modeling Plasmaspheric Dynamics With The Magnetospheric Specification And Forecast Model
9/28/95 Jiasheng Chen Louisana State Energetic Helium Isotopes Trapped in the Magnetosphere University
10/5/95 Sixto Gonzalez Arecibo Observatory Light Ions In The Topside F-Region At Arecibo
10/12/95 Roger Anderson University of Iowa GEOTAIL Plasma Wave Observations From The Earth's Magnetosphere To Its Deep Geomagnetic Tail
10/19/95 Berend Wilken MPAE/Germany Oxygen-rich Particle Bursts In The Distant Magnetotail: Observations With The Spectrometer HEP-LD On GEOTAIL
10/26/95 Mark Moldwin Fla. Institute of Tech. Substorms And Plasmaspheric Dynamics
11/2/95 Howard Singer NOAA/SEL Space Weather And Space Science From Geosynchronous Orbit
11/9/95 Margaret Kivelson UCLA Twisted Magnetic Fields In Space And The Currents That Produce Them
11/17/95 Craig Kletzing UNH Electron Acceleration By Inertial Alfven Waves
11/21/95 Michael Kelley Cornell On A New Paradigm For Mesoscale Ionospheric Structure At Mid-latitudes
11/23/95 THANKSGIVING GOBBLE GOBBLE
11/30/95 Rod Heelis U. of Texas at Dallas The Equatorial Ionosphere: A View From The Topside
12/7/95 David Anderson Phillips Lab Theoretical Modeling Of The 1994 Chile/MISETA Campaign
12/14/95 AGU NO TRESPASSING





DESCRIPTION



Robert Sheldon

Date: 8/31/95
Time and Place: 10:45 p.m. in CAS 500
Affiliation: Formerly of the University of Bern, he has joined the Boston University Center for Space Physics

Observation And Theory Of Ring Current Ion Populations


The Earth's ring current, composed of protons and electrons circling the earth at an altitude of about 10,000 miles, is responsible for changes in the magnetic field that are clearly observable on the surface of the earth, especially during "magnetic storms". Long before spaceflight, it was these fluctuations of the compass that provided the first evidence of space plasmas and the extended magnetic influence of the earth, the magnetosphere. With the advent of spaceflight and instrumented satellites, we have learned a great deal about these space plasmas, yet surprisingly, we do not fully understand basic questions about the ring current: where it comes from, how intense it becomes, how it is transported, how it dissipates. In the past ten years we have accumulated satellite data sets that can shed light on these questions, and the burden now rests on the modellers. I will discuss past and current modelling efforts, as well as some of the potential uses for a dynamic ring current model.

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EMAIL: rsheldon@buasta.bu.edu
Telephone: 617-353-7448

Vania K. Jordanova

Date: 9/7/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: University of Michigan Department of Atmospheric, Oceanic and Space Sciences

Kinetic Model Of The Terrestrial Ring Current


A kinetic model of the terrestrial ring current, including losses due to charge exchange, Coulomb collisions (both energy degradation and pitch angle scattering) and wave-particle interactions is developed. The kinetic equation is averaged over a bounce period and solved numerically for arbitrary pitch angle. General expressions for quasi-linear diffusion coefficients for energetic particles resonating with EMIC waves are derived, considering the presence of heavy ion components in the plasma, and incorporated in the model. The recovery phase of a typical moderate magnetic storm is studied, using a time-dependent Volland-Stern potential model and a dipole geomagnetic field. Energy and pitch angle measurements of the H+, O+ and He+ ring current populations, supplied by the CHEM spectrometer on the AMPTE satellite are used as initial conditions. The spatial regions of ion cyclotron wave instability are determined by: (1) calculating the convective growth rates from the dispersion relation using the ring current characteristics as supplied by the model; (2) integrating the convective growth rates along the wave paths, assumed to be field-aligned; (3) selecting regions of maximum wave amplification. Spectral power density of 1 nT^2/Hz is adopted within the unstable regions according to the new statistical study of Pc 1-2 magnetic pulsations at low L values, obtained by the AMPTE/CCE magnetic field experiment. The time evolution of the ring current population, together with calculations of energy deposition rates, and ion precipitating fluxes are presented. The precipitation losses are compared to the losses in a pure electron-proton plasma.

EMAIL: jordanova@sprlc.sprl.umich.edu
Telephone:

Rick Lambour

Date: 9/21/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: United States Air Force Phillips Laboratory


Modeling Plasmaspheric Dynamics With The Magnetospheric Specification And Forecast Model


We have modified the Rice Magnetospheric Specification and Forecast Model (MSFM) to include a low-energy (E < 100 eV) plasmaspheric population to facilitate investigation of the local-time distribution and evolution of cold plasmaspheric ions at geosynchronous orbit. We utilize measurements of dense, cold (1-100 eV) ions from the Los Alamos Magnetospheric Plasma Analyzers (MPA) as a basis for comparison with output from the MSFM. The MSFM is an operational space weather model which makes use of dynamic input data consisting of ground-based geophysical indices and spacecraft observations to trace particle motion in the inner and middle magnetosphere. The model has been able to reproduce the formation and evolution of the observed geosynchronous plasmaspheric intervals quite well, and has provided an explanation for previously puzzling observations. We will briefly review the large-scale structure and dynamics of the plasmasphere, the structure and operation of the MSFM, and present detailed comparisons between the model and the observations.

EMAIL: lambour@amenra.phl.af.mil
Telephone: 617-377-2431

Jiasheng Chen

Date: 9/28/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Louisiana State University Department of Physics and Astronomy

Energetic Helium Isotopes Trapped in the Magnetosphere


Helium nuclei (40-100 MeV/nucleon) have been measured within the magnetosphere (L < 6) by the ONR-604 instrument on CRRES during the 1990/1991 period. ONR-604 resolved the individual helium isotopes with a resolution of 0.1 amu. Each geomagnetically trapped isotope can be represented by a power law energy spectrum, and the energy spectrum of the 3He is different from that of 4He. In the energy range 51-86 MeV/nucleon, the 3He/4He ratio is 7.4 (+/-2.6) for L = 1.15-1.3 and 2.2 (+/-0.6) for L = 1.8-2.15. At L between 2.15 and 6.0, as L decreases the 3He/4He ratio increases, the He/proton ratio decreases, and the helium energy spectrum softens. At L < 2.15, however, these trends are no longer observed. Potential sources, including the inward diffusion and the atmospheric interaction, will be discussed.

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Telephone:

Sixto Gonzalez

Date: 10/5/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Arecibo Observatory

Light Ions In The Topside F-Region At Arecibo


New measurements of light ions in the topside ionosphere over Arecibo will be presented. We will discuss the altitude and temporal variations of the three major ion species in the topside ionosphere (oxygen, hydrogen, and helium ions). The ISR spectra are reduced using a a non-linear least squares fitting algorithm which allows for Te, Ti, [O+], [H+], and [He+] to be free simultaneously. One of the more striking features of the ion distributions is the formation of a He+ layer during the night at altitudes near the O+/H+ transition region. Typical results were found to be as follows. The transition altitude between O+ and H+ (ht) was generally between 1200 and 1500 km during the day, with a dramatic postsunset collapse, of several hundred kilometers, and reaching 550 km before sunrise. The helium ion concentrations tend to be quite low, 10-15 percent of the topside plasma. In this seminar we will first discuss some details of the ISR experimental technique, then show the results and finally compare the data with theoretical simulations.

EMAIL: sixto@naic.edu
Telephone:

Roger R. Anderson

Date: 10/12/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: University of Iowa Department of Physics and Astronomy

GEOTAIL Plasma Wave Observations from the Earth's Magnetosphere To Its Deep Geomagnetic Tail


Since its launch in July of 1992, GEOTAIL has made many traversals of the Earth's geomagnetic tail with apogee ranging from 30 Re to more than 210 Re. The GEOTAIL Plasma Wave Instrument has detected a fascinating variety of electric and magnetic field emissions both in the near-earth magnetosphere and throughout the geomagnetic tail. Electromagnetic whistler-mode chorus and electrostatic electron cyclotron harmonic emissions dominated the outer magnetosphere. Intense very low frequency electromagnetic and higher frequency electrostatic emissions were detected near magnetopause and bow shock crossings. Detections of Langmuir waves or the low frequency cutoff of continuum radiation at the electron plasma frequency have provided useful identification of the boundaries and regions throughout much of the GEOTAIL orbit. Broadband electrostatic noise is usually detected when high speed plasma flows occur. Auroral kilometric radiation provides remote monitoring of geomagnetic disturbances. Plasma wave observations during events such as continuum storms and passages of plasmoids or flux ropes down the tail help us understand the dynamics of geomagnetic storms. The characteristics of the various plasma waves observed and their possible origins will be discussed.


EMAIL:
Telephone:

Berend Wilken

Date: 10/19/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Max Planck Institute for Aeronomy

Oxygen-rich Particle Bursts In The Distant Magnetotail: Observations With The Spectrometer HEP-LD on GEOTAIL


The HEP-LD spectrometer identifies the mass (A) of energetic atoms by a combined time-of-flight (T) and energy (E) measurement. The novel design of the detector system uses the principle of a one-dimensional 'projection camera' to determine the particle's direction of incidence over an angular range of 180 degrees (12 intervals) as a function of A, E, and T; in combination with the sectored spin motion of the spacecraft this leads to a contiguous coverage of the unit sphere in phase space with 192 pixels.

In January and February 1994, when GEOTAIL was in the plasmasheet, HEP-LD detected intense oxygen beams with mean energies around 250 keV and durations of 10 to 20 min. The tailward flowing beams were associated with significant variations in the magnetic field components By and Bz. The observed angular anisotropies support strong convection (stationary density gradients or Speiser orbits are less likely alternatives). The oxygen bursts seem to occur in conjunction with substorm related activities observed by geostationary satellites.

EMAIL: wilken@linax2.mpae.gwdg.de
Telephone:

Mark Moldwin

Date: 10/26/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Florida Institute of Technology Department of Physics and Space Sciences

Substorms And Plasmaspheric Dynamics


The plasmasphere (the region of cold, dense plasma corotating around the Earth) is important to the overall configuration and dynamics of the Earth's magnetosphere and ionosphere. Though the plasmasphere has been extensively studied for over 30 years, many fundamental questions about its structure and dynamics are not well understood. These include: What mechanism creates the extremely sharp plasmapause gradient?, What is the source mechanism for the electric fields responsible for the plasmasphere's motion?, and What is the role of the substorm in creating dense plasmaspheric regions in the inner magnetosphere? This talk will outline some of the current thinking in plasmaspheric dynamics and introduce a new model that addresses the questions posed above.

EMAIL: moldwin@galileo.pss.fit.edu
Telephone:

Howard Singer

Date: 11/2/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: NOAA/Space Environment Laboratory

Space Weather And Space Science From Geosynchronous Orbit


Particle and magnetic field measurements have been made from geosynchronous orbit for more than 20 years. These measurements continue to provide a unique data base for studies of the earth's magnetosphere and solar-terrestrial interactions as well for monitoring "space weather." This presentation will focus on the past, present and future of magnetic field measurements in geosynchronous orbit with an overview of the history of the measurements, their importance for space weather, and a discussion of selected scientific contributions. Examples will be presented of progress in our understanding of magnetic pulsations, substorms, and current systems that has benefited from the availability of geosynchronous magnetic field data.

EMAIL: hsinger@sel.noaa.gov
Telephone: 303-497-6959

Margaret Kivelson

Date: 11/9/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: University of California at Los Angeles Institute for Geophysics and Planetary Physics

Twisted Magnetic Fields In Space And The Currents That Produce Them


The space around the Earth is filled with plasmas, gases of charged particles that are bound to the planet by the magnetic field within which they are embedded. Changing plasma motion in one location drives current along the magnetic field and thereby produces responses many earth radii away. If a field-aligned current becomes strong enough, it can twist the field line along which it is flowing into a helical structure that is referred to as a flux rope. Such field configurations have been observed at Earth and elsewhere in space. This talk will link some features of observed flux ropes to both theoretical analysis and to computer simulations. The flux ropes that appear in computer simulations carry current between the ionospheres in the northern and southern hemispheres. Noting that large scale currents in space plasmas must ultimately close on themselves, one must consider how the flux rope currents close; this question will be discussed.

EMAIL: mkivelson@igpp.ucla.edu
Telephone:

Craig Kletzing

Date: 11/17/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: University of New Hampshire Physics Department and Space Science Center

Electron Acceleration By Inertial Alfven Waves


As Alfven waves with finite extent perpendicular to the magnetic field propagate, there is a region of parallel electric field in the ``wave front'' of the propagating wave. For short perpendicular wavelengths this parallel electric field can be large enough to accelerate electrons resonantly. This short- wavelength limit is of interest to the space physics community because Alfven waves propagating from the magnetosphere to the ionosphere are thought to accelerate auroral electrons via this process. The problem is solved for the case of uniform plasma density and background magnetic field. The parallel electric field solution is then applied to a background Maxwellian plasma to study the effects of the acceleration due to this field on the electron distribution function. Two effects are found: (1) a modest acceleration of the bulk of the background electrons and (2) a Fermi-like resonant acceleration of a small component of the electrons up to velocities of the order of twice the Alfven speed. Although both effects always occur, the response of the background electrons for the resonant acceleration process is a sensitive function of the magnitude, wavelength, and timescale associated with the driving perpendicular electric field and does not produce a significant signature for all conditions. However, for reasonable values of perpendicular electric field magnitude and scale size, and plasma parameters appropriate for auroral field lines at altitudes around 7000 km near where the Alfven speed peaks, the effect can be significant.

EMAIL: kletzing@unhedi2.unh.edu
Telephone: 603-862-3187

Michael C. Kelley

Date: 11/21/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Cornell University School of Electrical Engineering

On A New Paradigm For Mesoscale Ionospheric Structure At Mid-latitudes


In January of 1993 researchers from Cornell and Boston University carried out another of a long series of joint observing programs. This highly productive cooperative effort spans more than a decade and much of the globe. In the 1993 effort the emphasis was on the comparison of mid-latitude airglow images and simultaneous radiowave observations. The results of this study have led the speaker and (now) former graduate student Clark Miller to propose a new way of thinking about the ionospheric structures imaged by BU and probed by the Arecibo radar. For decades now ionospheric plasma structures have been considered to be a passive response of the ionization to to an atmospheric gravity wave. Indeed the whole field of gravity wave research was inspired by the observation of traveling ionospheric disturbances. Peculiarities in the properties of TID's were then interpreted as originating in the gravity waves which they passively represent. The data obtained in January 1993 along with the numerical simulations and analysis carried out by Clark Miller have led us to quite another viewpoint. It seems that of the various possible modulations of the nighttime ionosphere caused by gravity waves, a subset is enhanced by extracting energy from the background plasma medium while the rest are damped. The result represents the observable set which may be a far cry from the original distribution of the gravity waves themselves. Upon reflection it is realized that the only way we have to detect gravity waves in the thermosphere is through their effect on the plasma! The extreme limit of the plasma response in our model results in the turbulent high velocity upwellings reported in the last two solar minimum periods at Arecibo in the 70's and Japan in the 1980's. We hope to explore this phenomenon in the next few years over Arecibo, and to test the hypothesis presented here.

EMAIL: mikek@ee.cornell.edu
Telephone: 607-255-7425

Rod A. Heelis

Date: 11/30/95
Time and Place: 10:30 a.m. in CAS 500
Affiliation: University of Texas at Dallas William B. Hanson Center for Space Sciences

The Equatorial Ionosphere: A View From The Topside


The dynamics and composition of the topside equatorial ionosphere are sensitive functions of processes occurring in the F-region and below at tropical latitudes. On large temporal (months) and spatial (>50 deg longitude) scales, the behavior of the ionosphere is primarily influenced by changes in the composition and dynamics of the neutral atmosphere. Effects due to changes in photoionization and ExB drift motion are largely functions of local time. The effects of neutral wind induced motions are also dependent of the orientation of the magnetic field with respect to the geographic meridians thus leading to longitudinal variations in the topside ionospheric composition and dynamics. At smaller temporal and spatial scales the topside ionosphere may also be the site of plasma irregularities customarily termed plasma bubbles. Such structures originate in the bottomside F-region and rather specific conditions are required to observe bubbles at high altitudes in the topside ionosphere. The conditions prevailing during such observations may provide indicators of the mechanisms at work. Here we will describe some of the large and small scale features observed by the Defense Meteorological Satellite at altitudes around 800 km in the equatorial region of the ionosphere. At large scales longitudinal variations in the topside ionospheric composition will be described and reconciled with variations induced in neutral wind induced plasma transport. At smaller scales we will describe observations of upward moving bubble plasma and the local time restrictions implying the role of dynamo electric fields in the observed phenomena.

EMAIL: heelis@utdallas.edu
Telephone: 214-883-2851

David Anderson

Date: 12/7/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: United States Air Force Phillips Laboratory

Prelim: Ionospheric Modelling/Equatorial Aeronomy


During the Chile/MISETA campaign, 27 Sept. to 3 Oct., 1994, a number of ground-based and satellite-borne instruments obtained data on electron density profiles, neutral wind velocities, vertical and horizontal ExB drift speeds, optical and radar signatures of equatorial bubbles and spread-F/scintillation occurrences. In this talk we will briefly discuss the various sensors, what they measure and how these measurements can be used to understand the basic physical processes operating in the equatorial ionospheric F region. We use the Phillips Laboratory Global Theoretical Ionospheric Model (GTIM) to calculate electron and ion densities as a function of altitude, latitude and local time and compare these calculated ambient ionospheric profiles with specific observations on specific campaign days. Included as inputs to the time-dependent, theoretical model are 1.) the observed vertical ExB drifts from the Jicamarca incoherent scatter radar facility and 2.) observed nighttime meridional neutral winds measured by a Fabry-Perot interferometer at Arequipa, Peru . Supplementing these inputs are neutral temperature and densities from the MSIS86 model and neutral winds from the HWM87 model. A primary objective of the study is to calculate fluxtube -integrated plasma instability growth rates to try to better understand the physical mechanisms which are responsible for initiating or suppressing the growth of low latitude plasma instabilities which are observed on some nights but not on others.

EMAIL: danderson@phl.af.mil
Telephone: 617-377-3310


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