TRESPASS SPRING 1995 SCHEDULE

DATE	SPEAKER	AFFILIATION	TOPIC
1/19/95	George Siscoe	Boston University	Energy Flow Through The Magnetosphere
1/26/95	Larry Lyons	Aerospace	A New Theory For Magnetospheric Substorms
2/2/95	Eberhard Mobius	UNH	Sources Of Energetic Particles Upstream Of The Bow Shock: In-Situ Acceleration And Magnetospheric Leakage
2/9/95	Terry Onsager	UNH	Structure Of The Plasma Sheet And Its Boundary Layers
2/16/95	John Craven	University of Alaska	Quantitative Evaluation Of A Magnetic Mapping Between The Poleward Boundaries Of The Auroral Oval And The Plasma Sheet
2/23/95	Robert Schunk	Utah State	Ionospheric Variations At High Latitude During Storms And Substorms
3/2/95	Michael Hesse	NASA/GSFC	Substorms In The Magnetotail: Analytical Theory And Numerical Modeling
3/9/95	SPRING BREAK	NO TRESPASSING
3/16/95	Mary Hudson	Dartmouth	New Radiation Belts In The Magnetosphere
3/23/95	Tony Lui	APL	How Do Current Disruptions Fit To Substorm Models?
3/30/95	Manuel Grande	Rutherford Lab	Substorm Composition And Morphology In Storm And Quiet Times: Observations Of The Magnetospheric Ion Mass Spectrometer on CRRES
4/6/95	Greg Ginet	Phillips Lab	Radiation Belt Dynamics: Some Analysis And Modeling Of The CRRES Database
4/13/95	Ray Greenwald	APL	Preliminary Results From SuperDARN: Imaging Convection And Birkeland Currents
4/20/95	Roger Arnoldy	UNH	Magnetic Impulse Events Measured At High Latitudes
4/27/95	John Foster	MIT/Haystack	Mid-Latitude Storm Effects: A Multi-Instrument Perspective
5/4/95	Andy Christensen	Aerospace	Auroral Effects On The Upper Atmosphere: The ARIA Rocket Project
5/11/95	Dan Baker	U. of Colorado	Global Magnetospheric Processes And Nonlinear Substorm Dynamics

DESCRIPTION

George Siscoe

Date: 1/19/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Boston University Center for Space Physics

Energy Flow Through The Magnetosphere

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

Larry Lyons

Date: 1/26/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: The Aerospace Corporation

A New Theory For Magnetospheric Substorms

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Eberhard Mobius

Date: 2/2/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: University of New Hampshire Physics Department and Space Science Center

Sources Of Energetic Particles Upstream Of The Bow Shock: In-Situ Acceleration And Magnetospheric Leakage

I am going to talk about the identification of the different sources of upstream ions, solar wind, magnetosphere and interstellar pick-up ions. I will also cover the current views on shock acceleration, diffusive, simulations etc. and a few things we hope to achieve with CLUSTER.

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Terry Onsager

Date: 2/9/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: University of New Hampshire Physics Department and Space Science Center

Structure Of The Plasma Sheet And Its Boundary Layers

Low-altitude spacecraft traversing the nightside auroral oval on magnetotail field lines provide a snapshot of the entire plasma sheet, extending from near the Earth out to the distant reconnection site. The low-altitude signature of the plasma sheet contains distinctive spatial structure and also exibits dramatic temporal variations. Data from the Akebono spacecraft have been used to investigate the spatial structure in the distant plasma sheet and the variations in the plasma sheet density and temperature over periods of many hours. The spatial features observed in individual spacecraft passes at low altitudes often includes velocity-dispersed ion structures and regions with an absence of ion precipitation. These features are discussed in terms of the downtail plasma sheet structure, and proposed interpretations are compared. The plasma sheet properties observed on consecutive spacecraft passes are then investigated, and the temporal variations in the plasma sheet are inferred. We observe periods of both cooling and heating of the plasma sheet that appear to be related to the orientation of the interplanetary magnetic field and to overall geomagnetic activity.

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Seminar Review

John Craven

Date: 2/16/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: University of Alaska Geophysical Institute and Physics Department

Quantitative Evaluation Of A Magnetic Mapping Between The Poleward Boundaries Of The Auroral Oval And The Plasma Sheet

Auroral features and boundaries are increasingly being mapped magnetically into the magnetotail using magnetic field models such as those of Tsyganenko. However, quantitative evaluations are lacking that show the models are reasonable for quiet periods, much less for more active intervals when the field configuration is changing rapidly. The objective here is to use two observed physical boundaries assumed to be nearly identical, and to quantitatively evaluate the mapping between the two boundaries for varying levels of magnetic activity and the orientation of the IMF Bz component. The high-latitude boundaries of the plasma sheet (at high altitudes) and the auroral oval (at low altitudes) are used. Position of the plasma sheet boundary is first determined using ISEE-1 or -2 measurements of the flux of 2-keV electrons, and it is then mapped magnetically to auroral altitudes (*isee). Simultaneous measurements with DE 1 are used to determine the poleward boundary of the aurora (*de) at the mapped local time of ISEE. Fifty six mappings are available in the Southern Hemisphere for the April- July period in 1983 under either quiet or active conditions. Initial analysis indicates that the difference *de - *isee is dependent on the Ygsm position of ISEE and the sign of Bz. The results can also be presented using distances from a model current sheet. A successful mapping from the auroral oval to the plasma sheet boundary will aid in the identification of reasonable magnetic field models and in the mapping of structures at progressively lower latitudes throughout the region of discrete auroral features.

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Seminar Review

Robert Shunk

Date: 2/23/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Utah State University Center for Atmospheric and Space Sciences

Ionospheric Variations At High Latitude During Storms And Substorms

Significant progress has been made during the last decade with regard to simulating the response of the ionosphere-thermosphere system to variations in the solar, interplanetary, magnetospheric and mesospheric drivers. However, the bulk of the effort has been directed toward simulating the climatology of the system. In comparison, there have been very few simulations pertaining to ionospheric weather. The weather disturbances occur during geomagnetic storms and substorms as well as during changes in the interplanetary magnetic field. Ionospheric weather features include propagating plasma patches, subauroral ion drift channels, sun-aligned polar cap arcs, and ionospheric convection vortices. Thermospheric weather also occurs and is induced both by ionospheric weather and by upward propagating tides and gravity waves from the mesosphere. The current status of ionospheric and thermospheric weather simulations will be discussed.

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Seminar Review

Michael Hesse

Date: 3/2/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: NASA/Goddard Space Flight Center Laboratory for Extraterrestrial Physics Electrodynamics Branch

Substorms In The Magnetotail: Analytical Theory And Numerical Modeling

In recent years, major progress has been made in the modeling of magnetospheric dynamics, in particular in the area of magnetospheric substorms. This progress is based both on advances in analytical theory and numerical modeling. We present results of analytical theory applied to the problem of energy transfer and local energy balance in the magnetosphere. These results will be put in a large scale modeling context by both magneto-hydrodynamic and kinetic simulations of magnetic reconnection, plasmoid formation and evolution, and inner tail processes in the magnetotail. We will also discuss the pre-onset formation of thin current sheets, and their role as loci of dissipative processes required to drive a large scale unstable evolution. The large scale evolution involves the transition of magnetic reconnection to the magnetotail lobes, which can significantly shorten dynamical time scales and increase energy transfer rates. We will conclude with a discussion of the next steps in theoretical substorm research.

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Seminar Review

Mary Hudson

Date: 3/16/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Dartmouth College Physics and Astronomy Department

New Radiation Belts In The Magnetosphere

The rapid formation of new electron and proton radiation belts at L = 2.5 following the March 24, 1991 Storm Sudden Commencement (SSC) observed at the CRRES satellite has been modelled using a relativistic guiding center test particle code. The SSC is modelled by a bipolar electric field and associated compression and relaxation in the magnetic field, superimposed on a background dipole magnetic field. The proton source population is assumed to consist of both solar and trapped inner zone protons. The simulations show that both populations contribute to drift echoes in the 20-80 MeV range, and to the broad spectral peak observed in the 20-40 MeV range by CRRES. With the same field model, proton acceleration by the SSC differs from electrons in having different source populations and non-relativistic conservation of the first adiabatic invariant which leads to greater energization of protons for a given decrease in L than for relativistic electrons. Drift echoes, energy spectra and flux distribution in L at the time of injection are consistent with CRRES observations, while there is some evidence for subsequent or continued acceleration during the ensuing geomagnetic storm. Hydromagnetic wave interaction with the newly formed radiation belt will be discussed.

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Seminar Review

Tony Lui

Date: 3/23/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Johns Hopkins University Applied Physics Laboratory

How Do Current Disruptions Fit To Substorm Models?

One of the grand challenges in magnetospheric discipline is to identify and understand the physical processes occurring during a magnetospheric substorm. Key substorm phenomena and several prominent substorm models are first reviewed. A plausible substorm model based on a synthesis of existing ones is constructed. This synthesis model can account well for the near-Earth substorm activities such as current disruptions and substorm current wedge formation as well as distant-tail substorm features such as flux ropes or plasmoids. The role of magnetic reconnection in substorm dynamics for this model will be elaborated.

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Seminar Review

Manuel Grande

Date: 3/30/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Rutherford Appleton Laboratory Lab

Substorm Composition And Morphology In Storm And Quiet Times: Observations Of The Magnetospheric Ion Mass Spectrometer on CRRES

The Magnetospheric Ion Mass Spectrometer on the CRRES satellite was an ideal instrument to observe storms and substorms at near geosynchronous altitude. Its design enabled simultaneous measurements to be made of the mass, charge and energy of ions in the range 30-400 keV/Q. These energies are typical of ions accelerated by substorm dipolarisations; the charge and mass resolution enables us to separate out components with Ionospheric and Solar Wind sources. In the life of the mission we accumulated a data base of some 95 dispersionless substorms, during both quiet and storm times. The talk will consist of a review of work in progress, and will center on attempts to answer the following questions:

What are the sources of the material energised at dipolarisation in a substorm?
What are the sources of storm time material in the ring current?
Are there differences between substorms in Storm and Quiet times?
Are there differences in occurrence and composition between single and multiple substorms?
What can we say about small-scale substorm morphology?

CRRES provided data relevant to all these questions, and the talk will attempt to place these in context, and indicate future areas for consideration.

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Seminar Review

Greg Ginet

Date: 4/6/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: United States Air Force Phillips Laboratory

Radiation Belt Dynamics: Some Analysis And Modeling Of The CRRES Database

A wealth of data on energetic electron and proton dynamics in the radiation belts was obtained by the Combined Radiation and Release Effects Satellite (CRRES) which operated in a geosynchronous transfer orbit for 14 months near solar maximum. Time scales range from the long decay period (thousands of days) of the inner proton belt during quiet periods to the prompt formation of new radiation belts in two minutes after the 24 March 1991 Sudden Storm Commencement. After a brief overview of the data to illustrate the variety of dynamic phenomena, the presentation will focus on an analysis of the Dartmouth pulse model for the prompt formation of electron radiation belt observed during the 24 March 1991 event. Details of the physical mechansims will be addressed and scaling relations giving the maximum penetration distance as functions of first adiabatic invariant, initial distribution, and the pulse parameters will be shown. The applicability of the pulse model to smaller events will also be discussed.

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Seminar Review

Ray Greenwald

Date: 4/11/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: Johns Hopkins University Applied Physics Laboratory

Preliminary Results From SuperDARN: Imaging Convection And Birkeland Currents

Currently, five of the northern hemisphere radars of the SuperDARN HF radar network are in operation. These radars are sensitive to backscatter from small-scale ionospheric irregularities located principly in the F-region of the high-latitude ionosphere. The Doppler information available from the backscattered signals may be used to study the large-scale structure and dynamics of high-latitude convection. In addition, it has been recently shown that the vorticity information derivable from two dimensional convection observations may be used to study the two dimensional structure and dynamics of Birkleland current regions. In this talk, I will review the techniques that we are currently using to obtain convection and Birkleland current images. I will then apply these techniques to several topical issues in space physics research including: a) polar cap convection under northward IMF, b) extended local time coverage of convection and Birkeland current dynamics, and c) global convection responses to substorms. The implications of these observations in relation to current ideas and models will be discussed.

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Seminar Review

Roger Arnoldy

Date: 4/20/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: University of New Hampshire Space Science Center

Magnetic Impulse Events Measured At High Latitudes

Ground measurement of bursts of Pc 1 pulsations (minutes duration) are a common dayside phenomena at high latitudes. For the past several years, dayside ground measurements of similar duration bursts of Pc 5 period pulsations [MIE] have attracted a great deal of interest concerning their role in dayside reconnection. From an analysis of several years of induction antenna data from southern and northern hemisphere sites in the Antarctic, Greenland, and Canada, it is found that about 70% of all isolated MIE events are associated with Pc 1 bursts, and about half of all events are conjugate between hemispheres. There appears to be no definitive phase relationship between the onset of the Pc 1 bursts and the MIE, suggesting that both might be produced by the same event on the dayside but have different source locations. Correlative data from ground and spacecraft measurements suggest this to be the case and also show that the Pc 1 are waves inside the magnetosphere propagating into the ionosphere. Finally, a timing study between ground sites separated by two hours local time shows that the isolated MIEs are measured first near the subsolar point and at later times down both flanks of the magnetosphere, suggesting a source mechanism for these events which has an E-W component of the motion which when projected to the equatorial plane is the order of the solar wind speed. As this source moves down the magnetospheric flanks it creates well within the magnetosphere conditions [pressure pulse?] ripe for the ion cyclotron generation of the Pc 1 bursts associated with the MIE.

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Seminar Review

John Foster

Date: 4/27/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: MIT/Haystack Observatory

Mid-Latitude Storm Effects: A Multi-Instrument Perspective

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Seminar Review

Andy Christensen

Date: 5/4/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: The Aerospace Corporation

Auroral Effects On The Upper Atmosphere: The ARIA Rocket Project

Energy sources (particle and Joule heating ) and momentum sources (ion drag) affect the composition and neutral winds in the upper atmosphere. The composition, reflected in the amount of atomic oxygen relative to nitrogen, is observed to decrease during substorms. Strong shears are observed in the neutral winds and the vorticity in the wind field drives field aligned currents back into the magnetosphere. These processes have been investigated in the Atmospheric Response in Aurora (ARIA) project. In situ measurements with instrumented rocket payloads, chemical releases and ground based techniques have been used in this frontier study of mesoscale processes.

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Dan Baker

Date: 5/11/95
Time and Place: 3:45 p.m. in CAS 500
Affiliation: University of Colorado Laboratory for Space Physics

Global Magnetospheric Processes And Nonlinear Substorm Dynamics

The interaction of the magnetosphere with the solar wind represents a remarkable sequence of events. Energy is extracted very episodically from an essentially stochastic driver [the solar wind] and is stored in a global-scale reservoir [the magnetotail]. Then, despite the vast distances and the long propagation time scales involved, after a rather fixed and narrowly constrained time period the magnetosphere unloads the stored energy. This unloading apparently represents a very coherent and repeatable set of processes that occur throughout the magnetotail and the polar ionosphere. Fundamentally, we find clear evidence of a repetitive dynamical cycle during such "substorms" that must involve the nearly simultaneous initiation of microscale instabilities and mesoscale processes at many locations throughout the magnetosphere-ionosphere system. The latest thinking concerning these phenomena in substorms is discussed and viable models for linking together local processes into a coherent global sequence are discussed.

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Seminar Review

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