Mark Koepke, West Virginia University
Dramatic effects of shear in perpendicular plasma flow on ion-cyclotron waves

Abstract:
Current-driven electrostatic ion cyclotron waves require a relative drift of the electrons with respect to the ions parallel to the magnetic field. In the presence of adjacent layers of unequal perpendicular plasma flow, a common feature during geomagnetic storms, the equilibrium is changed and the parallel current's ability to excite ion-cyclotron waves improves dramatically, as demonstrated by laboratory experiments. These results have been used by the space physics community to interpret rocket and satellite data collected in the aurora borealis wherein occurs the most common and intense ion heating in the Earth's space environment. This talk will describe the context, present the lab results, compare the space results, and provide some perspective associated with these findings.

Frank Lind, University of Washington
Passive Radar Observations of the Aurora

Abstract:

Barry Uscinski, Cavendish Laboratory, Cambridge University
Phase-Screens - The Key to Random Wave Propagation, Part 3.

Abstract:
(see below)

Barry Uscinski, Cavendish Laboratory, Cambridge University
Phase-Screens - The Key to Random Wave Propagation, Part 2.

Abstract:
(see below)

Barry Uscinski, Cavendish Laboratory, Cambridge University
Phase-Screens - The Key to Random Wave Propagation, Part 1.

Abstract:
The model of a thin phase-modulating layer, or "phase-screen" was first used to explain experimental observations of wave scattering in ionospheric physics and radio astronomy in the l950's. The phase screen formed the basis of early theories of random wave propagation and allowed many important problems to be solved. It later formed an integral part of the most modern theoretical methods.

This set of lectures provides an introduction to random wave propagation by considering these early experiments and shows how the phase screen produced the concepts that explained them. The phase screen is then used to derive one of the most powerful of modern approaches to random propagation, that of the moment equations. These are then solved in terms of phase screens.

The lectures can be understood by any first year University student with a knowledge of the wave equation and Fourier Transforms. They provide the physical intuition that is necessary for successful use of random wave propagation theory.

Kirsten Lorentzen, University of Washington
Final Exam (Geophysics)
Precipitation of Relativistic Electrons on the Duskside

Abstract:
On August 20, 1996, a balloon-borne X-ray pinhole camera and high resolution germanium X-ray spectrometer observed an intense X-ray event near Kiruna, Sweden, at 1835 MLT, on an L-shell of 5.8. This X-ray event consisted of seven bursts spaced 100-200 seconds apart, with smaller 10-20 second variations observed within individual bursts. The energy spectra of these bursts show the presence of X-rays with energies greater than 1 MeV, which are best accounted for by atmospheric bremsstrahlung from mono-energetic 1.7 MeV precipitating electrons. The X-ray imager observed no significant motion or small-scale spatial structure in the event, implying that the bursts were temporal in nature. Ultra-violet images from the Polar satellite and energetic particle data from the Los Alamos geosynchronous satellites show a small magnetospheric substorm onset about 24 minutes before the start of the relativistic precipitation event. Since the balloon was south of the auroral oval and there was no associated increase in relativistic electron flux at geosynchronous altitude, the event must be the result of some mechanism selectively precipitating ambient relativistic electrons from the radiation belts.

The balloon X-ray observations are analyzed in a magnetospheric context, in order to determine which of several mechanisms for selective precipitation of relativistic electrons can account for the event. Resonance with electromagnetic ion-cyclotron mode waves on the equator is the most likely candidate. The drift of substorm-injected warm protons is calculated using input from the geosynchronous satellites. Wave growth in the model is driven by temperature anisotropies in the warm proton population. A numerical solution of the wave dispersion relation shows that electromagnetic ion-cyclotron waves can be excited in high-density duskside regions such as the plasmasphere or detached plasma regions. These waves can selectively precipitate relativistic electrons of energy 1.7 MeV in regions of density greater than 10 cm^-3, given the appropriate warm proton temperature, density and anisotropy. The model is used to investigate the effects of variations in these free parameters, and shows that only a narrow range of values can produce waves that interact with 1.7 MeV electrons.

Steven A. Cummer, NASA/Goddard Space Flight Center
Remote Sensing with Electromagnetic Radiation from Lightning

Abstract:
Lightning discharges radiate the bulk of their electromagnetic energy in the very low frequency (VLF, 3-30 kHz) and extremely low frequency (ELF, 3-3000 Hz) bands. This energy, contained in impulse-like signals called radio atmospherics or sferics, is guided for long distances over the Earth by multiple reflections from the ground and lower ionosphere (the region where the upper atmosphere becomes electrically conducting). These two facts suggest that sferics radiated from lightning and received at long distances (>1000 km) from the source discharge contain a great deal of information about both the state of the ionosphere along the propagation path and the dynamics of the current in the lightning discharge. This information can be extracted from measured sferics provided that electromagnetic propagation in this anisotropic waveguide formed by the ground and ionosphere can be accurately modeled.

To measure the source current waveforms of individual lightning discharges, we use a non-iterative deconvolution technique to extract the source current from observed broadband ELF radio atmospherics and a propagation impulse response calculated with an ELF/VLF propagation model. Of particular interest are those lightning discharges which cause sprites, the recently discovered transient optical flashes which occur at altitudes from approximately 50-90 km above thunderstorms. It has been hypothesized that an unusually large cloud-to-ground transfer of charge in the lightning stroke is responsible for the creation of sprites, but the results of this work show that the actual magnitude of this charge movement to the ground is consistently smaller than predicted by existing theories, suggesting that factors not considered in the models may play a role in sprite production.

To measure the characteristics of the ionosphere along the sferic propagation paths, broadband VLF magnetic field observations are compared to results from the same ELF/VLF propagation model which has been adapted to simulate the broadband signals considered in this work. This technique can provide accurate, propagation path averaged measurements of the free electron concentration in the nighttime D region of the ionosphere (altitudes of 60-90 km), a region which is extremely difficult to probe by other means.

Robert Winglee, University of Washington
Update on Mini-Magnetospheric Plasma Propulsion

Abstract:

Mark Wilber, University of Washington
Surveying the Magnetopause Encountered by Wind, Step 1: Boundary Classification

Abstract:
A large body of literature has demonstrated the existence of particle structures both interior and exterior to the magnetopause, yet the conditions under which they can be found are not always well known or understood. Between late 1994 and late 1998 the Wind spacecraft made more than 25 equatorial orbits around the Earth, encountering more than 150 seperate magnetopause crossings. This data set provides a significant sample which can be used for better characterizing the various boundary layer structures. The study disccused here is, as a first step, an attempt to simply describe each boundary crossing as locally `open' or `closed', in terms of macroscopic plasma properties under the assumptions of stress balance and bi-Maxwellian distributions. The tests employed are straightforward, but only after boundary normals first have been determined. After reviewing the different approaches used for finding boundary normals, survey progress will be discussed.

Matt Fillingim, University of Washington
Coincident UVI and WIND Observations of Pseudobreakups.

Abstract:

Bill Peria, University of California, Berkeley
A Statistical Study of Field-aligned Currents from the FAST satellite.

Abstract:

Ted Freeman, University of Washington
Final Exam (Physics)
A Study of Fermi Acceleration of Suprathermal Solar Wind Ions

Abstract:
The Wind spacecraft has observed numerous sunward bursts of ~2 MeV ions upstream of the Earth. Previous observations had only detected ions up to ~300 keV, and models which explained the bursts as Fermi acceleration of solar wind ions showed a similar upper limit. In this study, however, we present a particle simulation of Fermi acceleration to demonstrate that solar wind O⁶⁺ ions are the most likely source of these bursts. The model achieves MeV energies by using the highly turbulent interplanetary magnetic field data. We also show that it is possible to accelerate magnetospheric O⁺ from ~500 keV to MeV energies, but these particles scatter diffusively in the solar wind, rather than forming concentrated bursts. Hydrogen and Helium ions are ruled out because they would penetrate the electron detectors, which is not observed. We therefore predict that ion composition measurements will show these bursts to be solar wind O⁶⁺ ions.

Ben Barnum, University of Washington
Final Exam (Geophysics)
Electromagnetic and Optical Characteristics of Lightning Measured in the Earth's Ionosphere

Abstract:

Kerry Deutsch, University of Washington
A Global Study of Green Line Airglow Behavior

Abstract:

Kirsten Lorentzen, University of Washington
Precipitation of Relativistic Electrons by Electromagnetic Ion-Cyclotron Waves

Abstract:
In this talk, I will present some unusual balloon observations of high-energy X-rays, relate these observations to magnetospheric conditions, and discuss a wave-particle interaction model that can account for these observations.

For more information, see the INTERBOA balloon campaign page.

Damien Chua, University of Washington
Polar-UVI science in the ISTP extended mission

Abstract:
Although the nominal 1.5 year mission duration of the the International Solar Terrestrial Physics (ISTP) project has been completed, it is anticipated that the instruments aboard the Polar spacecraft and other ISTP platforms will continue to provide data on auroral plasma processes into the next millennium. Significant results from the studies using the UVI dataset are reviewed. The key role played by UVI imaging in collaborative studies with ground-based investigations and modeling in the ISTP extended mission will be discussed.

John Williams, University of Washington
Pulsating Aurorae

Cancelled due to illness

Ted Freeman, University of Washington
Upstream energetic particles: Fermi acceleration of solar wind oxygen ions

Abstract:
A simulation of Fermi acceleration of solar wind ions demonstrates that the 1.4 MeV upstream bursts observed by WIND are most likely to be solar wind O⁶⁺ ions.

George V. Khazanov, University of Alaska, Fairbanks
Global Superthermal Electron Transport

Abstract:
Two time-dependent kinetic models of superthermal electron transport are combined to conduct global calculations of the nonthermal electron distribution function throughout the inner magnetosphere. It is shown that the energy range of validity for this combined model extends down to the superthermal-thermal intersection at a few eV, allowing for the calculation of the entire distribution function and thus an accurate heating rate to the thermal plasma. Because of the linearity of the formulas, the source terms are separated to calculate the distributions from the various populations, namely photoelectrons (PEs) and plasma sheet electrons (PSEs). These distributions are discussed in detail, examining the processes responsible for their formation in the various regions of the inner magnetosphere. It is shown that convection, corotation, and Coulomb collisions are the dominant processes in the formation of the PE distribution function, and that PSEs are dominated by the interplay between the drift terms. Of note is that the PEs propagate around the nightside in a narrow channel at the edge of the plasmasphere as Coulomb collisions reduce the fluxes inside of this and convection compresses the flux tubes inward. These distributions are then recombined to show the development of the total superthermal electron distribution function in the inner magnetosphere and their influence on the thermal plasma. PEs usually dominate the dayside heating, with integral energy fluxes to the ionosphere reaching 1010 eV/cm2/s in the plasmasphere, while heating from the PSEs typically does not exceed 108 eV/cm2/s. On the nightside, the inner plasmasphere is usually unheated by superthermal electrons. A feature of these combined spectra is that the distribution often has upward slopes with energy, particularly at the crossover from PE to PSE dominance, indicating that instabilities are possible.

Eric Lund, University of New Hampshire
New Perspectives from FAST

Ted Freeman, University of Washington
Energetic Upstream Ions Observed by WIND: Fermi Acceleration of Solar Wind Oxygen Ions

Bob Holzworth, University of Washington
The Physics of Sprites, Jets and Elves

* Note the unsual day, time and location for this seminar.

Abstract:
Transient optical events in the upper atmosphere over thunderstorms includes a zoo of newly discovered phenomena called red sprites, blue jets and elves. Red Sprites, the most intensively studied of this zoo so far, are sometimes referred to as "cloud-to-ionosphere" lightning. Recent measurements of the optical properties indicate that the light emissions begin a few milliseconds after the parent positive cloud-to-ground lightning stroke and can last for several milliseconds. The optical spectra of these transient events indicate the red light is predominantly from the N2(1 pos) bands. The first indirect evidence that the emissions are, in fact, related to electrical discharge between 40 and 90km altitude comes from the effects on VLF waves propagating in the earth-ionosphere waveguide. While early physical models of these phenomena are more tightly bound by these high quality measurements, we still have no in-situ measurements of any of them.

George Parks, University of Washington
Equator-S

George Parks, University of Washington
Do Cosmic Snowballs Really Exist?

* Note the unsual day, time and location for this seminar.

Abstract:

Ron Elsen, University of Washington
Can global simulations produce the theta aurora?

Abstract:

Bob Holzworth, University of Washington
The Physics of Lightning Above the Clouds

Abstract:
What is our physical understanding of middle atmosphere and ionosphere perturbations caused by lightning? Electric currents and electromagnetic energy from lightning pass through the middle atmosphere and occasionally result in direct optical phenomena such as Red Sprites, Blue Jets, and Elves. Additionally low frequency electromagnetic energy from lightning penetrates entirely through the ionosphere, interacting with the ionospheric plasmas at all levels. These high altitude optical and electrical effects from lightning were not predicted and were thus a great surprise and continue to be exciting interest in the scientific community. Recent balloon, rocket and satellite experiments will form the basis for a review of the in-situ electrodynamical measurements above thunderstorms. So far no one has actually succeeded in making direct measurements in the luminous region of a Red Sprite, but we do know many things about them from remote measurements. This talk will attempt to review our state of understanding of the physical phenomena in the middle atmosphere and ionosphere which is caused by lighting. The talk will concentrate on experimental evidence.

Bring your lunch.

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• 20 Oct., 3 Nov. 1998: Lyons: Magnetospheric Processes Leading to Precipitation,
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• 21 October 1997: Berdichevsky et al.: Evidence for Multiple Ejecta; April 7-11, 1997 ISTP Sun-Earth Connection Event,
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  Geophys. Res. Lett., in press, 1997
  
• 7 October 1997: Pasko et al.: Heating, ionization and upward discharges in the mesosphere due to intense quasi-electrostatic thundercloud fields,
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• 3 June 1997: Reiff and Burch: IMF-Dependent Global Convection Model,
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