Last Updated: Mon Feb 7 11:51:08 EST 2005
January 11, 18, 25, February 01, 08, 15, 22 March 01 08
- All talks start promptly at 4:00 in Room 200, Cummings Hall, Thayer School of Engineering (see map for directions)
We will discuss the physics of the Sommerfeld and Brillouin precursors in the context of broadband pulse propagation in dielectric media. The emphasis will be on visible femtosecond pulse propagation in water but we will also consider electromagnetic pulse propagation in other media such as ionized plasmas, semiconductors, and waveguides.
Pulse Propagation in Dielectric Media
by
Dr. Ulf Osterberg
Thayer School of Engineering
Dartmouth College
4:00 p.m.
Tuesday, January 11, 2005
Room 200 Cummings Hall
Thayer School of Engineering
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Transport of Solar Wind Plasma into Earth's Magnetosphere under Northward Interplanetary Magnetic Field
by
Dr. Hiroshi Hasegawa
Thayer School of Engineering
Dartmouth College
Space weather phenomena such as magnetic storms and aurorae are caused by charged particles originating in the solar wind and thus understanding how solar wind plasma enters Earth's magnetosphere is of great importance. It is generally believed that magnetic reconnection is the dominant entry mechanism, especially during southward interplanetary magnetic field (IMF) conditions when the IMF and geomagnetic fields are antiparallel at the low-latitude magnetopause. But satellite observations show that the plasma content in the outer magnetosphere in fact increases during northward IMF periods when reconnection should be less efficient. In this talk, we review mechanisms that could account for the plasma entry under northward IMF and show evidence for one of the candidate mechanisms other than reconnection--entry mediated by the Kelvin-Helmholtz instability. We also try to provide constraints on theoretical models from the observational viewpoint.
4:00 p.m.
Tuesday, January 18, 2005
Jackson Conference Room Cummings Hall
Thayer School of Engineering
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Geomagnetically Induced Currents: The End of the (Space Weather) Line
by
Dr. Simon Shepherd
Thayer School of Engineering
Dartmouth College
The end result of a long chain of geomagnetic events beginning at the Sun is the induction of currents in conductors near the surface of the Earth. These so-called Geomagnetically Induced Currents (GICs) can cause serious effects to the technological systems in which they flow. Accurate predictions are, therefore, critical in mitigating the potential impacts of GICs to an evermore technology-dependent society. We are developing an integrated space weather model to predict the occurrence of the large electric and magnetic fields associated with large GICs. Techniques used to calculate GICs will be discussed in addition to results from our latest modeling efforts and some basic GIC theory.
4:00 p.m.
Tuesday, January 25, 2005
Room 200 Cummings Hall
Thayer School of Engineering
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The Structure and Dynamics of Magnetospheric Cusp: Cluster Observations
by
Dr. Qiugang Zong
Center for Space Physics
Boston University
I will present Cluster observations in the magnetospheric cusp region with emphasis on the importance of the solar wind azimuthal and north/south flow as a dynamic driver of the cusp, and even the entire magnetosphere.
4:00 p.m.
Tuesday, February 01, 2005
Room 200 Cummings Hall
Thayer School of Engineering
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Guiding-Center Fokker-Planck Collisions
by
Dr. Alain J. Brizard Department of Chemistry and Physics
Saint Michael's College
A new formulation for collisional kinetic theory is presented based on the use of Lie-transform methods to eliminate fast orbital time scales from a general bilinear collision operator. As an application of this new formalism, a general guiding-center bilinear Fokker-Planck (FP) collision operator is derived following the elimination of the fast gyromotion time scale of a charged particle moving in a nonuniform magnetic field. Classical transport processes in strongly magnetized nonuniform plasmas can, thus, be described in terms of this reduced guiding-center FP kinetic theory.
4:00 p.m.
Tuesday, February 08, 2005
Room 202 Cummings Hall
Thayer School of Engineering
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Sounding Rocket Measurements of Thermal Electrons in Active Nightside Aurora
by
Dr. Elizabeth MacDonald
University of New Hampshire
On January 14th 2002 the SIERRA sounding rocket was launched from Poker Flat Research Range, Alaska into active substorm expansion aurora and reached 735 km. For the first time, direct measurements of the cold ionospheric population in darkness were made by the UNH Thermal Electron Detector (TED). At these middle altitudes, understanding this population is important because the thermal electrons can carry currents coupling the lower ionosphere and the magnetospheric auroral source. This thesis, focusing on the development and analysis of this new instrument, incorporates the study of two distinct areas. One area is the direct measurement of the ambient thermal electrons which both form the background of the dynamic high latitude ionosphere and contribute directly to its behavior by modifying the plasma environment for other constituents. The second focus area is the concept that any attempt to measure thermal electrons must also be a careful study of potentials forming near conducting bodies in a plasma, a still poorly understood subject. The TED instrument response shows that a non-monotonic potential barrier can form in the sheath around the detector and prevent access to the core of the thermal electrons. A technique has been developed for reconstructing the plasma distribution which enables key measurements of temperature, density, and flow. Thermal electron core temperatures are seen to vary greatly, from as low as ~0.1 eV in the polar cap to a maximum of ~0.8 eV in auroral arcs. Outside active precipitation the density agrees with an independent calculation from the HF wave receiver. This verifies the method used for estimating the payload potential. In the ``inverted V'' and Alfvenic regions the HF measure of density was used to normalize our results for the changing payload potential. The thermal data indicate that in the dark, the non-negligible auroral and secondary emission currents must be accounted for in order to understand what controls the spacecraft potential. Finally, it is shown that, given this understanding of the potential structure and a quantitative measure of the payload potential, the critical thermal electron drift should be measurable with this new instrument.
4:00 p.m.
Tuesday, February 15, 2005
Room 200 Cummings Hall
Thayer School of Engineering
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PICTURE: A Rocket Experiment for Direct Imaging of an Extrasolar Planet
by
Dr. Supriya Chakrabarti
Director of the Center for Space Physics,
Boston University
We have recently been awarded a sounding rocket program to obtain a direct image of an extrasolar giant planet. The Planet Imaging Concept Testbed Using a Rocket Experiment (PICTURE) is a collaboration between Boston University, Jet Propulsion Laboratory, Massachusetts Institute of Technology and NASA Goddard Space Flight Center. It is scheduled for launch in 2007. Most extrasolar planets have been discovered using the radial velocity technique. However, to obtain fundamental physical parameters of these planets (for example, mass and orbital inclination), we need additional measurements. PICTURE will use a nulling interferometer developed at JPL for the Terrestrial Planet Finder mission along with other enabling technologies to demonstrate their flight worthiness. Additionally, we will improve the capabilities of sounding rocket subsystems, such as the attitude control system, for other applications. The target for PICTURE is Epsilon Eridani (Eri b). It is a nearby (~3.2 pc) K2 V star (0.8 solar mass) whose estimated age is 0.5 – 1 Gyr. A dust ring, with characteristics similar to the Kuiper belt, was discovered around this star in 1998. Based on the morphology of the ring structure, a hypothetical second planet (Eri c) was also suggested. The radial velocity detection indicated a highly eccentric (e ~ 0.61) orbit and an astrometric observation reported its mass to be about 1.2 MJ. In this talk, I will outline the challenges we face and our approach. I will also provide a status report.
4:00 p.m.
Tuesday, February 22, 2005
Room 200 Cummings Hall
Thayer School of Engineering
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Studying Solar Energetic Events with Ice Cores
by
Dr. Larry Kepko
Boston University
It is known that energetic solar proton events can penetrate deep into the Earth's polar atmosphere, dissociating O3 and N2 and leading to the formation of odd nitrogen compounds (or generically referred to as NOy). Several recent works have examined ice core nitrate data and observed impulsive nitrate enhancements within weeks of large known solar proton events. It has been suggested that the nitrate molecules produced by large solar proton events can precipitate downward rapidly and be deposited by snowfall into polar regions.
In the past few years, advancements in ice core analysis techniques have allowed for the production of much higher-resolution data than previously available. In this paper we present the results of a comparison between extremely high-resolution ice core measurements and space-based cosmic ray data. The nitrate data are the highest-resolution available today, are accurately dated, and come from multiple cores. We will address the question of whether the previously observed correlation, which was based on a limited number of events, is reproducible.
4:00 p.m.
Tuesday, March 01, 2005
Jackson Conference Room Cummings Hall
Thayer School of Engineering
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Causes and Consequences of Filamentary Structure in the Polar Ionosphere
by
Dr. Joshua Semeter
Department of Electrical and Computer Engineering
Boston University
Plasma transport through the polar cap ionosphere is governed by electrodynamic coupling with the magnetosphere and solar wind. As a consequency of this coupling, coherent patches of plasma entering from the dayside deform into filamentary horizontal structure in the nightside auroral zone. Complementary to this process is electron precipitation, which produces filamentary structures in the field-parallel direction. In either case, this structure is synonymous with horizontal gradients, and these gradients occur in regions where plasma flow velocities are particularly large. The initial filamentation driven by magnetospheric coupling should, thus, cascade to smaller scales via Rayleigh-Taylor-type instabilities. How this filamentation process affects magnetosphere-ionosphere coupling is not understood. In this talk I will discuss these issues from a combined experimental and modeling perspective, and attempt to frame some of the questions we need to address.
4:00 p.m.
Tuesday, March 8, 2005
Room 200 Cummings Hall
Thayer School of Engineering
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