Space Physics Seminar - winter-2014

Jan. 10, 2014
3:30 p.m. - 5 p.m.
6704 Geology

Presented By:

• Jasper Halekas - Space Sciences Laboratory, UC Berkeley

The Earth's Moon, often thought of as a passive absorber of plasma, is in fact a surprisingly prolific source of non-thermal ions. As we have learned in recent years, a significant fraction of the incident solar wind proton population reflects above magnetized regions of the lunar crust. In addition, sputtering from the surface and ionization of the tenuous exosphere produce heavy lunar ions. Both populations react to the convection electric field, with lunar ions following cycloidal trajectories, and reflected protons following prolate or curtate cycloids, depending upon their initial velocity after reflection. Reflected protons interact with the incoming solar wind, driving foreshock-like turbulence and large scale perturbations of the plasma environment around the Moon. Lunar ions, on the other hand, have little apparent effect on the ambient plasma, but carry information about the lunar atmosphere and its sources, composition, and dynamics. These two ion populations, both readily observed by ARTEMIS, allow us to understand the Moon's interaction with the ambient plasma, by utilizing remote ion observations to unfold the details of processes occurring at or near the surface.

Jan. 17, 2014
3:30 p.m. - 5 p.m.
6704 Geology

Presented By:

• Toshi Nishimura - UCLA

Plasma transport in the plasma sheet and auroral oval is known to involve a significant amount of transient fast flows that are longitudinally localized and occur in various magnetic conditions. Recently, those fast flow channels are found to play a crucial role in triggering substorm auroral onset, whose pre-onset sequence has been in strong debate in the community for decades. Not only substorm onset, but many other phenomena such as steady magnetospheric convections (SMCs) and Pi2 pulsations are also identified to involve fast flow channels. On the other hand, these findings led to many interesting questions in broader aspects of the magnetosphere-ionosphere coupling: (1) How are plasma sheet flow channels triggered? Is there any precursor on open field lines? (2) What is the mechanism of the substorm onset instability? And (3) how do flow channels affect the inner magnetosphere? This talk will address those issues by using the growing capability of ground-based auroral and radar observations as well as conjugate satellite observations.

Jan. 24, 2014
3:30 p.m. - 5 p.m.
6704 Geology

Presented By:

• Yuhou Wang - UCLA

Seminar Description coming soon.

Jan. 31, 2014
3:30 p.m. - 5 p.m.
Slicther 6850

Presented By:

• Michael Nicolls - Center for Geospace Studies, SRI International

The weak radiowave scattering from electrons in the ionosphere is referred to as incoherent scatter (IS). The power spectrum of the scattered signal is related to the intrinsic density fluctuations of the medium through one of the most well-developed theories in plasma physics. IS measurements are particularly sensitive to ion motions in the upper atmosphere, allowing for studies of coupling to both the neutral and electron gases. In particular, observations with the Advanced Modular Incoherent Scatter Radar (AMISR) systems deployed at Poker Flat, Alaska and Resolute Bay, Nunavut are revealing dynamical properties of the ionosphere. I will discuss some of these areas, which include turbulence generation in the collision-dominated D-region, gravity wave dissipation and forcing throughout the lower thermosphere, and energy dissipation, heating, and plasma convection associated with solar wind-magnetosphere-ionosphere coupling.

Feb. 7, 2014
3:30 p.m. - 5 p.m.
6704 Geology

Presented By:

• Margaret Chen - Aerospace Corporation

The ring current consists of oppositely drifting ions and electrons with energies of ~ 10 to 200 keV in the same region of the Earth’s magnetosphere that the radiation belts occupy. During geomagnetic storms, these particle populations at ring current energies are significantly increased. Associated with the storm-time ring current is a perturbation magnetic field that distorts the inner magnetospheric magnetic field, thereby affecting radiation-belt dynamics. In this seminar I will discuss briefly early idealizations of ring current formation and then focus on recent advances in understanding ring current dynamics using more realistic self-consistent guiding-center drift and loss simulations. A magnetically and electrically self-consistent treatment of particle transport tends to limit the formation of the ring current as compared to simpler treatments. The ring current intensity and spatial distribution are also significantly affected by variations in the plasma sheet, the major source to the ring current. Comparisons of in-situ magnetic field, proton and electron data, and energetic neutral atom (ENA) intensity with corresponding quantities from our self-consistent ring current simulation model during storm events will be shown. Such comparisons test the ability of our model to characterize the ring current plasma environment and magnetic field and challenge further our understanding of ring current dynamics.

Feb. 14, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Tamas Gombosi - Univ. of Michigan

The term "Space Weather" refers to conditions in space that can endanger our technology or human health. This research area emerged in the 1990s and rapidly became the dominant theme of solar, interplanetary, magnetospheric, ionospheric and thermospheric research. This talk will review the evolution of space weather research from the 1990s through the present and briefly discuss the state-of-the-art in space weather prediction. The talk will conclude with the discussion of some new research that might lead to actual predictive capabilities in the not too distant future.

Feb. 21, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Michael Schulz - Lockheed Martin

Seminar Description coming soon.

Feb. 28, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• S. R. Kaeppler - SRI International

The Auroral Current and Electrodynamics Structure (ACES) mission consisted of two sounding rockets launched nearly simultaneously into a dynamic multiple-arc aurora with the goal of obtaining multi-point observations of the closure of field-aligned current and electrodynamics associated with a discrete auroral arc system. The payloads were flown along nearly conjugate magnetic field footpoints, separated in altitude with small temporal separation. The high altitude payload (ACES High) took in situ measurements of plasma and electrodynamic parameters that mapped from the magnetosphere, which form the input signature into the lower ionosphere. The low-altitude payload (ACES Low) took similar observations within the E-region ionosphere where perpendicular cross-field closure current can flow. A case study is presented of a quasi-stable auroral arc crossing, and in situ electron flux, electric field, and magnetic field observations for this event are presented. Poker Flat Incoherent Scatter Radar (PFISR) observations of plasma velocity flows are compared with in-situ observations. A model describing the precipitating auroral electron flux has been developed and the model parameters were adjusted to be consistent with the electron flux observed by the ACES Low payload. The enhanced Hall and Pedersen conductivities resulting from the auroral precipitation are calculated, along with other parameters determined from the electron flux. For the condition that the divergence of the current is equal to zero within the arc, the current structure is determined using in situ electric fields and the model conductivities. The magnetic field perturbations from the model currents are compared with the in-situ observations. Multi-point in-situ data, ground-based data, and modeling are used to investigate the current structure and energy dissipation associated with a discrete auroral arc. These data are further used to test the 2-D auroral arc model put forth by Bostrom [1964].

March 7, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Tamitha M. Skov - Aerospace Corporation

At 1 AU, the association between multiple spacecraft observations of solar transient structures is not always straightforward. Differences are apparent even when separation distances of the spacecraft are small. This means detailed understanding of the three-dimensional geometry of these transients and their associated sub-structures remains elusive. A new spatial mapping technique promises advancement beyond existing models (Mulligan et al., 2012) in that it creates contour maps of solar wind parameters to quantitatively follow spatial variations in both radial and azimuthal dimensions. What is distinctly different about this technique is that it reveals aspects of transient geometry and dynamics in a far more visually intuitive way than previously accomplished.