Space Physics Seminar - spring-2013

April 5, 2013
3:30 p.m. - 5 p.m.
6704 Geology

Presented By:

• Mikhail Malkov - UCSD

Seminar Description coming soon.

April 12, 2013
3:30 p.m. - 5 p.m.
6704 Geology

Presented By:

• Jamesina Simpson - Univ. Utah

Seminar Description coming soon.

April 19, 2013
3:30 p.m. - 5 p.m.
6704 Geology

Presented By:

• Chih-Ping Wang - AOS/UCLA

Seminar Description coming soon.

April 26, 2013
3:30 p.m. - 5 p.m.
6704 Geology

Presented By:

• Wen Li - AOS/UCLA

Seminar Description coming soon.

May 3, 2013
3:30 p.m. - 5 p.m.
6704 Geology

Presented By:

• Gerhard Haerendel - Max Planck Institute for Extraterrestrial Physics

The lecture will review the gross steps in the solar wind-magnetosphere interaction leading to driven convection in the high-latitude magnetosphere or temporary storage of magnetic energy in the tail (and subsequent release during the substorm). Both processes work during the growth phase. The main questions that will be addressed in the lecture are: (1) What is the nature of the growth phase arc? (2) What are the auroral steamers arising from poleward boundary intensifications (PBI’s)? (3) What process is behind the correlation between substorm onset and near-contact of the two aforementioned arcs? (4) Which type of current system is connected with substorm breakup? Possible answers to these questions will be approached by analyzing published and new data on the growth phase arc and auroral streamers as well as on the relation between substorm onset and dipolarization fronts in the near-earth tail.

May 10, 2013
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Xianzhe Jia - University of Michigan

Despite the high degree of axial symmetry in its intrinsic magnetic field, Saturn’s electromagnetic radiation (SKR), its magnetic perturbations and its particle populations all exhibit rotation-associated modulations at periods close to the planet’s rotation period. Furthermore, recent Cassini observations reveal that the electromagnetic period not only drifts slightly over a time scale of years but also differs for sources at high latitudes in the north and south. Identifying the cause of the periodicities has proved challenging because different parts of the system are tightly coupled. The upper atmosphere/ionosphere, with low enough inertia to allow drift and high enough inertia to maintain phase coherence, has been considered to be a plausible source region of the periodicities. This presentation will describe results from an atmospheric vortex model put forward to account for the various observed periodicities. Using the global magnetohydrodynamic (MHD) model, BATSRUS, we have quantitatively characterized how Saturn’s magnetosphere would respond to vortical flows in the ionosphere. Our initial modeling focused on the magnetospheric modulations at the dominant southern period by including a localized vortical flow structure in the southern high-latitude ionosphere that rotates at roughly the rate of planetary rotation. The model is found to reproduce a variety of observed magnetospheric periodicities associated with the period of the dominant southern SKR. Emboldened by the initial success, we have extended our atmosphere vortex model to investigate the contributions of northern hemisphere perturbations at a different period by including an additional vortical structure in the northern ionosphere. The dual-source model is shown to reproduce many well-documented results of Cassini data analysis including the features that appear distinctly at each of the two periods and those that appear as a carrier signal with amplitude modulation and phase shifts.

May 17, 2013
3 p.m. - 5 p.m.
Geology 6704

Presented By:

• Christine Gabrielse - UCLA

Motivated by recent observations of intense electric fields and elevated energetic particle fluxes within flow bursts beyond geosynchronous altitude [Runov et al., 2009, 2011], we apply modeling of particle guiding centers in prescribed but realistic electric fields to improve our understanding of energetic particle acceleration and transport towards the inner magnetosphere through model-data comparisons. Representing the vortical nature of an earthward traveling flow burst, a localized, westward-directed transient electric field flanked on either side by eastward fields related to tailward flow is superimposed on a nominal steady-state electric field. We simulate particle spectra observed at multiple THEMIS spacecraft located throughout the magnetotail and fit the modeled spectra to observations, thus constraining properties of the electric field model. We find that a simple potential electric field model is capable of explaining the presence and spectral properties of both geosynchronous altitude and “trans-geosynchronous” injections at L-shells greater than 6.6 RE in a manner self-consistent with the injections’ inward penetration. In particular, despite the neglect of the magnetic field changes imparted by dipolarization and the inductive electric field associated with them, such a model can adequately describe the physics of both dispersed injections and depletions (“dips”) in energy flux in terms of convective fields associated with earthward flow channels and their return flow. The transient (impulsive), localized, and vortical nature of the earthward-propagating electric field pulse is what makes this model particularly effective.

May 17, 2013
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Xiaojia Zhang - UCLA

Electron cyclotron harmonic (ECH) waves have long been considered a potential driver of diffuse aurora in Earth?s magnetotail. However, the scarcity of intense ECH emissions in the outer magnetotail suggests that our understanding of the amplification and the relative importance of these waves for electron scattering is lacking. We conduct a comprehensive study of wave growth and quasi-linear diffusion to estimate the amplitude of loss-cone-driven ECH waves once diffusion and growth balance but before convection or losses alter the background hot plasma sheet population. We expect this to be the most common state of the plasma sheet between episodes of fast convection. For any given wave amplitude, we model electron diffusion caused by interaction with ECH waves using a 2-D bounce-averaged Fokker-Planck equation. After fitting the resultant electron distributions as a superposition of multi-component subtracted bi-Maxwellians, we estimate the maximum path-integrated gain using the HOTRAY ray-tracing code. We argue that the wave amplitude during quasi-steady state is the inflection point on a gain-amplitude curve. During quasi-steady state, ECH wave amplitudes can be significant (~1mV/m) at L~8, but drop to very low values (<~0.1mV/m) in the outer magnetotail (L~16), and likely fall below the sensitivity of typical instrumentation relatively close to Earth mainly because of the smallness of the loss cone. Our result reinforces the potentially important role of ECH waves in driving diffuse aurora and suggests that careful comparison of theoretical wave amplitude estimates and observations is required for resolving the equatorial scattering mechanism of diffuse auroral precipitation.

May 24, 2013
3:30 p.m. - 4:30 p.m.
Geology 6704

Presented By:

• Prof. Gregory Howes - University of Iowa

Heliophysics is presently entering an exciting new era, with a fleet of missions this decade---including the Van Allen Probes, Interface Region Imaging Spectrograph (IRIS), Magnetospheric Multiscale (MMS), Solar Orbiter, and Solar Probe Plus missions---set to drive breakthroughs in our understanding of the flow of energy from the sun, through interplanetary space, to the magnetospheres of the Earth and other planets, and to the outer boundary of the heliosphere. Some of the outstanding problems in heliophysics we hope to solve include the heating of the solar corona and acceleration of the solar wind, the storage and explosive release of magnetic energy in the solar atmosphere and the propagation of these disturbances through the heliosphere, the energization and loss of energetic particles trapped in the Earth's magnetosphere, and the effects of the variable solar wind forcing on the coupled system of Earth's magnetosphere, ionosphere, and thermosphere. Key to progress in our understanding of these numerous science challenges is the discovery and characterization of the fundamental processes that govern the evolution of the heliospheric plasma, in particular the three grand challenge problems of plasma turbulence, magnetic reconnection, and energetic particle acceleration. The volume and quality of spacecraft measurements have transformed heliophysics into a deeply quantitative field, and the investigation of the underlying kinetic plasma physics of the heliospheric plasma is essential to exploit this data to the fullest degree and to progress in solving these grand challenge problems. In this talk, I will highlight recent successes in the effort to develop a comprehensive understanding of turbulence in kinetic plasmas, a research program involving a broad but coordinated approach of theoretical modeling, massively parallel gyrokinetic numerical simulations, novel analyses of spacecraft measurements, and laboratory experiments. The detailed investigation of the kinetic plasma physics of turbulence and its dissipation has driven the cutting edge of this research program to the realm of electron-scale current sheets and magnetic reconnection. Ultimately, the ubiquity of plasma turbulence in the heliosphere suggests that a mature understanding of the nature of kinetic plasma turbulence will be critical to fully explaining the explosive release of magnetic energy in reconnection and the acceleration of energetic particles in heliospheric plasmas.

May 31, 2013
3:30 p.m. - 4:30 p.m.
6704 Geology

Presented By:

• Jianbao Tao - UC Berkeley SSL

Electron phase-space holes (EHs) are good indicators of nonlinear activities in space plasmas and have attracted many interests in both observational and theoretical work. In a traditional theoretical picture, EHs are understood as purely electrostatic structures. However, THEMIS observed electromagnetic EHs, which cannot be fully described with traditional theory, in the plasma sheet boundary layer. This work seeks to understand the magnetic signals of the observed electromagnetic EHs. In addition to the interpretations of the observed magnetic signals, a statistical study of the properties of the observed electromagnetic EHs reveals that those electromagnetic EHs feature fast speeds, large sizes, and strong potentials, which intrigues interests in their generation mechanism and influences on the space plasma environment.

June 7, 2013
3:30 p.m. - 4:30 p.m.
Geology 6704

Presented By:

• Andrei Runov - UCLA

It is well established that high-speed flows in the magnetotail plasma sheet, separated from the ambient plasma by dipolarization fronts, are braked in the tail-dipole transition region of the near-Earth magnetotail. Kinetic and electromagnetic energy of the flow burst and dipolarization front is therefore converted to thermal energy of plasma and radiated by electromagnetic and plasma waves. Details of the energy conversion as yet remain unclear, largely due to the lack of multi-point observations in the transition region. Taking advantage of THEMIS probes and geosynchronous (GEO) satellite conjunctions repeated in two events, we can study physical connections of the dipolarization front braking between X=-11 and -9 RE and magnetic and plasma oscillations observed at X=-8 RE and at GEO. It has been found that, despite different background plasma conditions in both events, slow-mode oscillations were excited in the dipole-dominated magnetotail region in response to the front braking in the transition region. No signatures of front rebounding were found. The slow-mode wave, observed at X=-8 RE, was not directly driven by dipolarized flux tube oscillations. The data analysis has shown that the slow-mode oscillations observed were triggered by the plasma pressure enhancements ahead of the front.