Space Physics Seminar - Winter-2018

Jan. 12, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Wen Li - BU

Juno is the first spacecraft to explore the low-altitude polar magnetosphere of the Jupiter. The ultraviolet spectrometer instrument on board Juno showed extensive diffuse aurora observed equatorward of the main auroral oval. In the region where these diffuse auroral emissions were observed, the JEDI and JADE particle instruments measured nearly full loss cone distributions for the downward-going electrons over energies of 0.1–700 keV, but very few upward-going electrons. The coordinated measurements of diffuse aurora and energetic particle precipitation provide the direct evidence of the origin of Jupiter’s diffuse aurora. Interestingly, near the region where the diffuse aurora emissions are observed, the energetic electron pitch angle distribution exhibits a butterfly-shaped pitch angle distribution, which is often associated with an electrostatic wave below the proton cyclotron frequency. This butterfly distribution is suggested to be formed by parallel acceleration of electrons through Landau resonance with the electrostatic waves. At last, I will briefly discuss a few other highlights on the interesting scientific discoveries from the Juno mission.

Jan. 19, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Dr. Stein Haaland - MPI Gottingen

Seminar Description coming soon.

Jan. 26, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Dr. Phil Pritchett - UCLA

Seminar Description coming soon.

Feb. 2, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Dr. Drew Turner - Aerospace Corp.

Earth's radiation belt electrons were the first scientific discovery of the space age, yet understanding the nature and extreme variability of radiation belt electrons continues to challenge researchers. In the past decade, three NASA missions have contributed many new insights on the nature of the radiation belts: THEMIS, Van Allen Probes, and MMS. This talk highlights recent observational results from the THEMIS, Van Allen Probes, and MMS mission concerning Earth's radiation belt electrons. In particular, the talk focuses on: extreme variability and the effects of geomagnetic storms; flux "dropouts" and their relationship to multiple intensity peaks in the radial profile of the outer radiation belt; the dominant acceleration mechanism of outer radiation belt electrons and the importance of substorm activity for enabling source processes; new and unexpected discoveries concerning electrons in the inner radiation belt; and the global structure and morphology of the full electron radiation belt system.

Feb. 9, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Prof. Yu Lin - Auburn University

Seminar Description coming soon.

Feb. 16, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Prof. Yue Deng - UTA

A recent significant change in our understanding of the ionosphere-thermosphere system is the frequent driving by dynamic meso-scale structures (50 km - 500 km) that couple to the magnetosphere in the polar cap region, the dayside cusp and along auroral oval and sub-auroral magnetic field lines. These structures play a critical role in Space Weather dynamics, interacting with the more slowly changing, large-scale structure that is more directly driven by interaction with the solar wind. The Global Ionosphere Thermosphere Model (GITM), a self-consistent non-hydrostatic model in the upper atmosphere with a flexible resolution, is suitable for studying transient meso-scale phenomena. To improve the description of meso-scale structures in geomagnetic forcing and to evaluate the influence of such structures on the global dynamics of the upper atmosphere, various data and models are utilized to investigate the variations of energy inputs in the cusp, sub-auroral regions and within flow bursts, and their influences on the coupled thermosphere-ionosphere system.

Feb. 23, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Dr. Dave Mitchell - SSL/UCB

The enhancement of heavy isotopes in Mars’ atmosphere indicates that loss of atmosphere to space has played an important role in transforming the planet’s climate. This loss can take place through a variety of mechanisms, and has been aided by a weak gravity and the cessation of a global magnetic field ~4 Ga ago. Jeans escape for hydrogen and photochemical escape for oxygen appear to be the dominant loss processes today; however, ion outflow down the tail might contribute significantly. Ion outflow can take place through several processes, depending on the magnetic configuration and the acceleration mechanism (ambipolar, V x B and J x B electric fields, as well as wave heating). Magnetic topology plays an important role, since the configuration of Mars’ magnetotail is complex and dynamic, and access to a dense source of planetary ions significantly affects the loss rate. Estimates of the total oxygen ion loss down the tail have increased tenfold over the past 10 years, largely as a result of measuring and including lower energy ions in the calculation. Measuring the escape flux from ~10 eV down to the escape energy (~4 eV for O2+) is especially difficult, because corrections for spacecraft motion and spacecraft charging are large. Since August 2016, the Mars Atmosphere and Volatile EvolutionN (MAVEN) spacecraft has been conducting a series of observing campaigns designed to measure cold ion outflow down to escape energy. As the orbit precesses and sweeps through the tail, the spacecraft reorients from 1200 to 5000 km altitude to optimize the fields of view for the Supra-Thermal and Thermal Ion Composition (STATIC) instrument and the Solar Wind Electron Analyzer (SWEA). Data from SWEA and the Magnetometer (MAG) are used to determine the magnetic field topology, and in particular whether field lines are open, closed, or draped, and if open or deeply draped whether they have access to the day-side or night-side ionosphere. STATIC, SWEA, and the Langmuir Probe and Waves (LPW) experiment determine the spacecraft potential throughout the Mars environment using multiple, cross-calibrated methods. Simultaneous observations by STATIC are used to measure the density, composition, and velocity of planetary ions on these same field lines, all corrected for spacecraft motion and spacecraft potential. Combining data from four sweeps of MAVEN's orbit through the tail (~600 orbits), we have built up a database from which we can map statistics and develop a picture of ion outflow in Mars' tail.

March 2, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Dr. Mostafa El-Alaoui - UCLA

The dynamics of flow channels and dipolarizations complicate the expected field aligned current pattern during substorms. We have used a global magnetohydrodynamic simulation to investigate how meso-scale magnetotail structures participate in forming the substorm current configuration. We focus, for the most part, on the March 1, 2008 substorm, which was observed by THEMIS spacecraft. The simulation shows a sequence of fast flows and dipolarization events similar to what is seen in the data, though not at precisely the same times or locations. Both earthward and tailward flows were found in both the observations and the simulations. The simulation shows that the flow channels can have convoluted paths that are slowed and diverted as they reach the inner magnetosphere. We will use our simulation results combined with the observations to investigate the global convection systems and current sheet structure during this event, showing how meso-scale structures fit into the context of the overall magnetotail dynamics during this event. Rather than a single current wedge in the tail, several smaller structures are seen at which field aligned currents originate. Our study includes determining the location, timing and strength of several current wedges and expansion onsets during an 8-hour interval. A major consequence of the complex flow structure is the establishment of large scale vortices that start a turbulent cascade that affects transport and reconnection.

March 9, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Dr. Didier Mourenas - Commissariat Energie Atomique (CEA), DAM, DIF, France

Since the advent of the industrial revolution in the nineteenth century, our rapidly progressing technological society has only become more and more vulnerable to the multiple hazards associated with strong magnetic storms. In the past decades, intense storms have caused the loss of various satellites, wreaked havoc on the electric power grid, and interrupted operational long-range radio communications. More than half of all geomagnetic storms are followed by significant flux enhancements of MeV “satellite killer” electrons. Such electron fluxes can seriously damage satellite electronic equipment, especially onboard upcoming satellites that will use solar electric propulsion on geostationary transfer orbits and will consequently spend half a year in the heart of the outer radiation belt, where only hardened GPS and scientific spacecraft have usually been orbiting. Various works have demonstrated that strong relativistic electron flux enhancements in the heart of the outer radiation belt mainly result from a combination of local acceleration by whistler mode chorus waves and inward radial diffusion by ultra-low-frequency waves. This presentation is devoted to consideration of relativistic electron generation and shall address four questions: Is it feasible to forecast the effects of geomagnetic activity on the Radiation Belts and satellites through usual Dst or Kp/ap indices? How are MeV electron flux increases happening? Can we derive scaling laws for the inner structure of the Radiation Belts based on the traditional quasi-linear diffusion paradigm? Are traditional quasi-linear diffusion codes of the Radiation Belts challenged by many recent observations of very intense chorus waves during periods of high geomagnetic activity?

March 16, 2018
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Dr. Chris Chaston - Space Sciences Lab, UC Berkeley

Observations from the Van Allen Probes have revealed the prevalence of broadband electromagnetic oscillations through the ULF to ELF range in the spacecraft-frame in the inner magnetosphere. In this presentation the properties of these field variations are reviewed. It is shown how these waves pervade the inner magnetosphere during storm times and how their small-scale or kinetic nature may allow interactions with both electrons and ions via means not traditionally considered in ULF/ELF waves through this region of space. From analytical considerations and simulations, the importance of these interactions for modifying the distribution of energetic particle populations in the inner magnetosphere is explored. The results from this exploration suggest that these field variations may be an important, yet largely unrecognized, driver of inner magnetospheric particle dynamics.