Space Physics Seminar - spring-2014

April 4, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Jacob Bortnik - UCLA/NJIT

Resonant interactions between energetic electrons and whistler mode waves play an essential role in controlling the dynamic variability of the Earth’s natural radiation belts, which is a topic of extreme interest at the moment. Although the theory describing resonant wave-particle interaction has been present for several decades, it has not been hitherto tested in a controlled laboratory setting. In this talk, I will describe the first laboratory experiment to directly detect resonant pitch angle scattering of energetic (?keV) electrons due to whistler mode waves, which was conducted in UCLA's Large Plasma Device. I will first review the basic ideas behind wave-particle resonant interactions, and show that the whistler mode wave deflects energetic electrons at precisely the predicted resonant energy, and discus the effect of varying both the maximum beam energy, and the wave frequency.

April 11, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Steve Morley - Los Alamos

Seminar Description coming soon.

April 18, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Qingjiang Pan - UCLA

An important question regarding the magnetosphere is how charged particles (both electrons and ions) are energized to hundreds of keV energies in the magnetotail during substorms. In this talk, I will first review previously proposed acceleration mechanisms, which can be separated into two types: mechanisms that operate near the reconnection site and mechanisms that occur during plasma earthward transport. Then I will show our results obtained from realistic global MHD/LSK simulations, which are benchmarked by multipoint satellite measurements. The results will be discussed with two emphases: (1) separating and quantifying energization by different processes; (2) comparing electron and ion energization and transport. I will end this talk by discussing implications and future work.

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

Presented By:

• J. F. Drake - Maryland/Berkeley

The heliopause (HP)is the boundary that separates the plasma environment of the sun from that of the interstellar medium. I will discuss the recent Voyager spacecraft observations of this outer boundary and parallel theory and modeling efforts that suggest that the boundary is much more complex than a simple magnetic field rotation that separates two disparate plasma regions. Dropouts of energetic particles produced within the heliosphere and corresponding increases in the strength of the magnetic field measured by Voyager 1 in 2012 suggested that the spacecraft had crossed the HP. However, the absence of a corresponding rotation in the direction of the magnetic field convinced the Voyager science team that the spacecraft remained within the heliosphere. A parallel modeling effort of the global heliosphere and local processes at the HP suggested that Voyager 1 had crossed the HP. This conclusion was confirmed when wave measurements revealed that the plasma density at Voyager 1 had dramatically increased above heliospheric values. The present picture of the magnetic structure of the outer heliosphere and HP is that the large-scale magnetic field rotates gradually from its interstellar direction to that of the Parker spiral magnetic field at the HP. Locally at the HP magnetic reconnection has produced a complex set of nested magnetic islands leading to a porous HP in which galactic cosmic rays enter the heliosphere and heliospheric particles can exit into the local interstellar medium. However, not everyone is in agreement. There is a significant contingent who are convinced that Voyager 1 remains within the heliosphere. The reasons for the continued controversy will be discussed.

May 2, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Takuma Nakamura - Los Alamos

The Kelvin-Helmholtz instability (KHI) is a key process for the transport of solar wind plasma across the Earth’s magnetospheric boundary (magnetopause). When both magnetic and velocity shears coexists within a boundary as commonly seen at the magnetopause, the resulting KHI leads to generation of vortices and subsequent triggering of magnetic reconnection. Our recent large-scale 3D fully kinetic simulations of this so-called vortex-induced reconnection (VIR) process for symmetric boundary layers demonstrated the copious formation of oblique flux ropes, which leads to a chaotic mixing of the plasma within the vortex layer. THEMIS observations at the dusk-flank magnetopause indeed show similar features of flux ropes between observed KH vortices. More recently, we performed additional 3D fully kinetic simulations considering the effects of density and temperature asymmetries, which also commonly exist across the magnetopause. Past 2D simulations have shown that such asymmetries can lead to an excitation of secondary instabilities along the edge of the vortex in the absence of a finite magnetic field component parallel to the k-vector of the KHI (B_k). Since B_k is expected to be finite at the magnetopause, here we explore the effect of B_k on secondary instabilities in 3D. We find that the suppression of the secondary instabilities due to B_k is an artifact of the 2D simulations, whereas in 3D the instabilities can grow over a range of oblique angles even when there is a finite B_k. The non-linear growth of these instabilities disturbs the structure of the edge layer of the vortex and transports the mixed plasmas produced by VIR more deeply into the magnetospheric region. The estimated mixing and transport rates are enough to form the tail-flank low-latitude boundary layer (LLBL) and the cold-dense plasma sheet (CDPS) both of which contain a mixture of plasmas of solar wind (magnetosheath) and magnetosphere origins. In this presentation, we will show detailed results of these 3D simulations as well as a brief history of theoretical, numerical and observational studies on the KHI at the magnetopause.

May 9, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Christine Gabrielse - UCLA

Energetic particle injections in the near-Earth plasma sheet are critical for supplying particles and energy to the radiation belts and ring current. Their origin, however, has been elusive due to the lack of equatorial, multi-point observations. After the launch of NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission in 2007, intense electric fields and elevated energetic particle fluxes have been observed to accompany localized (1-4 RE wide) bursty bulk flows and to propagate from the mid-tail regions (at geocentric radial distances R > 25RE) towards Earth, up to and at times inside of geosynchronous orbit (GEO, R=6.6RE). Motivated by these observations, I model simultaneous multi-point observations of electron injections using guiding center approximation in prescribed but realistic electric and magnetic fields to better understand the nature of their acceleration. Additionally, I perform a statistical analysis of the electron and ion injections to better understand their properties observationally. I find a good correlation between injections and azimuthally localized fast flows, reconnection fronts and impulsive, dawn-dusk electric field increases. This correlation is present regardless of distance, from inside GEO out to 30 RE. The findings are inconsistent with the classical concept of injections forming from an azimuthally wide injection boundary moving earthward from ~9-12 RE to GEO under an enhanced, large-scale, duskward electric field. Modeling of electron injections assuming a localized, impulsive, potential electric field transported from mid-tail to near-Earth at bursty flow speeds of ~400 km/s successfully reproduces the observations at multiple spacecraft. Addition of a small, inductive electric field component, related to the dipolarizing magnetic field consistent with observations, further improves the agreement between modeled and observed electron spectra. The impulsive, localized, and vortical nature of the earthward-propagating electromagnetic pulse is what makes this model particularly effective in reproducing both the injection and the dispersed decrease in energy flux often observed simultaneously with the injection but at lower energies. The results suggest that particle acceleration and transport towards the inner magnetosphere can be thought of as a superposition of individual bursts of varying intensity and cadence depending on global geomagnetic activity levels.

May 16, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Richard Elphic - NASA Ames

The Lunar Atmosphere and Dust Environment Explorer (LADEE) was launched from Wallops Flight Facility on 6 September, 2013 aboard the very first Minotaur V, a Peacekeeper ICBM converted to civilian use. The launch was perfect, and LADEE entered lunar orbit on 6 October, 2013. In the following weeks, the first laser communications from deep space achieved 622 Mbits/sec downlink, paving the way for a revolution in space communications. Following instrument checkout and commissioning, LADEE commenced science operations on 21 November, 2013. Over the next 100 days, LADEE's Ultraviolet/Visible Spectrometer (UVS) systematically mapped sodium, potassium and other species in the tenuous lunar exosphere, while the Neutral Mass Spectrometer (NMS) systematically mapped argon, helium, and discovered neon in the lunar exosphere. At the same time, the Lunar Dust EXperiment (LDEX) discovered and characterized the dust exosphere, caused by continual bombardment of the Moon's surface by micrometeoroids. After the nominal science mission, LADEE continued to acquire more science data, culminating in a set of observations at very low altitudes (<10 km) above the sunrise terminator. Data from UVS show that the Moon’s sodium exosphere varies with lunar phase, with density increasing as the Moon waxes toward Full then falling after. An additional wrinkle on this behavior is the apparent reduction in sodium while the Moon is in the Earth’s geomagnetic tail, suggesting that sodium production is diminished when out of the solar wind. Potassium and other metals show variations on this behavior, including responses to meteoroid streams, particularly the Geminids. NMS mapping of argon-40, a constituent arising from potassium-40 decay in the lunar interior, shows that the gas “freezes out” on the very cold lunar nightside (~100K), but produces a dawn bulge of enhanced density as the cold lunar surface rotates around into sunlight and warms up. While this behavior was seen in Apollo data, and modeled, NMS has observed new twists to this basic surface boundary exosphere process. NMS also observed helium and found a relationship with the He++ being delivered to the Moon by the solar wind. LDEX has mapped out the height- and local time dependence of the tenuous lunar dust veil, finding that dust densities are highest on the ram side of the Moon, facing the direction of motion of the Earth-Moon system around the sun. This much may be expected, but LDEX is revealing surprising new features. Occasionally, LDEX observes a large, short-term (less than a few minutes) increase in dust density. Evidently this is due to the impact of much larger meteoroids within a few minutes and tens to 100s of kilometers of LADEE. This talk will describe the mission and some of the initial science results.

May 23, 2014
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Christina Cohen - Caltech

By the 1990’s sense had finally been made of the variable composition observed in solar energetic particle (SEP) events. The importance of solar flares was modified by the observation of coronal mass ejections (CMEs) and their ability to drive interplanetary shocks. The ‘two-class’ paradigm was established allowing the characteristics of an SEP event to be directly related to the acceleration mechanism at work. This neat picture was disrupted by the first observations from the Solar Isotope Spectrometer on the Advance Composition Explorer, launched in August 1997. Although the two acceleration mechanisms remain a distinguishing aspect of SEP events, additional puzzles have arisen in explaining the observed composition in some events. With the launch of the twin Solar Terrestrial Relations Observatory spacecraft in October 2006, the capability of routinely observing an SEP event from multiple vantage points was obtained. This talk will present the evolution in our understanding of SEP event composition, including how this new tool has contributed.

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

Presented By:

• Justin Lee - UCLA

Seminar Description coming soon.

June 6, 2014
3:30 p.m. - 3 p.m.
Geology 6704

Presented By:

• Greg Hallinan - Caltech

Seminar Description coming soon.