Space Physics Seminar - fall-2016

Sept. 23, 2016
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Anna Tenerani - UCLA EPSS

Seminar Description coming soon.

Sept. 30, 2016
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Yingjuan Ma - UCLA

Magnetic reconnection is a fundamental physical process in space plasmas that changes magnetic topology and converts magnetic energy into both kinetic energy and thermal energy. It is believed as a common process occurring at the magnetospheres of magnetized planets such as Earth, both on the dayside magnetopause and in the magnetotail when the direction of the interplanetary magnetic field is opposite to the planetary magnetic field. Even through Mars does not have a global intrinsic magnetic field, various magnetic reconnection signatures have been observed at Mars, from both previous Mars Global Surveyor (MGS) and the ongoing Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Here we use a coupled approach to numerically study the detailed physical process and its global consequences of the magnetic reconnection process in the near-Mars magnetotail. Such a coupled approach solves the solar wind-Mars plasma interaction using a global MHD model with an embedded kinetic model (particle-in-cell). This approach takes advantages of both models: the efficiency of the global MHD model and the ability to include kinetic effects by the PIC model. Our model results show that the Martian magnetotail is highly dynamic and the magnetic reconnection process does enhance the ion escape rate of heavy ions by ~ 30%.

Oct. 14, 2016
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Anton Artemyev - UCLA EPSS

Electron current sheets supporting the near-Earth magnetotail during current sheet thinning

Formation of intense, thin current sheets (i.e., current sheet thinning) is a critical process for magnetospheric substorms, but the kinetic physics of this process remains poorly understood. Using a triangular configuration of the three THEMIS spacecraft at the end of 2015 we investigate field-aligned and transverse currents in the magnetotail current sheet around 12 Earth radii downtail. Combining the curlometer technique with direct measurements of ion and electron velocities, we demonstrate that intense, thin current sheets supported by strong electron currents form in this region. Electron field aligned currents maximize near the neutral plane Bx~0, attaining magnitudes of ~20 nA/m2. Carried by hot (>1 keV) electrons, they generate strong magnetic shear, which contributes up to 20% of the vertical pressure balance. Electron transverse currents, on the other hand, are carried by the curvature drift of anisotropic, colder (<1 keV) electrons and gradually increase during the current sheet thinning. In the events under consideration the thinning process was abruptly terminated by earthward reconnection fronts which have been previously associated with tail reconnection further downtail. It is likely that the thin current sheet properties described herein are similar to conditions further downtail and are linked to the loss of stability and onset of reconnection there. Our findings are likely applicable to thin current sheets in other geophysical and astrophysical settings.

Oct. 28, 2016
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Bea Gallardo-Lacourt - UCLA

Properties of meso-scale flows in the nightside auroral and subauroral ionosphere

In addition to the traditional large-scale convection, nightside plasma sheet transport involves a significant amount of meso-scale fast flows that carry a large amount of magnetic flux. Measuring flows and aurora in the ionosphere allows us to evaluate the instantaneous two-dimensional evolution of these flow bursts. Auroral manifestations of such fast flows include auroral streamers, substorm onset, and enhancements within sub-auroral polarization streams (SAPS and SAID). At the substorm onset, the formation of auroral beads have been studied in detailed using auroral imagers; however, there has been almost no information about their flow pattern, which is fundamental to understand substorm onset instability. In this talk we first determine the flow pattern associated with substorm auroral onset beads, which are considered as the auroral manifestation of the substorm-onset instability occurring in the near-Earth plasma sheet. Our results show that auroral beads are associated with fast and periodic flow structures. We demonstrate the presence of a clockwise flow shear around each auroral bead, consistent with converging electric fields associated with upward field-aligned-currents in the shear center. In the second part of this talk, we analyze SAPS, which are strong westward flows occurring equatorward of the electron auroral oval. It has been reported that SAPS present large variabilities that are not correlated with any of the global indices. We demonstrate that the SAPS have large meso-scale flow enhancements, and that these enhancements are associated with auroral streamers. This implies that these flow enhancements can be understood as a coupling of meso-scale fast flows at auroral and subauroral latitudes. Finally, we present a comparison between SAPS and SAID event. The formation of these two phenomena is usually explained in terms of voltage or current generators, which is called the SAID/SAPS paradigm. A full understanding of the SAPS and SAID development has not yet been achieved, therefore an analysis comparing the conditions under which these phenomena occur is necessary. A preliminary survey interestingly suggests that broad SAPS events show the location of the electron equatorward boundary poleward than the proton boundary; while for narrow (~<1-2°mlat) SAID type of events this boundary location is reversed. Our case study suggests that a difference in the location of the injection region could be responsible for the reversal of the boundaries.

Nov. 4, 2016
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Jøran Moen - University of Oslo, Norway

4D Space Research Activities at the University of Oslo

The Earth’s atmosphere coupling to space offers us an opportunity to study multi-scale plasma physical processes of critical importance in order to develop space weather forecast models for e.g. ionospheric scintillations of radio signals and atmospheric drag on satellites. This talk presents prioritized space research at the University of Oslo, Norway. The 4DSpace strategic research initiative was kicked off three years ago. The long term vision for this initiative is to understand the role of plasma turbulence in coupled space plasma systems. Plasma turbulence processes represent one of the outstanding major challenges in classical physics, where central problems have not yet been adequately understood. This requires a multi-scale approach and there is need to develop new experimental tools. UiO has developed a sounding rocket program to take advantage of combining ground-based remote and in-situ measurements of auroral processes. Recent results will be presented along with further plans to develop the next generation experiments to observe turbulence in ionospheric plasma. This is fundamental research that is motivated by applications. International collaboration, miniaturization of instruments, and combining experiment, theory and numerical works are keys to success. The purpose of the Grand Challenge Initiative – Cusp multi-rocket campaign will be presented. This is a US, Japan and Norway collaborative rocket campaign that will be conducted in Svalbard and North Norway the winter of 2018/19. This project is open for contributions by satellites and ground based observations, as well as theory and modelling efforts.

Nov. 9, 2016
noon - 1 p.m.
6850 Slichter Hall

Presented By:

• S.S Cerri - University of Pisa, Italy

Hybrid-kinetic approach to solar-wind turbulence below the ion gyroradius: what have we learned?

The understanding of the kinetic processes at play in plasma turbulence is a major problem in plasma physics, on which space plasma research is currently focusing. Here we want to investigate the properties of turbulence from the end of the magnetohydrodynamic (MHD) cascade to scales well below the ion gyroradius (i.e., the so-called “dissipation” or “dispersion” range). To this end, we have performed high-resolution simulations of driven turbulence in a 2D3V phase-space (two real-space and three velocity-space dimensions) with a hybrid Vlasov-Maxwell (HVM) code. A range of values of the plasma beta parameter typical of the solar wind (SW) are investigated. Several aspects of turbulence at small-scales emerging from the simulations are presented and discussed. Finally, a comparison with completely different hybrid particle-in-cell (HPIC) simulations will be presented, showing the independence of these kinetic-scale cascades from the large-scale properties. Even wplithin the limitations of the hybrid approach in 2D3V, these results have relevant implications to understand kinetic-range turbulence and, in particular, SW turbulence.

Nov. 18, 2016
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

Seminar Description coming soon.

Dec. 2, 2016
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Seth Dorfman - UCLA

Growth rate measurement of ULF waves in the ion foreshock

Waves generated by accelerated particles are important throughout our heliosphere. These particles often gain their energy at shocks via Fermi acceleration. At the Earth's bow shock, this mechanism accelerates ion beams back into the solar wind; the beams can then generate ultra low frequency (ULF) waves via an ion-ion right hand resonant instability. These waves influence the shock structure and particle acceleration, lead to coherent structures in the magnetosheath, and are a possible source of the ULF waves that play a key role in magnetospheric dynamics.

The present study represents the first satellite measurement of the ULF wave growth rate in the upstream region. Using the flux gate magnetometer and electrostatic analyzer instruments aboard the two ARTEMIS spacecraft at ~60 Re from Earth, we characterize crescent-shaped ion beams and relatively monochromatic ULF waves. The selected event features spacecraft separation in the solar wind flow direction along a nearly radial Interplanetary Magnetic Field. We estimate the ULF wave growth rate and find it to match dispersion solver predictions during the initial growth time. Observed frequencies and wavenumbers are also within the predicted range. Other ULF wave properties such as the phase speed and obliquity are consistent with expectations from prior satellite measurements. Multiple frequency peaks observed in ARTEMIS data and additional events characterized by diffuse ion beams are currently under investigation.

Dec. 9, 2016
3:30 p.m. - 5 p.m.
Geology 6704

Presented By:

• Leon Ofman - Catholic University, USA

The Origin of the Slow Solar Wind

The solar wind is one of the major drivers of Space Weather activity producing a variable stream of plasma that impacts the earth’s magnetosphere. The solar wind is classified into the fast and slow solar wind streams, with the slow wind reaching ~400 km/s and the fast wind is about twice faster and half denser near Earths’ orbit. While major advances were made in solar wind research, the origin and formation of the slow solar wind (SSW) are still outstanding questions in solar physics. The wealth of present day remote sensing observations and models provide important clues on the magnetic structure and the possible acceleration mechanics of the SSW. Understanding the origin of the SSW is a major objective of the planned Solar Probe Plus and Solar Orbiter spacecraft missions. I will review the important outstanding questions requiring further analysis: What are the source regions on the Sun and their contributions to the SSW? What is the role of the magnetic topology in the corona for the origin, acceleration and energy deposition of the SSW? What are the possible acceleration and heating mechanisms for the SSW? I will discuss the present status of our understanding of the origin and formation of the SSW, and review the significant progress that has been made recently in the study of SSW thanks to spacecraft observations, such as Ulysses, Wind, ACE, and STEREO. I will present the results of advanced numerical models of the SSW that address the above open questions.