Space Physics Seminar - fall-2019
Propagation of Alfven Waves in a Two Ion Species Plasma
Oct. 4, 2019
3:30 p.m. - 5 p.m.
6704 Geology
Presented By:
- Jeffrey Robertson - UCLA
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Understanding the behavior of plasma waves in mixed-species plasmas is important for explaining many observations seen in both space and laboratory plasmas. The addition of a second ion species in a magnetized plasma introduces new behavior in the propagation of waves in the ion cyclotron region, such as the ion-ion hybrid cutoff frequency for parallel propagating shear Alfven waves [1]. Previous experiments on the Large Plasma Device (LAPD) have demonstrated the existence of a propagation gap for shear waves between the ion cyclotron frequencies of the two ion species [2], while more recent work has expanded the range of plasma conditions in which this was observed. Additionally, the ion-ion hybrid cutoff is documented for various mix ratios in order to determine its viability as a diagnostic for the ratio of ion densities. `
Microphysics of ion and electron energization in the topside ionosphere: Results from CASSIOPE/e-POP
Oct. 11, 2019
3:30 p.m. - 5 p.m.
6704 Geology
Presented By:
- Yangyang Shen - University of Calgary
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Ionospheric ion (mainly O+) and electron energization and field-aligned transport are critical processes of magnetosphere-ionosphere-thermosphere coupling. The Canadian Enhanced Polar Outflow Probe (e-POP) satellite carries particle and field instruments specifically designed to study micro-scale characteristics of ion energization and outflow processes in the topside (325-1,500 km) ionosphere. The Suprathermal Electron/Ion Imager (SEI) instrument onboard e-POP has the capability of resolving two-dimensional low-energy (from sub-eV to 325 eV) particle distributions at time scales of up to 10 ms, or spatial scales of less than 100 m. This talk aims to present several discoveries resulting from direct measurements of particles and waves from e-POP. In particular, we will focus on observations and test particle simulations of transverse O+ ion heating from broadband extremely low frequency (BBELF) waves in the collisional ionosphere. We will also show the first direct observations of suprathermal (tens to hundreds of eV) electron acceleration perpendicular to the magnetic field in the topside ionosphere.
Fine structure of substorm and geomagnetically induced currents
Oct. 18, 2019
3:30 p.m. - 5 p.m.
6704 Geology
Presented By:
- Vlacheslav Pilipenko - Institute of Physics of the Earth, Moscow, Russia
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The rapid changes of magnetic fields, that is high dB/dt, associated with substorms can excite large geomagnetically-induced currents (GICs) that can have harmful effects on technological systems. We have analyzed the characteristics of the dB/dt enhancements observed in Fennoscandia in 2015 using data from the magnetometer array IMAGE, covering a range of magnetic latitudes from 68° to 78°. The abrupt magnetic field variations may be associated with substorm onsets, isolated nightside magnetic impulsive events (MIEs) with ~10 min duration, and Ps6/Pc5 pulsations (periods 3-15 min). For a detailed examination of the latitudinal structure of magnetic variability enhancements and their association with auroral oval boundaries we applied the technique of “magnetic keograms”. This technique helps to visualize the fine structure of a substorm, namely the time and latitudinal localization of dB/dt enhancements. A location of the auroral oval boundaries in a given local time sector has been estimated with the OVATION-prime model based on energetic particle measurements from the DMSP satellites. Auroral substorm onset provided the largest magnetic response on the ground and most intense GIC (few tens of A) when the poleward moving intensification of dB/dt crossed the latitude of power line. Isolated nightside MIEs are also effective in excitation of GICs (>10 A), but they are relatively rare. Quasi-periodic series of MIEs, known as Ps6 / Pi3 pulsations, are effective in excitation of GICs with magnitude about 20 A and even higher. Monochromatic Pc5 pulsations are capable to induce noticeable GICs, up to ~13 A.
Mercury’s Magnetosphere and Exosphere: Recent results from MESSENGER data
Oct. 25, 2019
3:30 p.m. - 5 p.m.
Geology 6704
Presented By:
- Jamie Jasinski - Jet Propulsion Laboratory, Cal. Inst. of Techn.
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Mercury’s Magnetosphere and Exosphere: Recent results from MESSENGER data Jamie Jasinski, JPL, Caltech MESSENGER observations of Mercury’s magnetosphere and exosphere have shown them to be highly dynamic. Dayside magnetic reconnection drives magnetospheric dynamics, injecting solar wind plasma into the cusps which precipitates onto the planet’s surface and sputters neutral atoms and ions into Mercury’s exosphere and magnetosphere. I will present new results from analysis of MESSENGER data which help us to better understand the dynamics and coupling between Mercury’s magnetosphere and exosphere.
Non-adiabatic dynamics: transport, mixing, and resonances in plasma
Nov. 1, 2019
3:30 p.m. - 5 p.m.
Geology 6704
Presented By:
- Dmitri Vainchtein - Drexel University
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In many wave-particle systems, to describe the acceleration of charged particles one must step beyond the confinements of the quasi-linear theory. When the waves are strong enough, the nonlinear effects, such as nonlinear scattering on resonance and trapping into resonance, become prominent. In my talk I overview several problems that we studied recently, from the model problems that reveal interesting nuances of the resonance interactions to more realistic systems somewhat accurately describing configurations observed in the Earth magnetosphere.
Solar wind turbulence: from Helios to Parker Solar Probe and Solar Orbiter
Nov. 8, 2019
3:30 p.m. - 5 p.m.
Geology 6704
Presented By:
- Raffaella D'Amicis - IAPS, Istituto Nazionale di Astrofisica, Rome, Italy
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The solar wind provides an ideal laboratory for the experimental study of astrophysical plasma turbulence. As the solar wind expands, it carries fluctuations in the plasma quantities, namely velocity, magnetic field and density, that in many ways resemble the well-known hydrodynamic turbulence described by Kolmogorov. However, the presence of a large-scale magnetic field implies that, at scales significantly larger than the ion skin depth or Larmor radius, a magnetohydrodynamic (MHD) framework is needed to understand the evolution. Solar wind fluctuations often display what is called “Alfvénic” turbulence: a turbulence that, together with a well developed power spectrum, also shows the strong correlation between velocity and magnetic field fluctuations typical of Alfvén waves propagating away from the Sun. Because the nonlinear interactions in MHD are mediated by Alfvén waves propagating in opposite directions along a mean field, the presence of Alfvénic correlations in the turbulence is crucial to the evolution of the turbulence. Turbulence in the solar wind also depends on the large scale properties of the wind in which it is embedded: the solar wind comes in at least two distinct ‘flavours’, fast and slow, which are characterized by a a different Alfvénic content. Schematically, Alfvénic fluctuations dominate in high speed wind, while the slow wind turbulence contains more standard, evolved fluctuations in which no prevalence of outwardly propagating modes may be found. However, recent studies have shown the existence of peculiar slow wind streams that are similar from many points of view to the fast wind, especially regarding the Alfvénic content of the fluctuations. This presentation will give an overview on turbulence in the solar wind highlighting the role that Parker Solar Probe and Solar Orbiter will have in allowing a better understanding of solar wind origins, of the correlation between wind speed and Alfvénicity, and the processes responsible for the observed evolution with distance from the Sun.
What is the Origin of Crustal Magnetic Anomalies on Mercury and the Moon?
Nov. 15, 2019
3:30 p.m. - 5 p.m.
Geology 6704
Presented By:
- Lon L. Hood - Lunar and Planetary Laboratory, U. of Arizona
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Magnetometer measurements from orbiting spacecraft have mapped magnetic anomalies due to magnetized material in the crusts of both the Moon and Mercury. Although there is now general agreement that the Moon once possessed a global dynamo magnetic field, the exact origin of lunar magnetic anomalies is considered to be one of the outstanding unresolved problems of lunar science (e.g., presentation by R. C. Weber at special session on 50 years of lunar science at the most recent Lunar and Planetary Science Conference). Both volcanic sources consisting of magmatic intrusions (e.g., dikes) and magnetized deposits of impact ejecta have been proposed as source materials for these anomalies. Recent mapping of magnetic anomalies on Mercury (a planetary body with many similarities to the Moon) has shed new light on this question. In addition, further mapping of existing lunar orbital data has very recently uncovered new evidence that favors one of these two models. Evidence at both bodies will be summarized and a probable answer to this unresolved question will be given.
Magnetospheric Particle Precipitation at Titan
Nov. 22, 2019
3:30 p.m. - 5 p.m.
Geology 6704
Presented By:
- Emilie Royer - Planetary Science Institute
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The Cassini spacecraft observed Titan’s upper atmosphere and its airglow from 2005 to 2017 and in the past decade, results from the Cassini-Ultraviolet Imaging Spectrograph (UVIS) instrument greatly improved our understanding of airglow production at Titan. However, combining remote-sensing datasets, such as Cassini-UVIS data, with in-situ measurements taken by the Cassini Plasma Spectrometer (CAPS) instrument can provide us with a more rigorous assessment of the airglow contribution. It is now established that the solar XUV radiation is the main source of dayglow, while magnetospheric particle precipitation principally acts on the nightside of the satellite. One of the questions that might stay unanswered after the end of the Cassini mission concerns the role and quantification of the magnetospheric particle precipitation and other minor sources such as micrometeorite precipitation and/or cosmic galactic ray at Titan. In this presentation, I will be reporting on Ultraviolet (UV) observations of Titan airglow enhancements correlated with magnetospheric changing conditions occurring while the spacecraft, and thus Titan, are known to have crossed Saturn’s magnetopause and have been exposed to the magnetosheath environment. In addition, the processing and interpretation of 13+ years of airglow observations at Titan allows now for detail studies of the upper atmosphere as a function of the Saturn Local Time (SLT) and the solar cycle. UVIS observations of Titan around 12PM SLT (near Saturn’s magnetopause) present evidence of Titan’s upper atmosphere response to a fluctuating magnetospheric environment. Correlations between data from simultaneous observations of in-situ Cassini instruments (CAPS, RPWS and MIMI) has been possible on few occasions and events such as electron burst and reconnections can be associated with unusual behaviors of the Titan airglow.
Parker Solar Probe: First Results
Dec. 6, 2019
3:30 p.m. - 5 p.m.
Geology 6704
Presented By:
- Marco Velli - EPSS, UCLA
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Parker Solar Probe (PSP) launched on August 12th, 2018, its mission to carry out the first in situ exploration of the outer solar corona and inner Heliosphere. Observations of solar-wind plasma at a distance of ~ 36 RS, well inside the radius at which stream interactions become important, have shown that Alfvén waves organize into structured velocity spikes up to minutes long that are associated with propagating S-like bends in the magnetic-field lines. These are associated with measured magnetic field patches of large, intermittent reversals with enhanced Poynting flux interspersed with a smoother and less turbulent flow with a near-radial magnetic field. This slow, Alfvénic solar wind emerged from a small, rapidly expanding equatorial coronal hole, and the wind was still accelerating at this distance. The measured circulation of the wind around the Sun, peaking at 35-50 km/s, exceed classical predictions of a few km/s, challenging models of circulation in the corona and calling into question our understanding of how stars lose angular momentum and spin down as they age. Plasma-wave measurements suggest the existence of electron and ion velocity-space micro-instabilities associated with with plasma heating and thermalization processes. Not many energetic particle events were observed over the first encounter, while the white light imager observed pseudostreamer and streamer stalks emitting small intermittent blobs, potential evidence of reconnection.