Space Physics Seminar - fall-2018

Sept. 28, 2018
3:30 p.m. - 4:30 p.m.
Room 6704 Geology

Presented By:

Parker Solar Probe (PSP) launched successfully on a Delta 4 heavy in the early morning of August 12th, 2018, its mission to carry out the first in situ exploration of the outer solar corona and inner Heliosphere. Direct measurements of the plasma in the closest atmosphere of our star should lead to a new understanding of the questions of coronal heating, solar wind acceleration, and the generation, acceleration and propagation of solar en ergetic particles. I will start from an introduction to our present knowledge of the magnetized solar corona and wind before describing the PSP scientific objectives, orbit, and instrument suites. Emphasis will be on how PSP will confirm or falsify present models as well as the potential new discoveries stemming from the first exploration of the space inside the orbit of Mercury. I will also discuss how synergies with Solar Orbiter might lead us to accurately understand the state of the solar wind all the way from the corona into interplanetary space, elucidating like never before the role and dynamics of active magnetized plasmas throughout the universe.

Oct. 5, 2018
3:30 p.m. - 5 p.m.
Room 6704 Geology

Presented By:

Seminar Description coming soon.

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

Presented By:

Starting with 22 years of contemporary observations of the solar corona we readily see bands of activity- long-lived patterns that mark out the 22-year solar magnetic activity cycle. The modulation of these bands can explain the landmarks of the sunspot cycle – that only occurs over about half of the magnetic cycle span. Exploiting routine observations of the green-line corona that go back to the late 1930s and of solar filaments that go back to the dawn of H-alpha photography in the late 1870s we demonstrate that the 22-year magnetic cycle is extremely robust and is predictable through this continuous observational record. Using this record we explore the ”climatology” of the system and the root drivers of solar variability and activity. Given the apparent predictability in the system we look at sunspot cycle 25, how it has evolved since first appearing in 2012/2014, what it may yield in terms of activity, and also what may follow…..

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

Presented By:

The transition from the outer solar corona to the inner heliosphere is, in several important senses, the last unexplored frontier of the solar system. It spans a gap in understanding that arises in part from the difficulty of both sampling (used to study the solar wind) and remote imaging (used to study the solar corona). Simultaneously, those two techniques have led to separate specialized scientific communities with their own jargon and modes of understanding. In recent years, image processing has developed enough to reveal global and cross-scale structure in the young solar wind; and the Parker Solar Probe is now on its way to sample this transition zone directly. These two converging developments promise a unified understanding of this last segment of the corona. I will present several recent results derived from careful post-processing of images from the STEREO coronagraphs and heliospheric imagers, and their implications for what Parker Solar Probe is likely to encounter. Important results include direct measurement of the onset of hydrodynamic turbulence in the solar wind; detection of a highly structured, inhomogeneous outer corona; of a gradual (rather than sudden) transition from coronal to solar wind dynamics; and of some enigmatic new phenomena near 10 Rs from the Sun. These results, together, point to a paradigm that is more nuanced and far more complex than current models imply, with unexpected and emergent cross-scale phenomena for PSP and future imagers to explore.

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

Presented By:

Seminar Description coming soon.

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

Presented By:

In this talk, we present measurements of steady state and wave Poynting flux, as well as ion and electron energy flux flowing parallel to the magnetic\ field in the cusp region of the Earth's magnetosphere in order to assess the in flow and out flow of energy along these magnetic flux tubes. These measurements are obtained by the Polar spacecraft at 3-5 Re geocentric distances and by the FAST spacecraft at 1.6 Re and below. We find that during "active times" at Polar altitudes, there is a very substantial and steady net flow of ion energy flux away from the Earth which ranges between 10 and >100 mW/ m2 (normalized to flux tube area at 100 km). Average values of the net ion energy flux at 3-5 Re during less active periods are on the order of 1 mW/m2. The energy flux of ions and electrons at the lower altitudes observed by FAST are generally downward. The observations of large net energy flux out of the ionosphere indicate that the process of ion energization and outflow in the cusp is one of the most energy intensive processes in the Earth's magnetosphere rivaling the energy invested in the collisionless acceleration of electron beams associated with auroral arcs. During extreme events, it involves the formation of a low beta (0.1) subsonic wind of plasma flowing away from the Earth on cusp field lines at velocities of 50 km/s to several hundred km/s. A related question is what powers this system. The Polar spacecraft measurements provides evidence for large values of "steady state" and "wave" Poynting flux flowing earthward along magnetic field lines over a band-pass from 0.1 mHz to 1 Hz (spacecraft frame) and there is strong evidence that this is the only mode of energy transfer parallel to the magnetic field capable of powering this energetic wind. A comparison of incident Poynting flux to outflowing ion energy flux shows that the energy coupling/acceleration mechanism is likely to be quite efficient. In addition, measurements show the Poynting flux is concentrated in the large-scales, not in the smaller scale waves. These observations motivate interest in a number of unresolved issues related to if and how the large scale Poynting flux is transferred to small scales waves that can efficiently heat the plasma. This energy flow and its partitioning is an interesting contrast to that observed in conjunction with auroral electron acceleration on the nightside. This wind is also analogous in some important ways to the solar wind, which is also believed to be driven by Poynting flux. In principle, similar winds could also exist at other planetary magnetospheres.

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

Presented By:

The solar wind is far from thermodynamical equilibrium. Both protons and electrons display highly anisotropic velocity distribution functions (VDF) that evolve with radial distance possibly due to a combination of expansion effects and kinetic instabilities [Maksimovic 2005, Matteini 2013]. Fully kinetic Particle In Cell (PIC) simulations can help achieving a better understanding of electron and ion VDF evolution in the solar wind. In this talk, we present a new tool to simulate large and small scale kinetic instabilities in the solar wind and the effects of solar wind expansion: the fully kinetic, semi-implicit Expanding Box Model (EBM) code EB-iPic3D [Innocenti, Tenerani, Velli, under review]. The main ingredients of our code are its semi-implicit temporal discretisation (the Implicit Moment Method, IMM [Brackbill 1982, Lapenta 2006], implemented in the code iPic3D [Markidis 2010]) and the Expanding Box Model [Velli 1992, Grappin 1996, Liewer 2001]. The IMM formulation allows the freedom to choose to resolve either the small-scale, fast, electron dynamics or the larger-scale, slower ion dynamics. Spatial and temporal resolution and domain of the simulation in space and time can be adjusted according to the process of interest, rather than to the strict stability constraints of explicit discretisation. The EBM describes the dynamics of a parcel of plasma while it is advected away from the Sun at constant radial speed. The radial expansion is mimicked within a locally cartesian geometry where the radial (x) direction stays unaltered while the perpendicular directions (y and z) expands at a rate proportional to the distance from the Sun. The EBM variable change allows to follow the propagation of a parcel of solar wind over times and distances that would soon become prohibitive for a non EBM simulation. The IMM EBM method has the potential of comprehensively simulating solar wind expansion, accounting for both ion and electron dynamics, over scales unreachable with explicit formulations. Here we present the constitutive equations of the model, the results of our validation activity and preliminary results.

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

Presented By:

Observationally, flux transfer events (FTEs) are characterized by an enhancement of the magnetic field strength, a bipolar magnetic field in the direction transverse to the direction of motion of the structure, a dominant field-aligned current throughout the structure and the mixture of plasma from both magnetosphere and magnetosheath. FTEs are important for the space environment since they provide a means for the solar wind plasma, momentum and energy to be transferred into the terrestrial magnetosphere. In phase 1a of magnetospheric multiscale mission (MMS) we found 47 flux transfer events. However, during the same period, we also found another 52 flux ropes (FRs) which share the same magnetic topology as FTEs but have no signature of plasma from either magnetosphere and magnetosheath. With the help of the tetrahedron of the MMS spacecraft, it is possible to accurately calculate the cross-sectional radius, the total flux content as well as the speed of the FTEs and FRs. In this paper, we compare the properties of the FTE and the FR. In addition, the solar wind conditions associated with these events are also compared in order to test whether the FTEs and FRs are related to the southward IMF conditions, and hence magnetic reconnection. Those statistical properties of FTEs and FRs are very similar, indicates that FTEs and FRs may be different parts or different evolution stages of the same phenomena.

Nov. 30, 2018
3:30 p.m. - 5 p.m.
Room 6704 Geology

Presented By:

Close-in planets represent a significant part of the 3000+ know planets as they are most favourable to detect with our current technique. In contrast with the solar-system planets, they generally are expected to orbit in a sub-alfvénic stellar wind, where the perturbations they excite in the corona of their host star are able to travel upwind down to the stellar surface, and potentially induce observable phenomena. The effective connection between the planet and its host takes the form of two Alfvén wings. Depending on the topology of the planetary and stellar magnetic fields, on the rotation profile of the corona, and on the orbital parameters, it is possible that none, one, or the two of the Alfvén wings connect together the star and the planet. I will explore the formation and sustainment of Alfvén wings in global three-dimensional simulations under the magneto-hydrodynamic formalism with the PLUTO code. I model globally the stellar wind of a typical cool star in which a close-in orbiting planet is introduced as a boundary condition. By varying the magnetic topologies of the planetary and stellar magnetic fields, I explore the variety of Alfvén wings that can develop and quantify the Poynting flux flowing through those wings. With an extensive set of simulations, I deduce scaling laws of the amount of magnetic energy such magnetic interactions can channel to the lower stellar corona, as well as the amount of angular momentum that can be exchanged between the two bodies due to magnetic torques. As a result, I parametrize the accessible energy available to modify the apparent magnetic activity of the star. I will also quantify the phase and latitude offsets that can be expected between the planetary subpoint on the stellar surface and the actual location where energy is deposited. I will conclude by showing some preliminary attempts to apply these results to the cases of realistic systems with more complex, non-axisymmetric topologies using of the observed magnetic fields of Kepler-78.

Dec. 7, 2018
3:30 p.m. - 5 p.m.
Room 6704 Geology

Presented By:

Extremely Low (ELF) and Very Low Frequency (VLF) emissions are naturally occurring magnetospheric plasma waves in the frequencies of 3 Hz to 30 kHz. Through wave-particle interactions they can accelerate electrons to higher energies or scatter them into the atmosphere by changing their pitch angle. Thus, they play a fundamental role in radiation belt dynamics. We use simultaneous and conjugated observations in ground and space to report propagation characteristics of mainly chorus and quasi-periodical (QP) emissions. Waves were observed on the ground at Kannuslehto (MLAT=64.4N, L=5.46, KAN), Finland and by the Japanese Arase (ERG) satellite in the inner magnetosphere. During the 2017-2018 campaign we studied 84 days of possible conjugated observations. We used magnetic field and electric field measurements on board ERG to calculate the observational electric to magnetic field ratio (E/B_obs). Using measured plasma parameters and the cold plasma dispersion relation, we theoretically estimate the E/B ratio (E/B_th) for a range of wave normal angles. Comparing both ratios, we discuss the direction and manner of wave propagation. We compare these results with those obtained separately by the Single Value Decomposition method. We use the lack or presence of waves at KAN, as well as actual one-to-one correspondence between KAN and ERG to further discuss wave propagation properties. For selected cases, showing one-to-one correspondence, we calculate the ray path that the waves follow from their detection in space until they reach the ionosphere above KAN. Using these ray tracing calculations based on observational facts we further discuss wave propagation and quantify the proportion of unducted and ducted propagation.