CSPAR Colloquium Archive Older

Throughout the Fall Semester Space Science and CSPAR will be conducting a Colloquium. We invite both faculty and students to join us! Refreshments for the audience are served after the talk. Check for dates, speakers, and topics below. For further information on the Colloquium, please contact space_science_colloquium@uah.edu.

Date: 9/23/22
Speaker: Gang Li, Professor, UAH
Type: in-person, talk
Title: “Configuration of solar wind magnetic field and energetic electrons in the inner heliosphere”

Abstract:

In the solar system, our Sun is Nature's most efficient particle accelerator. In large solar flares, electrons can be accelerated to multi-MeV and ions to several hundred MeV/nuc, causing the observed hard X-rays and gamma rays.  These events are often classified as impulsive events. While the underlying acceleration mechanisms in these events is still under debate,  in-situ energetic electrons in these events have offered a practical tool in understanding the solar wind magnetic field configuration. On some occasions, it also provides stringent constraints on the underlying acceleration mechanisms.  In this talk, I will discuss a recently developed data analysis method, called the Fractional Velocity Dispersion Analysis (FVDA).  Employing the FVDA, I show how one can use in-situ energetic electron observations to obtain the release times of these electrons at the flare site, as well as the corresponding turbulence spectrum index. Furthermore, using FVDA one can also examine the solar wind magnetic field configurations.  Examples of electron reflection beyond 1 AU will be shown, illustrating the large variety of the IMF.

Date: 10/14/22
Speaker: Haimin Wang Distinguished Professor of Physics, NJIT
Type: in-person, talk, (may change subject to covid)
Title: "Study Solar Activity with High Resolution Observations and Machine Learning"

I will first summarize some discoveries using the 1.6m Goode Solar Telescope

(GST) at Big Bear Solar Observatory (BBSO) and explain why GST and newly

built 4-m Danial K. Inouye Solar Telescope (DKIST) are complementary in

research. I will the summarize some of scientific results: (1) The small scale

magnetic structure evolution leading to solar eruptions. (2) With highest resolution observations, the photospheric magnetic structure changes can be tracked from flaring polarity inversion lines (PIL) propagating outwards. These include the sudden flare-induced rotation of sunspots and the increase of transverse magnetic fields near PIL. This provides some clear clues to the so-called “Dog vs. Tail” problem. (3) We recently found extremely strong (>5500G) fields in PIL of flaring

sunspot in the famous solar active region of September 2017. (4) Flares ribbons may show absorptions instead of emissions. Modeling can explain those negative flares. Finally, I will introduce applications of machine learning and artificial intelligence in processing the “Big Data” from our observations. These examples will include automatic feature recognition and tracking, as well as the forecasting of solar eruptions. In particular, I will introduce a ML tool to generate vector magnetograms from line-of-sight magnetograms and Halpha images, extending synoptic vector magnetograms to SOHO/MDI era, as well improving spatial resolution for HMI data using GST data as a training set.

Date: 10/21/22
Speaker: Gary Zank, Distinguished Professor, UAH
Type: in-person, talk, (may change subject to covid)
Title: “On Magnetohydrodynamics, Fluctuations, Structures, and Turbulence"

Small amplitude fluctuations in the solar wind are measured by a single spacecraft at a particular Doppler-shifted frequency or set of frequencies and a corresponding wave number vector k can be inferred using various techniques. In the magnetohydrodynamics (MHD) description, fluctuations are typically expressed in terms of the wave modes admitted by the system. An important question is how to resolve an observed set of fluctuations, typically plasma moments such as the density, velocity, pressure and magnetic field fluctuations, into their constituent fundamental MHD components. Surprisingly, this problem has not yet been fully resolved despite its importance in understanding the most basic elements of waves and turbulence in the solar wind. For example, a decades long argument has persisted about whether turbulence in the solar wind is Alfvenic (i.e., dominated by Alfven waves) or dominated instead by magnetic structures (i.e., dominated by flux ropes, aka magnetic islands and vorticity). Unfortunately, a method was not hitherto developed to identify between wave modes and advected structures such as magnetic islands. Here, we discuss quite generally the identification of wave modes in an MHD plasma from a set of plasma and magnetic field fluctuations observed by a single spacecraft at a specific frequency and an inferred wave number. We discuss some applications of our approach to fluctuations in the solar wind and to the interaction of fluctuations at shock waves

Special colloquium

10/26/22, Wednesday,  room 2096, 4pm-5pm

Shuichi Matsukiyo ,  in-person

ESST Kyushu University, Japan

Title : *Trajectory Analysis of Galactic Cosmic Ray Protons Invading the Virtual Heliosphere*

The trajectories of galactic cosmic-ray protons invading the heliosphere are investigated by using numerical simulations. A time stationary global heliosphere is first reproduced by using a high-resolution MHD simulation. Then, motions of a number of test particles (protons) distributed in the virtual heliosphere are numerically solved. When the initial particle Lorentz factor is 10 (∼10 GeV), the motions of particles are strongly affected by small-scale heliospheric structures reflecting the small gyroradii of the particles. Particles can enter the heliosphere from many parts (nose, flank, and tail) of the heliopause. Once they have entered, they expand in the region where the magnetic field is locally weak, such as the heliopause and the heliospheric current sheet. On the other hand, particles have difficulty invading upstream of the termination shock. We found a variety of invading particle trajectory patterns such as current sheet drift, polar drift, spiral motion, shock drift, and Fermi-like acceleration. In the latter two, particles are accelerated. When the initial particle Lorentz factor is 1000 (∼1 TeV), the particles are insensitive to the small-scale structures of the heliosphere due to their large gyroradii. Some particles show eccentric motions due to resonant interaction with the large-scale eddy in the heliotail. Some other particles passing by the heliosphere are mirror reflected due to the bottleneck structure of interstellar magnetic field surrounding the heliosphere and return back to enter the heliosphere. We further discuss some statistics of the particles reaching the inner boundary of the MHD simulation at 50AU from the sun.

Date: TBD
Speaker: Daniele Telloni, Researcher | National Institute for Astrophysics Astrophysical Observatory of Torino, Italy
Type: virtual
Title: “Multi-spacecraft and multi-instrument study of the solar wind in the corona and heliosphere”

Abstract: The evolution of waves and turbulence in the expanding solar wind is mostly studied statistically using broad ensembles of measurements taken at different times, at different heliocentric distances, and under different solar wind and solar conditions. Standard techniques, including power spectra and structure functions, multifractal analysis, third-order scaling laws and energy transfer, Alfvénicity, wave coherence, structure identification, non-Maxwellian features of particle distribution functions, are normally used to describe the properties of the fluctuations and how they heat and energize the plasma. However, due to the intrinsic variability and inhomogeneity of the solar wind and of its solar sources, this approach cannot capture the fundamental dynamical evolution of turbulence and the related plasma heating, necessary for understanding the general physical processes and correctly modeling the heliosphere. Using specific configurations to obtain rare measurements of the same plasma parcel by two radially aligned spacecraft may allow understanding the actual evolution of waves, turbulence and heating under different conditions. Additionally, compared observation of the solar/coronal sources and in-situ properties, possible during quadratures, will help

address the origin of turbulence and its dependency on the solar structure. As a matter of fact, linking plasma kinetic properties (waves, instabilities, energy deposition) with large-scale coronal structures will represent a breakthrough to the long-standing problem of coronal heating, onset of plasma instabilities, and wave generation. This talk reviews the most recent results obtained by exploiting the joint in-situ and remote-sensing observations during the first Parker Solar Probe - Solar Orbiter radial alignments and quadratures, and in particular the radial evolution of solar wind turbulence and solar-wind connectivity with coronal sources.

Date: 11/18/22
Speaker: Patrick H. Diamond, CASS and Dept. of Physics, UC San Diego
Type: in-person, talk
Title: “Elastic Turbulence: A Case Study of SIMPLE Examples”

Abstract: In this colloquium, I will review some basic concepts of hydrodynamic turbulence and of elastic fluids, with emphasis on the origin of ‘memory’ in the latter, and how it modifies the conventional ideas of turbulence. I’ll then discuss one simple example of elastic turbulence in some depth. This is Cahn-Hilliard Navier-Stokes turbulence, in which elasticity results form droplet tension. I’ll discuss the ‘what?’ and ‘why?’ of this system, before proceeding to explore interactions and transport in it. I’ll conclude with a look at the lessons learned.