Space Physics Seminar - winter-2025
Asymmetric Drift-Orbit bifurcation: Models and Observations
Jan. 17, 2025
3:30 p.m. - 4:30 p.m.
Zoom only
Presented By:
- Sergei Kamaletdinov - EPSS, UCLA
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Radial transport of energetic electrons is a key process driving variability in the outer radiation belt. This transport involves a violation of drift motion. One mechanism that enables such a violation, and the associated radial transport, is drift-orbit bifurcation. This naturally arises from solar wind compression of the dayside magnetosphere, creating a local maximum in field strength at the equator and two off-equatorial minima at the north and south segments of the field line. Trapping and subsequent de-trapping from these local minima during azimuthal drift violates the conservation of the second adiabatic invariant. The resulting jumps in the second adiabatic invariant allow for radial transport. While radial transport due to drift-orbit bifurcation has been extensively studied in symmetric East-West and North-South magnetospheric configurations, the effects of IMF By and its variations have largely been overlooked. In this study, we provide a comprehensive analysis of jumps in the second adiabatic invariant caused by global magnetospheric asymmetries associated with IMF By. We demonstrate that East-West asymmetry induces large jumps in the adiabatic invariant. These jumps can be naturally explained through the theory of separatrix crossings in Hamiltonian systems with slow and fast variables, specifically as “geometric jumps.” These jumps have magnitudes comparable to the initial invariant values and are dictated by the magnetic field topology. We show that the long-term evolution driven by such geometric jumps extends beyond the scope of canonical diffusion, resulting in rapid (exponential) phase-mixing. Furthermore, using ELFIN and THEMIS observations in conjunction with ARTEMIS data, we speculate on the potential observational signatures of asymmetric drift-orbit bifurcation caused by abrupt changes in solar wind conditions.
Alfven-Acoustic Energy Channeling: From Fluid to Kinetic Scales in Earth's Magnetopause Boundary Layer
Jan. 24, 2025
3:30 p.m. - 4:30 p.m.
Slichter Hall # 3853
Presented By:
- Xin An - EPSS, UCLA
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In space plasmas, large-amplitude Alfven waves can drive compressive perturbations, accelerate ion beams, and lead to plasma heating and ion acoustic wave excitation at kinetic scales. This energy channeling from fluid to kinetic scales represents a complementary pathway to the classical turbulent cascade. We present observational and computational evidence validating this hypothesis by simultaneously resolving fluid-scale Alfven waves, kinetic-scale ion acoustic waves, and their imprints on ion velocity distributions in the Earth's magnetopause boundary layer. Our findings reveal that two coexisting compressive modes, driven by the magnetic pressure gradients of Alfven waves, not only accelerate the ion tail population to the Alfven velocity but also heat the ion core population near the ion acoustic velocity and generate Debye-scale ion acoustic waves. Consequently, Alfven-acoustic energy channeling emerges as a viable mechanism for plasma heating near plasma boundaries where large-amplitude Alfven waves are present.
The 1/f Range in Solar Wind Turbulence: Insights from Parker Solar Probe
Jan. 31, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Zesen Huang - UCLA, EPSS
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TBA
Solar Energetic Particle Age-Dating of Interplanetary Dust
Feb. 7, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Andrew Poppe - UC Berkeley
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Interplanetary dust originates from comets, asteroids, and Kuiper Belt objects and subsequently migrates throughout the solar system. During such migration, interplanetary dust grains are exposed to the entire spectrum of charged-particle populations present in the heliosphere, from keV solar wind to GeV galactic cosmic rays. Among several consequences of this exposure, laboratory observations have shown that high-mass (Z>26) solar energetic particles near ~1 MeV/nuc can leave observable damage tracks within interplanetary dust grains. The density of such tracks can then be used as an empirical “clock” for dating the space-exposure age of interplanetary dust and in turn, help to identify the sources and dynamics of interplanetary dust. Here, I will describe (i) the fundamental mechanisms of damage-track creation within interplanetary dust, (ii) observations of damage tracks within interplanetary dust recovered from the Earth’s stratosphere, (iii) efforts to establish an empirical “calibration” for track formation rates based on Apollo lunar samples, and (iv) implications of track density measurements for the possible flux of Kuiper Belt dust at the Earth. In particular, I will touch on major outstanding issues including disagreements between in-situ and lunar-sample derived SEP fluxes and an incomplete understanding of high-Z SEP dynamics throughout the heliosphere.
The Optical Reef: Key Space Technologies to enable Very Large Apertures
Feb. 14, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. David Barnhart - ISI, USC
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The growth of In Space Assembly and Manufacturing (ISAM) and On Orbit Servicing (OOS) has exploded in recent years. Cargo transfer and offload, refueling, materials for manufacturing etc. all are now enabled and pursued with technology here-to-fore unavailable. Growth in ISAM/OOS now involves hundreds of companies across the globe. The value proposition of this growth relies upon discovering and now realizing large scale “missions” that are now only possible through this new technical area. Being able to “build” in orbit opens up the possibility for very large structures, assemblies and systems to be created, well beyond the size of the ISS. However, cooperative technologies, procedures and processes are all required to affect any type of building, refueling, assembling in space using OOS/ISAM actions. To begin to address the rich research and development opportunities of in orbit build the University of Southern California’s Space Engineering Research Center (SERC) has created a conceptual project called “The Optical Reef” to help guide the thought and focus of research pursuits. This presentation will present some of the key areas in this early technology ontology breakdown by introducing both current and proposed PhD level research in some candidate areas including sensor fusion, morphing robotics, distributed platform control, wavefront manipulation, cooperative/communicative rendezvous and docking, etc.
Electron Energization in the Substorm Magnetotail: Insights from ELFIN and CIRBE Observations
Feb. 21, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Prof. Xiaojia Zhang - UT Dallas
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Magnetic reconnection and the subsequent magnetic field reconfiguration, often referred to as the collapse of magnetic traps, are well-established mechanisms for charged particle acceleration in planetary magnetotails and solar flares. The efficiency of these mechanisms depends on various geometric and plasma characteristics, with the most reliable insights obtained from direct measurements of accelerated electron spectra. Traditionally, observations in Earth’s magnetotail have reported electron populations energized to several hundred keV, typically up to 500 keV, starting from initial thermal energies of 1–10 keV. Recent low-altitude CubeSat missions, ELFIN and CIRBE, have revealed the presence of accelerated electron populations with energies reaching several MeV—unexpected for the relatively compact accelerator of Earth’s magnetotail. In this presentation, we will present an overview of ELFIN and CIRBE observations of ultra-relativistic electrons, highlighting the energy ranges and spectral characteristics of these accelerated populations. We will also discuss simulations of electron acceleration, demonstrating that if the initial magnetic reconnection can energize electrons to 10–50 keV, subsequent adiabatic heating during magnetic field reconfiguration can produce multi-MeV electrons, consistent with observations. These results offer valuable insights into electron energization processes in substorm magnetotails.
Investigating the Impact of Imbalance on Inertial and Sub-Ion Scale Solar Wind Turbulence
Feb. 28, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Nikos sioulas - UC /Berkeley
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Recent theoretical advances indicate that the statistical properties of sub-ion scale turbulence are strongly influenced by the degree of imbalance in counter-propagating wave packet fluxes at MHD scales. In this study, we leverage data from the Parker Solar Probe (PSP) and Wind missions to investigate electric and magnetic field fluctuations in the near-Sun solar wind. We examine how three-dimensional anisotropy, higher-order statistics, and helicity associated with Kinetic Alfvén Waves (KAWs) differ between globally balanced and imbalanced intervals. Our findings provide observational constraints and offer new insights into the physical mechanisms driving the turbulent cascade, shedding light on their role in solar wind heating and acceleration.
What is the Aurora about?
March 7, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Xiaoyan Zhou - UCLA, EPSS
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Part-I The BALBOA Project Updates In my last seminar on 29 May 2020 (The BALBOA Project: Then, Now, and Next), we introduced the project background, compelling science, and initiation. Today’s updates include the camera system and science payload development, flight tests from Fort Sumner, NM, and ground auroral campaigns at Poker Flat, AK. Part-II What Is Aurora about? Often, we say aurora is the most visible space physics phenomenon. However, auroral investigations are all about the illumination’s invisible drivers and counterparts thousands of kilometers away. This fascinating phenomenon has caught wide public attention and raised enthusiasm tracing back to the 10th century B.C.E. All the public and professionals have been driven by curiosity - how could that be? It is the same as today’s discussion about the events of the auroral vortex array recorded from Poker Flat during our 2023 winter campaign. Such arrays started from the beading of a pre-existing and stable east-west red arc in the southern sky, then evolved to curls and spirals while extending eastward, leading to a substorm expansion within only ~2 minutes. Based on multiple wavelength observations through the magnetic zenith, we found the average energy and energy flux were 6-7 keV and 30-40 mW/m^2 at the brightest vortex that has the dimensions of ~30x40 km. The auroral morphology strongly suggests a remote shear force may have initiated a Kelvin-Helmholtz instability, which rolled up the magnetic flux that carried the Field Aligned Currents (FACs) in analogy to the roll-up of a carpet Instead of axial, the upward FACs warping with the magnetic carpet drew the spiraling auroral footprint in the ionosphere
Excitation of whistler waves in laboratory plasma: From LAPD to CUDA PIC simulation
March 14, 2025
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall
Presented By:
- Dr. Donglai Ma - EPSS/UCLA
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Whistler waves in near-Earth space play a crucial role in accelerating electrons to relativistic energies and scattering them in pitch angle, driving their precipitation into the Earth's atmosphere. In this talk, I will report the laboratory excitation of whistler waves driven by electron transverse-temperature anisotropy - the same mechanism responsible for their excitation in space. Hot electrons, energized by perpendicularly propagating microwaves at the equator of a magnetic mirror, provide the free energy for whistler excitation. The observed waves exhibit repetitive excitation, akin to whistlers in space. Particle-in-cell simulations reveal that the competition between microwave heating and whistler-induced scattering leads to cycles of anisotropy accumulation and relaxation, driving periodic whistler emissions. These findings illuminate the repetitive nature of whistler waves in space environments and establish a laboratory platform for studying wave-particle interactions relevant to space physics. I will further introduce the recently developed CUDA-based GPU PIC simulations used in this study and the promising future of GPU computing.