Special Guest Seminar - spring-2023

April 28, 2023
3:30 p.m. - 4:30 p.m.
3853 Slichter Hall

Presented By:

• Anthea Coster - MIT/Haystack

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This seminar will review current questions that are being explored as part of a NASA Focused Science Topics group. In particular, our project is focused on unveiling the hemispheric asymmetries that are due to electro-dynamical coupling in the magnetosphere-ionosphere (MI). Our intent is that, in doing this, more light will be shed on those processes that are driven by other forces. We have identified the following questions in particular: (1) What is the nature of the observed dynamics and spatial distribution (specifically the longitudinal variations) of the sub-auroral polarization stream (SAPS) electric field structures and the storm enhanced density (SED) feature during geomagnetic storms? (2) What are the drivers and mechanisms causing the observed tongue of ionization (TOI) and related density structures over the polar caps, and the patterns of E×B ionospheric convection pattern, and their observed hemispheric asymmetries? (3) What processes control the hemispheric asymmetry in both the location and strength of the equatorial ionospheric anomaly (EIA) structures as observed during both quiet and disturbed conditions? We will begin with a review of these features: SED, SAPS, TOI’s and the EIA, as well as provide examples of the observed asymmetries. We are using a combined ionosphere-magnetosphere coupling approach guided by careful examination of ground and satellite-based data. In particular, this project aims to examine which phenomena are related to, or are driven by, asymmetries and variability in the solar wind and interplanetary magnetic field (IMF), the higher-order moments (e.g. the South Atlantic Anomaly) and dipole tilt in the intrinsic geomagnetic field and the resulting dynamical processes in plasma behavior. An accompanying goal will be the further development of the coupled first-principles ionosphere-inner magnetosphere numerical model SAMI3/RCM. This task will include updating both the ionospheric model (SAMI3) and the magnetosphere model (RCM), and their coupling, to use the most recent version of the International Geomagnetic Reference Field (IGRF-13) model available." Magnetospheres are a ubiquitous feature of magnetized bodies embedded in a plasma flow. Large planetary magnetospheres in the heliosphere have been studied for decades by spacecraft, while ion-scale ``mini'' magnetospheres have been observed around comets, weakly-magnetized asteroids, and localized regions on the Moon. These mini-magnetospheres provide a unique environment to study kinetic-scale plasma physics, in particular in the collisionless regime, but are difficult to study directly. Laboratory experiments on mini-magnetospheres can thus provide a controlled and reproducible platform for understanding fundamental magnetospheric physics while helping to validate models of larger, planetary magnetospheres. In this work, we present the results from experiments on ion-scale magnetospheres performed on a new high-repetition-rate (1 Hz) experimental platform developed on the Large Plasma Device (LAPD) at UCLA. The experiments utilize a high-energy laser to drive a supersonic plasma flow into a pulsed dipole magnetic field embedded in a uniform background magnetic field. 2D maps of magnetic fields with high spatial and temporal resolution are measured with magnetic flux probes and examine the evolution of local and global magnetosphere and current density structures for a range of dipole and upstream parameters. The results are compared to PIC simulations to further identify the magnetospheric structure, kinetic-scale structures of the plasma current distribution, and dynamics of the laser-driven plasma.