Physics and Astronomy Thesis Defense - Spencer Hatch - Dartmouth College
Title: "Stormtime and Interplanetary Magnetic Field Drivers of Wave and Particle Acceleration Processes in the Magnetosphere-Ionosphere Transition Region"
Location
Haldeman 41 (Kreindler Conference Hall)
Sponsored by
Physics & Astronomy Department
Audience
Public
Abstract: The magnetosphere-ionosphere (M-I) transition region is the several thousand–kilometer stretch between the cold, dense and variably resistive region of ionized atmospheric gases beginning tens of kilometers above the terrestrial surface, and the hot, tenuous, and conductive plasmas that interface with the solar wind at higher altitudes. The M-I transition region is therefore the site through which magnetospheric conditions, which are strongly susceptible to solar wind dynamics, are communicated to ionospheric plasmas, and vice versa.
We systematically study the influence of geomagnetic storms on energy input, electron precipitation, and ion outflow in the M-I transition region, emphasizing the role of inertial Alfvén waves both as a preferred mechanism for dynamic (instead of static) energy transfer and particle acceleration, and as a low-altitude manifestation of high-altitude interaction between the solar wind and the magnetosphere, as observed by the FAST satellite.
Via superposed epoch analysis and high-latitude distributions derived as a function of storm phase, we show that storm main and recovery phase correspond to strong modulations of measures of Alfvénic activity in the vicinity of the cusp as well as premidnight. We demonstrate that storm main and recovery phases together account for more than 65% of global Alfvénic energy deposition and electron precipitation, and more than 70% of the coincident ion outow.
We also compare observed interplanetary magnetic field (IMF) control of inertial Alfvén wave activity with Lyon-Fedder-Mobarry global MHD simulations predicting that southward IMF conditions lead to generation of Alfvénic power in the magnetotail, and that duskward IMF conditions lead to enhanced prenoon Alfvénic power in the Northern Hemisphere. Observed and predicted prenoon Alfvénic power enhancements contrast with direct-entry precipitation, which is instead enhanced postnoon. This situation reverses under dawnward IMF. Despite clear observational and simulated signatures of dayside Alfvénic power, the generation mechanism remains unclear.
Last, we present premidnight FAST observations of accelerated precipitation that is best described by kappa distributions, which signals a nonthermal source population. Guided by theoretical work performed by Dors and Kletzing, [1999], we examine the corresponding implications for the commonly used Knight Relation.
Location
Haldeman 41 (Kreindler Conference Hall)
Sponsored by
Physics & Astronomy Department
Audience
Public
