Magnetosphere-ionosphere coupling during active aurora

Date
2016
Authors
Grubbs, Guy, II
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Abstract

In this work, processes which couple the Earth's magnetosphere and ionosphere are examined using observations of aurora from ground-based imaging, in situ electron measurements, and electron transport modeling. The coupling of these regions relies heavily on the energy transport between the two and the ionospheric conductances, which regulate the location and magnitude of the transport. The combination of the datasets described are used to derive the conductances and electron energy populations at the upper boundary of the ionosphere. These values are constrained using error analysis of the observation and measurement techniques and made available to the global magnetosphere modeling community for inclusion as boundary conditions at the magnetosphere and ionosphere coupling region. A comparative study of the active aurora and incident electron distributions was conducted using ground-based measurements and in-situ sounding rocket data. Three narrow-field (47 degree field-of-view) electron-multiplying charge-coupled device (EMCCD) imagers were located at Venetie, AK which took high spatio-temporal resolution measurements of the aurora using different wavelength filters (427.8 nm, 557.7 nm, and 844.6 nm). The measured emission line ratios were combined with atmospheric modeling in order to predict the total electron energy flux and characteristic electron energy incident on the atmosphere. These predictions were compared with in-situ measurements made by the Ground-to-Rocket Electrodynamics-Electrons Correlative Experiment (GREECE) sounding rocket launched in early 2014. The GREECE particle instruments were modeled using a ray-tracing program, SIMION, in order to predict the instrument responses for different incident particles. Each instrument model was compared with data taken in the lab in order to compare and update the models appropriately. A rocket emulation system was constructed for lab testing prior to and during instrument integration into the rocket and used throughout the project to test instrument response and output. EMCCD imagers were calibrated using known light sources in order to find the imager response at each pixel prior to and during deployment. Electron transport models were modified to use the most recent versions of empirical atmospheric models and chemical reaction rates. The electron transport models showed less than 20% and 50% error for intensity measurements 10 degrees and 20 degrees from magnetic zenith, respectively. An inversion technique was developed in order to derive the characteristics of the in situ electron populations using only the spectral ground-based imaging. The electron populations and atmospheric conductances were characterized, using the inversion technique and the modified Robinson relation, during the St. Patrick's Day storm on 18 March 2015. Discrete arcs contained the most energetic electrons and highest conductances, followed by pulsating aurora and then diffuse aurora. These techniques can be used to constrain the electrons and ionospheric conductances responsible for different types of aurora using imaging data taken over long time periods, when in situ measurements are unavailable.

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Keywords
Aurora, Conductances, Electron Transport Model, Imager Calibration, Ionosphere, Reaction Rates
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Department
Physics and Astronomy