Empirical Auroral Conductance Relations Derived with Incoherent Scatter Radar and All Sky Imagers
An important consequence of auroral particle precipitation is the enhancement of electron densities in the ionosphere, at all altitudes. These electron density enhancements cause enhancements in the Hall and Pedersen conductivities, which has important consequences for high latitude electrodynamics and energy transfer from the magnetosphere into the ionosphere-thermosphere system. Empirical models have been developed using various data sources to specify Hall and Pedersen conductance (field-aligned conductivity). In particular, the empirical conductance relation specified by Robinson et al., [1987], i.e., “the Robinson formulas”, has become one of the de-facto formulas which connect energy flux and average energy to Hall and Pedersen conductance. Despite the ubiquitous use of these formulas, these formulas were developed and validated on a surprisingly small set of incoherent scatter radar-satellite conjunctions.
We present empirical conductance relations that are derived from incoherent scatter radar observations and correlated with all sky imager observations to identify the morphology of the aurora. We use 75,461 events collected using the Poker Flat Incoherent Scatter Radar (PFISR) with associated all sky imagers observations spanning the years 2012–2016. In addition to classifying these events based on auroral morphology, we estimated the Hall and Pedersen conductance and the differential number flux from which the energy flux and the average energy can be calculated. The differential number flux was estimated using the maximum entropy inversion method described in Semeter and Kamalabadi [2005], but now incorporating the Fang et al. [2010], ionization model. The main results of this investigation are the power law equations that describe the median, 90th, and 10th percentile Hall and Pedersen conductance as a function of energy flux and average energy. These power law fits are performed for different auroral morphology including all events, discrete, diffuse, and pulsating auroral events.
The goal of this effort is to provide the modeling community with easy-to-calculate conductance models that can be incorporated into ionosphere-thermosphere-magnetosphere models.
Dr. Stephen R. Kaeppler is an Assistant Professor at Clemson University. His research focuses on observational and data analysis studies of auroral and high-latitude electrodynamics, and ionospheric effects on high frequency radio wave propagation. Dr. Kaeppler uses sounding rockets, incoherent scatter radar, and HF ionospheric sounding techniques to address these scientific questions. Dr. Kaeppler earned his Ph.D. in physics from the University of Iowa under Dr. Craig Kletzing and previous to Clemson University was a postdoctoral fellow and research engineer at SRI International. He has a B.S. in physics from the University of Wisconsin – Madison.