Statistical Relations Between Auroral Electrical Conductances and Field‐Aligned Currents at High Latitudes

Abstract

Field‐aligned currents from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) were combined with simultaneous and coincident observations of ionospheric conductivities made by the Poker Flat Incoherent Scatter Radar (PFISR) in Alaska for 20 geomagnetically active days. The height‐integrated conductivities (conductances) were determined from the electron densities measured by the radar between 80 and 200 km altitude. Binning and averaging the data by field‐aligned current density and magnetic local time, we find that the currents correlate with conductances in both upward and downward current regions over some magnetic local times. The strongest correlation is seen in the late evening and morning sectors, with the Hall conductances two to three times larger than the Pedersen conductances for the same values of the field‐aligned current. The observed correlations reflect the mean energy of auroral precipitation, the contributions from electrons and protons to producing enhanced conductances, and the availability of charge carriers on auroral field lines. We apply linear fitting and smoothing to the correlations to construct an empirical model for specifying auroral conductances globally from AMPERE field‐aligned current maps. The energy fluxes from precipitating particles derived from the model conductances compare well with those derived using AMPERE data combined with satellite‐based measurements of far ultraviolet emissions, suggesting the results obtained at Poker Flat may be applicable to all high latitude locations. The ability to estimate conductances from AMPERE field‐aligned current maps provides the means to develop a global conductance model for the auroral ionosphere.

The Case for Improving the Robinson Formulas

“…In a direct follow‐on to Ridley et al (2004), Mukhopadhyay et al (2020) modified the methodology and expanded the dataset to a full year of AMIE results—all of 2003, which included several superstorms—to create a model of the FAC‐conductance relationship applicable to extreme event conditions. Another relationship between FACs and conductance has been created by Robinson et al (2020), who used nine storm days of Poker Flat Incoherent Scatter Radar (PFISR) observations with AMPERE‐derived FACs.…”

Determination of Auroral Electrodynamic Parameters From AMPERE Field‐Aligned Current Measurements

“…As noted by Robinson et al (2020), the conductances calculated by this approach may not be accurate in regions where the field-aligned currents are small.…”

“…In Section 2, we show how conductances and field-aligned currents are used to determine electric fields and horizontal currents at high latitudes. Section 3 describes the specification of global conductances from AMPERE data by applying the statistical results of Robinson et al (2020). Section 4 describes the calculation of electric fields and horizontal currents, and in Section 5 we use the horizontal currents to estimate ground magnetic perturbations that are compared with ground-based magnetometer data.…”

“…We use the AMPERE field-aligned currents to derive auroral conductances from the statistical results derived by Robinson et al (2020), who combined AMPERE data with conductances calculated from simultaneous and coincident electron density measurements made by the Poker Flat Incoherent Scatter Radar (PFISR).…”

Auroral Energy Flux and Joule Heating Derived From Global Maps of Field‐Aligned Currents

“…Robinson, Kaeppler, et al. (2020) used a similar methodology to derive statistical relations between field‐aligned currents and auroral conductances based on AMPERE and Poker Flat Incoherent Scatter Radar observations, respectively. Robinson, Zanetti, et al.…”