Empirical model of Poynting flux derived from FAST data and a cusp signature

Abstract

[1] Empirical models of the Poynting flux and particle kinetic energy flux, associated with auroral processes, have been constructed using data from the FAST satellite and are available online. The models output flux maps as a function of several geophysical parameters: (1) clock angle of the interplanetary magnetic field (IMF), (2) magnitude of the IMF in the GSM y-z plane, (3) solar wind speed, (4) solar wind number density, (5) magnetic dipole tilt angle, and (6) the AL index (optional for Poynting flux). The choice of parameters is motivated by the Weimer potential model. Because the Poynting flux distribution has a heavy tail, care must be taken in applying the model to events that may be uncommon, and the model output includes a measure of quality based on the density of FAST orbits in the parameter space. The models are constructed by fitting the data to a sum of empirical orthogonal functions (EOFs), with coefficients modeled by quadratic equations in the geophysical parameters. The EOFs are constructed from the same data set using singular value decomposition, along with a smoothing/interpolation algorithm that minimizes curvature and incorporates uncertainty. Potential applications include specification of the auroral energy input for general circulation models. Basic findings from the model include verification of the importance of the auroral electrojets as features of auroral Poynting flux deposition and identification of the cusp as a third important feature. The cusp makes an important contribution to the overall energy budget when the IMF is north of˙90 ı .

Ionosphere-thermosphere (IT) response to solar wind forcing during magnetic storms

“…In general, observations of Poynting flux, Joule heat, and other forms of energetic response are averaged to yield an empirical result. As pointed out by Cosgrove et al (2014), this results in a ''smearing'' of the data. This kind of analysis brings out large-scale, steady-state phenomena but it does not represent well highly dynamic events like magnetic storms.…”

“…The widely accepted paradigm is documented in papers by Weimer (2005), Cosgrove et al (2014), McHarg et al (2005, and others, in which the auroral zones and cusp dominate highlatitude energy input. The main reason for the discrepancy between our results and previous work lies in the way the data have been treated.…”

“…Poynting fluxes have been calculated for the ionosphere for some time (Kelley et al 1991;Wilder et al 2012;Cosgrove et al 2014). DMSP routinely measures the ion drifts from which the convective electric field (E) can be extracted, as well as magnetic perturbations (dB) about the Earth's magnetic field.…”

Modes of high‐latitude auroral conductance variability derived from DMSP energetic electron precipitation observations: Empirical orthogonal function analysis

“…Alternatively, high correlations demonstrate a relationship exists but do not necessarily provide information about causation. EOFs are not necessarily organized according to physical cause. They capture the direction of most variability in the data subject to the constraint that it is orthogonal to each previous, more prominent, direction of variability, and irrespective of the correlation with physical drivers [ Cosgrove et al , ].…”

IMF Control of Alfvénic Energy Transport and Deposition at High Latitudes

“…Knipp et al () report extremely enhanced energy deposition, sometimes locally reaching 170 mW/m 2 , associated with strong IMF B y conditions. Cosgrove et al () introduce a comprehensive empirical Poynting flux model as a function of several IMF and solar wind parameters. All of these studies deal with total Poynting flux.…”