Energy coupling during the August 2011 magnetic storm

Abstract

We present results from an analysis of high-latitude ionosphere-thermosphere (IT) coupling to the solar wind during a moderate magnetic storm which occurred on 5-6 August 2011. During the storm, a multipoint set of observations of the ionosphere and thermosphere was available. We make use of ionospheric measurements of electromagnetic and particle energy made by the Defense Meteorological Satellite Program and neutral densities measured by the Gravity Recovery and Climate Experiment satellite to infer (1) the energy budget and (2) timing of the energy transfer process during the storm. We conclude that the primary location for energy input to the IT system may be the extremely high latitude region. We suggest that the total energy available to the IT system is not completely captured either by observation or empirical models.

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

“…In a comparison of particle precipitation with solar radiation and Joule heat, Knipp et al (2004) arrived at a ratio of particle to Joule heat of approximately 1:10 for large storms. In our study of the August 2011 storm, we estimated the precipitation power as well as the observed Poynting flux and reached similar ratios (Huang et al 2014a). It is clear that Poynting flux is the dominant form of energy input to the IT system.…”

“…Figure 1 shows the solar wind conditions for the three storms presented here. The first storm onset occurred on August 5, 2011 and was the subject of our earlier paper on the energy budget (Huang et al 2014a). We take the end of the main phase (MP) to be at the minimum in Sym H at 0327 UT, or Day of Year (DOY) 218.14.…”

“…This assumption is based on the effect of particle precipitation which gives rise to intense auroral emissions and high conductivity in the auroral zone (Evans et al 1977;Vondrak & Robinson 1985;Fuller-Rowell & Evans 1987;Coumans et al 2004, and many others). While conductivity is essential to Joule heating of ions, it was not until comparisons of energy input from solar radiation, electromagnetic waves in the form of Poynting flux, and particle precipitation were carried out that the relative contributions to the IT energy budget were realized (Knipp et al 2004;Huang et al 2014a). In these and other studies, it was shown that Poynting flux is by far the dominant source of energy into the IT system, with typical ratios of 3 to 10 of Poynting flux to particle precipitation power.…”

“…The main point of our previous study of IT coupling during the August 2011 magnetic storm (Huang et al 2014a) was the magnitude of the energy required to explain Joule heating of the thermosphere. We hypothesized that the Poynting flux extrapolated from the Weimer model (Weimer 2005) (hereafter W05) modified by Defense Meteorological Satellite Program (DMSP) measurements underestimates the power available to the IT system via the polar cap.…”

“…Continuing on from the study by Huang et al (2014a), we examine details of where Poynting flux is observed in local time, and where ion temperature and neutral density variations occur during three selected storms which occurred on August 5-6, 2011, September 26, 2011, and January, 2012. Our goal is to determine the locations at which high Poynting flux is observed, and to examine the Joule heating response in the observed ion temperatures (T i ) and neutral densities (q).…”