Frictional heating, frequently termed Joule heating, results from the difference in ion and neutral flows in the Earth's upper atmosphere and is a major energy sink for the coupled magnetosphere-ionosphere-thermosphere system. During disturbed geomagnetic conditions, energy input from the Earth's magnetosphere can strongly enhance ion velocities and densities, which will generally increase the rate of Joule heating. Previous theoretical and experimental studies have shown that small-scale variations in Joule heating can be quite significant in the overall energy budget. In this study, we employ high-resolution fitting of ion velocities obtained by Super Dual Auroral Radar Network (SuperDARN) coherent scatter, along with spatially resolved neutral wind data from the Poker Flat Scanning Doppler Imager, to examine the spatial and temporal structure of F region ion temperature enhancements, as well as changes in Joule heating rates due to the neutral wind. These results are compared to those obtained using Poker Flat Incoherent Scatter Radar in order to assess the validity of this analysis, with the objective of developing a method that can be applied to any current or future neutral measurements worldwide, thanks to the global coverage of SuperDARN. We examine the agreement between the ion temperatures predicted using the Scanning Doppler Imager-SuperDARN method and the temperatures measured directly by Poker Flat Incoherent Scatter Radar and discuss possible reasons for any discrepancies. We observe significant spatial structure in both the ion temperature and Joule heating rates during periods of magnetic activity.
Available at: http://works.bepress.com/andrew-kiene/2/
The SuperDARN research was supported by NSF Grants 1443504 and 1341902. All SuperDARN observations used in this study are available from the SuperDARN database, which can be accessed from http://vt.superdarn.org. The magnetometer data were obtained from the Alaska Satellite Facility website at https://www.asf.alaska.edu/magnetometer. SDI data are available from http://sdi_server.gi.alaska.edu/sdi_web_plots/. SDI operations were primarily supported by NSF Grant AGS1140075. Other optics data used are available at ftp://optics.gi.alaska.edu/. The data collection and analysis for the all-sky camera and spectrograph were supported by NSF cooperative agreement ATM-0608577. PFISR is operated by SRI International under NSF cooperative agreement AGS-1133009, and PFISR data are available through the Madrigal Database (isr.sri.com/madrigal). The codes used to produce the LDFF results are publicly available (see Bristow & Kiene, 2018). A. Kiene would like to thank A. Reimer and the rest of the SRI International team for helpful discussions and PFISR data processing.