Intellectual Merit: This project was to investigate unusually deep and sudden plasma (ions and electrons) density depletions (troughs) observed in the Poker Flat, Alaska Incoherent Scatter Radar (PFISR) data in mid-summer of 2007 and 2008. PFISR is operated by SRI International on behalf of the National Science Foundation. The troughs were observed in the pre-midnight sector during periods of weak magnetic and solar activity. The density recovered to normal levels around midnight. At the time when the electron density was undergoing its steep decrease, there was usually a surge of the order of 100 to 400 K in the ion temperature. The sudden decreases in the electron density are difficult to explain in summer because the high latitude region remains in sunlight, producing ionization, for most of the day. This research used computer modeling to show that the summer density troughs most likely result from convection to Poker Flat of lower latitude plasma (ions and electrons). This plasma has a low density because it had initially been rotating with the Earth in darkness for several hours after sunset before being whisked to Poker Flat. This situation is facilitated by the unusual structure of the Earth’s magnetic field in the American sector. The sudden increases in ion temperature (spikes) are also difficult to explain because the cooling rates are very strong. The spikes were also attributed to the enhanced ion convection, which causes a temporary increase in ion frictional heating from collisions between the positively charged ions and neutral atoms.This work is important because it investigates how the high latitude ionosphere responds to the exceptionally low solar and magnetic activity of the solar minimum of 2007-2008. It helps understand how the sun interacts with the high latitude ionosphere.

Broader Impact: This research contributes to our understanding of fundamental plasma processes: namely the interaction of neutral and ionized particles. It also contributes to our understanding of the sun-Earth interaction by illuminating how the solar wind affects high latitude ion convection. This is crucial for understanding space weather effects on satellite infrastructure and communications. The proposal helped support two George Mason University graduate students who learned how to model the ionosphere. This work research was facilitated by collaboration with Dr. St.-Maurice and his graduate student Lindsay Goodwin at the University of Saskatchewan. Ms. Goodwin received her Master’s degree with her study of the ion temperature spikes. Dr. St.-Maurice was an original co-investigator on the grant. This funding also supported continued development and distribution of the FLIP ionosphere model, which is already used by many colleagues around the globe. The FLIP model, with enhancements developed under this grant, was used extensively in a University of Colorado Ph.D. dissertation by Dr. Robert Redmon to study the role of electron precipitation in the auroral zone in driving thermal O+ upward flow.

Products: 5 refereed journal articles. Improved ionosphere model.

Last Modified: 08/26/2014
Modified by: Philip G Richards