This is a 3-year modeling and data analysis study aimed at understanding an unusual electron density behavior associated with ion temperature spikes that have been observed in the Poker Flat Incoherent Scatter Radar (PFISR) data over the summer 2007-2008. The spikes were only found in summer and when both the solar and magnetic activities were very low. The spikes are associated with strong westward convection velocities and steep electron density depletions that are most likely the signature of a high latitude ionization trough. The detection of this phenomenon was facilitated by the continuous running of PFISR and also because of the special conditions provided by the exceptionally low magnetic activity in the solar minimum of 2007-2008. The PFISR data offers a unique perspective on the generation and evolution of the high latitude ionization trough. First, a thorough search and analysis of the PFISR data will be performed to identify as many examples of the trough events as possible from 2007 onward. Secondly, the field line inter-hemispheric plasma (FLIP) model, developed by the PI and used successfully in several previous studies to reproduce PFISR observations, will be employed to simulate the PFISR electron density observations. The ultimate goal is to gain a greater understanding of the chemical and dynamical processes that create and maintain the high latitude ionization trough.
There are valuable broader impacts resulting from the project as well. Notably, a graduate student would be trained as part of the project. Further, the FLIP model, which is used by many other researchers, would be improved, thereby enhancing its value to the research community.
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.
