Low-latitude severe space weather is typified by the phenomenon of equatorial spread F (ESF), which is an explosive release of stored gravitational energy, usually occurring in the post-sunset period. The occurrence and severity of an ESF event depends on the condition of the local equatorial ionosphere, as well as that of the plasma in electrical contact with it (namely, the off-equatorial E region) through coupling within the appropriate magnetic flux tube. Convective plumes of turbulent plasma that develop during strong ESF events can degrade communications from high frequencies to the L-band and can last for several hours as the plumes drift with the background plasma. A major current area of interest relates to the causal mechanisms that drive the day-to-day variability of ESF. ESF has been convincingly linked to variations in the strength of the pre-reversal enhancement (PRE), which is an increase in the vertical drift velocity during the post-sunset period that drives equatorial plasma to higher altitudes where conditions are more conducive to instability. This project focuses on global measurements of E-region densities and applies them to understand the day-to-day and longer-term variability of ESF. The global measurements will come from instruments onboard the COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) satellites and will include high-resolution Global Positioning System occultation measurements of the total electron content (TEC), ultra-violet photometer measurements related to the integrated ionospheric electron density, and tri-band TEC measurements along the trajectory of the satellite. The measurements will be combined using tomographic inversion and data assimilative techniques to estimate the two-dimensional distribution of electron density, including the horizontal plasma density gradients of the E region densities. Results will be validated and errors and resolutions quantified using ground-truth measurements from the Arecibo and Jicamarca radars. One of the project's broader impacts lies in the database of E region densities that will be assembled which could be useful for global assimilation models and perhaps important in reproducing equatorial ionospheric variability, particularly in terms of prediction. A graduate student will be involved in the projectas well as a new young investigator for whom this is the first proposal as principal investigator.
