Middle-Latitude Ionospheric Irregularities and Their Relationships with the Ring Current and Auroral Oval Expansion during Geomagnetic Storms

To study ionospheric irregularities, global maps of ionospheric irregularities and scintillation (GMIIS) have been generated at the Jet Propulsion Laboratory. Each GMIIS visualizes a snapshot of global measurements of the rate of TEC index (ROTI) in a 5-minute interval, and the measurements are derived from GPS observations collected from thousands of GNSS stations. In our analysis GMIIS are used to investigate occurrence and evolution of irregularity and scintillation activities in different regions, particularly under disturbed space weather conditions. A number of middle-latitude ionospheric irregularity events are captured using GMIIS that show the irregularities can expand down to sub-auroral and middle latitudes (well below 50 degree dip latitude) during certain geomagnetic storms. The affected middle-latitude region can be a major part of the U.S. continent. Such events are remarkably different from the well-established global picture in which ionospheric irregularities and scintillation predominately occur at low and high latitudes. It is also discovered that all major events examined so far are associated with significant ring current enhancement, and the GMIIS pictures are consistent with DMSP auroral images that show auroral oval expansion. The relationships between the activities of irregularities, ring current, and auroral oval expansion indicate that the ring current expansion into the plasmasphere is likely responsible for the middle-latitude irregularity phenomenon. Under this condition the plasma convection and charged particle precipitation driven by the magnetospheric processes penetrates into middle latitudes, and their variations can cause ionospheric irregularities as seen in GPS data. In this presentation we will show major events of middle-latitude irregularities and their relationships with the ring current and auroral activities. The responsible mechanisms will be discussed. The presentation will add the middle-latitude ionospheric irregularities and scintillation to the global picture of ionospheric irregularity and scintillation distribution.