Changes in the dayside ionosphere during extreme magnetic storms

Extreme space weather has a major impact on the dayside ionosphere. The ionospheric response to extreme events will cause significant satellite-based navigation errors, disruptions in HF communication, and radar tracking errors. These consequences include denial of aircraft precision approach services over the United States and other continents. Another consequence of extreme storms is increased satellite drag, leading to significantly degraded orbit determination accuracy. Our focus in this presentation is the daytime superfountain that occurs during the main phase of severe geomagnetic storms. The cause of dayside ionospheric perturbations is prompt penetration electric fields that reach as far as the geomagnetic equator, causing rapid uplift of oxygen ions and enhanced diffusion of ionospheric plasma along geomagnetic field lines. Large, rapid (~1-2 hours) increases in ionospheric total electron content (TEC) reach middle latitudes, creating TEC peaks on either side of the geomagnetic equator resembling a strongly enhanced equatorial anomaly feature. To clarify the impact of extreme events, we focus on the October 30 2003 severe geomagnetic storm. The peak geomagnetic index Dst was -390 nT during this “Halloween” storm. By comparison the 1–2 September 1859 Carrington magnetic storm was considerably stronger, reaching a peak Dst estimated at -1760 nT. TEC data clearly show an enhanced equatorial anomaly feature caused by the daytime superfountain during the Halloween event. We use a modified version of the NRL SAMI2 ionospheric code to investigate details of the plasma transport. We find that the near-equatorial region (latitudes up to ± 15°) is swept free of plasma within 15 minutes (or less) of storm onset. Oxygen ion density enhancements are found to be located within the broad range of latitudes ~ ±(25°–40°) at ~500–900 km altitudes. Ion densities within these peaks are ~6x10⁶ oxygen ions-cm^-3 at ~700 km altitude, approximately +600% quiet time values. Measurements from DMSP satellites confirm that O+ ions are uplifted to satellite altitudes of ~850 km, reaching peak densities of ~9x10⁵ cm^-3. The oxygen ions alone at the high-altitude portions (850–1000 km) of storm-time features will cause significantly increased satellite drag compared to quiet time conditions. Calculations are currently being performed on possible uplift of oxygen neutrals by ion-neutral coupling to determine if there might be further significant satellite drag forces present.