High Altitude Plasma Redistribution During Storms

2-D ionospheric mapping has shown the value of global total electron content (TEC) maps from ground-based TEC data. However, the 2-D technique provides no information about the vertical ionospheric structure. The four-dimensional ionospheric imaging algorithm Ionospheric Data Assimilation Three-Dimensional (IDA3D) is used to study the altitude distribution of electron density at equatorial and mid-latitudes during geomagnetic storms. This technique can determine what kind of change in the altitude distribution is responsible for the TEC changes. It can also detect pure changes in the altitude distribution that would produce no change in TEC. Thus, observations of the high-altitude distribution of equatorial and mid-latitude plasma during storms can provide important insights into the driving mechanisms for the ionospheric changes. It is thought that during storms, the equatorial plasma is lifted to higher apex altitudes and then diffuses along magnetic field lines to produce enhanced peaks in electron density at higher latitudes than during non-storm conditions. The source of plasma for storm enhanced density (SED) at mid-latitudes is still unknown, and may be the equatorial region. Understanding how high-altitude plasma is transported during storms is key to understanding the source of SED plasma. SED plasma is observed to be uplifted to altitudes in excess of 600 kilometers, and recent results have demonstrated that similar uplifts occur in the mid-latitude trough in Europe at earlier UT times: there may be a connection between these observations. An important new data source for studying high-altitude plasma redistribution is the so-called over-satellite electron content (OSEC) obtained from navigation GPS receivers upon low-Earth orbiting (LEO) satellites such as GRACE, CHAMP, SAC-C and COSMIC. IDA3D routinely ingests this new data source along with ground GPS TEC, LEO occultation data, ground-based measurements of electron density from incoherent scatter radars (ISRs) and ionosondes, and satellite-based in situ measurements of electron density. IDA3D produces global 3D images of electron density with a typical cadence of 5 minutes. IDA3D results will be presented for several recent geomagnetic storms, with a focus on SED events and the high-altitude plasma distribution in the North and South American sectors. In addition, the effect of the occultation and OSEC data from the recently launched COSMIC constellation of 6 satellites will be presented for a recent minor storm.