The investigators will study the source and evolution of the large scale (several hundred kms) and small scale (tens-of-km to tens-of-m) plasma at mid-latitudes during the main phase of magnetic storms. During major magnetic storms, the interaction between the solar wind and the magnetosphere under interplanetary magnetic field (IMF) southward conditions causes a change in the region 1 field-aligned currents leading to a sudden increase in the dawn-to-dusk polar cap potential. The region 2 field-aligned currents associated with an inner magnetospheric electric field directed in the dusk-to-dawn direction are no longer able to shield the mid- and equatorial latitudes from high-latitude electric fields. This results in a near-instantaneous penetration of an electric field from high latitude to the middle and the equatorial ionosphere. The prompt penetration electric field is eastward during the daytime to dusk sector and westward in the midnight to dawn sector. Thus this penetration electric field leads to a significant re-distribution of plasma throughout the plasmasphere and ionosphere by enhancing the layer height, and thereby the plasma density, during daylight hours and increasing the decay rates of ionization in darkness. The recent extension of several NSF-funded instrument arrays at American longitudes and assimilation models have made this collaborative research possible for the first time. The large scale plasma density behavior is best tracked by following the GPS measured total electron content (TEC) from equatorial regions using a newly-formed array through the Caribbean and into the continental US to determine the low latitude contribution to mid-latitude enhancements known as storm enhanced density (SED). A variety of data-assimilation models are now available to model the generation of the SED and test the extent of the equatorial contribution to this mid-latitude feature, thereby developing a climatology of such coupled phenomena. This collaborative research will be the first attempt to determine the contribution of the low latitude TEC on mid-latitudes at American longitudes to understand the source of ionization in the SED, to determine the 2D structure and velocity of hundreds of km scales to decameters and to determine the impact of TEC gradients and phase scintillations on space-based navigation systems. This research is also important for better implementation of the Wide-Area Augmentation System (WAAS), which supports civilian and commercial aviation.
