Use of LEO GNSS and in-situ electron density for ionospheric gradients modeling

Within the scope of MIGRAS, an ESA funded project of Swarm DISC, the German Aerospace Center (DLR) has developed two new data products that focus on monitoring mid-scale plasma density irregularities with horizontal spatial scales in the order of about 100 km.The measurements take benefit from the coordinated flight of satellites Swarm-A and -C at an orbit height of about 460 km.The two new Swarm products are the total electron content (TEC) Gradient Ionosphere indeX (TEGIX) and the electron density (NE) Gradient Ionosphere indeX (NEGIX) derived from topside TEC and in-situ electron density measurements onboard GPS receivers and Langmuir probes, respectively.The TEGIX estimates spatial TEC gradients in the topside ionosphere (Swarm up to GNSS orbit), whereas the NEGIX estimates the spatial electron density gradients at Swarm height.The TEGIX and NEGIX results during the St. Patrick's Day Storm on March 17, 2015, will be presented (see Figure 1) and discussed for both North-South and West-East components.For the same storm day, the NEGIX and TEGIX products are validated against the Gradient Ionosphere IndeX (GIX) derived from data acquired with numerous ground GNSS stations over the European region.We found that the northward component of the TEGIX and NEGIX products (blue traces in the right-side panels of Figure 1) correlate very well with the same component of the ground-based GIX data.On the other side, the eastward component of NEGIX and TEGIX (red traces in the right-side panels of Figure 1) differ between each other and when compared with the estimates of GIX.We discuss about these results and the utility of the newly developed ionospheric gradient indices.