Global-Scale Ionospheric Tomography During the March 17, 2015 Geomagnetic Storm

The correct representation of global-scale electron density is crucial for monitoring and exploring the space weather. This study investigates whether the ground-based Global Navigation Satellite System (GNSS) tomography can be used to reflect the global spatial and temporal responses of the ionosphere under storm conditions. A global tomography of the ionosphere electron density is constructed based on data from over 2,700 GNSS stations. In comparison to previous techniques, advances are made in spatial and temporal resolution, and in the assessment of results. To demonstrate the capabilities of the approach, the developed method is applied to the March 17, 2015 geomagnetic storm. The tomographic reconstructions show good agreement with electron density observations from worldwide ionosondes, Millstone Hill incoherent scatter radar and in-situ measurements from satellite missions. Also, the results show that the tomographic technique is capable of reproducing plasma variabilities during geomagnetically disturbed periods including features such as equatorial ionization anomaly enhancements and depletion. Validation results of this brief study period show that the accuracy of our tomography is better than the Neustrelitz Electron Density Model, which is the model used as background, and physics-based thermosphere-ionosphere-electrodynamics general circulation model. The results show that our tomography approach allows us to specify the global electron density from ground to similar to 900 km accurately. Given the demonstrated quality, this global electron density reconstruction has potential for improving applications such as assessment of the effects of the electron density on radio signals, GNSS positioning, computation of ray tracing for radio-signal transmission, and space weather monitoring. Plain Language Summary Computerized tomography allows the 3D imaging of several objects based on radio frequency signal measurements. Given the measurements and geometry of the current GPS (Global Positioning System) satellite constellation, there is an opportunity to apply tomography techniques and extract 3D snapshots of the Earth's atmosphere. This work presents an advanced global-scale tomography that can represent the electron density in the Earth's upper atmosphere in a relatively high spatial and temporal resolution in the region of similar to 100-1,000 km above the Earth's surface; referred to as the ionosphere. The work also validates the tomography results with multiple ionospheric observations from satellites and ground-based radar instruments and compares with empirical and physical models. It is usually a challenge for models to reproduce the ionospheric system dynamics accurately during active space weather conditions, such as geomagnetic storms. This work, using the severe geomagnetic storm on March 17, 2015 as a case-study, shows that the tomography is well poised for this task. The developed method could be extended to benefit several applications, such as space weather monitoring, GPS positioning and navigation, as well as to improve our understanding of the morphology and dynamics of the ionosphere.