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The Earth’s ionosphere affects the propagation of signals from the Global Navigation Satellite Systems (GNSS). Due to the non-uniform coverage of available observations and complicated dynamics of the region, developing accurate models of the ionosphere has been a long-standing challenge. Here, we present a Neural network-based model of Electron density in the Topside ionosphere (NET), which is constructed using 19 years of GNSS radio occultation data. The NET model is tested against in situ measurements from several missions and shows excellent agreement with the observations, outperforming the state-of-the-art International Reference Ionosphere (IRI) model by up to an order of magnitude, especially at 100-200 km above the F2-layer peak. This study provides a paradigm shift in ionospheric research, by demonstrating that ionospheric densities can be reconstructed with very high fidelity. The NET model depicts the effects of numerous physical processes governing the topside dynamics and can have wide applications in ionospheric research.

The GRACE (Gravity Recovery and Climate Experiment) satellites, which comprises two spacecraft, GRACE-A and GRACE-B, were launched on 17 March 2002 into a near-circular, polar (inclination = 89◦ ) orbit with an initial altitude of about 490 km. The two satellites follow each other at a distance of about 200 km. The primary objective of the GRACE mission is to provide global high-resolution models of the Earth’s gravity field. The instruments supporting our study are the K-Band Ranging System (KBR), and the GPS Space Receiver (GPS). The K-Band Ranging System (KBR) system is the key science instrument of GRACE which measures the dual one-way range change between both satellites with a precision of about 1 μm per second. From the KBR1B data we can get the change of Total Electron Content (TEC). In addition the GPS Navigation Data (GNV1B) can provide us the position of the two satellites. From these data we can derive the average electron density between the two satellites. The data are stored as daily ASCII files using the file naming convention 'KBRNE_YYYY_MM_DD.dat'. Headers in each data file contain a short name for each column. A more detailed description is provided in the readme file.

Various ESA projects and several proposals to first Swarm DISC Call for Ideas (May 2016) suggested possible evolution for the current Swarm Level 2 FAC products, and the implementation of quality flags for the FAC products. The Field-Aligned Currents—Methodology Inter-Comparison Exercise (FAC-MICE) consisted in comparison of the various methods to determine the FAC from Swarm data, with a test dataset of 28 Swarm auroral crossings delivered to participants last June. Eight groups performed the FAC-MICE analysis. The results of this exercise, discussed in the dedicated ‘Swarm Ionospheric Currents Products workshop’ in ESTEC on September 2017, highlighted the strengths of the various methods/approaches. Following discussion with the participants to this workshop, we are now working to develop an open source platform for user-definable FAC calculation.

In this study we investigate the longitudinal variations in the mean densities of field-aligned currents (FACs) at high latitudes in different seasons, by using high resolution magnetic field data from SWARM A and C satellites. Longitudinal variations are about a factor of 1.2~3.2 larger in the Southern Hemisphere than in the Northern Hemisphere. A tidal analysis is applied to FACs. D0 and DW2 are the dominant non-migrating components. DW2 is larger than D0 in summer and equinox. The longitudinal variations in solar illumination can explain D0 wave in FACs, with more solar illumination at near pole longitudes than at far-from-pole longitude. Factors like the geomagnetic field strength and dipole tilt angle might contribute to the observed DW2 features in FACs. The FACs simulated by the global ionosphere and thermosphere model only show D0 wave. The theoretical study reveals that the role of neutral wind is comparable to that of the electric field in the formation of D0 wave.

It has been known for many decades that the lunar tidal influence in the equatorial electrojet (EEJ) is noticeably enhanced during Northern Hemisphere winters. Recent literature has discussed the role of stratospheric sudden warming (SSW) events behind the enhancement of lunar tides and the findings suggest a positive correlation between the lunar tidal amplitude and lower stratospheric parameters (zonal mean air temperature and zonal mean zonal wind) during SSW events. The positive correlation raises the question whether an inverse approach could also be developed which makes it possible to deduce the occurrence of SSW events before their direct observations (before 1952) from the amplitude of the lunar tides. This study presents an analysis technique based on the phase of the semi-monthly lunar tide to determine the lunar tidal modulation of the EEJ. A statistical approach using the superposed epoch analysis is also carried out to formulate a relation between the EEJ tidal amplitude and lower stratospheric parameters. Using these results, we have estimated a threshold value for the tidal wave power that could be used to identify years with SSW events from magnetic field observations., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 517