Geospace II: Neutral and Charged Environments

Recently a new method for monitoring the plasmapause location in the equatorial plane was introduced based on magnetic field observations made by the CHAMP satellite in the topside ionosphere (Heilig and Lühr, 2013). Related signals are small-scale field-aligned currents (some 10km scale size). We now apply the technique to the SWARM constellation. Making use of the special constellation of SWARM we will be able to discriminate between temporal and spatial variations in the plasmapause more clearly.

We plan to build an empirical plasmapause model, similar to the CHAMP-based model (Heilig and Lühr, 2013). The model will be validated by means of ground (EMMA magnetometer network) plasmapause observations, as well as by the in-situ plasma observations of the Van Allen Probes.

Heilig, B., and H. Lühr (2013) New plasmapause model derived from CHAMP field-aligned current signatures, Ann. Geophys., 31, 529-539, doi:10.5194/angeo-31-529-2013

We assess the quality of high-latitude ionospheric bulk upflows and downflows measured by Electric Field Instruments (EFI) on the European Space Agency’s Swarm mission. Processed EFI data include calibrated vector flow measurements at 2 Hz, and uncalibrated vector flow measurements at 16 Hz. Statistical binning of EFI data in terms of magnetic latitude and local time, solar wind conditions, and geomagnetic activity serves to assess well-known patterns, such as auroral and magnetic cusp upflows, reported in the literature from platforms such as Dynamics Explorer 2 (DE-2), the Defense Meteorological Satellite Program (DMSP), and ground-based radars. We further report on efforts to calibrate the 16 Hz flows using the 2 Hz data as reference.

After depletion of GOCE's xenon fuel on the morning of October 21, 2013, when the satellite's mean geodetic altitude was 239 km, it took 3 weeks before the satellite disintegrated during re-entry, shortly after UTC midnight on November 11. A continuous record of scientific and housekeeping data from the satellite's mass memory was received until about 7 hours before re-entry, at which point the satellite's minimum geodetic altitude was just 138 km. After that time, during the final four ground station passes limited telemetry was received.

Although the along-track axes of the accelerometers on GOCE were saturated two days before the re-entry, accurate acceleration data could still be derived from the continuous GPS tracking up to the final day. The analysis of the accelerations is facilitated by the availability of attitude determination and control data. These final three weeks of GOCE data therefore provide a unique opportunity to investigate the satellite dynamics and thermosphere variability in the 140-240 km altitude range and perform a benchmarking of the acceleration models and related environment models.

The analysis will be performed using panelized satellite geometry models for GOCE. The use of analytical force model equations will be compared with the results of a Monte-Carlo Test Particle simulation method. The influence of atmospheric variability on the accelerations will be studied using semi-empirical models, such as NRLMSISE-00. In addition, a numerical model, in this case the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X), will be used to study atmospheric drivers that are not well represented in the semi-empirical models, such as forcing from the lower atmosphere.

Over the past years, a lot of effort has been put into characterising and correcting the various disturbance signals that were found in the accelerometer data provided by the Swarm satellites. This effort was first and foremost aimed at the Swarm C along-track axis data, which seems to be the least affected and most promising data for scientific use. The goal to make the Swarm C accelerometer along-track axis data ready for further processing into level 2 thermosphere density data has now been accomplished, with the help of information on the satellite motion from the GPS tracking as well as on the attitude from the star trackers.

This presentation looks into the features of scientific interest that are found in the currently available density data set, as well as makes an assessment of the density data accuracy. We assess how the current quality level of the data in combination with the correction approach, affects the possibility of determining densities from the accelerometer measurements of the Swarm A and B satellites. We also investigate the possibility of determining crosswind speeds from Swarm data.

In the meantime, we have investigated the possibility of deriving thermosphere neutral density data from the Swarm GPS observations only, with a much lower temporal resolution. We analyse the differences in the data between the three Swarm satellites as well as between the accelerometer-derived and GPS-only-derived densities for Swarm C.

The new method to detect the ionospheric irregularities/plasma bubbles using GPS measurements from Precise Orbit Determination GPS antenna onboard Low Earth Orbit (LEO) satellites is presented. We use GPS measurements onboard the new ESA’s constellation mission Swarm, as well as GRACE and TerraSAR-X satellite, that have rather similar orbit altitude of about 500 km. We demonstrate that LEO GPS can be an effective tool for monitoring the occurrence of the topside ionospheric irregularities and may essentially contribute to the multi-instrumental analysis of the ground-based and in situ data. In the present study we analyze the global distribution of the equatorial ionospheric irregularities during post-sunset period, as well as the occurrence of more rare night-time and morning-time equatorial plasma bubbles. To support our observations and conclusions, we involve into our analysis in situ plasma density provided by Swarm constellation, GRACE KBR, DMSP satellites, as well as ground-based GNSS and digisonde networks.