Swarm A and C Accelerometer - data analysis and scientific outcome

The ESA Swarm mission was launched in November 2013, and it consists of a constellation of three identical satellites. The main mission objective is to model and analyze the geomagnetic field through the data provided by a vector and a scalar magnetometer on board of each spacecraft (A, B, C).  To fulfill the secondary objectives, the satellites do also carry other instruments, such as an accelerometer expected to measure the non-gravitational forces acting on each satellite. However, the quality of the data retrieved from this instrument was not at the anticipated level and, therefore, the post-processing required to calibrate the signal was significant. Therefore, initially the calibration focused on Swarm C only because it had the best signal-to-noise ratio of the constellation. For this satellite the calibrated accelerometer data are available since the beginning of the mission and they are disseminated bi-monthly. At the end of 2021, the first Swarm A dataset was released and it comprises some months in 2014. Swarm A and C, called the “lower pair”, have flown side-by-side for most of the mission with a separation that spanned from four to ten seconds. Therefore, their measurements are supposed to be nearly identical after calibration.

A recent publication, which is discussed in this talk, demonstrated that a comparison between Swarm A and Swarm C calibrated accelerometer dataset shows the expected correlation. After applying a high-pass filter to both satellites’ dataset, very similar features are visible at the equator and at the poles. The “long time scale” events at the equator show a correlation between the equatorial mass anomaly and the equatorial ionization anomaly. At the poles, the “short time scale” events can be related to the Polar Cap index and to the field-aligned currents, which are measured on board by the Swarm magnetometers. Furthermore, these features agree with previous literature based on CHAMP and GRACE data.

For the first time the Swarm accelerometer data deliver scientific results, in particular in the field of thermosphere and ionosphere coupling.