Abstract
The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission carries magnetometers that are dedicated to enhance the satellite’s navigation. After appropriate calibration and characterisation of artificial magnetic disturbances, these observations are valuable assets to characterise the natural variability of Earth’s magnetic field. We describe the data pre-processing, the calibration, and characterisation strategy against a high-precision magnetic field model applied to the GRACE-FO magnetic data. During times of geomagnetic quiet conditions, the mean residual to the magnetic model is around 1 nT with standard deviations below 10 nT. The mean difference to data of ESA’s Swarm mission, which is dedicated to monitor the Earth’s magnetic field, is mainly within ± 10 nT during conjunctions. The performance of GRACE-FO magnetic data is further discussed on selected scientific examples. During a magnetic storm event in August 2018, GRACE-FO reveals the local time dependence of the magnetospheric ring current signature, which is in good agreement with results from a network of ground magnetic observations. Also, derived field-aligned currents (FACs) are applied to monitor auroral FACs that compare well in amplitude and statistical behaviour for local time, hemisphere, and solar wind conditions to approved earlier findings from other missions including Swarm. On a case event, it is demonstrated that the dual-satellite constellation of GRACE-FO is most suitable to derive the persistence of auroral FACs with scale lengths of 180 km or longer. Due to a relatively larger noise level compared to dedicated magnetic missions, GRACE-FO is especially suitable for high-amplitude event studies. However, GRACE-FO is also sensitive to ionospheric signatures even below the noise level within statistical approaches. The combination with data of dedicated magnetic field missions and other missions carrying non-dedicated magnetometers greatly enhances related scientific perspectives.
Highlights
Low Earth orbiting (LEO) satellite missions dedicated to accurately measure the geomagnetic field have revolutionised the capability of monitoring Earth’s magnetic field
These are either non-high-precision magnetic observations, e.g., the mission did not measure the magnitude of the total field together with the variations of the magnetic components, or it did not carry an optical bench on the magnetometer boom (e.g., China Seismo-Electromagnetic Satellite (CSES), Communications/Navigation Outage Forecasting System (C/NOFS), Defense Meteorological Satellite Program (DMSP), and e-POP, in the following examples)
By discussing selected scientific applications on auroral field-aligned currents and signatures of the magnetospheric ring current, this section aims at further outlining opportunities and limitations of the GRACE-FO data set
Summary
Low Earth orbiting (LEO) satellite missions dedicated to accurately measure the geomagnetic field have revolutionised the capability of monitoring Earth’s magnetic field. Parameters for calibration The raw magnetic field vector provided by the L1b data is represented in the three directional components within the instrument FGM frame as E = (E1, E2, E3)T (see Table 1 for corresponding field names) given in units of nT.
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