Day 4

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Paper title Extended Climatological Model of Non-Polar Geomagnetic Daily Variations
  1. Pierre Vigneron Université de Paris, Institut de physique du globe de Paris, CNRS
  2. Gauthier Hulot Université de Paris, Institut de physique du globe de Paris, CNRS Speaker
Form of presentation Poster
  • B2. Earth Explorer missions
    • B2.05 Swarm - ESA's Extremely Versatile Magnetic Field and Geospace Explorer
Abstract text Geomagnetic daily variations at mid and low-latitudes are generated by electric currents in the E-region of the ionosphere, around 110 km altitude. As part of the Swarm level 2 project, we developed a series of global, spherical harmonic models of quiet-time, non-polar geomagnetic daily variations from a combination of Swarm and ground-based measurements. The latest model, Dedicated Ionospheric Field Inversion 6 (DIFI-6), was released in November 2021. It includes almost eight years of Swarm data providing excellent local time, longitudinal and seasonal coverage, and was extensively tested and validated. DIFI-6 can be used to predict geomagnetic daily variations and their associated induced magnetic fields at all seasons and anywhere near the Earth surface and at low-Earth orbit altitudes below +/-55 degree latitudes. In a second phase of this project, we investigated the year-to-year variability of ionospheric currents in relation with internal magnetic field changes such as, e.g., the slow movement and shape change of the magnetic dip equator. We used the DIFI algorithm to calculate models of non-polar geomagnetic daily variations over a three-year sliding window running through the CHAMP satellite era (2001-2009) and the Swarm era (2014-2021). The obtained models span almost two solar cycles and a period during which the main magnetic field intensity changed by as much as 5% in some locations. They confirm the main features previously observed in the DIFI models, including strong seasonal and hemispheric asymmetries and the anomalous behavior of the Sq current system in the American longitudinal sector. We also find that the total Sq current intensity might have decreased over twenty years in the American longitudinal sector. During the same time period, the dip equator moved northwest by about 500 kilometers. Whether or not both changes are related remains to be confirmed. Future satellite-based magnetic field data collection by Swarm and other low-Earth orbit missions such as, for example, NanoMagsat, will be key in improving our understanding and modeling of non-polar geomagnetic daily variations.