Geomagnetic field activity ranged from quiet to minor storm levels with brief major storm levels at high latitudes. An interplanetary shock passed the ACE spacecraft at approximately 22/0514Z, likely indicating the arrival of the halo-CME observed on 19 January. This was followed by a geomagnetic sudden impulse (SI) at 22/0614Z (31 nT, Boulder USGS magnetometer). Field activity increased to unsettled to minor storm levels following the SI.
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