Magnetic disturbances in September 2026
Magnetic disturbance of 23–24 September 2026: Vernadsky (Ukrainian Antarctic station on Galindez Island, Argentine Islands archipelago, near the Antarctic Peninsula) and Nurmijärvi (Finland).
Today, the trend towards “network” science in space weather research reflects a fundamental shift from isolated local measurements to global, large-scale monitoring. Synchronously combining standardized datasets from many distributed stations makes it possible to build accurate dynamic models of the magnetosphere and ionosphere and to capture the integrated response of the Earth, composed of many local and regional responses to solar disturbances. One such “geomagnetic network” is INTERMAGNET, a global network of magnetic observatories that collects high-precision, standardized data on the Earth’s magnetic field. The network operates as a voluntary international consortium of scientific institutes and works closely with the International Association of Geomagnetism and Aeronomy (IAGA); all INTERMAGNET observatories are affiliated with IAGA. Thanks to the considerable efforts of the National Antarctic Scientific Center of Ukraine and the S. I. Subbotin Institute of Geophysics of the National Academy of Sciences of Ukraine, the geomagnetic observatory at the Antarctic station Akademik Vernadsky has been a member of INTERMAGNET since 2004 (code AIA), and anyone, including Latvian scientists, can take part in studying disturbances of the Earth’s magnetic field in the Antarctic region using its freely available data.
As an example, let us consider an interesting event, the geomagnetic disturbance of 23–24 September 2026, by comparing the regional geomagnetic response recorded by the vector magnetometers at Akademik Vernadsky (Antarctica) and Nurmijärvi (Finland).
The event
A fast solar wind stream reached the Earth from a coronal hole on the Sun, a region where the magnetic field is open to interplanetary space. It was preceded by a compression region: the fast plasma caught up with the slower wind ahead of it and compressed it together with its magnetic field. The disturbance turned out to be weak: the Kp index reached 4.33 out of 9, whereas a storm on the NOAA scale starts at Kp 5.
| Time (UT) | In interplanetary space | On Earth |
|---|---|---|
| 23 Sep, 00–17 | Slow wind, weak field | Quiet: Kp ≤ 1, only the usual daily variation |
| 23 Sep, 17–24 | Compression region arrives; the interplanetary field points north | Dst rises to +32 nT; pulsations switch on at both stations; Kp < 2 |
| 24 Sep, 00–24 | The field turns south and stays south; wind speed increases | Dst falls from +29 to −33 nT (minimum at 17–18 UT); Kp up to 4.33 at 09–12 UT |
What the stations saw
Akademik Vernadsky (Antarctica, AIA) and Nurmijärvi (Finland, NUR) lie in opposite hemispheres, at magnetic latitudes of −52° and +58°. The field lines through them extend into space to 2.6 and 3.4 Earth radii, and the stations are 6 hours apart in magnetic local time.
- Most of the range is the ordinary daily variation. During the day the Sun heats the upper atmosphere, winds in the ionosphere drive electric currents, and the field changes by 40–50 nT even on a quiet day. So the 83–93 nT range over the two days is mostly this variation, not the storm.
- Nurmijärvi sees the electrojets. These are strong currents in the ionosphere at an altitude of about 100–120 km along the auroral oval. On the morning of 24 September a westward current flowed over the station (the northward field component decreased). In the evening an eastward current flowed north of the station (vertical component +70 nT), and at night, in the same place, a westward current again (−75 nT). When a current flows north of the station, the vertical component increases for an eastward current and decreases for a westward one.
- Vernadsky is farther from the oval. There, bays of about ±45 nT are seen in the eastward component at 07–11 UT. They were caused by currents along the field lines that link the magnetosphere with the ionosphere during a substorm (09–12 UT).
Fig. 1. Example of geomagnetic pulsations on 23–24 September 2026 in the 150–600 s period band (Pc5) at the Antarctic station Akademik Vernadsky and the Finnish station Nurmijärvi.
Magnetic pulsations
Pulsations are slow oscillations of the magnetic field. The analysis uses the period bands 2.5–10 min (Pc5) and 10–30 min (Pc6). The typical amplitude is 0.4–1.7 nT, reaching 5–8 nT at peaks: no more than ~0.02% of the Earth’s field (37,000–53,000 nT).
- They started before the storm. Pulsations appeared simultaneously at both stations at 17–19 UT on 23 September, while the interplanetary field was still northward. This means they were excited by the dense wind itself: its pressure fluctuations push the boundary of the magnetosphere, and on its flanks the fast flow excites waves, like wind over water.
- 1.4–2 times stronger at Nurmijärvi. The station is closer to the auroral oval and to the high-latitude sources of the oscillations.
- A common “note” with a period of 13–14 min. An interesting feature revealed by spectral and cross-spectral analysis. Both stations show the same spectral peak at 1.21–1.27 mHz (13.8–13.1 min), and it is coherent between the stations. For stations in opposite hemispheres and 6 hours apart, this means an oscillation of the whole magnetosphere or a rhythm set by the solar wind. The natural oscillations of the local field lines here are much faster, with periods of typically 10–150 s.
- But the common part is small. At these frequencies, only 7–25% of the oscillation power is common to the two stations. The rest comes from local processes: ionospheric currents and impulsive bursts during substorms.
- Mirror symmetry. Measured from the magnetic meridian, the major axis of the oscillations is rotated by +32° at Vernadsky and by −32° at Nurmijärvi, and the sense of rotation is opposite. The patterns are mirror images about the meridian: the north–south component is the same, and the east–west component is opposite. This is exactly how oscillations that are symmetric about the magnetic equator behave.
- Seasonal factor. Near the September equinox (23 September in 2026), geomagnetic activity is statistically higher when the interplanetary magnetic field points away from the Sun, i.e. has positive polarity (the Russell–McPherron effect). The positive-polarity stream with a persistently southward Bz after 00 UT on 24 September is consistent with this.
- Over the observation interval of 23–24 September 2026, AIA was most active in the late evening and before dawn, and NUR in the afternoon and evening (horizontal components, local time).
Fig. 2. Example of the cross-wavelet spectrum between the geomagnetic stations AIA (Antarctica) and NUR (Finland) – the geomagnetic X component is compared in the Pc6 band (600–1800 s); only areas with at least 10% of the maximum cross-power are shown. Top panel – real (Re) part, middle panel – imaginary (Im) part of the cross-spectrum, bottom panel – cross-spectral power. Re shows how much the two stations oscillate in step: positive means that the field at both stations deviates in the same direction at the same time, negative means in opposite directions. Im shows which station leads the other: positive means that the oscillation arrives at Nurmijärvi first, negative means at Vernadsky first.
The pulsations were excited by the solar wind itself: they appeared under northward IMF, at the peak of the magnetospheric compression, before the storm began. The dominant Pc5 periods differ between the stations: about 6 min at Vernadsky and about 5.3 min at Nurmijärvi. This means these oscillations are local. Only the line at about 13 min is common, and it points to a global oscillation of the magnetosphere or a rhythm of the solar wind. The broadband impulsive spectra indicate a response to pressure bursts and substorms rather than to steady resonances (in the period bands of the quasi-periodic Pc5 and Pc6 pulsations, irregular Pi3-type pulsations dominate, with only a weak quasi-periodic component at about 13 min). The horizontal components are mostly in phase at stations about 15,800 km apart. This is a sign of a global magnetospheric source. The polarization is mirror-symmetric, which indicates that the processes are symmetric about the magnetic equator. Nurmijärvi is more active because it is closer to the auroral oval.
Author: Artem Sukharev, PostDoc researcher
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