G1 – Minor geomagnetic storm watch in effect for December 23 and 24


A series of positive polarity, polar connected, coronal hole high speed streams (CH HSS) are expected to affect our planet in the days ahead, resulting in G1 – Minor geomagnetic storming.

The area of impact is primarily poleward of 60 degrees Geomagnetic Latitude. Under G1 conditions, weak power grid fluctuations can occur, minor impact is possible on satellite operations while aurora may be visible at high latitudes.

In 24 hours to 12:30 UTC on December 22, solar activity was at very low levels and is expected to remain at very low levels through December 24, with only a slight chance for C-class flares.

There is only one numbered active region — AR 2794 — on the solar disk. It remained stable and inactive throughout the period. 

The greater than 2 MeV electron flux was at normal to moderate levels and is expected to reach moderate to high levels on December 22 through 24 due to CH HSS influence. The greater than 10 MeV proton flux remained at background values and is expected to continue at background levels.

Image credit: SWPC

Image credit: NASA/SDO, LMSAL

Image credit: NASA SDO/HMI

Solar wind parameters reflected the influence of a co-rotating interaction region (CIR) and the subsequent onset of a positive polarity CH HSS.

The total field averaged near 4 nT for most of the period, but reached a maximum near 19 nT at 23:22 UTC on December 21 at the peak of the CIR transition. The Bz component saw a maximum southward deflection of -13 nT at 20:56 UTC, before returning to near nominal levels for the remainder of the period.

The solar wind speed increased from approximately 375 km/s to near 550 km/s, with a peak of 575 km/s 05:02 UTC today. 

Phi angle was mostly negative the first half of the period before rotating into a mostly positive orientation after 22:30 UTC on December 21.

Solar wind parameters are expected to be enhanced over the next 24 hours due to the arrival of a series of positive polarity, polar connected, CH HSSs.

The second enhancement is expected around mid to late day on December 23.

Image credit: SWPC

The geomagnetic field was quiet to unsettled, with an isolated active period, likely due to CIR effects.

Primarily unsettled to active levels are expected on December 22 due to continuing CH HSS influences.

Unsettled to active conditions are expected on December 23, with likely periods of G1 storm conditions late, due to escalating CH HSS influences.

Featured image: Solstice Aurora by Alan C Tough – December 21, 2020 @ Hopeman, Moray, Scotland. via SpaceWeather


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