G1-G2 Aurora activity for Late September 2020

Northern Lights Now – Geomagnetic activity reached G2 storm levels on September 27 bringing stunning views of aurora to high latitude regions. The activity is the result of a coronal hole high speed stream and is expected to continue for the next three days.

NLN forecast shows periods of G1 and G2 activity each of the next three days
NLN forecast shows periods of G1 and G2 activity each of the next three days

Update 07:30 UTC 9/29/2020 03:00 EDT

Geomagnetic activity reached G1 levels occasionally this evening as predicted. Conditions have moderated and the aurora is much less active now. At the beginning of the period, solar wind speed were around 625 km/s. They have since decreased to around 575 km/s. The biggest factor in the decrease in activity is the Bz. Look at how variable it has been over the last 12 hours:

Bz has been variable over the last 6 hours.
Bz has been variable over the last 6 hours.

During the period of G2 storming, there was over 4 hours where Bz was sustained south. Any deviation into north (positive on the chart) puts an immediate damper on northern lights activity. The CH HSS is expected to remain geoeffective for the next 24-48 hours, it is very possible we could get another sustained period of south-oriented Bz. Keep an eye on the solar wind data!

Original Post

Solar wind speeds reached 640 km/s, the highest readings Since the beginning of August. The higher activity is associated with a Northern Hemisphere coronal hole. The coronal hole has a wide longitudinal opening – meaning that it will influence Earth’s magnetosphere for several consecutive days. In addition, the remains of AR 2773, shown below as a brighter area to the left, are just to the East of the CH and have the potential to inject higher wind speeds and density into the stream.

Late September 2020 coronal hole with the refinements of AR 2773 just to its east
Late September 2020 coronal hole with the refinements of AR 2773 just to its east

To know exact timing of the expected activity, keep and eye on the solar wind. Generally, the more bars there are on the chart, and the taller they are, the more likely there will be higher KP readings.