Storm Recap – G1 Storming Gives Canadians a Show On May 10-11 2019

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Northern Lights Now – Geomagnetic conditions reached G1 storm level over the weekend. Aurora hunters across Canada were treated to a show. Even with low solar wind speeds that just touched 400 km/s, a long duration of south oriented Bz combined with high plasma density was enough to activate the magnetosphere. The recorded 3-hour observations from the storm show one period of Kp=5 in the first period of May 11 followed by sever periods of KP=4

G1 storm levels reached between 12:00am  and 3:00am on Saturday May 11.
G1 storm levels reached between 12:00am and 3:00am on Saturday May 11.

There was not a storm watch posted in advance of this activity, but the SWPC daily forecast discussion mentioned the possibility. The forecaster’s note from May 9 read “The anticipated arrival of the 6 May CME is expected to result in unsettled to active conditions, with a chance for an isolated period of G1 (Minor) geomagnetic storm levels, later on 11 May.” NLN was posting on the Twitter feed that there was a chance for activity in advance of the storm, but the activity exceeded our expectations.

As the storm arrived, it became clear that Earth was going to be in the core of the arriving CME and that it was oriented favorably for Northern Lights. Proton density was high for hours in advance of the CME arrival shock. Once it arrived, Bz dipped south and stayed oriented south for 5-6 hours. Wind speed did not increase above 400km/s in the first part of the core of the storm, as so geomagnetic activity remained muted. But the long duration south oriented Bz primed the magnetosphere for the second phase of the storm.

Long duration of southward Bz Orientation
Long duration of southward Bz Orientation

As the second phase arrived, Bz dropped deeply south and stayed consistent. This drove the KP to storm levels and it coincided with night across much of Western Canada.

Happy Hunting!