Negative polarity CH HSS sparks geomagnetic storming

geomagnetic-storm-february-28-2019

An isolated, negative polarity Coronal Hole High Speed Stream (CH HSS) is affecting our planet on February 27 and 28, 2019, causing isolated periods of geomagnetic storming.

Solar winds over the past 24 hours were indicative of an anticipated Solar Sector Boundary Crossing (SSBC) followed by the likely arrival of Co-rotating Interaction Region (CIR) ahead of an isolated, negative polarity CH HSS. 

Total IMF strength increased to over 10 nT shortly after 12:00 UTC on February 27 and reached a maximum value of 12 nT. The Bz component underwent a few periods of short duration, pronounced southward deviations. Solar wind speed also increased after 12:00 UTC and reached over 450 km/s around 15:30 UTC. The phi angle switched from positive to a mostly negative orientation shortly after 08:00 UTC, February 27.

CH HSS influences are expected to continue and gradually increase on February 28 due to improved geoeffective connection. Elevated solar wind speed is likely to continue into March 1 and 2 as CH HSS influences persist. 

Primarily unsettled to active levels, with isolated periods of G1 – Minor storm conditions are expected on February 28 due to CH HSS effects. Quiet to active levels are expected on March 1 and 2 as CH HSS influences persist.

Geomagnetic K-index of 4 threshold was reached at 22:41 UTC followed by K-index of 5 (G1 – Minor geomagnetic storm) at 23:11 UTC and K-index of 4 again at 05:52 UTC.

The greater than 2 MeV electron flux was normal and the greater than 10 MeV proton flux remained at background values over the past 24 hours. The greater than 2 MeV electron flux is expected to increase and may likely reach moderate levels on February 28 and March 1, with a chance for high levels by March 1, due to increasing CH HSS influences. High levels are likely on March 2 as CH HSS effects continue. The greater than 10 MeV proton flux is expected to maintain at background levels.

Solar activity remained very low and the visible disk is spotless. Very low levels are expected to continue.

Featured image: Aurora over Alta, Norway on February 28, 2019. Credit: H.+J. Sperr

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