26 November 2021 - Mission Day: 9492 - DOY: 330
Pick of The Week

Halloween Storm 2021 (October 31, 2021)

It was 18 years ago to the day, on 28 October 2003, when the Sun gave us a spectacular show, releasing a series of powerful flares and Coronal Mass Ejections (CMEs). That event has since been remembered as the Halloween Storm of 2003 (see: Hotshot and Pick of The Week).

SOHO's LASCO C3 view of the November 28, 2021 CME
(click to enlarge)

This year, the Sun unleashed another spectacular storm that included an X1-class flare, the second largest of solar cycle 25 so far, and a powerful, Earth-directed CME.

The event also triggered a "proton storm", in which energetic particles are accelerated to velocities close to the speed of light. These energetic particles bombarded LASCO's Charge Coupled Device (CCD) cameras and appear as white specks in the LASCO images.

LASCO C2 view and movie

Movie: MP4 [2.3M]
Image: JPG [1.0M], Hi-res TIFF [3.0M]

LASCO C3 view and movie

Movie: MP4 [6.6M]
Image: JPG [886K], Hi-res TIFF [3.0M]

Starting on 2021-10-28 at 15:57:49 UTC, SOHO's Energetic and Relativistic Nuclei and Electron (ERNE) instrument detected high levels of these energetic protons.

SOHO's ERNE view of the Proton measurements
(click to enlarge)

Space weather forecasters predicted a direct hit of Earth by the CME on October 31st, but it did not end up sparking the expected bright polar lights. The Sun hurled another large CME towards the Earth on November 2nd, which did spark the most spectacular polar lights in recent years.

Animation of the CME impacting Earth
(click to enlarge)

Credit: Community Coordinated Modeling Center (CCMC) at NASA GSFC.

It will be interesting to study why the two events caused such remarkably different responses in geospace.


SOHO began its Weekly Pick several years ago after sending a weekly image or video clip to the American Museum of Natural History (Rose Center) in New York City. There, the SOHO Weekly Pick is displayed with some annotations on a large plasma display. Today, we use this area as 'Solar Picks' to highlight stories, events or activities but not as often as every week.


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Last modification: July 27, 2020

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