SOHO/LASCO Halo CME 20251231

Halo Alert: halo-message.20251231

UCMEO 93001 51231 1845/
51231 61400 81524 0291/ 029// 333// 40722
51231 61312 81351 12419 14324 1112/
99999

PLAIN

SOHO/LASCO HALO CME December 31, 2025

C2 Start Time: 14:00 UT

C3 Start Time: 14:30 – 17:54 UT

Type of CME:
Partial HALO CME — FRONTSIDE
pa1: 29      pa2: 29       Total Width: 360 degrees

Velocity Measurements:

C2 6 points 711.0 km/sec @ PA 29
C3 5 points 666.6 km/sec @ PA 29
Average through both fields: 722.6 km/sec Acceleration: -3.90 m/sec^2.

COMMENT: A partial HALO event can be seen in LASCO C2/C3 in the Northeast
                      quadrant @ 14:00 UT. As reported by NOAA, the CME is associated
                      with a M7.1 solar flare in AR 14324 [N24,E19]. Opening lines
                      associated with the CME can be viewed in SDO/AIA 193 starting
                      at 13:12 UT in the Northeast quadrant along with an EUV wave
                      and post-eruption arcades.

STEREO BEACON Data
                COR2 A shows a bright, asymmetric partial HALO CME in the Northeast
                quadrant 13:53 - 16:53 UT. Preliminary time/height measure shows 4 points
      with velocity measured 844.8 km/sec @ 54.92 deg.

Preliminary UCMEO velocity and position measurements are delivered first.
Images, movies, and time/height information for this event will be available at:

https://umbra.nascom.nasa.gov/lasco/observations/halo/2025/251231/

Best Regards,

--Taylor Lanier

BT

[Images from the original alert message are omitted here]

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SOHO/LASCO C2 Diff	SOHO/LASCO C3 Diff	SDO AIA 195 angstrom

GOES-19 CCOR1	SDO AIA 195 angstrom Diff	STEREO/COR2 AHEAD Diff

SOHO/LASCO C2	SOHO/LASCO C3	GOES-19 SUVI 195A