SOHO/LASCO Halo CME 20250821

Halo Alert: halo-message.20250821

UCMEO 93001 50821 1550/
50821 60824 91030 0432/ 042// 333// 41804
50821 60742 80821 ///// ///// /////
99999

PLAIN

SOHO/LASCO HALO CME August 21, 2025

C2 Start Time:     08:24 UT

C3 Start Time:        08:30 - 10:30 UT - in progress @21.9 Rsun

Type of CME:
Partial HALO CME — BACKSIDE
pa1: 043      pa2: 042       Total Width: 360 degrees

Velocity Measurements:

C2    3 points    1927.7 km/sec @ PA 043
C3    9 points    1782.3 km/sec @ PA 043
Average through both fields:     1804.1 km/sec Acceleration: -58.64 m/sec^2.

COMMENT: SDO AIA 193A data shows emission over the East hemisphere
          beginning aproximately 07:42 - 08:21 UT as the event is near limb
          on the backside.

     LASCO C2/C3 shows an asymetric full HALO CME over the East.

     STEREO Beacon Data
     COR2 A, shows a bright asymetric HALO CME over the West 07:53 - 09:38 UT.
     Preliminary time/height measure shows 4 points - 1661.4 km/sec @297 deg.


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

https://umbra.nascom.nasa.gov/lasco/observations/halo/2025/250821/

Best Regards,

--Kevin Schenk

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

STEREO/COR2 BEHIND Diff	SDO AIA 195 angstrom Diff	STEREO/COR2 AHEAD Diff

SOHO/LASCO C2	SOHO/LASCO C3	GOES - CCOR