| SB PROP @ ARL $ARLP011
ARLP011 The ARRL Solar Report
ZCZC AP11
QST de W1AW
Propagation Forecast Bulletin 11 ARLP011
From ARRL Headquarters
Newington CT March 28, 2025
To all radio amateurs
SB PROP ARL ARLP011
ARLP011 The ARRL Solar Report
On Wednesday, March 26, around 2130 UTC a Major Storm occurred. At one point, the Planetary A Index was 49, and the Planetary K Index was at 6.
Solar wind parameters are expected to remain enhanced due to continued coronal hole high-speed stream influences with waning effects likely by March 29.
The Solar Radiation Storm Forecast for March 29 and 30 has a 1 percent chance of a S1 or greater storm.
No S1 (Minor) or greater solar radiation storms are expected. No significant active region activity favorable for radiation storm production is forecast.
The Radio Blackout forecast calls for a chance for isolated R1-R2 (Minor-Moderate) radio blackouts due to M-class flare activity will persist through March 30 primarily due to the potential exhibited by AR4043.
From Space Weather Prediction Center: “Since February 25, 2025, the Space Weather Prediction Center (SWPC) has presented new coronagraph images and data from the GOES-19 Compact Coronagraph-1 (CCOR-1). The images and data are updated every 15 minutes.
“Imagery from the Compact Coronagraph (CCOR) instruments is used by the SWPC Forecast Office to characterize activity in the outermost part of the Sun’s atmosphere known as the corona. This includes monitoring data for transient events like coronal mass ejections (CMEs), as well as monitoring the impacts the corona has on the steady stream of plasma, referred to as the solar wind, emanating from the Sun. Ultimately, information derived from CCOR images will be used as inputs to the WSA-Enlil model to forecast the impacts of CMEs and the solar wind on Earth.
“Note: Until such time as GOES-19 becomes operational, currently planned for April 4th, the animations and data are to be considered ‘preliminary and non-operational.’ In particular, CCOR-1 data will not update between 3/21 and 4/1 due to the spacecraft drifting to its operational location.”
Weekly Commentary on the Sun, the Magnetosphere, and the Earth’s Ionosphere – March 27, 2025, by F. K. Janda, OK1HH:
“Most forecasts, including those from NOAA, have been consistent over the past week that a strong G3-class geomagnetic storm would develop on Sunday, March 23. In fact, a CME was expected to directly impact the Earth. Although the source of the CME was only the M1-class solar flare from AR4028, even weaker CMEs can produce strong geomagnetic disturbances, especially on days around the equinoxes. In the end, however, paradoxically, 23 March was the relatively quietest day.
“However, a large coronal hole caught our attention this week, while we expected that once it reached the central meridian region, the solar wind stream would head directly towards Earth. This is what happened and in the following days, especially on March 26, a G2 class geomagnetic storm developed. The solar wind speed increased from 400 km/s to 700 km/s. On March 27, the increase continued to over 800 km/s (1.8 million mph).
“Shortwave propagation conditions were particularly degraded along paths through the higher latitudes of the Northern Hemisphere. Outside of these, there was also a more pronounced decrease in MUF on routes that crossed South America and the South Atlantic where geomagnetic anomalies are located.
“While late March and early April are periods with traditionally better-than-average shortwave propagation conditions, this time our expectations will only be partially met. Solar activity is lower than would be consistent with the current phase of the solar cycle – and disturbances are relatively common.”
A partial Solar Eclipse occurs on March 29, 2025. Details can be found at: https://science.nasa.gov/eclipses/future-eclipses/mar-29-2025-eclipse.
For more information concerning shortwave radio propagation, see www.arrl.org/propagation and the ARRL Technical Information Service web page at, www.arrl.org/propagation-of-rf-signals. For an explanation of numbers used in this bulletin, see www.arrl.org/the-sun-the-earth-the-ionosphere. Information and tutorials on propagation can be found at: http://k9la.us.
Also, check this: “Understanding Solar Indices” from September 2002 QST.
https://bit.ly/3Rc8Njt
The predicted 10.7 centimeter flux for March 29 to April 3 is 160, 165, 165, 170, 170, and 175, with a mean of 167.5. The predicted Planetary A Index is 8, 5, 5, 5, 5, and 10, with a mean of 6.3. The predicted Planetary K Index is 3, 2, 2, 2, 2, and 3, with a mean of 2.3.
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