SB DX @ ARL $ARLP013 ARLP013 DX News ZCZC AP13 QST de W1AW Propagation Forecast Bulletin 13 ARLP013 From ARRL Headquarters Newington, CT, March 27, 2026 To all radio amateurs SB PROP ARL ARLP013 ARLP013 The ARRL Solar Report Solar activity was at low levels with seven numbered active regions on the disk. The largest event of the period was a C3.7 flare on March 25 from Region 4400. Region 4403, which was numbered last period, is the suspected source of several flares observed beyond the limb before its rotation onto the disk. Due to its proximity to the northeast limb, foreshortening continues to prevent a definitive characterization of its complexity and extent. The remaining disk regions exhibited varying degrees of decay and evolution. Region 4397 has dissipated into a small unipolar group, while Region 4398 underwent penumbral decay. Region 4399 remained largely stable, though it continues to fluctuate between a unipolar and bipolar state due to the short-lived trailing spots. Significant internal changes were noted in the more complex groups: Region 4400 experienced extensive reconfiguration and flux emergence, and gained a gamma configuration. Similarly, Region 4401 exhibited persistent flux emergence and an expansion of penumbral area in its trailing spots. Region 4402 showed a decline in its leader spot cluster. No Earth-directed coronal mass ejections (CMEs) were observed in available coronagraph imagery. Solar activity is expected to be low with a chance for M-class (R1-R2/minor-moderate) flares through March 28. For the first several hours of the reporting period, solar wind parameters reflected the continued waning influence of a negative polarity coronal hole high-speed stream (-CH HSS). During this time, solar wind speed decreased from approximately 550 km/s to 515 km/s. On March 25, a transient CME began its passage through the near-Earth environment. Accompanied by a rise in solar wind speed to a peak of 633 km/s. Solar wind parameters are expected to remain mildly enhanced as current influences diminish. Additional enhancements are anticipated on March 26, following the arrival of another component of the March 22 CME. Following this passage, a gradual return to a nominal, slow-speed regime is forecast through March 28. Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, March 26, 2026, by F. K. Janda, OK1HH: Solar activity declined during the first half of March. Despite preliminary forecasts of a subsequent increase, it not only remained low for another week, but observations also showed no signs of an impending rise. Eventually, however, solar activity did begin to rise, while the power flux of solar radio noise at a wavelength of 10.7 cm (abbreviated as solar flux) rose to the level seen in early February. The increase in geomagnetic activity also came as a surprise. Although it initially recurred as expected after 27 days (i.e., March 13ñ14), the next recurrence not only came later, but the disturbance lasted twice as long as expected, while it was particularly intense on March 22 (reaching G3 instead of the anticipated G1ñG2). However, given the presence of large coronal holes No. 31 and 33 in the center of the solar diskóthat is, facing Earthóthe intensity of the disturbance may not have been a surprise. Similarly, regarding future developments, it can be assumed that the next geomagnetic disturbance will occur later, and the same applies to the expected increase in solar activity; however, this will still be during the third decade of April, when we can expect the first occurrences of the sporadic E layer in the mid-latitudes of the Earthís northern hemisphere. This, combined with the expected increase in daily MUF values, should improve the DX signal propagation on the upper shortwave bands The Predicted Planetary A Index for March 28 to April 3 is 5, 8, 15, 10, 5, 5, 18, with a mean of 9.4. The Predicted Planetary K Index is 2, 3, 4, 3, 2, 2, 5 with a mean of 3. 10.7 centimeter flux is 130, 128, 125, 125, 130, 120, 120 with a mean of 125.4. 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 NNNN /EX |
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