\n<\/p>\n
Solar activity was at low levels with seven numbered active regions<\/p>\n
on the disk.<\/p>\n
\u00a0<\/p>\n
The largest event of the period was a C3.7 flare on March 25 from<\/p>\n
Region 4400. Region 4403, which was numbered last period, is the<\/p>\n
suspected source of several flares observed beyond the limb prior to<\/p>\n
its rotation onto the disk. Due to its proximity to the northeast<\/p>\n
limb, foreshortening continues to prevent a definitive<\/p>\n
characterization of its complexity and extent.<\/p>\n
\u00a0<\/p>\n
The remaining disk regions exhibited varying degrees of decay and<\/p>\n
evolution. Region 4397 has dissipated into a small unipolar group,<\/p>\n
while Region 4398 underwent penumbral decay. Region 4399 remained<\/p>\n
largely stable, though it continues to fluctuate between a unipolar<\/p>\n
and bipolar state due to the short-lived trailing spots. Significant<\/p>\n
internal changes were noted in the more complex groups: Region 4400<\/p>\n
experienced extensive reconfiguration and flux emergence, and gained<\/p>\n
a gamma configuration. Similarly, Region 4401 exhibited persistent<\/p>\n
flux emergence and an expansion of penumbral area in its trailing<\/p>\n
spots. Region 4402 showed a decline in its leader spot cluster.<\/p>\n
\u00a0<\/p>\n
No Earth-directed coronal mass ejections (CMEs) were observed in<\/p>\n
available coronagraph imagery. Solar activity is expected to be low<\/p>\n
with a chance for M-class (R1-R2\/minor-moderate) flares through March<\/p>\n
28.<\/p>\n
\u00a0<\/p>\n
For the first several hours of the reporting period, solar wind<\/p>\n
parameters reflected the continued waning influence of a negative<\/p>\n
polarity coronal hole high-speed stream (-CH HSS). During this time,<\/p>\n
solar wind speed decreased from approximately 550 km\/s to 515 km\/s.<\/p>\n
\u00a0<\/p>\n
On March 25, a transient CME began its passage through the near-Earth<\/p>\n
environment. Accompanied by a rise in solar wind speed to a peak of<\/p>\n
633 km\/s. Solar wind parameters are expected to remain mildly<\/p>\n
enhanced as current influences diminish. Additional enhancements are<\/p>\n
anticipated on March 26, following the arrival of another component<\/p>\n
of the March 22 CME. Following this passage, a gradual return to a<\/p>\n
nominal, slow-speed regime is forecast through March 28.<\/p>\n
\u00a0<\/p>\n
Weekly Commentary on the Sun, the Magnetosphere, and the Earth’s<\/p>\n
Ionosphere,\u00a0 March 26, 2026, by F. K. Janda, OK1HH:<\/p>\n
\u00a0<\/p>\n
Solar activity declined during the first half of March. Despite<\/p>\n
preliminary forecasts of a subsequent increase, it not only remained<\/p>\n
low for another week, but observations also showed no signs of an<\/p>\n
impending rise. Eventually, however, solar activity did begin to<\/p>\n
rise, while the power flux of solar radio noise at a wavelength of<\/p>\n
10.7 cm (abbreviated as solar flux) rose to the level seen in early<\/p>\n
February.<\/p>\n
\u00a0<\/p>\n
The increase in geomagnetic activity also came as a surprise.<\/p>\n
Although it initially recurred as expected after 27 days (i.e., March<\/p>\n
13\u201314), the next recurrence not only came later, but the disturbance<\/p>\n
lasted twice as long as expected, while was particularly intense on<\/p>\n
March 22 (reaching G3 instead of the anticipated G1\u2013G2). However,<\/p>\n
given the presence of large coronal holes No. 31 and 33 in the center<\/p>\n
of the solar disk\u2014that is, facing Earth\u2014the intensity of the<\/p>\n
disturbance may not have been a surprise.<\/p>\n
\u00a0<\/p>\n
Similarly, regarding future developments, it can be assumed that the<\/p>\n
next geomagnetic disturbance will occur later, and the same applies<\/p>\n
to the expected increase in solar activity; however, this will still<\/p>\n
be during the third decade of April, when we can expect the first<\/p>\n
occurrences of the sporadic E layer in the mid-latitudes of the<\/p>\n
Earth\u2019s northern hemisphere. This, combined with the expected<\/p>\n
increase in daily MUF values, should improve DX signal propagation on<\/p>\n
the upper shortwave bands<\/p>\n
\u00a0<\/p>\n
The Predicted Planetary A Index for March 28 to April 3 is 5, 8, 15,<\/p>\n
10, 5, 5, 18 with a mean of 9.4. The Predicted Planetary K Index is<\/p>\n
2, 3, 4, 3, 2, 2, 5 with a mean of 3. 10.7 centimeter flux is 130,<\/p>\n
128, 125, 125, 130, 120, 120 with a mean of 125.4.<\/p>\n
For more information concerning shortwave radio propagation, see<\/span>
http:\/\/www.arrl.org\/propagation\u00a0<\/span>and the ARRL Technical Information<\/span>
Service web page at,\u00a0<\/span><\/span>http:\/\/arrl.org\/propagation-of-rf-signals. For<\/span>
an explanation of numbers used in this bulletin, see<\/span>
http:\/\/arrl.org\/the-sun-the-earth-the-ionosphere\u00a0<\/span>. Information and<\/span>
tutorials on propagation can be found at,\u00a0<\/span><\/span>http:\/\/k9la.us\/\u00a0<\/span>.<\/span><\/p>\n