Solar activity has remained at low levels, with frequent C-level activity in the SE quadrant of the solar disk. The largest flare of the period was a C3.8 on June 24 from Region 4478, which is the large sunspot that Solar Orbiter had been tracking across the Sun’s far side.

While the majority of the flaring activity this period came from 4478, Region 4475 also produced several small C-flares as additional trailing spots began to emerge. Regions 4472 and 4473 continued to decay throughout the period. Region 4479 was numbered this period. No Earth-directed CMEs were observed in available coronagraph imagery.

Solar activity is expected to continue at predominately low levels on June 25 to 27 with a high chance for M-flares (R1-R2/minor-moderate) and a slight chance for X-flares (R3/strong), primarily due to the potential of Region 4478. Solar wind parameters were elevated this period from a mix of negative polarity coronal hole high speed stream (CH HSS) onset and minor magnetic transient influences.

The solar wind speed began the period averaging 350 km/s, then increased sharply on June 24 to ~450 km/s. This was followed by another notable jump in speed, also beginning June 24, ending the reporting period at approximately 600 km/s. Phi was predominantly negative (towards the Sun). Solar wind conditions are expected remain elevated/disturbed through June 27 due to the continued influence of the negative polarity coronal hole high speed stream.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere June 26 by F.K. Janda, OK1HH: After the last and largest sunspot group in the chain as observed by the Solar Orbiter appeared on the southeastern limb of the solar disk, we can expect another increase in solar activity to a level somewhat higher than expected.

At the same time, there are three coronal holes near the central meridian, with additional active regions just ahead of them. As a result, the solar wind intensified significantly on June 24, triggering a geomagnetic disturbance. The maximum southern (i.e., longitudinal) component of Bz reached -12 nT, whereas this trend appears set to continue through June 27. This will result in highly variable shortwave propagation conditions. Furthermore, propagation will be more affected by the sporadic E layer than in recent days.

The Predicted Planetary A Index for June 27 to July 3 is 8, 5, 5, 5, 5, 5, and 18 with a mean of 7.3. The Predicted Planetary K Index is 3, 2, 2, 2, 2, 2, and 5 with a mean of 2.6. 10.7 centimeter flux is 130, 130, 132, 135, 145, 138, and 140 with a mean of 135.7.

For more information concerning shortwave radio propagation, see http://www.arrl.org/propagation and the ARRL Technical Information Service web page at, http://arrl.org/propagation-of-rf-signals. For an explanation of numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere . Information and
tutorials on propagation can be found at, http://k9la.us/ .

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"Understanding Solar Indices" from September 2002 QST.