Papers from a recent NASA workshop on solar cycle 24 suggest that we are at or close to solar maximum and that this will be among the weakest peaks on record. By all conventional measures this has been an extremely quiet cycle. However, the analysis adds that most major events, such as large flares or major magnetic storms, tend to come during the declining phase of a cycle. So there can still be interesting times ahead as we move towards solar minimum at the end of the decade. A fuller report is at the www.spaceweather.com page for 19 May.
Turning to the present, this week’s figures may give the impression that the decline is already under way—but they are no more than normal daily variation. Solar activity was low or very low, with only minor C-class flares. The solar flux declined from 139 to 111, averaging 122 units—a drop of 36 on the previous week. The less volatile 90-day average was down two to 148. The X-ray flux was also down, from an average B6.8 to B4.0. Geomagnetic activity was mostly low, with the Ap index averaging only 5 units, though the period ended with an unsettled Ap of 9. Particle densities were mostly in single figures, but there were brief spikes to 80 units per cubic centimetre on the 21st and 70 on the 22nd. Bz showed relatively little daily variation, mostly between plus and minus 5 nanoTeslas. Solar wind speeds reported by the ACE spacecraft were also mostly below average, ranging between 276km/sec and 429km/sec.
Finally, the forecast for the week ahead. Overall, the present pattern appears likely to continue. Solar activity will be predominantly low, with C-class flares on most days and, possibly, the occasional M-class flare. There are currently no indications of Earth-directed coronal mass ejections, though these can emerge with little warning. The solar flux seems unlikely to drop much below current levels and there could be a modest revival by next weekend.
MUFs at equal latitudes should be in the region of 24MHz, while darkness lows are expected to be about 14MHz. Paths to Australia should have an MUF—that’s a 50 percent chance of a contact—of 25MHz. The Optimum Working Frequency, at which there should be a 90 percent chance of success, will be about 21MHz. The path should be best between 0600 and 1200UTC. VHF Sporadic-E should occur on most days, with openings up to 70MHz on several days. Propagation at 144MHz cannot be excluded but is a very long shot.
Category: GB2RS Propagation News