The solar flux index remained above 130 last week, being at 137 on Thursday as this report was prepared. It peaked at 165 on Sunday and reached a massive 180 on Wednesday the 18th. All this means that DX is workable on the upper HF bands with the 3D2RRR DXpedition on Rotuma Island near Fiji being chased from the UK. A little closer to home, V51WW in Namibia has also been putting in an appearance.
Sporadic-E has also seen some short-skip signals from Europe on 10 metres, but we haven’t seen many rock-crushingly strong signals as yet.
The Sun remains very active with a CME associated with an M1.3 flare detected around region 3016 at 1824UTC on Wednesday, the 25th of May. The bulk of the plasma released was off the Sun-Earth line, although closer examination revealed a fainter Earth-directed component was evident and could sweep past Earth within 48-72 hours. If correct, this means the Kp index may rise this weekend.
Coronal mass ejections remain a risk to HF propagation with a massive one on the far side of the Sun being observed on the 24th of May. We have been lucky last week with the Kp index generally in the ones and twos, that is, indicating settled geomagnetic conditions. But we think it is only a matter of time before we get hit with a “big one”, which could cause disruption and a general reduction in maximum usable frequencies.
Next week, NOAA predicts that the SFI may decline into the 130s or even 120s. In fact, by the 5th of June it thinks it will be at a low of 114 before rising again. Luckily, NOAA also predicts that the Kp index will remain low. This will help the ionosphere develop and should bring good conditions. However, we issue a caution that a single Earth-directed CME could put paid to low Kp indices and bring disruption. As always, keep an eye on solarham.com for updates.
VHF and up:
The next period of weather is dominated by high pressure, although not in exactly the right place for good Tropo conditions everywhere. The main position of the high will tend to drift away to the northwest, which leaves room for a cool northerly pattern over most areas. This will probably confine the best Tropo conditions to the southwestern half of the UK.
Elsewhere, the main weather type will include summer showers, possibly heavy, and likely to be of interest for rain scatter activity. Showers in a cold northerly airmass are usually strictly diurnal, so rain scatter prospects are for the afternoon and early evenings.
Sporadic-E is showing good signs of coming to life and we are starting to hear limited openings for traditional CW/SSB QSOs and more widespread activity for digital modes. Some promising multi-hop paths have been seen to Asia in the mornings and the States and the Caribbean in the evenings.
This week contains potentially the most exciting meteor shower of the year. The Tau Herculids shower, associated with Comet 73P and discovered in 1930, appears early during Monday night into Tuesday morning. In 1995 the comet was seen to suddenly brighten. This was discovered as being due to its nucleus starting to break up, creating a debris cloud. Comet 73P orbits the Sun at 5.4-year intervals. The Earth next crosses its orbit on the night of the 30th of May, into the morning of the 31st. It is due to peak in the UK at about 0500UTC on the 31st.
Depending on how the nucleus started to eject debris, we may have a spectacular shower or something that is, at best, disappointing. As it will be light in Europe during the peak the visual display may not be very impressive, but the possibility for a radio reflection shower must be strong. This is one to look for, as a meteor scatter enthusiast.
The new Moon occurs on the 31st May and illumination will be low all the following week.
A maximum declination of +28.1 degrees occurs on the 2nd, and this also coincides with the greatest distance from Earth to Moon, which in turn means the highest path loss.
From experience, this should still be a good week for EME on the microwave bands despite the path loss. The VHF EME bands will suffer noise from the proximity of the Moon to the Sun for the first few days of the week. (rsgb.org)