Propagation News – 30 July 2023
It was a mixed bag last week with periods of settled conditions, but two periods when the Kp index was above four. These unsettled geomagnetic conditions impacted HF, subduing signals and generally not helping at all.
The cause was a coronal mass ejection, or CME, that passed Earth late on Tuesday 25 July. This triggered a minor G1 geomagnetic storm with the solar wind speed above 500km/s and the Bz component of the interplanetary magnetic field pointing south.
By the early hours of Thursday morning, the Kp index was down to 2.33, but there was talk of another CME threatening to push it up again.
We ‘dodged a bullet’ on the 24 July when a large halo CME was observed leaving the Sun. It was so powerful that, despite taking place on the other side of the Sun, energetic proton levels streamed past Earth. By Wednesday lunchtime things were back to normal.
By Thursday there were ten active regions visible on the Sun, with a solar flux of 167.
Daytime HF conditions are still relatively poor, although the evenings are beginning to show an improvement. We probably won’t see a return to excellent HF conditions until September or October.
Having said that, at 1230UTC on Thursday there were openings on 15m FT8 to Japan, Australia, Indonesia, Puerto Rico, Cuba and Anguilla, despite the predicted MUF over 3,000km being around 19MHz. In other words, make sure you actually listen on the bands!
Next week NOAA predicts that the Solar Flux Index will be in the range 155 to 170. The Kp index is forecast to be around two. There may be a blip on Wednesday 3 August when it is forecast to rise to three.
As always, this is likely to change if we get more solar flares and associated CMEs.
VHF and up
The coming week is likely to continue its unsettled theme although, unlike last week, this time we may find a temporary ridge of high pressure building over southern England at the end of the week.
It’s some way off and much could change before we get there, but there is a hint of some Tropo next Friday, perhaps lasting into the Saturday afternoon for the 144MHz Low Power Contest.
The rest of this week and much of next will, however, stay firmly in the unsettled pattern with just rain scatter to console us.
The Sporadic-E season often provides activity on the 6m band into the first week of September, so plenty of time to look for those chance QSOs. Last week saw a huge opening to Japan and a smaller opening to North America so there is still plenty to look for.
The current spell of unsettled weather is driven by a strong jet stream across the Atlantic into northern Europe and may be a positive sign for Sporadic-E paths that cross it, say to Iberia, round through Italy to the Balkans.
Other modes are relatively-low probability when compared with Sporadic-E, but the disturbed solar conditions could make aurora a contender on those occasions when the Kp index is above five.
Meteor scatter activity continues to increase as we head into the August Perseids, which peak around the 12 and 13 August.
The Moon reaches minimum declination on Sunday, becoming positive again late next Saturday so there will be short Moon windows early in the week. Perigee is on Wednesday so path losses are low. 144MHz sky noise is high this coming weekend turning low late Monday.
Category: GB2RS Propagation News
