Propagation News – 23 July 2023
The Sun continues to be peppered with spots with a solar flux index of 189 on Thursday the 20 July. However, sunspots can bring solar flares and Coronal Mass Ejections, or CMEs, which can be detrimental to good HF conditions.
We have been relatively lucky over the last week as the flares have mostly been minor C-class and a few M-class events. There have been no X-class flares, so ionospheric disturbances have been minor.
A large CME observed from active region 3363 is expected to mostly miss our planet. But the edge of the plasma cloud was still forecast to deliver a glancing blow to our geomagnetic field on Thursday 20 July.
A Polar Cap Absorption, or PCA, event was also in progress from the morning of Monday 17 July. This was caused by the proton flux rapidly increasing and affecting HF paths over the poles. The proton flux is gradually decreasing but may still have a detrimental effect for a while yet.
Region 3363, which was massive, has now disappeared behind the southwest limb and will no longer be a threat. That is, at least until its return in about two weeks’ time. It will be interesting to see how big it is on its return.
Other than the Kp index hitting 4.67 on the 16 and 17 July, geomagnetic conditions have been quiet with the Kp index at one or two over the past few days, which means HF conditions have been quite good.
Daytime MUFs over a 3,000km path have been consistently above 18MHz and often above 21MHz at times. Nighttime MUFs over the same path have been higher than 14MHz, and often 18MHz, at least during the first part of the night.
This means that if you hear signals on 24 or 28MHz the likelihood is that they are due to Sporadic-E propagation.
Next week NOAA predicts that the Solar Flux Index will remain at about 160 to 170. It is also predicting a Kp index of two all week. If that happens, we can probably expect good HF conditions for this time of year. However, with this many sunspots there is always the strong risk of solar flares and CMEs. So, keep an eye on solarham.net for real-time conditions.
VHF and up
The continuing spell of unsettled weather will stay with us for the coming week, so any signs of Tropo will be very limited indeed. This means that rain scatter will once again be a predominant propagation mode for those equipped on the GHz bands to use it.
Higher temperatures in summer mean strong convective cells, like thunderstorms, and better reflectivity from the larger raindrops, which can be held aloft by the stronger updrafts in the storm clouds. The reflectivity depends upon the 6th power of the diameter of the raindrop and the number of drops in the beam, so even a small increase in drop size gives a big increase in reflectivity.
Sporadic-E remains in play for a good while yet, so stay alert to cluster reports and, in particular, 10m and 6m beacons. If time is limited, check 1600 to 1700UTC to gain maximum benefit.
The usual other modes are still possibilities, of course. Starting with aurora, in view of the recently disturbed solar conditions, you should monitor the Kp index for large values above say Kp=5.
Secondly, the Perseids meteor shower will peak between the 12 and 13 August, but evidence of meteor material from the Perseids is already appearing.
Officially, the shower starts to appear from around the 17 July. The 50MHz and 144MHz bands have already produced some very short-lived bursts of FT8 signals that may be due to meteors.
The Delta Aquariids may also be responsible for these very sporadic bursts. As we move towards the Perseids peak you should expect an increasing number of bursts.
As the Moon begins its monthly descent towards minimum declination on the 29, path loss will decrease. However, the Moon will be close to Sagittarius A on the 28 July, leading to very high noise. This will be prevalent on the lower VHF bands.
Category: GB2RS Propagation News
