Propagation News – 7 July 2024

| July 5, 2024

After a rough spot last weekend, the Sun has since behaved itself, allowing HF propagation to get back to normal. To recap, the Kp index hit 7.67 on Friday 28 June, thanks to incoming plasma from a coronal mass ejection. For a time, it looked like we might have a repeat performance of the 10 May when the Kp index hit 9 and there was a visible aurora across the UK.

This time around, however, conditions calmed down again and 24 hours later the Kp index was back to 2.33. Since then, the Sun has remained calm with only two M-class and zero X-class flares, and the Kp index is back in the 1 to 3 range.

This means that the ionosphere has had a chance to build up and we have been seeing MUFs over a 3,000km path exceeding 21MHz and often reaching 24MHz. That’s pretty good considering we are in the Summer HF doldrums.

An analysis of the Sun’s active sunspot regions shows that two are growing, five are declining and one is stable. shows that signals have been getting to the UK from Australia, New Zealand, Japan and the Far East on the 15m band, while 28MHz is still mainly open to short-hop Sporadic-E contacts across Europe.

The solar flux index has declined over the past week and was sitting at 167 on Thursday 4 July. Next week, NOAA predicts it will remain around the 170 mark, with quiet geomagnetic conditions.

However, solar flares and coronal mass ejections remain hard to predict so keep an eye on and for a real-time view of solar and geomagnetic conditions.

VHF and up 

The weather sequence to the end of next week is much like an autumn pattern in that the story is all about areas of low pressure, showers and weather fronts. None of this suggests that Tropo will be a feature of the weather. In fact, high-pressure systems simply do not appear on the charts at all.

We can leave rain scatter on the list and, since it is technically summer, or meant to be, there is a lot of energy in any showers. Indeed, some may be heavy and thundery and are probably good rain-scatter candidates. Meteor scatter, in the absence of major showers, is most likely around the dawn period when random meteors tend to be more prevalent.

The solar conditions continue to offer much variability and it is always worth checking for elevated Kp index values, which can be a signal for aurora to occur. As a general guide check the bands when Kp reaches 5 or higher.

The Sporadic-E season continues, although recently there have been some higher-than-ideal Kp indices, which unlike for aurora need to be at lower values, say below a Kp index of 3, for ideal Sporadic-E conditions.

The other ingredient that tends to promote Sporadic-E is the presence of jet streams in the upper atmosphere around 10 to 15km up. It is believed that these can generate atmospheric gravity waves that can propagate up to the E region at 110km where they become part of the process for making Sporadic-E.

This unsettled autumn-like weather is providing plenty of jet streams, so it continues to be worth checking for Sporadic-E. A quick look at the upper air pattern suggests that paths towards Scandinavia and the Baltic may be productive, and perhaps to Iberia later next week.

Moon declination is close to maximum positive this coming weekend so Moon peak elevation will be high. Moon apogee is on Friday 12 July so EME path losses continue to increase. 144MHz sky noise is low all week.


Category: GB2RS Propagation News