venerdì 25 maggio 2018

Propagation News – 27 May 2018

A glancing blow from a high-speed solar wind stream caused the K-index to rise to three on Wednesday. This was a little unexpected as it came from a polar coronal hole on the Sun that didn’t look like it would impact the Earth. This brought mixed blessings as an initial positive phase saw the maximum usable frequency over 3,000km exceed 18MHz. But conditions soon dropped back and 20 metres became the highest viable band for F-layer propagation. 

Sporadic E has been bringing some good short skip to the higher bands so do make the most of it, with the peaks generally around mid-to-late morning and again in the late afternoon and early evening. 

The good news is we are seeing some sunspot activity, albeit very weak. At the time of writing there were two small visible regions and another coming around the sun’s limb. Nevertheless, NOAA predicts the solar flux will remain around 70. 

Geomagnetic conditions are set to be settled this week, at least until Friday the 1st when NOAA has the K index rising again. This is due to another coronal hole, which may cause unsettled conditions over the weekend of the 2nd and 3rd with a maximum predicted K index of six. 

So better HF conditions may occur in the first half of the week, but the weekend might not be the best time for DX. A high-speed solar wind may also not be conducive to stable Sporadic E cloud formation either, although this is an area that needs some more research. 

VHF and up:
The next week carries on in similar fashion with low pressure close to southern Britain, offering a chance of rain scatter in any showers. The north of the country remains close to high pressure over Scandinavia with a chance of further patches of enhanced tropo across the North Sea. 

The southern half of the country will be nearer to low pressure over the continent and will have an enhanced risk of showers, some thundery. This will make rain scatter a possibility for the microwave bands. 

Sporadic E is amongst us and hopefully this next week will continue to provide options. However, since jet streams are often implicated in the formation of sporadic E, the news is not so good in that the main Atlantic jet stream is displaced well to the north of Europe. 

The main operating rules are to check the clusters and beacons for activity, initially on 10m, but then upwards through 6m to 4m and 2m as the opening develops. Conditions may only happen for brief moments, so keep the overs short with report and locator in case the path fades. 

Moon declination is negative this week, and apogee just a week away so losses are approaching their highest and moon windows will be at their shortest. This means low antenna elevations and increasing noise at VHF and UHF.