Propagation News – 31 March 2024
What a tumultuous time we had last week. Active region 3614 produced an X1.1 solar flare and coronal mass ejection, or CME, in the early hours of the 23 March. This impacted Earth’s geomagnetic field sending the Kp index to 8 on the 24 March.
In fact, there were simultaneous flares from active region 3614 and the larger region AR3615.
The solar wind speed reached more than 850 kilometres per second at the height of the geomagnetic storm, peaking at 880 kilometres per second.
The CME started to impact the Earth early in the afternoon of the 24 March and, according to Digisonde data, its full effects on the ionosphere started to be felt by 1540UTC.
The large AR3615 sunspot cluster continues to evolve as it moves into the Sun’s southwest quadrant. Moderate flaring will remain likely in the short term with a lower chance for another strong X-class flare, although it is around the side of the Sun and is not considered a threat today, Sunday 31 March .
All this was not good news for HF propagation, which saw maximum useable frequencies over a 3,000km path plummet on the 24 March to less than 18MHz. The ionosphere didn’t fully recover until two days later, with the MUF struggling to get above 18MHz on the 25 March.
It wasn’t until the afternoon of Wednesday the 27 March that we saw the 10m band behaving normally again with the Kp index back in the range of 1 to 3.
So, this is what can happen if we have an X-class flare and associated CME. We can expect more of the same to come.
Next week, NOAA predicts that the solar flux index will remain high at around 175 to 190. Unsettled geomagnetic conditions are forecast from the 3rd to the 5th April when the Kp Index could rise to 4.
But keep an eye on solarham.net for a near real-time guide to current solar conditions.
VHF and up
The period leading up to the Easter Weekend, and the following week, shows up on the forecast charts as dominated by low pressure, feeding several periods of rain and showers across the country.
This unfortunately means that Tropo is again off the menu of weather-related VHF propagation.
Of course, wet weather is usually very supportive of rain scatter propagation on the GHz bands and this prolonged period of rain or showers will give the UHF and SHF operators something to occupy their time.
Meteor scatter prospects are once again just random, which tends to be better in the hours just before dawn. We can start to look forward to the April Lyrids, which are active in the second half of April with a peak around the 22nd. It’s worth checking out the operating conventions and frequencies now so that you can be ready.
Strong aurora has been reported recently, with a Kp index of 8, and a quick listen for fluttery signals on the 80m or 40m bands is often a good clue if you don’t have access to the Kp index at the time.
The main mode of interest for the coming months is Sporadic-E and some early propagation is possible, mainly on digital modes on the 10m or 6m bands, but probably very fleeting.
During the summer Sporadic-E season, it’s well worth checking the propquest.co.uk graphs to see what is occurring and get an idea of how it may relate to jet stream weather patterns by cross-checking with the Sporadic-E blog upper air charts.
The Sporadic-E Probability Index, or EPI, maps are also potentially useful to see how the favourable regions change with time. In the current pre-season period, it’s more typical to find trans-equatorial propagation, or TEP, as an exotic mode offering paths to the south into South Africa and possibly into South America.
For EME operators, Moon declination reaches minimum on Easter Monday, so we’ll see short Moon windows with low elevation. Path losses are falling all week and 144MHz sky noise is moderate, rising to a peak of more than 3,000 Kelvin on Easter Monday before returning to low levels.
Category: GB2RS Propagation News
