Propagation News – 20 April 2025
Last week was characterised by increased Kp index numbers and severe geomagnetic storms, peaking at G4. These drove down maximum usable frequencies and disrupted DX contacts, especially on the higher HF bands.
The solar wind speed increased from 380 kilometres per second to around 500 kilometres per second on 15 April and an increase in plasma density was noted as well. Subsequently, the Kp index peaked at 7.67 on Wednesday 16 April, causing visible aurora alerts in the UK.
This was caused by a pair of CMEs that left the Sun on Sunday 13 April. We had a total of 22 M-class solar flares over four days, so a CME event was inevitable.
Unsettled geomagnetic conditions are a feature on the declining side of a solar cycle, so we could unfortunately be in for many more.
According to Propquest, MUFs over a 3,000km path fell to below 18MHz for long periods on Wednesday 16 April , before climbing to around 21MHz at the end of the day.
Meanwhile, the solar flux index fell from a high of 170 on Friday 11 April to a low of 148 on Wednesday 16 April.
Next week, NOAA predicts that the SFI will start the week around 145 but could increase to 165 as the week progresses. Unsettled geomagnetic conditions are forecast for the 22 to the 24 April, with a predicted maximum Kp index of four.
As always, keep an eye on solarham.com for daily updates, but more importantly, get on the bands, which are a much more effective guide to HF propagation!
VHF and up
The current period of unsettled weather looks likely to continue into the coming week. This does not mean rain every day, but periods of rain or showers with some intervening drier spells. These drier interludes are not really dominated by high pressure, just gaps between the wetter periods, so it’s unlikely to produce much significant Tropo.
In terms of propagation, there may be some rain scatter, although it won’t be very reliable. However, the prospects for meteor scatter are more promising with the peak of the Lyrids due on Tuesday 22 April. It is worth checking up on procedures for meteor scatter working if you’ve not done it before and you may find a new part of the hobby to add to your operating schedule.
The prospects for aurora continue to be raised by what seems like an almost daily supply of aurora alerts. Continue to monitor the Kp index for signs of elevated values, where Kp is above five, for radio activity. Early signs such as fluttery signals on the LF and HF bands may suggest it’s worth looking on the VHF bands for auroral activity.
As we move towards the new season it is good to get into the habit of looking for Sporadic-E. The Propquest website shows several useful components for analysing the Es prospects. If you look at the position of the jet streams shown on the Es blog tab, these can produce favourable conditions geographically to give a hint of the right direction in which to listen. The opening season typically favours 10m or 6m.
EME path losses are now decreasing towards perigee on Sunday 27 April. Last Friday, 18 April, saw minimum Moon declination, so Moon windows will lengthen along with peak elevation. 144MHz sky noise starts this week very high but decreases to low as the week progresses.
Category: GB2RS Propagation News
