Propagation News – 27 October 2019

| October 25, 2019

The solar disturbance predicted in the last report, which was due to hit Earth last weekend, didn’t amount to anything. However, the large coronal hole that has just completed its 27 day transit around the Sun’s surface certainly did. The ACE spacecraft shows that the solar wind speed increased rapidly on the morning of Thursday, the 24th, to more than 500 kilometres per second. The temperature of the ions in the solar wind increased too, at the same time as the interplanetary magnetic field or Bz shifted sharply southward. As a result, the Kp index rose from one to four as the solar wind coupled to the Earth’s magnetic field, and subsequently the HF bands were affected. Initially they showed an enhancement in HF propagation, with showing the maximum useable frequency reaching more than 21MHz, even hitting 24MHz, over a 3,000km path. Quite how this will pan out over CQ Worldwide weekend we’ll have to wait and see.

Next week NOAA shows the sunspot number remaining at 0 with the solar flux index at 66. Once the current geomagnetic disturbance has passed we should then see more settled conditions for the rest of the week. Make the most of the autumnal HF conditions, where higher maximum usable frequencies and good transatlantic propagation make a pleasant change to the HF doldrums we had over the summer.

VHF and up

We entered a period of unsettled weather to end the past week, but can look forward to a new high pressure over northern Britain by midweek. In some models, this slips southeast across the North Sea into northern Europe to allow an Atlantic low to move in by next weekend. In complete contrast to this, another model takes the high west into the Atlantic and allows low pressure to develop close to southern Britain. It all sounds complicated and will certainly change between now and then; however there are some useful propagation outcomes. The period of high pressure up to midweek obviously produces a chance of tropo, whichever way it drifts off afterwards, although it is relatively short-lived and not looking like a prime tropo event.

The rest of the propagation options are probably pinning hopes on some strong convection over the warmer waters surrounding the UK. This is a typical late autumn phase in our weather and means the chance of rain scatter on the GHz bands from heavy showers around the coast.

Moon declination is negative now, but perigee was yesterday so losses are still low. At 144MHz, sky noise reaches a peak of nearly 2500K on Friday.

No major meteor showers this week so back to the pre-dawn morning random enhancement.

Category: GB2RS Propagation News