Propagation – 7 April 2013

| April 7, 2013

Now the solar report for the period from Friday March 29th to Thursday the 4th of April, compiled by Martin Harrison, G3USF, on Friday April 5th.

Solar activity was again very low. During the entire period only four small C-class flares were reported and these had no impact on propagation. The solar flux level rose from 105 on the 39th to 129 on the 4th to average 116 over the week – an increase of 20 points on the previous week. However, the 90-day average dropped one point to 114. The X-ray flux rose steadily to average B2.6. The weel began with the geomagnetic field was at minor storm level. This was the result of a high-speed coronal wind stream that sent the Ap index for the 29th to reach 23 units. That was enough to trigger bright Arctic auroras and radio auroras at 50 and 144MHz lasting several hours on the afternoon an early evening of the 29th. But, as so often happens, these were almost wholly restricted to stations at high latitudes. HF propagation was below par for much of the day as a result. The disturbance died down during the 30th and, for the rest of the period geomagnetic activity stayed low, with the daily Ap in single figures. Solar wind speeds recorded by the ACE spacecraft reached 540km/second during the disturbance on the 29th, then declined to 274km/second on the 3rd of April. Particle densities were generally low. Bz – that’s the interplanetary magnetic field – varied between plus and minus 4 nanoTeslas on quiet days and between minus 10 and plus 8 nanoTeslas during the disturbed days.

Now the forecast for the coming week. Solar activity is expected to remain low or very low, with only occasional flares, mostly of modest C-class dimensions. There are no indications of any highly active areas currently on the far side of the Sun rotating into view. Solar flux levels appear likely to fall back from the level of recent days but are expected to remain above the 100mark. Geomagnetic activity should stay low. MUFs at equal latitudes will be around 24MHz in the south and 21MHz in the north. Darkness lows will stay in the region of 10MHz. Paths to Japan should have a maximum usable frequency of about 25MHz, where there should be a 50 per cent chance of a contact. There should be a 90 per cent success rate at the Optimum Working Frequency of 20MHz. The path should be its best between 1000 and 1300UTC.

And that’s all for another week from the propagation team.

Category: GB2RS Propagation News

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