RSGB Propagation News

Solar data for the period from 11 to 17 April,
compiled by Neil Clarke, G0CAS.

Solar activity was ‘very low’ but due to a few small C-class solar flares activity increased to ‘low’ on the 12th and the 17th. The largest solar flare of the period was a C4 on the 17th. The solar flux varied little day to day and averaged 85 units. The 90-day solar flux average on the 17th was 93, that’s three units down on last week. X-ray flux levels declined from A9.2 units on the 11th to A5.3 by the 15th. The average was A6 units.

Geomagnetic activity started at ‘active’ levels due to a recurring coronal hole. The Ap index was 30 units on the 12th but by the 17th was down to 5. The average was Ap 16 units. The ACE spacecraft saw solar wind speeds decline from 650 kilometres per second on the 13th to 380 by the 17th. Particle densities peaked at 30 particles per cubic centimetre on the 11th but then declined to 1 particle per cubic centimetre by the 15th. During the coronal hole disturbance the Bz varied between minus 12 and plus 11 nanoTeslas but on the quiet days varied between minus 5 and plus 4 nanoTeslas.

The combination of the coronal hole disturbance and the lower-than-expected solar flux was bad news for HF operators. 24 and 28MHz were poor, though 14 and 18MHz remained in reasonable shape and there were some good spells on 21MHz. Sometimes disturbances that bring misery to the HF bands produce good aurora for VHF operators. Not so this week. Auroral events were reported on the 11th, 12th, 13th and 14th but were confined to high latitudes and favoured North America rather than Europe.

The solar forecast. We should see the quiet side of the sun looking our way during the week of 24 to 30 April. Solar activity is expected to be very low to low. The solar flux should decline and be in the 70s for most of the week. Geomagnetic activity should be mostly quiet throughout the week. MUFs during daylight hours at equal latitudes should be around 19MHz for the south and 16MHz for the north. The darkness hour lows should be about 10MHz.

Paths this week to Australia should have a maximum usable frequency, with a 50 per cent success rate, of about 19MHz. The optimum working frequency, with a 90 per cent success rate, should be around 16MHz. The best time to try this path should be between 0900 and 1200UTC. The start of the summer Sporadic E season could occur during the week of 24 to 30 April. Watch for openings on 28MHz at first, then 50 and 70MHz later.

The RSGB propagation news is also available in a Saturday update, posted every Saturday evening and for more on propagation generally, see http://www.rsgb.org/society/psc.htm.

Source: GB2RS News - Courtesy of the RSGB

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