Propagation News – 23 September 2018

| September 21, 2018

First, the sunspot reported a few weeks ago as possibly being from the new sunspot cycle 25 was in fact from cycle 24. Although it had a reverse magnetic polarity signature than other cycle 24 spots, scientists now say that its low solar latitude means it was not from the new cycle. Scientists are also now predicting that sunspot minimum may be in September 2019, so we can expect poor conditions to last for some time yet.

Over this last week the solar flux index was pegged pretty much at 68. Geomagnetic conditions were mainly settled in the latter half of the week with the K-index zero at times. Next week NOAA predicts the solar flux index will remain in the range 68-69. Geomagnetic conditions are forecast to be poor on Sunday, the 23rd, and Monday, the 24th, due to a small coronal hole that will contribute to the high speed solar wind. Expect the K-index to reach at least four, with conditions improving as the week progresses.

We are now moving into the autumnal propagation season so we can expect to see modest rises in maximum usable frequencies, perhaps passing 18 and even 21MHz at times.

VHF and up

This weekend looks to be in the grip of unsettled weather with more strong winds possible. One model puts a deep low over southern England today with the potential for very strong winds in the south. Another model doesn’t develop this strong feature, so check the forecasts regularly and make sure your antennas are secure.

There is better news for the coming week as high pressure is expected to return to bring more settled conditions, giving a chance for tropo to develop. The overnight and early morning autumn mists are a good weather clue for tropo conditions since they indicate cool moist air near the surface, overlain by warmer drier air above. It’s this contrast of moisture which is the major contribution to changes in the refractive index of the air and hence ducting or tropo.

The Moon is past apogee now and declination goes positive on Tuesday meaning increasingly longer moon windows and decreasing EME path losses as the week progresses.

There’s a light meteor shower peaking next Saturday. The daytime Sextantids is not well known to visual observers as its radiant lies close to the sun, meaning trails are only visible during the last couple of hours before dawn. Meteor rates are very low so nothing to get excited about from a meteor scatter point of view.

Category: GB2RS Propagation News