Satgen229 Satellite Propagation Worldwide Part 2 by GM4IHJ 14 Aug 93 BID of this msg is SGEN229 Please use this BID if you retransmit the msg Part 1 discussed Asymetric HF satellite communications and the effect of aurora on satellite communications. This part 2 discusses AURORAL Es, a form of propagation which can benefit both the satellite and the terrestrial user but which is only available where stations have the aurora above their horizon. It is no use to stations below latitude 35 The aurora is an oval curtain around the magnetic pole where incoming solar bombardment finds an easy way down to the atmosphere by travelling between the open polar magnetic field lines. The oval is squashed and pushed away from the Sun , which moves the oval centre well over to the anti Sun side of the magnetic pole. This off centre, combined with the fact that the magnetic pole is not at the geographic rotation pole , causes the edge of the oval as seen from further south , to oscillate so that it is furthest north in the late morning,and nearest to you (furthest south) around local midnight. In this way , what ever the auroral state , quiet near the mag pole or disturb , well south away from the mag pole, from a station in UK the edge of the oval appears to move about 500 kms towards UK between late morning and midnight. So even if the aurora stays quiet the auroral curtain comes to the far northern UK horizon in the late evening. If the Sun is disturbed , the auroral oval expands south, to be in range of UK to the north from about noon and overhead UK in the late evening. There is therefore an ionised curtain north of UK ( and stations at equivalent magnetic latitude ) all day. In the evening ,in quiet conditions the top of the aurora is visible to stations in the north of UK, and by pointing an antenna at it you can get HF and VHF propagation forward scattered through the auroral curtain to locations in say Northern Sweden , or to satellites in the same direction but at far longer range. At between 1600 and 1900 local in quiet auroral conditions RS12 on the Pacific side of the North pole can be accessed from UK on at least one evening in three, when it is 10 degrees below the horizon. This "THROUGH THE AURORA" propagation has been called Auroral Es for a long time because it was first recognised during major auroral storms ,when after several "rough signal" contacts using the aurora to talk by back scatter to middle Europe , GM and GI stations lost backscatter comms but suddenly found they had a clear signal path to Northern Sweden. This clear signal via Auroral Es does not neccessarily use the E layer, in fact it more often uses the F layer at heights up to 400 km. Through the auroral events, occur between 1600 and 1900 local when the aurora is quiet, but when it is disturbed they can occur only during the passage of the "HARANG DISCONTINUITY" the mid evening spin of the earth which brings the split in the auroral circulation pattern past your station. Please note that the more disturbed the Aurora, the earlier part 1 aurora back scatter ends and, the end occurs as the Harang Disciontinuity goes through. After the passage of the discontinuity , Auroral Es in disturbed conditions , cease, and normal back scatter part 2 rough signal aurora may begin. Please Note. Auroral Es terrestrial DX and satellite DX has only been reported by stations above magnetic latitude 50N. There have been no reports from the Southern Hemisphere. Reports of Auroral Es outside Europe would be welcomed by GM4IHJ. PS PERSEIDS Forecast Monster Shower. In fact it was a poor one. Apologies to all. 73 de GM4IHJ @ GB7SAN