Es_22012010

Sporadic E opening of 22 Jan 2010

Additions 26 Jan 2010

This opening on 50MHz was very unusual in that it was outside the normal seasonal times for sporadic E (around the mid-summer solstice with a minor peak around the mid-winter solstice).

The opening lasted for over two hours during which the centre of reflection moved very roughly from south-eastern France to south-western France. A picture of the dx cluster is shown here. Click on the image for a large size version.
What this image doesn't show is the propagation to TA from a number of countries including OK, DL, HA, I and G. A QSO was made between G4IGO (IO80nw) and TA2ZAF (KM69kv) around 1621z. The distance is 3009 km, which would could be double hop Es but given the weak signal in IO80/81 could also be a combination of single hop Es and tropo.

The question of whether it is sporadic E is answered by the Chilton ionogram, shown here. Click on the image for a large size version. The image is for 1620z. The presence of a strong Es layer at about 110km height is visible, together with the multiple 2 and 3 times around reflections.

Also seen below are ionograms for Pruhonice near Prague (Czech Republic) on the left (1630z) and Dourbes (Belgium) on the right (1530z). Strong Es layer reflections are noted at a height of 110km although not at high enough a frequency to support the 50MHz observations.

During the opening Ken G4IGO alerted the ON4KST chat to the presence of an auroral sounding signal from the Spanish TV vision carrier on 48.250MHz. This station is located at Navacerrada (IN70xr). The signal peaked on a bearing of about 120 degrees initially, slowly moving to around 150 degrees. The true bearing from IO80NW is 184 degrees.

The spectrum of the signal is shown here. Again you can click for larger image. The signal spectrum is about 100Hz wide and reasonably symmetrical.

It is speculated that the propagation here is FAI (field-aligned-irregularity) - due to the auroral sound and the indirect side-scatter path. This is observed on 144MHz, but I am not aware that is seen often on 50MHz. The mode is analagous to Aurora in that the irregularities are aligned with the geomagnetic field. It is a relatively weak effect, requiring high power, thus the signal here is not very strong despite originating from a 250 kW transmitter. A combined Es forward scatter and FAI side scatter event on 144MHz in June 2007 was described in Dubus 3/2007 and is summarised on the DF5AI website. According to the VHF/UHF Handbook (2002, p3.3) the mechanism is believed to occur in the E region and the signal is scattered from a volume often situated near to the Swiss Alps or close to other mountainous areas at about the same latitude. The bearing of Mont Blanc (JN35kv) from IO80nw is 124 degrees.