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Unusual Aurora QSO between DK3UZ and UA1ZCL

Volker Grassmann, DF5AI

Febuary 14, 2003

Introduction

Eddi, DK3UZ, reports an unusual Aurora QSO from many years ago, see the below email. In 1988, he worked Alex, UA1ZCL, in the 144 MHz band at a noteworthy distance of 2.132 kilometers. Just after this QSO, Alex also managed another QSO to Jürgen, Y22ME. Eddi argues that this QSOs cannot be interpreted in terms of the boundary-fence theory. He discussed his observation with OM Lange-Hesse, scientist at the former Max-Planck-Institute for Ionospheric Research, who speculated about Auroral backscatter originating in the ionospheric F-region (300 km).

Eddi's email from January 16, 2003:

Lbr Volker,

1988-02-22 hatte ich (damals noch in EN20c) um 1452UTC ein Aurora- QSO mit UA1ZCL (RC08c). Nach mir hat Alex dann noch den Juergen, Y22ME, aus HM53a gearbeitet. Beide Verbindungen lagen deutlich ausserhalb dessen, was die Boundary-Fence-Theorie zulaesst. Siehe auch DUBUS 1989/01, S50. Interessant ist m.E. auch, dass das Reflexionsgebiet nicht auf halber Strecke zwischen den Stationen liegt, sondern Alex' EME-Station die Hauptarbeit geleistet hat. Spaeter traf ich in Weinheim einen im Max-Planck-Institut fuer Ionosphaerenforschung arbeitenden OM (Lange-Hesse?), der meinte, dass die QSOs ueber Nordlicht in hoeheren Schichten stattgefunden haben koennten. Oftmals befaenden sich sichtbare rote Nordlichter in bis ca. 300km Hoehe! (Das waere dann also in der F2-Schicht.)

73, Eddi

UA1ZCL

ScatterGeometry1F-region backscatter

The above observation was analysed by using the BeamFinder analysis software [1], version 2.1.2. In this special version, the aspect angle and the scatter height is adjustable between 60 to 90 degree and 90 to 400 km, respectively. The aspect angle is generally close to 90 degree and the scatter height is generally around 105 kilometers in Auroral backscatter.

Remarks: The aspect angle is defined the angle between the difference vector kRX - kTX and the magnetic field line B which penetrates the scatter volume S. kTX denotes the wavevector from the transmitter TX to the scatter volume S and kRX denotes the wavevector from the scatter volume S to the receiver RX.

The above hypothesis of F-region backscatter was tested by varying the scatter height between 120 and 400 km with a constant aspect angle of 88.5 degree. Using BeamFinder's Scatter curve function, no potential scatter volume was however found in this analysis. Thus, there is no evidence for an unusal scatter height in this Aurora QSO.

Aspect angle sensitivity

Since off-normal Auroral scatter was published in amateur radio [2], the author received emails from many radio amateurs reporting unusual Aurora QSOs. Apparently, this type of Aurora dx communication may be observed more often as expected (and the advantage of high-powered amateur radio stations is possibly smaller than expected). In all cases, the scatter volume was easily identified by adjusting the aspect angle between, say, 85 and 75 degree.

In this particular Aurora QSO, no scatterer was found even with the lowest aspect angle supported by the software at that time, i.e. 70 degree. However, increasing the scatter height from 105 to 110 km finally revealed two scatterers above central Scandinavia, see the map. The scatter height of 110 km corresponds to the upper limit of Auroral backscatter. On the other hand, it is surprising that the difference between 110 km and 105 km is crucial in this particular Aurora QSO. The aspect angle of 70 degree is also noteworthy because it corresponds to the largest ever observed deviation from perpendicularity in amateur radio.

The special BeamFinder version 2.1.2 supports aspect angle settings between 60 and 90 degree. Therefore, the QSO was analysed again to examine the aspect angle without changing the scatter height. In fact, an aspect angle of 69 degree and a scatter height of 105 km may indeed explain the dx communication between DK3UZ and UA1ZCL. The size of the backscatter region is similiar to the size of the Y22ME scatterer in the above map, i.e. this Aurora QSO indeed corresponds to a very small target area in the E-rtegion of the ionosphere.

Calculating the aspect angle in Auroral backscatter requires accurate information on the direction of the magnetic field penetrating the scatter volume. This raises the question on the software's accuracy when analysing Auroral backscatter in periods of geomagnetic disturbances. One might argue that the true aspect angle in this QSO was much closer to perpendicularity because the software's magnetic field model cannot calculate the deflection of the Earth's magnetic field in geomagnetic storms. However, the strength of the main field is around 40.000 nT which is very large in comparison to the field pertubations even in major geomagnetic disturbances. For example: assuming a field pertubation of, say, 1.000 nT the direction of the Earth's magnetic field would vary by less than 1.5 degree. This is in the order of the model's accuracy, i.e. the impact of geomagnetic disturbances may be neglected in this type of amateur radio propagation studies.

Summary

The Aurora QSO between DK3UZ and UA1ZCL may be interpreted by Auroral backscatter at an aspect angle around 70 degree. This aspect angle shows the largest ever observed deviation from perpendicularity in amateur radio. There is no reason to assume that the backscatter originated above 110 km, i.e. there is no evidence for F-region backscatter. Considering the small size of the scatter regions, the three radio operators discovered a rariety in Aurora dx communication - this Aurora QSO is indeed remarkable in various aspects.

Thanks for the email, Eddi.

References

[1]

BeamFinder Analysis Software

Grassmann, V., DF5AI, http://www.df5ai.net/BeamFinder/bfintro.html

[2]

Unusual Aurora Observations in the 144 MHz Band

Grassmann, V., DF5AI, Dubus 4, p. 39-41, 2002

see also: http://www.df5ai.net/ArticlesDL/ONScatter/ONScatter.html

From: http://www.df5ai.net

Copyright (C) of Volker Grassmann. All rights reserved. The material, or parts thereof, may not be reproduced in any form without prior written permission of the author.