After the huge and very interesting Aurora contacts of November 2003, time has come to learn more about these rare Auroral opportunities for Australian Amateurs.

STRANGE POST AURORAL EVENT ON 17 MAY 2005

This event was recorded by monitoring NZ Invercargill TV on 45.250 MHz using Spectrgram (Copy Attached)

The line you see at just above 1000 Hz is the normal TV carrier frequency on meteor pings.

You can see that at about 6 ksecs along the Spectrogram (13:30 UTC on 17 May) the background noise dropped indicating a strong signal in my passband was activating the AGC but out of the range of frequencies I was looking at.

At about 7.5 Ksecs the signal was producing a frequency within the Spectrum I was looking at and was falling rapidly from a positive Doppler shift to a negative Doppler shift.

By 10 ksecs the signal shows clearly as a carrier at about -750 Hz and sidebands due to the TV frame frequency 50 Hz each side.

If we focus on the carrier which is the strongest we can see that up to around 11.5 Ksecs there was a rapid reduction in Doppler with very little short-term spread that is typical of Au.

After 11.5  ksecs and up to around 13.5  ksecs the signal is more stable and shows the typical Doppler spreading of Au. However, the overall shift of the carrier is around 750 Hz at 45 MHz which is much greater than I have previously recorded by a factor 7 to 10.

At around 13.5 ksecs the signal seems to stop abruptly of jumps in frequency.

ASSESSMENT

The Doppler appears to have moved from positive of more than + 500 Hz to -350 Hz over this period indicating a very rapid movement of the reflecting surface.  Such Doppler is more than 7 to 10 times what I see in normal Au events on ZL TV – and represents a movement of the Au or 7 to 10 times more that we have discussed previously as the maximum speed.  This event started at 13:30 UTC on 17 May and concluded at around 15:30 UTC.

Aurora Openings from  22 July 2004 to 28 July 2004 -

EVENING AU EVENT ON 10 NOVEMBER 2004 Local

This event ran from at least 6 pm to 9 pm and VK7MOs signals were monitored
by VK3AUU and reports also received from VK3HZ and VK2KRR.  The Costello
index increased from around 7 to 9 during this period.  The most northerly
station to report signals was VK1ZQR..

VK3AUU reported generally positive shifts of 200 to 500 Hz with the typical
shift being around 350 Hz.  He noted an occasional negative shift of up to
200 Hz that mostly occurred as a second signal.  Overall the vast majority
of signals gave positive shifts.

VK3HZ reported a positive shift of 440 Hz and VK2KRR a positive shift .

CONCLUSION

For this evening event the tuning shifts were dominantly positive with a
typical shift of around 350 Hz

MORNING AU EVENT ON 10 NOVEMBER 2004 Local

This morning event was monitored from 0830 to 1000 local.  It peaked at 8.5
observed on the Costello index.  VK7MO was monitored by VK3HZ and VK3AUU and
VK3UM saw only a few short indications of Au but with negative shifts.
VK2KRR was able to monitor Hamilton TV indicating the event was producing
propagation further North.  VK1ZQR reported no indication of Au.

VH3HZ reported that the typical Doppler shift was -290 Hz but that towards
the end it did cycle between -290 and +290 Hz.

VK3AUU reported that the Doppler was generally in the range -300 to -400 Hz
but that there were occasional positive swings up to +150 Hz towards the
end.

VK2KRR reported generally negatives shifts of around 300 Hz with a +400
shift near the end of the event.

The variable shifts at the end of this event were also reported on an
earlier evening event.

SUMMARY

While we still need more morning data I would summarise this as providing
negative shifts of 300 to 400 Hz through most of the event and some more
variable shifts including some positive as the event concluded

Rex.

8 November 2004

This event ran from 3.00 pm local to at least 10 pm local and exceeded the
maximum level of 9 on the Costello index from several hours.  it is the
strongest recorded over the last 2 years. It allowed 2 metre contacts as far
North as Port Macquarie to VK2EI with a maximum distance (VK2EI to VK3HZ) of
1009 km.  This is close to the limit on a North South path. ZL3TY worked a
number of stations on the east coast of Australia on 6 meters up to 2000 km
which is also near the maximum distance for an East-West path.

Measurements of tuning shift were made by VK7MO and VK3FMD from around 9.00
to 10:00 pm local using spectran.  This showed a positive shift of 200 to
500 Hz with the typical shift being 300 Hz.  Again this adds to the view
that the shift is positive in the evenings.

73 Rex VK7MO

SUMMARY OF AURORAL EVENT 27 JULY by Rex VK7MO WORD DOC

FINAL SUMMARY OF AURORAL EVENT 25 JULY by Rex VK7MO

This event ran for several hours in the afternoon an early evening of 25 July at a time when Kp was in the range 6 to 7.

From the broad data I have so far it looks like that while there were some short variations and a few negative shifts that for the bulk of the time the Doppler in Hz on each of the paths was in the following ranges:


Rxing                            7MO TXing                3HZ TXing

VK7MO                                                       +250 to +300
VK3HZ                        +350 to +450
VK3UM                        +500 to +600              +175 to +200
VK2KRR                    +800                                +250

VK2KRR recorded a particularly interesting Spectrogram, available on this site, with observations of Doppler shift from both VK7MO and VK3HZ showing major variations in Doppler between the two stations at the same time.

The pattern that shows up from this is that the largest Doppler shifts are from the stations who are furthest apart, even though all stations are looking roughly North-South and at the same general area of the Au.

I suspect that this might be explained by the fact that as the path increase the point on the where the angle of incidence equals the angle of reflection occurs changes with height and if the Doppler speed also varies markedly with height as reported by John Foster (http://www.haystack.edu/~jcf/papers/MPI.htm) this could be the result.

CONCLUSION

Apart from some short periods (less than 5% of the time) this evening event exhibited a positive Doppler shift

Speculation on Auroral Shift by Rex VK7MO

Leigh VK2KRR has produced rather spectacular results showing the Auroral
shift to be around 500 Hz on VK7MO and around half this on VK3HZ at the same
time and from the same general area of the Aurora.

The following reference  http://www.haystack.edu/~jcf/papers/MPI.htm concludes that "Narrow spectra with greatly different Doppler velocities are observed above and below the center of the irregularity layer (at altitudes of 103 km and 113 km). These observations are consistent with the existence of different irregularity processes at high and low altitudes under very strong electric field conditions."

Now for the Speculation - let us assume that the reflections from the Au are essentially as if from a mirror and thus for a signal to be received it must meet the criteria that the angle of incidence equals the angle of reflection. While the signals are from the same general area of the Aurora the fact that VK7MO is closer to the Au will change the point on Au where the criteria for reflection occurs. I then speculate that by changing this point of reflection only slightly we might move from reflections with substantially different Doppler velocities as indicated in the above reference and thus an explanation for the VK2KRR results.  From this we can conclude that the Auroral shift might be much more closely related to geometry of paths than to night or day and perhaps over time we will find an equal distribution of positive and negative shifts in the morning and evenings.

Summary of Auroral Observations 25 July (2004) by Rex VK7MO

A further Auroral Event occurred during the afternoon of Sunday 25 July. Again experiments were made to determine the extent of the Auroral shift and spread based on a single tone TXed using FSK441A  R27.

Transmissions were undertaken by VK3HZ and VK7MO on 144.220. The signals were received by VK2KRR, at the Rock near Wagga, VK3AUU, Druin, VK3UM Glenburn, VK2TWR Nimmitabel as well as VK3HZ and VK7MO.  ZL3TY and ZL1TN
also participated but did not copy Auroral Signals.

The event commenced with Au signals from ZL TV on 45.250  at 2.00 pm.  The NOAA site indicated that throughout the afternoon the Kp index held up at 6 or 7. Two meter test signals were copied from about 3 pm to 6 pm when the tests concluded.  But SSB contacts were being conducted until at least 7 pm.

All stations reported a positive shift of around 500 Hz and a spread of plus and minus 400 to 500 Hz around this. Signals varied from S9 down to nothing but signals were present almost all the time during the 3 hours of the tests.

One strange event was that at one stage the Auroral signal split into two with the lower frequency component dropping in frequency by around 1500 Hz in one minute.  This was observed by VK7MO and VK3HZ and as two peaks by VK3AUU.

Parallel observations were made of ZL TV with this showing a small negative shift for most of the time, but with occasional positive excursions of up to 100 Hz. I will send a copy of the ZL TV Spectrogram to VK2KRR who may be able to make it available on his web site.

This event adds a little weight to the view that for evening events, at least on a North-South path, the shift is positive although again the East-West path to ZL does not follow the pattern.  We still need many more observations.

Summary of Auroral Observations 22 July (2004) by Rex VK7MO

On 22 July from 0735 to 0917 Z Auroral signals were observed by VK3KAQ, East of Melbourne, and VK3AUU, Druin, from VK7MO near Hobart on 2 meters. The paths are approximately North-South and the distances around 570 to 600 Km. VK7MO beamed due South at 15 degrees elevation for most of the period. Checks by VK3UM and VK2KRR showed no evidence of signals at greater distances.

The observation method was to send a single tone using FSK441 R27 in 30 second cycles and to measure the shift and spread with Spectran.
Frequencies were calibrated with a tropo signal when VK7MO beamed North.

The signals showed a positive Doppler shift of between 400 and 500 Hz for the full period of almost 2 hours. Observations during the afternoon from ZL TV by VK7MO showed a negative shift of 50 to 100 Hz at 45.25 MHz.

These results compare with morning observations by VK3UM last November that where the same order over a similar period but produced negative shifts.

While a simple relationship that morning observations are negative and evening are positive seems convenient this would not be consistent with the ZL TV observations.

In the process of discussing these results on the VK-ZL logger VK2KRR found a very useful reference:

http://www.ursa.fi/ursa/jaostot/revontulet/radio/enradio.html which in turn quoted a further reference

http://www.haystack.edu/~jcf/papers/MPI.htm

These references show that typical Doppler velocities range from -1000 to +1000 m/s which is consistent with the observations.  The second reference indicates that in the E layer region there can be a sharp change in velocity from just above to just below 100 km that can explain the large shifts being observed.

The question our observations raises is why we get such a change from morning to evening? Of course two sets of observations is insufficient so we need to gather more data.

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