Latest Propagation Report dated 4th March 2012

The text below is a rolling forecast and report of long distance ( night time ) propagation conditions as I see them. The most recent addition to the report is in red.

Kyoto is now giving sensible Dst estimate values, but is still prone to occasional "data aberrations". I am still relying more on the Colorado data for my Dst estimates. Colorado usually gives a Dst value between 10 and 20 nT lower than Kyoto, so anything consistently above about -20nT can be regarded as an indicator of good LF propagation, or at least low excess absorption (attenuation) at night. Note that unfavourable multi-path fading can produce poor local conditions for some paths even when the Dst is high. This is particularly the case when two modes (say 2-hop and 3-hop), due to decreased absorption, are received at near the same level. In this case fading nulls can be very deep

Scott Tilley in VE7 is running a DCF39 plot, but so far whilst it is interesting to see this extreme range capture the signal is too close to the noise most of the time at present to use for daily comparisons. http://www3.telus.net/sthed/argo/

Current Report

My apologies for going AWOL for the last month. I am afraid this was due to the crashing of my main PC and my attempts to rebuild it without losing any of the files. I have now completed the job with a few stutters along the way and will now try and pick up the strands of LF propagation, which have been quite active whilst I have been in enforced dis-engagement. 

table updated....comment follows as I catch up on what is happening :-))

 

Note the table below. I have included a row for the value of Dst. This can be considered as a measure of the strength of the "Equatorial Ring Current". I believe good conditions will return about two days after this returns close to zero, anywhere above -20nT. The value given is the lowest, i.e. the most "stormy", value of the day, because I believe this is an indication of the maximum level of ions and electrons available for injection into the ionosphere. It is possible that peak values in either direction could be a measure of the transient effect of the distortion of the static geomagnetic field by a shock wave, and so may not be so pertinent to the actual content of the ring current. It is interesting to see the Dst level improving whilst the Kp index is "static" at 3, mimicking the steady return of better propagation conditions after a storm. The Dst index seems to be continually refined as more data becomes available, so expect changes for the most recent days.

Try  http://www.swpc.noaa.gov/wsa-enlil/ambient/  for an animation of the solar wind profile.

Table of Kp and Dst values in nT (Dst values in red are negative ..storm -400, quiet -20 to +30 )

March..................................................................................................................................................April
Day 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 2 3 4 5 6 7    
Kp 6 5 7 5 3 6 3 3 4 4 4 4 4 2 2 3 3 4 2 2 4 4 2 2 2 2 3 2 2          
Dst 80 50 140 75 60 60 50 55 50 60 70 55 40 40 20 40 25 25 10 8 55 60 20 10 2 30 31 33 24          

The Colorado site can be viewed at http://lasp.colorado.edu/space_weather/dsttemerin/dsttemerin.html John W1TAG suggests using the menu page http://swdcwww.kugi.kyoto-u.ac.jp/dstdir/dst1/quick.html to go to the Kyoto real-time text file page. They seem to be including the month number in the file address which would ease archiving, but will mean the URL changes every month.

The plots below are by courtesy of Scott Tilley VE7TIL. They are signal strength plots of the VOR  (Voice of Russia) BC station at about 6500km range. There are several European stations on this frequency so it is not so useful locally. The first plot is for the 26 Sept 2011 which is before the recent geomagnetic event. The second is for 27th Sept 2011 just after the event. Note an approximately 35dB drop in the signal levels. 

The following plot from Scott VE7TIL shows the received strength of the Russian BC station on 153kHz dierectly after a minor geomagnetic shock on the 9th October 2011. Compare with the upper plot for a "normal" profile. I believe the plot below shows the attenuating precipitated electrons decaying or perhaps diffusing away from the polar latitudes over a period of six hours.  

 

Dst

The Dst index (in nT) estimated value from Kyoto University, is based on a formula using Earth bound magnetometers, and correcting the result for the effect at the Equator. The Colorado University estimate mainly used here now is based on ACE Solar wind measurements, and seems less prone to wild excursions than the Kyoto data. Big negative values after a severe or major geomagnetic storm indicate a high "equatorial ring current". I believe that this is the "reservoir" which acts as the source of precipitated ions and electrons, which lead to high night-time absorption, during the (radio) recovery phase after a geomagnetic storm.  If this hypothesis is correct, good propagation conditions should occur about one or two days after the Dst value returns near to zero (Kyoto) or becomes positive. In the case of the Colorado Univ Dst estimate this corresponds to values above -20nT. Note the very good conditions around the 5th Jan 2003 correspond to "worst" values of zero (Kyoto), a condition not see again right through to the end of October 2003, but common over the period of the Solar Minimum during the last two years (2008-2009) of the cycle.

Alan Melia G3NYK in locator JO02PB
RSGB Propagation Studies Committee member

(c) A.J.Melia G3NYK 2008,2009,2010,2011

return to the main index