Latest Propagation Report dated 2nd July 2009

The text below is a rolling forecast and report of long distance 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 abberations". I am still relying more on the Colorado data for my 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. 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. Then fading nulls can be very deep

Geomagnetic activity returned yesterday (24th) with one period at Kp=4 and one at Kp=5, but the Dst has shown little signs of dipping. The KP is back to 2 again this morning (25th) but NOAA forecast some further activity today returning to "quiet" by tomorrow. I would think that this event will have little effect on night-time LF and MF DX propagation. The problem so close to the Solstice is that the "all darkness" period on most Northern Hemisphere paths is very limited, so there is little time for signal levels to build and fading to settle into a favourable state. For our new "members" in Australia conditions should be better, in time to celebrate their granting of access to 136kHz!! Get going quickly you Oz's these are the best conditions you will probably see for another 11 years !! I am hoping we will hear you around the Equinox!! My apologies for depriving you of reports for the passed few days I have been disincentivised by the sudden seizure of the Colorado Dst data again, and with Steve's path being almost all daylight I didnt feel I had much to say. Now the back data is available for Dst, I can summarise the events of the last five days. Everything continued quiet up until the 27th when a rather mild geomagnetic "storm" occured. It is almost too mild to call a storm for the Kp index only reached 4 in three separated four hour periods. Nevertheless after an intensly quiet period where the Colorado Dst estimate has hovered around zero for days on end, this event drove the Dst down to about -38nT just after midnight on the 28/29th. This is the lowest we have seen for many months. After the initial shock the Dst returned rapidly during the day to stand around -11nT this morning (30th). I expect that some paths will have seen a drop in night time signl levels but this should not have been too dramatic and I expect the conditions to be back to what we have been experiencing by the middle of the week. Up until Wednesday there is the possibility of further disturbance from the coronal hole event and it is possible this may add to the remenants of the 28th event giving rather greater depression in signals levels over longer night-time paths. All should return to quiet by the 2nd. I do not expect dramatic reduction in long distance signals, so I still rate LF and MF propagation conditions as good. As expected the geomagnetic activity has returned to quiet (2nd) and the Dst is up to -7nT again. Steve's plots of DCF39 and HGA22 have stalled again, though the path has a very short all darkness period at present so is not that useful for gauging expected signal strenths. I believe that LF and MF propagation should be back to good to very good again. I note that Warren' part 5 beacon WD2XGJ on 137.778kHz has been received well in QRSS in Europe over the last few days (thanks Jean-Pierre, Lubos and Henny).

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.

Table of Kp and Dst values in nT (Dst values in red are negative ..storm -400, quiet -10 to +30 )

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.

W3EEE Plot of DCF39 & HGA22 (at locator FN10sg)

The red box shows the normal levels experienced from DCF39 (Magdeburg) over a few very good nights in mid-January 2006 as a benchmark to compare with the recorded value for last night.(check the date/time on the axis). This is a path of about 6500km, passing through the English-Scottish border, the northern tip of Newfoundland, and skirting Boston. The most northerly lattitude is 56.5 degrees so it is usually well south of the auroral circle. This long path is very sensitive to increases in absorption because it makes three excursions through the ionosphere. Steve's web pages are at http://www.w3eee.com/ . The "darkness path" window is short in summer so the rise and fall of the signal draws in away from the winter template. Steve will disconnect when threatened by local thunderstorms. The HGA22 trace is from Lakihegy (Budpast) which is slightly fiurther away from Steve, but a very similar path.

Click here for an archive of the last 4 days of DCF39 and HGA22 plots from W3EEE in Mount Gretna, Pennsylvania, USA

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 that 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. I still believe that there is about a 2 day diffusion time ( dependent on latitude) from the injection point at high latitudes to the position of mid latitude path. If this hypothesis is correct, good propagation conditions should occur about two days after the Dst value returns near to zero 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.

Alan Melia G3NYK in locator JO02PB

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

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