Latest Propagation Report dated 7th 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

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). Geomagnetic activity continued at quiet through the last three days, with the Dst index hovering between -5 and -10nT. Steve's plots though running again are suspect on absolute level (note the level change on the interference). The Solar X-ray flux took a bit of jump as two new-cycle sum-spots appeared round the rim of the visible disc. These produced a flurry of low level radiation culminating in a Class-C1.7 flare at about 0710z this morning (5th) This would not normally rate a mention but for the fact it is the biggest flare seen in nearly 18months (from memory). I do not expect too much geomagnetic activity in a couple of days time when any associated CME would arrive. The spot is probably not "geoeffective" yet. Thus I expect LF and MF night-time DX propagation conditions to remain good to very good, into the first half of the week. Geomagnetic activity remains quiet (7th), and so LF and MF propagation conditions should remain good to very good.

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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