Well, no one predicted last week’s geomagnetic disturbance. In case you missed it, the Kp index rose to four on Monday the 11th January. This was caused by the arrival of an interplanetary shock wave from a coronal mass ejection on the Sun, which occurred on Thursday the 7th. NOAA had been predicting a settled Sun, which shows just how unpredictable our nearest star can be.
The CME’s effects on the ionosphere were quite startling. The Chilton Digisonde data, as plotted at propquest.co.uk, shows that the predicted MUF over a 3,000km path dropped to below 14MHz by 1530UTC, although it did recover to more than 18MHz within an hour. That night there were widespread reports of visible aurora, but the ionosphere had recovered by Tuesday afternoon with the Kp index back to one by 1500UTC. Other than that element of ionospheric excitement there has been little to report, with the solar flux index down as low as 72 by Thursday the 14th with zero sunspots. The only other noteworthy event has been widespread winter Sporadic-E, which saw 12, 10 and six metres become wide open to Europe this the week.
Next week, NOAA predicts that the solar flux index will remain in the mid to high 70s. The STEREO spacecraft show a coronal hole is about to rotate into view around the Sun’s eastern limb. The high-speed solar wind from this, and other polar coronal holes, may cause the Kp index to rise to four by Sunday the 17th and we may not see recovery back down to two until the 21st. So it looks like the latter half of the week may be best for HF DX.
VHF and up:
The current unsettled spell of weather should have taken a brief pause on Friday, but may have returned this weekend, with an active front crossing the country, followed by a transient ridge in the second half of the weekend. These ridges are rarely good for widespread Tropo and the unsettled regime returns for the bulk of the coming week. Strangely enough, you can find temporary enhancements of Tropo conditions parallel to, and just ahead of, approaching weather fronts. It’s marginal, but can make a difference to scores in the VHF/UHF UK Activity Contests. But GHz band rain scatter is probably a more reliable mode for the next week.
The unsettled story also implies some strong jet stream activity, so it’s still worth a look at the usual Sporadic-E bands of 10m and 6m for one more week, although this is probably our last chance before the mode returns in force in April.
Moon declination turns positive again on Tuesday, so we’ll have increasing Moon windows and peak Moon elevations this week. With apogee on Thursday though, path losses will be high. This trend of high declination and path loss only starts to reverse from May 2022, so get used to it! 144MHz sky noise is low.
There are no significant meteor showers this week so continue to check pre-dawn for the best random meteor contacts.
And that’s all from the propagation team this week. (rsgb.org)
