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Propagation News – 13 December 2015

This has been another week with an elevated solar wind stream from coronal holes. This had a negative effect on the geomagnetic field, which reached storm levels at times again with visible aurora at higher latitudes. The solar wind often had a south-facing magnetic Bz component, which meant it coupled more easily with the earth’s magnetic field. The solar flux index stayed around the 110 mark, but the geomagnetic Kp-index hit four, and even five at times, reflecting the storm conditions.
The Chilton ionosonde at Harwell showed a critical frequency of 7.8MHz at noon on Wednesday, indicating a maximum usable frequency of around 26MHz over a 3,000km path. This also showed that 40m was usable for inter-G contacts, at least around the late morning and early afternoon periods. Fifteen metres, 21MHz, remains the highest HF band to support reliable long distance communications.
Next week should see the solar flux index in the range 100-120. The Kp-index may indicate continued unsettled geomagnetic conditions, hitting four at times. The end of the week is likely to be more settled.
December remains a great month to get on the lower bands, including 160m, 80m and 40m, where DX may be found during the long nights.
VHF and up propagation news:
This week expect neutral tropospheric conditions at first, but we are starting to see some signs of a ridge of high pressure developing close to the south-east of England during the week.
This might give slight help for tropo paths into the continent and across the North Sea into southern Scandinavia. Unfortunately, this is not supported in all models, as some keep low pressure over the country through the whole week.
In these changeable patterns, the forecast models often diverge after a few days and since this is being written early, it is perhaps not surprising that there are variations beyond the following midweek.
Meteor activity is on the agenda again with a fairly broad peak of the Geminid shower centred on Monday night, 14 December. Look up the band plan and operating techniques, or simply listen in and watch the ON4KST chat to hear what goes on during these events. Try six, four and two metres.
Moon declination starts to increase again this week, so moon windows will lengthen and, after yesterday’s apogee, losses will start to decrease. From the UK the moon will be up from lunchtime to early evening, getting progressively later as the week goes on.

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