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.
