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Propagation News – 17 February 2019

We had another spotless week as the Sun continued its decline into solar minimum. Geomagnetic conditions were varied with the beginning of week seeing the Kp index hitting one and two. But this didn’t last due to ongoing coronal hole activity, which saw the Kp index climb to three and four by Wednesday, the 13th, and Thursday, the 14th.

To recap, coronal holes are lower energy areas on the Sun with open magnetic field lines. This allows the solar wind to flow out towards Earth. If the plasma’s ‘frozen in’ or embedded magnetic field has a south-facing component it is more likely to couple with the Earth’s, allowing the charged particles to enter the magnetotail. A magnetic recombination event can then see them accelerated back to the Earth’s magnetic poles, resulting in auroral displays and depressed maximum useable frequencies.

Coronal holes appear dark when the Sun is photographed in extreme ultraviolet light. Look for the images marked AIA 211 from the Solar Dynamics Observatory (SDO) at solarham.com.

Next week NOAA predicts a solar flux index of around 72 with unsettled geomagnetic conditions around the 18th, 20th and 21st, due to yet more coronal hole activity.

propquest.co.uk shows that the unsettled geomagnetic conditions can impact the critical frequency, which was topping out at around 4.5 to 5MHz during daylight at times. This means that 60 metres or the 5MHz band may struggle a little with NVIS, or near-local, signals.

Eighty metres may also struggle with close-in signals after dark as the critical frequency struggles around the 3-3.5MHz mark. The good news is that this should improve as the month moves on, which will no doubt be welcomed by participants taking part in the RSGB 80m Club Championships.

VHF and up:
The Es’hailSat 2 transponders have gone live and the 10GHz narrow-band downlink is at least as strong as expected using a satellite LNB and a 60cm dish. The 2.4GHz uplink is really sensitive with easy access via a second feed on the same dish, a small Yagi or patch antenna and a few Watts. More in the main news about this.

Back on Earth, the large high has done well with enhanced tropo conditions during last week, and although the theme of high pressure continues into next week there is one subtle difference—it’s simply where the air over the country is coming from.

Recent air flow has been from the Atlantic down to the south-west of the British Isles, and as a result, it contains plenty of moisture. This means more cloud than is ideal, but the moist layer of cloud provides a great contrast to the dry air above the temperature inversion at the top of the cloud layer. This is what gives the tropo conditions, since moisture is a big player in the value of the refractive index of the air and changes of the index are what produces the ducting.

As we move into next week, the flow of air round the high is coming from across the continent, so it will be drier and therefore may not be so useful for maintaining tropo. At the very least, we should expect tropo conditions to be more variable, despite the high pressure remaining in control.

Moon declination peaked yesterday and with perigee tomorrow it’s another good week for EME. Peak Moon elevation is around midnight, moving into the early hours as the week progresses.

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