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Propagation News – 7 March 2021

We had another week of geomagnetic disturbances due to high-speed solar wind streams. Although the week started well, with a Kp index of zero to three on Sunday, it went rapidly downhill. Monday saw the Kp index hit six and Tuesday evening saw it hit five after the solar wind speed exceeded 600km per second. The strongly-negative Bz field of the solar wind meant it coupled more easily with the Earth’s magnetic field—and plasma flooded in.

It was not all bad news for HF propagation though. Earlier on Tuesday, the 17m band was open simultaneously to the Far East and the Caribbean via FT8. You were able to work both South Korea and Saint Lucia at the same time, which felt novel. This may have been a pre-auroral enhancement, but by Wednesday, with the Kp index at five, conditions had taken a hit. Maximum usable frequencies were struggling to get up above 14MHz, at least in the morning.

There has been little to talk about regarding sunspots. We’ve had two groups, 2806 and 2807, but they have been relatively small, generating a solar flux index of 74 and a sunspot number of 30 on Thursday. As such, HF propagation has generally been a little lacklustre, other than the event noted earlier.

Next week NOAA predicts the solar flux index will be in the range 70-76. We should start the week with a relatively quiet geomagnetic field and a maximum Kp index of two. But by Friday, the 12th, the Kp index is predicted to rise to four due to returning coronal hole activity.

As we head towards the spring equinox we may expect geomagnetic disturbances to increase, due to the Russell-McPherron effect. The tilt of the Earth’s axis means the Sun and Earth’s geomagnetic field and solar winds all come into alignment and therefore encourage an enhanced chance of the particles emitted from the Sun entering our atmosphere.

Fingers crossed that we have better HF conditions for the Commonwealth Contest, which takes place across next weekend, the 13th and 14th.
VHF and up:

Good to see the return of some tropospheric propagation last week. It certainly perked up the 144MHz UK Activity Contest last Tuesday evening. All is set to change in the coming week though, so make the most of any lingering tropo this weekend. The high will decline early next week, and thereafter, the week offers a succession of fast-moving weather systems crossing the country, bringing rain and, at times, strong southwesterly winds.

At the end of the week, the unsettled weather comes more from the north-west, and it will turn colder again and perhaps wintry in the north. Either way, the main terrestrial mode of interest next week to VHF/UHF operators is likely to be predominantly GHz bands rain scatter.

We are in an extended period where lowest EME path losses coincide with low Moon declination. Declination is minimum this Sunday and Monday so moon visibility windows and peak Moon elevations will be at a minimum. As we passed perigee last Tuesday, path losses will still be low but increasing.

The Gamma Normids meteor shower is just starting, peaking on Sunday, 14 March with a zenithal hourly rate of six and lasting until the 23rd. Nothing special, so pre-dawn continues to be the best time for random meteor scatter contacts. (