I was out on my afternoon walk when I noticed a cloud formation which suggested enhanced propagation on VHF. It was a still sunny day on 31 July with some "nuisance" cloud towards the horizon. A careful look revealed a dark grey band below the distant cloud level. I recognised this as a band of still air above the North Sea, which indicates that a temperature inversion may be underway.
I put an inch to my step, hurrying down Ayton Law, past the alpacas sunning themselves in the still air, and home where I had a look at 2m and above.
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| Dark grey band just above the horizon, Ayton Law, 31 July 2024 |
Click to enlarge images if necessary, as per.
The dark grey band can form over the North Sea when pressure is high. When it comes ashore it produces the effect known in Scotland as the "haar". When warm air passes over the sea a foggy layer of condensation forms also known as a "sea fret". The large bank of air can be very still and stable, but the entire bank can sometimes extend ashore producing very strange conditions. When the haar arrives near GM4FVM it can be seen pouring over the headland to the south, spreading down the slopes and into the valley of the Eye Water in which this station is located.
On shore the haar produces a damp fog which feels wet and yet can be surprisingly cold for something produced below warm air. On 31 July when I approached home I also noticed a cold wind which often arrives at about the same time. This feels like the output from an air conditioner, and circulates around the stable air system. The Scots word haar is derived from a Dutch word for cold. Inside the fog it can be quite dark as if enveloped in cloud as in an aircraft, and with the Sun blocked out also strangely cold. A short distance away, outside the cloud, it will be sunny, still and warm. Overall these can be a remarkable effects.
A large bank of still air over the North Sea is just what is required for tropospheric propagation. The tropo predictions had not been too hopeful for that day, showing a detached patch of enhancement north of me and then some more over on the Denmark coast. Not promising as tropo requires a continuous path.
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| Hepburn Tropo Chart for 18:00 on 31 July 2024. |
It seemed likely that a mass of air had formed over the North Sea and this was allowing propagation. The QSOs showed two distinct paths, one to the east to to SM and OZ, and one to the south east to DL and PA.
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| 144MHz contacts at GM4FVM on 31 July 2024 |
Conditions on 144MHz have been pretty awful this year, reflecting the lack of these very conditions. So it was very agreeable to be able to work 15 stations across the North Sea, and the best DX to SM7KMJ in JO66 at 947km was pretty good.
On 70cm I worked across the North Sea to OZ2ND and PA3CWS both of whom I also worked on 2m. I saw nothing on 23cm, despite trying hard.
Haar coming ashore is fairly rare round here. This time it did not arrive on shore, well not as far inland as GM4FVM anyway. However, seeing it in the distance and feeling that cold wind on an otherwise warm day put me on alert.
Now two days later the pressure has fallen and the usual strong winds associated with a weather system coming from the West have returned. There is no possibility of still enough air over the North Sea to hold a bank of air, and the warm weather has gone. VHF conditions have returned to their usual sleep. Even the alpacas are sheltering under the trees today.
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| Alpacas sheltering on Ayton Law, 2 August 2024. |
Most propagation enhancements arrive silently and invisibly. Actually seeing one was a bit of a surprise.
73 Jim
GM4FVM
Hello Jim, very nice article. Especially about haar. Never heard of it before so I had to look it up on wikipedia. < A HREF="https://en.wikipedia.org/wiki/Haar_%28fog%29">https://en.wikipedia.org/wiki/Haar_%28fog%29. And was of course trying to find the dutch word or at least which word it was derrived from. Unfortunately that Dutch word doesn't exist anymore. Haar is derrived from an "middle" dutch (medieval) word "Haren". Languages change over the years it seems ;-). Haren would now mean hair and has nothing to do with cold. Anyway the relation with tropo is interesting. 73, Bas
ReplyDeleteBas, thanks. The village between me and the sea is called "Flemington". This because many years it was lived in by Flemish people (called Flemings here) who settled here. It is said that they built houses and brought us the red pan-tile roof which we have in this area. Mrs FVM is from Newcastle and she had Danish and Norwegian school friends. She can still understand some of these languages. It is not just high pressure we get from across the North Sea! Best wishes. 73, Jim
ReplyDeleteThe caption on the 1st picture says "31 June 2024" which I guess is a typo? :-)
ReplyDeleteDave - typo makes it sound like nobody got it wrong. No, I got it wrong. Thanks for pointing that out. I will correct it to July. I was there at the time and there was no 31 June that I recall. 73 Jim
ReplyDeleteGreat article Jim, I am surprised the Haar doesn't come inland where you are as we get it all too much, sometimes for days. When we are socked in at EGPH we are through it by about 500ft and you can see it coming up the Forth. As you say it doesn't venture far inland.
ReplyDeleteRegarding the red pan tiles I was told we have them because when ships went across the sea carrying coal they were heavy and when unloaded needed ballast so the tiles wouldn't spoil so were caried back and gave the needed ballast. Anyway I like them, a lot! Makes the house more interesting.
I think perhaps the haar rarely comes ashore here because of the cliffs at St Abbs and Burnmouth. This may produce a bit of a barrier. When we do see it, it often pours over the headland from the East like custard being poured over a pudding. It comes over the hills and runs down the slope into the valley.
ReplyDeleteI recall when I lived in East Lothian and worked in Edinburgh about 30 years ago. I left home one morning and approached Edinburgh in wam sunshine. In the office the building was then surrounded in dark grey haar. After about an hour I went down to the car to get something and I could not get in. The locks were frozen and the windscreen covered in ice. After a lot of work I get the key into the door but the door was frozen too. After an hour or two the haar cleared and the warm day returned. It must be crazy to view from an aircraft.
73 Jim