Fog and sunshine

[PaulMy]

We've had a few heavy fog mornings recently and after uploading to a new weather service where I have both Solar and sunshine hrs shown I was surprised to see the sunshine being recorder when the fog was as thick as I've ever seen it. At 8:00 am it recorded 0.4 hrs sunshine. Still somewhat foggy at the moment but at least can see the house across the street now, and 0.6 hrs sunshine. I have the Davis Plus with solar. Can it see/sense the sunshine through thick fog?

Enjoy,
Paul

[freddie]

Yes, it will sense solar through fog. You will have configured a threshold value to start recording sunshine, and that value would've been reached. Typically if you have fog that is thick horizontally then it tends to be fairly shallow vertically, with the concentration of water droplets at a maximum close to the ground and thinning with height. This enables some solar through (but not necessarily visible sunshine) due to the thinning of droplet concentration with height. In a mature fog, horizontal visibility becomes greater and the vertical thickness of the fog layer increases as convective overturning starts to happen. This results in a more even distribution of water droplets with height. When this happens, the likelihood of recording anything with your sensor decreases.

So to me it sounds like you experienced a non-mature fog with greatest droplet concentration near the ground giving very low visibility, but allowing some solar energy to reach your sensor due to the reduction of droplet density with height.

[mcrossley]

Plus our solar sensors are measuring total diffuse horizonal irradiation and try and determine sunshine by comparing that with a computed value.

It may be that you need to increase the threshold value a bit, but as @freddie says, it can still be fairly bright in fog.

A true sunshine detector would only measure direct irradiation - I keep toying with the idea of building one but never seem to get around to it!

Another alternative would be a sensor that measures both global diffuse and shadowed diffuse and comapres the two. Simpler to build in many ways as it does not need a tracker, just a bunch of sensors arranged around a sturdy pole and compare the highest and lowest readings.

[PaulMy]

Thanks for the info freddie and Mark. I had just never looked at it in the same way in the past. Now that the fog has cleared and mostly sunny, I am ready to complain that it is not recording enough - at only 0.67 hrs so far
If I still had by B-L I would have another compare but gave that to another user about 5 years when we moved to a new house and my wife wouldn't let me drill holes

Enjoy,
Paul

[access-mdb]

When I was at Kew Observatory in the late 60s, we had a number of different solarimters. The diffuse one had a ring which threw a shadow onto the sensor. This had to be raised and lowered as the sun changed its height through the year. We also had a Gorzinski Normal Incidence meter, photo attached. That went round onceevery 24 hours, so we had to unwind the signal cable - it was also clockwork IIRC. We also had to readjust for the seasonal changes. After a long cloudy period one of us had to run up to the roof to adjust it! Oh, and we also had a Campbell-Stokes sunshine recorder, seen behind it.

[mcrossley]

I like how the tracker uses stacked discs rather than a tube. I guess that was done to make it easier to manually adjust it.

[access-mdb]

It was old in 1966 when I first went there. I've no idea who Gorzinski was or when this was made. Kew Obserbatory had a number of people whose job was to develop new tech for weather observations. For expample, surrounds to different 5" rain guages, a gravimetric rain gauge (it weighed the rain!). An aspirated dry and wet bulb screen with electronic thermometers which we gave us a readout in the building and so much more. All the men who did this were old (but I was young then so perhaps not so old). The photo was taken when I was on detachment there, I left in 1969 to go Heathrow Met Office.

[HansR]

It was old in 1966 when I first went there. I've no idea who Gorzinski was or when this was made. Kew Obserbatory had a number of people whose job was to develop new tech for weather observations. For expample, surrounds to different 5" rain guages, a gravimetric rain gauge (it weighed the rain!). An aspirated dry and wet bulb screen with electronic thermometers which we gave us a readout in the building and so much more. All the men who did this were old (but I was young then so perhaps not so old). The photo was taken when I was on detachment there, I left in 1969 to go Heathrow Met Office.

Haha... so now You are old
Nice pieces of history btw

[De Hout]

I've no idea who Gorzinski was or when this was made.

At this weblink you'll find some info: https://www.kippzonen.com/News/572/The- ... yranometer

[access-mdb]

At this weblink you'll find some info: https://www.kippzonen.com/News/572/The- ... yranometer

Thanks that's interesting. We had a Polish scientist working with us at the Observatory, unfortunately I don't remember his name (a function of great age). I think his first name was Jan, so maybe that's the connection. Attached is a photo of most of the staff at the observatory - Jan is the one on the left. I'm pretty obvious (so young) and the lady next to me is my now wife. The window bewteen my wife and the man on the right hand end is the famous north wall, with its screen. I wish I had taken photos of it. It was a photo thermograph - we also had a photo barograph and a photo seismograph as well.

P0078.jpg