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When does sun evaporation stop in the uk?


zaax

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Posted
  • Location: Trimley St Martin
  • Location: Trimley St Martin
Sometime in the autumn the sun is so low that evaporation by the sun stops in the uk.

When is this date?
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Posted
  • Location: Canmore, AB 4296ft|North Kent 350ft|Killearn 330ft
  • Location: Canmore, AB 4296ft|North Kent 350ft|Killearn 330ft

I would have thought it would continue all year? As water can evaporate in warmer or colder conditions, otherwise puddles wouldn’t dry up lol. 

Plus sublimation occurs during winter when snow evaporates. Slightly different though as thats a solid to gas rather than liquid to gas. 

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Posted
  • Location: Sheffield
  • Weather Preferences: Sunny and dry, thunderstorms, mild temps (13-22°C).
  • Location: Sheffield

Seems like around this time of year. Ground is almost perma-damp til about late March most years.

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Posted
  • Location: Swindon
  • Location: Swindon

It isn't possible to seperate out temperature, wind, sunshine and humidity. When talking about pure evaporation off a surface, all these factors will play a part, as will the surface itself. On a winter's day with the sun out, we can expect the pavement to be dry where the sun shines, but on long grass, it'll be wet all day.

 

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Posted
  • Location: Dorset
  • Weather Preferences: warehamwx.co.uk
  • Location: Dorset

It depends on what the OP is directly asking.. Evaporation in the meteorological sense doesn't stop, it's called the water cycle.

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Posted
  • Location: Swindon
  • Location: Swindon
7 minutes ago, Mapantz said:

It depends on what the OP is directly asking.. Evaporation in the meteorological sense doesn't stop, it's called the water cycle.

Evapotranspiration isn't in the original question, but of course is a vital part of the equation also. 

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Posted
  • Location: Dorset
  • Weather Preferences: warehamwx.co.uk
  • Location: Dorset
3 minutes ago, richie3846 said:

Evapotranspiration isn't in the original question, but of course is a vital part of the equation also. 

Talking of which, since recording evapotranspiration on my station, I have never recorded zero.

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Posted
  • Location: Swindon
  • Location: Swindon
4 minutes ago, Mapantz said:

Talking of which, since recording evapotranspiration on my station, I have never recorded zero.

That is really interesting because I assumed that on a day in January with freezing fog all day and temps of -1, it would be zero

Edited by richie3846
Typo
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Posted
  • Location: Woodchurch, Kent.
  • Weather Preferences: Storm, drizzle
  • Location: Woodchurch, Kent.
10 hours ago, zaax said:

Sometime in the autumn the sun is so low that evaporation by the sun stops in the uk.

When is this date?

It's the energy technically that causes the evaporation, hotter substances have more energy so will evaporate easier than colder substances but unless they are absolute freezing they still have some some energy and sublimation can still occur.

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Posted
  • Location: Dorset
  • Weather Preferences: warehamwx.co.uk
  • Location: Dorset
11 minutes ago, richie3846 said:

That is really interesting because I assumed that on a day in January with freezing fog all day and temps of -1, it would be zero

Ice days are pretty rare here, with the last one on January 7th 2021. No sunshine recorded, not sure about fog, but still managed 0.2mm.

I haven't looked at my evap data for a long time, but just noticed it is at 768.73mm for the year. While my rainfall total is 488.6mm. You can certainly see why water sources got very low.

Edited by Mapantz
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Posted
  • Location: Swindon
  • Location: Swindon
13 minutes ago, Mapantz said:

Ice days are pretty rare here, with the last one on January 7th 2021. No sunshine recorded, not sure about fog, but still managed 0.2mm.

I haven't looked at my evap data for a long time, but just noticed it is at 768.73mm for the year. While my rainfall total is 488.6mm. You can certainly see why water sources got very low.

Yes I've been trying to make sense of all this, in this drought year. What I've observed 'on the ground' is that trees suck the moisture out of the ground more severely then grass. This can be observed by dead grass near trees (even with reasonable light levels) and sunken clay soils where trees grow. My observations suggest that evapotranspiration calculations are highly subjective and not very accurate.

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Posted
  • Location: Arnside ,where people go to die 9000m Asl
  • Weather Preferences: All weather
  • Location: Arnside ,where people go to die 9000m Asl

It doesn’t reduced yes 

 

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  • 1 year later...
Posted
  • Location: Coventry, 96m asl
  • Weather Preferences: Snow in winter, thunderstorms, warmth, sun any time!
  • Location: Coventry, 96m asl
On 21/10/2022 at 13:22, zaax said:

Sometime in the autumn the sun is so low that evaporation by the sun stops in the uk.

When is this date?

 

As others have said in here, in the UK it never stops, you still see roads, roofs, cars etc dry up even in the middle of winter as long as there is a drier, colder airmass and a breeze there will still be some evaporation albeit a lot less than in spring / summer of course. It's part of the water cycle. We also don't have the polar night, so the sun plays a role all year round, and can dry up various surfaces. This month there was some decent evaporation rates due to at times some quite low humidity values for mid winter during the easterly / northerly snap.

 

But the more appropriate question would be is "When does evaporation become strong enough to make soils dry for the first time in a given year and also weak enough to stop soils from becoming dry until the following year?"

To answer that from what i've seen in the last several years is, it's between the end of March to early October when the soil can dry out. The sun is usually strong enough by late March but the temperatures are not warm enough for a long enough duration for soils to dry up that much apart from exposed sunny spots. Usually in April there is enough warmth and dryness for it to start to become drier easily and quicker. April 2020 is a great example, but also 2021 as the humidity at times was extremely low following some warmth at the end of March 2021 and the April was very sunny.

The earliest i've seen it however was in 2022 by late March. The second half of that month was virtually rainless, and quite a few days temperatures were getting into the mid to high teens with plenty of sunshine. As a result the soil started to dry out in areas with a lot of sunlight.

The latest i've seen soils first become dry in the spring was last year, it took until Mid May as most of the spring was just wet, and there was no real warmth or extended dry spell until mid May.

In terms of when soils stop drying out, that tends to be late September / early October, as even though it's still not cold, and can even been quite warm such as last year, the sun is losing a lot of strength and daylength becomes quite short so evaporation rates lowers. Octobers recently have also been washouts as well.

Early October last year was quite warm and fairly dry until the 11th, so soils were about as dry as i've seen them in early October (though still not that dry ) before the deluge came by the 10th-11th, and soils were soaked from then. September had a fair amount of rain with not much in the way of anything drier from the second half. Late September 2020 and 2021 I remember it being quite dry following a lot of warmth and not much rain until the final few days.

It defintely varies from year to year, but I think the date when soils can become dry is becoming earlier, and the overall "dry soil season" is extending as the years become warmer. Although it may not always be the case in very wet years or specifically wet springs like 2023.

 

 

Edited by Metwatch
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