Sun Strength Relevance To Seasonal Cold Spells

[leicsnow]

I was recently involved in some somewhat off-topic discussion on another topic, and I thought I'd start one on it here!

Anyway, we were talking about 'sun strength' and how it affects the likelihood of a seasonal cold spell.

We established that November and January are almost identical in terms of sun strength as looking at statistics they have the same length days in a given place in the UK, rather than February having a weaker sun than November as it is considered Winter and November is considered Autumn.

I then clocked that October and February have the same length days, but I'm sure you know as well as I that you are much more likely to experience a cold snap in Feb in the UK than Oct.

So what makes February, on average, more cold than October, if they have the same length days? Same with September and March really.

I know this may sound like a stupid question but I have only recently developed an interest in weather.

Edited November 26, 2011 by torrch

[Cheshire Freeze]

February is colder than October because there is a solar heating lag effect. In October, after months of strong solar heating, the land and seas have more latent energy contained within them than February which comes months after the peak of solar heating in June and July the previous year.

Late January is when cold pooling reaches its peak ~ a month after the time of lowest solar heating (December 21st/22nd), this is also due to lag effect. Therefore you are more likely to see cold in Feb than Oct. I must also point out that sea surface temperatures are at their lowest around March. This is because the physical composition of water allows a slower release of latent heat than a land mass (hence why you can acheive frosts in September and October).

Edited November 26, 2011 by CreweCold

[Summer Sun]

This is for London

21 Nov 2011 - 07:28 - 16:04 - 8h 36m 17s

21 Jan 2012 - 07:54 - 16:30 - 8h 35m 22s

21 Feb 2012 - 07:04 - 17:25 - 10h 21m 31s

And for me in the North East it is like this

21 Nov 2011 - 07:46 - 15:55 - 8h 09m 31s

21 Jan 2012 - 08:12 - 16:21 - 8h 08m 28s

21 Feb 2012 - 07:14 - 17:24 - 10h 09m 12s

[leicsnow]

February is colder than October because there is a solar heating lag effect. In October, after months of strong solar heating, the land and seas have more latent energy contained within them than February which comes months after the peak of solar heating in June and July the previous year.

Late January is when cold pooling reaches its peak ~ a month after the time of lowest solar heating (December 21st/22nd), this is also due to lag effect. Therefore you are more likely to see cold in Feb than Oct. I must also point out that sea surface temperatures are at their lowest around March. This is because the physical composition of water allows a slower release of latent heat than a land mass (hence why you can acheive frosts in September and October).

I suppose that explains why each season is a month on from what it should be. It should be winter November to January, spring February to April, Summer May to July, Autumn August to October. But for the reasons you stated it's winter December to February, spring March to May, summer June to August, autumn September to November.

Thanks for the answer.

[Isolated Frost]

-solar lag (which makes 21 jan much colder than 21 dec)

-colder sea temps (at their height during oct, and their lowest in march)

-atlantic (very dominant and strong in oct, usually much weaker in feb)

[Bottesford]

Thermal lag is the basic answer as others have stated.

I always like to explain it to people in terms of boiling a saucepan of water on a stove (electrical hot plate type).

You put cold water in - the water is cold and is not getting warmer. This is winter.

You now turn the power up one notch at a time - energy begins slowly flowing into the water but still the water is cold (early spring - a month like Feb)

Turn up the stove higher and the water starts warming ever faster (April-May)

Stove is now at full power and eventually the water boils (June-July).

Now turn the stove down & down - the water stops boiling but is still hot (August into September)

The water remains warm for a good while but slowly cools as you keep notching the power down and down to off.

Eventually the water cools right down we're in winter.

[leicsnow]

I think we can actually measure the 'sun strength' for the different months in UV Index. Does any one know what sort of UV Index it is in February and November, etc?

[damianslaw]

Yes thermal lag is the key reason - the land takes a long time to heat up after the cold of Dec and Jan, whereas in october it is only very slowly cooling down. The european landmass is at its coldest in Feb, ground temps are also at there coldest. Easterlies tend to be at there coldest in Feb. October on average is milder than April proving how long it takes for the land and sea to heat up after the winter cold.

Indeed May can easily be colder than October as we have seen in quite a number of cases.. May 96 notably so.

[Gavin Hannah]

I don't think there is any solid data around that can highlight the links between sun strength and winter weather. (I may be wrong on that). However, even as we are approaching a solar maximum, I believe the actual solar output is way down on a typical solar maximum, but still a bit higher than last winter and far higher than 09/10.

[leicsnow]

Has anyone else noticed that in early Spring, it can get rather balmy on sunny days but when this happens, the temperature often drops heavily over night (and sometimes we get a frost). Meanwhile, in late Autumn, the temperature sometimes doesn't drop much overnight and the sun has little impact during the day.

[Kentish Kiwi]

Has anyone else noticed that in early Spring, it can get rather balmy on sunny days but when this happens, the temperature often drops heavily over night (and sometimes we get a frost). Meanwhile, in late Autumn, the temperature sometimes doesn't drop much overnight and the sun has little impact during the day.

Once again a result of the latent heat held by the land and sea and the residule cold after the winter.

[leicsnow]

Since starting this topic I have been thinking a lot and I think generally the suns increasing strength doesn't starting wielding it's axe until around the last third of February, and even February 1986 saw sub-freezing days in the last third.