Wednesday 4 March 2015

The Meteorological Spring

We are now officially in spring – that's if you go by the calendar which determines the meteorological seasons. Since 1780, when the Societas Meteorologica Palatina devised the system, the seasons have been split into four groups of three complete calendar months. As the UK is in the one of the temperate zones of the Northern hemisphere spring starts on 1st March, summer begins on 1st June, the autumn months commence on 1st September and finally winter comes upon us on 1st December.
It's not the case throughout the northern hemisphere that the seasons are so strictly defined. In parts of Scandinavia the seasons are actually defined by the weather or to be more precise the temperature. In Sweden and Finland the temperature needs to be above or below a certain temperature for seven consecutive days. For example spring is deemed to have started when the daily averaged temperature rises above 0°C (we are talking about areas close to the Arctic Circle!). It is said to be summer once the temperature gets to 10°C for seven consecutive days. This system has three points to it:

1. There is never a precise date when the seasons start. A balmy week in January could kick start spring whereas in other years prolonged frost may see spring delayed until April.

2. The seasons start at different times in different parts of the country due to temperature fluctuations.

3. The change in the season has already occurred after it has been declared. In some ways this is a strange concept since we mostly try to move into seasons quicker than are happening. How many times in January have you seen a green shoot and declared it a sign of spring despite it still being officially weeks away? Magazines on sale at the end of February have a cover date of April on them. On the clothes rails in shops there are vest tops and shorts despite the fact the temperature outside is around 6°C.
Many people may be surprised that the meteorological system of ordering seasons dates so far back as the astronomical system is still commonly referred to. The astronomical seasons are based on the spring and autumn equinoxes and the summer and winter solstices. The spring or vernal equinox is when the day and night are roughly 12 hours long each. The passage of the Sun means it crosses the celestial equator going northward. It you want to catch the sun at the beginning and ending of each day it will be rising exactly due east and sets exactly due west.
Although many people think the astronomical seasons start on a certain date they are determined each year by the exact times of transit of the sun and the tropics of Cancer and Capricorn for the solstices and the times of the Sun's transit over the equator for the equinoxes. Therefore this year the start of spring will be 10.45pm on 20th March. It just so happens that there is also going to be a solar eclipse earlier on that day. I'm hoping for a clear sky!
All the photographs for this post have been taken this week. Despite the bright sunshine there has also been a few snow flurries each day and those fabled March winds. If you are feeling cold I'm afraid spring in the UK isn't known for being warm. The highest average daily temperature for the period 1st March to 31st May according to the Met Office is 9.2°C recorded in 2011. Back in 1962 the coldest spring was noted with a daily average temperature of 5.8°C. Best not think about packing away those scarves and hats yet...

Linking with School Run Colours at RamblingThrough Parenthood and How Does Your Garden Grow? at Mammasaurus.

School Run Colours
How Does Your Garden Grow

16 comments:

  1. Gah, so it's not really Spring! I feel cheated, at least a few of the bulbs are as confused as the rest of us and showing us their delightfulness!

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    1. I guess it depends on which method you want to believe in!

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  2. I am almost so far in seasonal denial that I've nearly convinced myself it's Summer! Loving the long line of daffs, it's like their trumpets herald the colours of the year ahead !

    Thanks for joining in again my jibbery jabbery chum xx

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    1. There are lines of daffodils all through the paths where I live. Thankfully no one has decided to kick them down yet!

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  3. Bril - You've just answered lots of questions I've had about the differences between meteorological and astronomical springs!

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    1. I aim to educate at least one person with my posts!

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  4. Roll on the 20th March! :) I found your information about Scandinavian seasons really interesting. Great daffodil photo, it's like a big beaming sun!

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    1. I don't know how we would cope with such a system on the UK as we're already weather obsessed already!

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  5. As Gemma said roll on 20th March!!! I can't wait for spring to arrive. Lovely pictures x #HDYGG

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    1. I definitely want a proper spring now. I'm fed up with being so cold!

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  6. Really interesting post. I think I could cope with a varying date for the start of all the season except Spring - the idea of waiting past the 1st of March for this one just doesn't compute!

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  7. Oh, I've no intention of packing those hats away yet! It still feels like winter to me, though yes, I realise March is springtime. Those daffodils look lovely x

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  8. That tree looks so pretty. And nothing says spring better than daffodils. That historical bit was quite interesting to read. Thanks for sharing with #SchoolRunColours.

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  9. That must have taken you ages to plant all those daft and well worth it too they are going to look great once they all pop their heads open

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  10. Loved this post, so interesting and I love facts and figures. I hope we get one of those warm April's that we've had in the last few years. I'm a spring baby so love this time of year.

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  11. As a child I used to think each season should arriver on a given day and there was no going back. I know that to be so wrong now. This weekend we had temperatures nudging 18ºC yet 2 years ago on March 12th temperatures plummeted to -10ºC and we had snow drifts up to a meter deep ... that was rather freakish weather though!

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