Monday, 6 October 2014

Windermere Temperature Inversion.

Temperature inversions occur when temperatures in the troposphere (lowest portion of the earth's atmosphere) are reversed, i.e when cold air becomes overlain by warmer air.

 Spectacular inversions are especially likely to form over valleys with large bodies of water.  (Sometimes known as lake effect fog)

  Images above are taken from St. Catherine's and the Footprint Building at 8 am, October 2nd, showing a temperature/cloud inversion over Windermere, England's largest lake.

(View of the Langdale Pikes, Bow Fell, and Crinkle Crags well above the cloud base)

Temperature inversions usually occur during cold clear nights in autumn and winter.

Under these conditions heat escapes rapidly from the surface. (thermal radiation). As the  ground temperature drops the air at low level also cools becoming cold and dense. 

Conversely, air situated above the layer of air that is cooling down is now warmer and less dense, having retained more of the heat from the ground during the day.

 Water vapour condenses readily in cold air; masses of water droplets form on minute specks of dust to create low level, surface hugging clouds.  (radiation fog.) 

Cold air, on the valley's slopes, often sinks down to produce even more condensation. 

Water vapour rising up from the lake, into the cold night air, condenses into yet more water droplets and this also increases the density of the low-lying cloud or fog .

A closer view of the low cloud that has formed in the cold air. It is trapped and kept in place by the  warmer air above that acts like a barrier or a lid! This is known as an 'inversion cap'. While it is present 'atmospheric mixing' of cold and warm air is halted.

Long cold and still nights not only cause temperature inversions, they are also ideal for the formation of ground frosts.

Right in the thick of the cloud layer or radiation fog.

By 8.15 a.m heat from the rising Sun and a strengthening breeze has dispersed most of the low cloud and the ground frost has all but gone. Temperatures at the different levels are getting back to normal.

This image, taken at 8.30 a.m from the Grove Farm near Common Wood, shows the last traces of the inversion over Windermere below Claife Heights.

This image, taken at 1 pm, is an attempt to show how clear the air is after the inversion has lifted. Perhaps a better camera was needed to show the breathtaking clarity of the Langdale Pikes, but hopefully this will give some indication!

Inversions and ground frosts typically occur in autumn; the exceptional "Indian Summer" enjoyed by so many in the Lake District must be nearly over!

No comments :

Post a Comment