What are the general characteristics observed in Diurnal temperature in a cloudy day, Can we distinguish it with the day with more evaporation. Just want to discuss the degree of changes observed in Temperature in both of the cases.
DTR is mostly controlled by these two factors. But it is difficult to understand them separately. Clouds decrease Tmax but can increase Tmin whereas soil moisture will tend to decrease Tmax but I don't know how much influence it has on Tmin. Tmin is complicate to understand due to its dependency on PBL development. May be we can discuss more if only temperature factor is considered.
Annu,
Here's my take on it.
During the day, the solar radiation passes through the atmosphere without being absorbed and heats the surface. The terrestrial radiation from the surface then heats the air.
Clouds block the solar radiation so they produce cooler daytime (max) temperatures.
Wet soil absorbs solar radiation and cools the surface due to the latent heat of evaporation, and so produces less terrestrial radiation.
During the night, the surface cools by emitting terrestrial radiation, but not receiving any warmth from solar radiation. The terrestrial radiation from the surface then cools the air from the base upwards. (Ground frosts then perhaps air frosts.)
Clouds emit (terrestrial) radiation at their surface temperature, keeping the surface warm. The surface temperature equals the temperature of the base of the cloud.
Wet soil releases latent heat as it freezes, so delaying the fall in surface temperature past 0C.
The production of dew will also delay the fall in surface temperature due to the release of latent heat from condensation, and it will increase soil moisture.
The delay in the fall in surface temperature will delay the cooling of the air by terrestrial radiation.
I am not sure whether the specific heat of wet soil is greater or less than dry soil but latent heat effects will exceed those of specific heat.
It is more complicated than that, but I think you will find I have got the basics correct.
Yes it is a good way of taking all the effects in combination. The observations which we get are the result of all these effects. I would be interested if someone knows any study on these topic.
There is a study on item 1 here: Working Paper "Travels in the Alps" Volume 2, Chapter 35 by H-B de Saussur...
Item 5 is mentioned in de Saussure and the science discussed here: Evans, J. and Popp, B. (1985) ‘Pictet’s experiment: The apparent radiation and reflection of cold’, American Journal of Physics, vol. 53, no. 8, pp. 737–753.
I think you should be able to find the other items in the standard literature such as:
Oke, T. R. (1987) Boundary Layer Climates, 2 edition. London; New York, Routledge. and:
McIlveen, J. F. R. (1998) Fundamentals of Weather and Climate, Cheltenham, UK, Stanley Thorne (Publishers) Ltd.
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