August 2014 radiative cooling East Anglia, Northern Ireland, South Midlands
August 2014 there was a meteorological gift of both exceptional conditions and good data. What can be learnt?
Three Met Office sites showed a signature of exponential cooling. This requires clear sky and a calm. Given somewhat limited parameter hourly data the following shows the commonality. The computed terminal conditions are shown later in this article.
Benson and Santon Downham data has been normalised to Katesbridge, which has the least noisy data or the three.
Achieving a close overlay requires taking earth rotation into account, dusk and dawn move relatively both by geographic location and the peculiar movement throughout the year as night length changes, these do not move together . Fractional delay (less that the sample period) was used to equalize diurnal time. (see the two blog articles here)
Dusk appears to be the important factor, a surprising finding, I assume cooling is time from dusk, dawn terminates cooling.
General information, under essentially calm conditions wind drops for a period during the night then reappears just after dawn. (not shown here)
Temperature normalisation defined is for the cold period, not as accurate for Benson where the better site exposure (more open) led to more wind at times.
Lapse rate reduces Katesbridge by about 0.5C relative to Santon Downham which is close to sea level. Normalisation will include this in compensation. (91m vs. 6m)
I expected dawn to be the arbiter of time shift but I found a larger shift. Initially my reaction was site solar exposure at low angles: Katesbridge is surround by low hills; Newton Downham is effectively a large clearing in a forest. I know the Benson site and that is not far off the middle of an RAF base, very open even though urban housing is encroaching.
Benson tipped my thoughts. The time seems to follow time from sunset. More data is needed before this is a clear matter, a large work, would need automating.
Benson is a fairly complete Met Office site, the other two are minor.
Here we can see there is a certain amount of wind and how it affects the temperature. Visibility reduces as it gets cold, lot of humidity limiting cooling. Humidity sensors are notoriously very poor, one of the most difficult to measure parameters, Benson one is fairly good but will be slow responding. (dew point is shown)
This site includes “weather” information. Benson is a manned RAF, Police rotary wing base (possibly air ambulance too), so the weather data might be human logged.
Above from all station PDF created from Met Office Datapoint service under OGL 
Given no wind there is a common cooling profile between met stations. This has been shown from real data, not theory.
Terminal state and radiative figures
Katesbridge data is fairly clean so a good exponential match was possible, therefore a fair guess at the terminal temperature if dawn was delayed. There is a “flat” on the data at 0.0C. This together with another outlier were removed for law match purposes.
For over a year I have been collecting high resolution data from the Chilbolton Observatory, Hampshire . This includes pyranometer (short wave including visible) and pyrgeometer (longer wave) instruments. More recently full duplex instruments data became available, currently used to sanity check the earlier, which it does.
By visual inspection of the hundreds of day plots the radiation values for the kind of climate we have and under high humidity clear sky conditions at the temperatures involved here allowed me to place a guess on the outgoing radiative loss.
An example day which contains a variety of factors. Was a frost, probably melts leading to the rain gauge tip (one at 12 hours is normal). Essentially calm during the night, dawn flat calm, odd time of day. Pressure was falling, cloud and water was moving in through the day. Plot labelled IR shows the two figures, with the difference the heat lost by radiation, see net_IR_out, a computed figure.
The same exercise was done for Santon Downham and Benson (on raw data, not normalised)
The data is noisier, outliers were removed.
Benson data is somewhat noisy but wind data is available. I suspect the terminal should be a little lower.
Given suitable meteorological conditions estimates of final cooling and outgoing long wave is feasible. Whether this is useful is moot.
More useful is showing the commonality between significantly different sites.
Sounds like Sandtown might be an origin
The soil is light sand, and in 1688 in consequence of the sand being blown by continuous high winds from the hills of Lakenheath (distant 5 miles south-west), several houses were buried and destroyed. The river was choked up. One farmer of the period; named Wright, had all the approaches to his residence so blocked up that in order to reach it he had to pass over a wall eight feet high. The sand at one time filled his yard and reached to the edges of his roof.
Sandy soils seem to lead to a higher diurnal temperature range, Santon Downton appearing often in UK maximum and minimum figures, probably more often regionally. (I don’t collect them)
Norwich Airport is another with a light soil and that too is warm.
Quoted has a clue for this station, the former RAF / USAF Lakenheath is close by.
1. The Solex ephemeris program was used here to find the time of dusk and dawn for a particular geographic location.