1916-17.] The Formation of Anticyclonic Stratus. 
137 
IX. — On some Causes of the Formation of Anticyclonic Stratus 
as observed from Aeroplanes. By Lieut. C. K. M. Douglas. 
Communicated by M. M‘Callum Fairgrieve, M.A. 
(MS. received December 9, 1916. Read January 22, 1917.) 
Typical Form of Temperature Gradient in Anticyclones. 
In a paper published elsewhere * I have summarised various observations 
of anticyclonic stratus. These observations were made from an aeroplane 
in Northern France during the year 1916, and showed that when stratus 
clouds are present and cover any considerable portion of the sky, there is a 
rise of temperature above the clouds, and further that the rise sometimes 
exists when there are no clouds, but only haze up to the level of minimum 
temperature. In both papers I include under “ stratus ” all clouds with 
approximately level tops, and into this class fall some clouds that are 
usually called strato-cumulus. 
Since writing that paper I have made further numerous observations, 
which show clearly that round the northern and eastern sides of anti- 
cyclones the temperature gradient for a few thousand feet is usually 4 C or 
5° F. per 1000 feet (8° or 9° C. per km.) ; above this adiabatic region the 
temperature gradient is low, there being usually a well-marked rise of 
temperature for 500 or 1000 feet, followed by a gradual return to a gradient 
of about 3^° F. per 1000 feet. The top of the lower adiabatic region is 
easily recognised by the top of the haze, and usually some cloud is present. 
The height of this level above the surface varies between 3000 and 6000 feet, 
and averages about 4500 feet ; it is usually greater with northerly than 
with westerly winds, and greater near the boundary of the anticyclone 
than near the centre. In my earlier paper I gave the average total rise of 
temperature above layers of haze with patches of cloud as 4° F. ; this was 
founded on numerous observations from April to July 1916, mainly with 
northerly winds. Observations from August to October showed the same 
average rise, and the rise was usually rather greater with west winds 
than with north winds. On the only occasion on which I obtained 
temperature observations above an unbroken layer of stratus there was a 
total rise of 9° F. above the clouds; this was at 6 a.m. on June 21, 1916, 
and the temperature curve is given on p. 138. 
* “ Weather Observations from an Aeroplane,” Journal of the Scottish Met. Soc., vol. xvii, 
No. 33, pp. 65-73. 
