471 



NATURE 



[February 13, 19 19 



is diffused up by innumerable eddies 

 low >hei ts the process of mixing of 



. the 



.-in Nc 



. : cumulo-nimbus on ihe horizon ; large anvil, will] level 

 : the false cirrus in front of the sun. 5.20 p.m., Seplembe 



In the j adiabatii i"> saturated air. The majority of cloud- 

 saturated j --Inns are found under temperature "inversions," 



where the conditions are 

 mosl favourable for their 

 persistence. In a n I i- 

 cyclones large invi 

 are often found aboi i 

 the clouds, apparently 

 due i" iii' presenci 

 mass of air which slowh 

 descends ami is dynamic- 

 ally heated, but which 

 fails 10 reach the g ■ 

 For instant e, mar Ips- 

 wich 011 November 14. 

 1918, the ii mperature « as 

 iq° I . al Hi'- top of the 



11 j (1 



rose i" 1 ; I'', at 4.100 ft.. 

 In- relative humidity fall- 

 ing to 23 per cent. Ir 

 seems probable that on 

 these occasions the lower 

 air has been drawn from 

 a ■ old -.inn 1 e and thi a 



warmed at the sui fai e 

 during its passagi 

 1 elativel) « •inn si 

 there is always an adia- 

 batic lapsi -rate and a 

 ■<ood 'leal of turbulence 

 under tie- clouds, which 



n|i tin- a. 

 fn -in below . I he inver- 

 sion damps "at the tur- 

 bulenci and prevents the 

 clouds fj-om mixing « ith 



air of differenl tempera- 

 tures also plays a part, 

 the mixing being carried 

 out b\ eddies, which are 



- let mies of .1 ver; 



feeble character a n d 

 ..a el) in rceptibli 

 a e r op la n es. Edd\ 

 molion is set up by 

 frii 1 i"ii with the sur- 

 face, and usualh trans- 

 mitted i" soine i xtenl up 

 lo aboul 3000 ft., and 



sometimes In llnill ! 



sunn It ., w hen tile air is 



being healed at tile Sur- 



\t gi eater heights 



ddy motion may he di - 

 veloped throughout a 

 layei moo ft. or 2000 ft. 



thick when the lapse- 

 rati ol temperatun 

 (v or t i i a 1 temperature 

 gradient) equals the 

 adiabatii 



tlie intrusion ii .• 1 old 

 layer, a n d . t h e 

 humidity is high enough 

 clouds may form at the 

 top of the turbulent 

 layer. Sheets of rippled 

 " alto-cumulus" clouds 

 often develop in this 

 w ay. In noli r that the 

 1 louds may remain in 

 In form of a horizontal sheet, it i 

 the lapse-rate above thi m 



NO. 2 ,72, VOL. I02] 



1 mils of Fig. 1 take 



3. to pan., Septeml 



important that 

 1.1 I., low- the 



the thy air above, which would dissolve them entirely. 

 The clouds iii.n persist lone after the air has begun 



