970 



EXPERIMENT STATION RECORD. 



METEOROLOGY. 



New cloud classifications/ A. McAdle {Phil. 8oc. WasMngfon, 

 Bill., vol. 13, pp. 77-86). — The history of cloud classiflcatiou is briefly- 

 reviewed, and the system of Howard, proposed in 1802 and generally 

 adopted until within a comparatively recent period, and that of Hilde- 

 brande, Abercromby, and Koppen, as modified and recommended by 

 the International Meteorological Conference at TJpsala in 1894, are 

 e-^plained and criticised, as well as those of Davis and Ley. The first 

 is unsatisfactory in " that, being based purely on appearance, no account 

 is taken of the origin and manner of formation of the cloud." 



"Clouds of very dissimilar origin va^j have a similar appearance. Modern 

 meteorology demands more than a record of the appearance of the cloud. It seeks 

 the meaning of each formation and regards the cloud as an exponent of the physical 

 processes operating in the air and resultiug in cloudy condensation. The cloud is 

 primarily valuable not on account of its beauty, but because it makes manifest 

 motion in the atmosi>here, which is not otherwise discernible. It outlines to some 

 degree the storm mechanism at different levels in the atmosphere. Makipg due 

 allowance for the fact that the cloud does not always give the true motion of the 

 current in which it moves, as witness the Table cloud at Table Mountain, it is still, 

 wlicn rightly interpreted, a most significant index of air motion. There is no sound 

 reason why the forecaster should not derive as much information concerning the 

 mo\'emeuts of the air from a cloud map as from a pressure or temperature 

 map. . . . 



'* [The second] classification takes some account of the cloud's altitude; and in 

 diff'erentiating clouds formed by diurnal ascending currents in calm air, generally of 

 the summer cumulus type, from the clouds formed by widespread general uplifting 

 of the vapor, some of the nimbus formations, this classification takes some account 

 of cloud origin. In both of these directions the new system is preferable to the old; 

 but the criticism can be fairly made that in the matter of cloud origin the new 

 classification does not go far enough. . . . 



"In addition to the direction and relative velocity of the cloud (the only condi- 

 tions which have been thus far recognized or utilized in forecasting), it is demanded 

 of the future cloud classification that it take into account the level in which the 

 cloud is formed and the manner of formation. Some such scheme as the following 

 might be profitably used: 



Classification of cloudt. 



Altitude. 



Up to 



Atove 



Formation. 



Cooling by contact. 



Fogs — haze, di^st, 



and fiToand fogs. 

 Nocturnal radiation 



Mixture. 



Scud 



stratus 



Cuniulo-stratus 

 Billows 



Cirro-cumulus .. 



Cirro-stratus 



Cirrus , 



Ascension. 



Nimbus 



Summer cumuli. 

 Cumulo-nimbus. 



Cumulus 



Alto-cumulus. 



Electrical and 

 critical. 



Hail clouds. 

 Cumulo-nimboa. 



' Read before the Philosophical Society of Washington, March 2, 1895. 



