Fluctuations of temperature below cumulus clouds

Abstract

SUMMARYA description is given of one flight below cumulus clouds on 28 Aug. 1952. Small rapid fluctuations of temperature were observed by a sensitive resistance thermometer, records being obtained as a photographic trace. It is shown that, with respect to the frequency and type of fluctuation of temperature encountered, the space between cloud base, i.e., 3,100 ft, and ground level may be divided into three sections. The first, a layer extending from ground to about 800 ft, the second from 800 ft to about 2,800 ft, and the third from 2,800 ft to cloud base. A possible explanation for the formation of these layers is discussed.

An entraining jet model for cumulo-nimbus updraughts

“…I n those cases where the environment is considered to be unsaturated, it is implied that, although the updraught a t cloud-base level is a t the same virtual temperature as the surroundings, its moisture content is significantly higher; this would be so if the updraught originated in a well-mixed moist layer, the top of which lay a short distance below cloud base, and if this layer were surmounted by a somewhat drier and stabler region through which the clouds grew. This is consistent with some detailed soundings below and between rather smaller convective clouds (BUNKER et aZ., 1949; JAMES, 1953) which have indicated that just below the bases of cumuli there is frequently a stable layer within which the mixing ratio of water vapour decreases rapidly with height.…”

A Numerical Simulation of Observed Cumulus Humilis Clouds

“…The values of (*T00 which yield the best fit to the observational results are used in this paper. They are shown in Table. Temperature perturbations from the surface to a cloud base have been observed by James (1953) and Warner andTelford (1963, 1967). They showed that the perturbations were random near the surface, on the other hand, they were organized according to a height, taking with temperature excess of about 1*C and upward velocity of about 1 m/s.…”

Cumulus and cumulonimbus convection

“…From the results of investigations by a number of authors (e.g. BUNKER et al, 1949;JAMES, 1953;WARNER& TELFORD, 1963;GRANT, 1965) it appears that several layers can be distinguished, characterised by certain lapse-rates of potential temperature 8 and mixing ratio x. With the decrease in the mean values of these parameters from the base to the top of a layer indicated by the prefix A,, these layers are as follows:…”