Correspondence 551.521.11

SUNSHINE IN THE SOUTHERN SUDAN

By J. PEPPER

In the course of an investigation by the Meteorological Office reference was made to the

When Eq. (1) (p. 449), note on ' Sunshine in the Southern Sudan ' by W. D. Flower (Q.J., 65, p. 448, 1939) :

S = (100 - C) (1 + tC - a'W)

was checked, it was found that the values in Table 2 (p. 450) of mean cloud amount were in error. Not all the values in this table have been worked out, but I append the values I have found for the mean for Meridi (4" 55'N, 29" 30'E) (first row in the table) :

MEAN DAILY AMOUNT OF CLOUD IN TENTHS

J F M A M J J A S O N D 6.7 6 7 6.3 6 1 6 4 6.9 7.5 7.1 5.5 5.8 6.8 7.8

(4.0) (4.7) (3.8) (3.5) (3.8) (4.1) (4.6) (4.2) (3.2) (3.4) (4.0) (4.8)

The values in brackets are those of the author.

Meteorological Office, Harrow. 25 July 1953.

551.558.1 : 551.576.11

THE STABLE SUB-CLOUD LAYER AND CONVECTIVE UPDRAUGHTS

By A. F. BUNKER

It is desired to correct a misquotation and omission of pertinent data that occur both in the review paper by Ludlam and Scorer (Q.J., 79, p. 336, 1953) and in the paper by Ludlam (QJ., 79, p. 430, 1953). In reviewing the paper by Bunker, Haurwitz, Malkus and Stommel (Pap. Phys. Ocean. Met., M.I.T. and Woods Hole Ocean. Inst., 11, No. 1,1949) describing measure- ments of temperature and humidity over the Caribbean Sea, Ludlam and Scorer have stated that we interpret the existence of a stable sub-cloud layer as evidence that updraughts in the clouds do not extend down into the adiabatic layer. They then try to show that this reasoning is incorrect. Actually, the reasoning presented was not based on the existence of a stable layer but on the records of a water-column accelerometer carried in the sounding aircraft. This instru- ment records the accelerations normal to the plane of flight imparted to the aircraft by the tur- bulent air. A paragraph may well be repeated here since distribution of the paper in the British Isles is rather limited (it had been pointed out in the preceding paragraph that the average mean deviations in the mixing ratio were essentially the same under the cumulus as in the clear areas) :

Substantiating evidence that convection currents are not maintained far into the homogeneous layer is given by accelerometer records of the vertical motions of the plane as it flew under clouds and in clear areas. Table 32 gives the percentages of time that the accelerations of the plane were in the ranges 0.0 to 0.04 g; 0.04 g to 0.08 g, and greater than 0.08 g, for both clear and cloudy conditions. The bottom row gives the averages for each range and cloud condition above the plane. The small difference shown in the turbulence in the homogeneous layer under the clouds and in clear areas indicates that convection in the cloud layer does not produce any recognizable increase of the turbulence in the layer below it.

102