THE TEPHIGRAM 59 
Fig. 16. AIRPLANE SOUNDING AT MURFREESBORO, 
Tenn., plotted on the pseudo-adiabatie chart. 
The temperature curve is drawn as a full line 
with specific humidities written in to its right. 
The wet-bulb curve is drawn as a heavy dashed 
line with relative humidities entered beside it. 
This ease is of interest because it shows con- 
ditional instability in most layers but without 
real-latent or pseudo-latent instability. There 
is a little convective instability aloft (e¢., 
Just above 785 and 630 mb) where the wet 
bulb lapse rate is greater than the moist 
adiabat. 
Bodily lifting of the surface layers by 100 
mb or more would make some fairly thick Cu 
clouds whereas considerable solar heating of 
the surface layers will produce only Fe or 
Se, if any clouds at all, (because the con- 
densation level will be raised). 
The sounding is in general rather stable in 
spite of moderate to high relative humidities 
and conditional instability in the lower levels; 
this is because there is no latent instability in 
the first km or two.—R. G. S. 
In a study of some Indian tephi- 
grams, Sohoni and Paranjpe** have 
applied Normand’s suggestions and 
correlated their findings concerning 
the presence or absence of latent insta- 
bility in the soundings with air-mass 
type and weather. The estegrams cor- 
** Sohoni, V. V. and Paranjpe, M. M.-.: 
Latent instability in the atmosphere revealed 
by some Indian tephigrams, Mem. India Met. 
Beet Vol. XXVI, Part VII, 1937, pp. 131- 
responding to the tephigrams were 
drawn in each case as follows:—the 
dry adiabatic (isentropic) is drawn 
through the point at the surface level, 
and then the isohygric (constant 
mixing-ratio line) through the corres- 
ponding dew-point is drawn. The 
saturation adiabatic which runs 
through their point of intersection 
meets the isobar at the surface level 
at a point which has a temperature 
coordinate of T° A. This is the adia- 
batic wet-bulb temperature of the air 
particle at the surface level. The wet- 
bulb temperatures at the other levels 
are obtained in the same manner, 
and then the estegram is drawn by 
joining all of the points so obtained. 
Sohoni and Paranjpe found that the 
absence of latent instability is asso- 
ciated with dry, fine weather with 
occasional high clouds of non-convec- 
tional type, and latent instability with 
convectional types of clouds. Later 
studies in India confirm this and the 
wet-bulb curve is now widely used. 
It is also practicable to determine the 
presence of what Rossby calls “con- 
vective (or potential) instability” of 
a layer of air by use of the wet-bulb 
temperatures on a tephigram (also on 
the pseudo-adiabatic chart). In any 
layer of air in which the lapse rate of 
the wet-bulb temperature exceeds the 
moist adiabatic rate, the wet-bulb po- 
tential temperature, and, therefore, 
the equivalent-potential temperature 
decreases upwards. A layer of this 
type is convectively unstable according 
to Rossby’s definition. If such a layer 
is raised bodily and adiabatically in 
the atmosphere without mixing with 
its environment or distortion and in 
such a way that the difference of pres- 
sure between the top and bottom of 
the layer remains constant, then it can 
easily be seen that every layer in which 
the wet-bulb lapse rate is steeper than 
the saturated adiabatic must ulti- 
