THE TEPHIGRAM 57 
A SCHEMATIC TEPHIGRAM SHOWING 
Fic. 14. 
PRESENCE OF LATENT OR PSEUDO INSTABILITY 
for particles in the layer between E and G, 
which can be realized somewhere between B 
and D. The curve ACD is the temperature 
sounding; the curve EFGH is the wet-bulb 
temperature curve (estegram). The amounts 
of energy must be determined for any chosen 
particle in the usual manner; the shaded 
areas are not energy areas. EFGI merely 
marks the layer E-G, in which any chosen 
rising particle has real or pseudo-latent 
instability. which can be realized somewhere 
between B and D. 
The paths of a rising particle from A and 
from F are dotted lightly. It is evident that 
the particle at F has much more latent 
instability than that at A, while a particle 
between F and G has only ps2udo instability. 
Mixing and heating in the lowest layers would 
probably increase the dry and wet bulbs at 
A and K, so that in a forecasting problem 
one would draw the probable curves that 
would result from these effects and then 
consider the instability situation (see Fig 15). 
level. Then all particles in the layer 
EG (i.e., where the wet-bulb curve 
curve lies to the left of CGI) have 
latent instability. Extending the moist 
adiabat which is tangential to the 
wet-bulb curve at F, indicates the 
layer in the environment aloft where 
any particles of air forced up from 
the layers between E and G would 
be able to realize their latent in- 
stability. Note, however, that the 
amount of latent instability (i.e., ratio 
of positive to negative energy areas) 
varies greatly for the different parti- 
cles lying between E and G. One 
selects the particle which is likely to 
be heated, usually the surface one or 
a mean of particles near the surface, 
and draws the positive and negative 
areas for it in the manner described 
by Mr. Namias. However, the wet- 
bulb curve permits one to judge better 
how representative any given chosen 
particle will be for the trigger effects 
likely to occur (see figure 15). 
30° 40° 50° 60° 70° 80° 90°R 
Fic. 15. LATENT INSTABILITY ON A TEPHI- 
GRAM FOR A Day WITH SQUALLS AND A DUST- 
storm aT AGRA, INDIA, May 22, 1929.—(A case 
from the paper by B. N. Sreenivasaiah: A 
Study of the Duststorms of Agra, Memoirs of 
the India Met. Dept., Vol. XX VII, Part I, 1939.) 
On this date, a comparatively weak but rather 
prolonged duststorm occurred between 16:20 
and 18:45 h, I. S. T., with well marked squal!s 
at 16:20, 17:20, and 18:10 h. The synoptic 
weather charts showed that associated with 
the passage of a low pressure wave across 
north India, the seasonal low over northwest 
India became accentuated by the 21st morning 
and the pressure gradient over Sind and Balu- 
chistan became marked. Numerous duststorms 
occurred in northwest India on the 21st; Agra 
also had one on that evening. The 22nd 
morning chart shows a marked trough of low 
pressure extending from Baluchistan to the 
west United Provinces hills; the low pres- 
sure wave apparently passed northeastwards 
subsequently. The duststorm of Agra on the 
22nd was evidently associated with this spell 
of disturbed weather. 
A meteorograph was sent up at Agra at 
18:05 h (I. S. T.), ie., actually during the 
period of the weak duststorm but after the 
first two principal squalls of the duststorm 
had oceurred. There was a comparative lull 
in the phenomenon at the moment of the 
ascent, but within five minutes thereafter the 
last of the three squalls occurred. The tephi- 
and estegrams relating to the ascent are 
drawn. These show real latent instability for 
layers of air between the surface and about 
460-mb level, the environment of latent in- 
stability (where it can be realized) lying 
above 690 mb. The tephigram shows the exis- 
tence of a superadiabatic gradient of tem- 
perature between surface and 1-gkm level. 
The actual magnitude of this lapse rate is 
13.5F°/gkm, whereas, according to the criterion 
