THE TEPHIGRAM 53 
lapor Content per Kgm.Moist Air 2 
“eS 
le} 
I 
box N 
10 5) 
Lyag 
FIGURE 13. TEPHIGRAM FOR OKLAHOMA CITY, JUNE 20, 1935—E arty A.M. 
A would at first cool along the dry 
adiabat; that is, it would trace on the 
tephigram a horizontal line. But this 
could go on only until saturation 
occurred, for beyond this point the 
sample of rising air would no longer 
cool at the dry adiabatic rate but at 
the rate of expansional cooling for 
saturated air given by the pseudo- 
adiabats. With the help of the 
diagram this point of saturation is 
readily determined. As the particle 
ascends the mass of water vapor per 
unit mass of air (the specific humi- 
dity) remains constant until condens- 
ation begins. When saturation is 
reached the specific humidity of the 
rising particle is the maximum 
amount of moisture possible at that 
temperature and pressure. These 
lines of maximum (or saturation) 
specific humidity are given in the 
tephigram by the dashed lines which 
slope upward slightly to the right of 
the vertical. Consequently in order 
to find the point of saturation one 
has merely to trace a line horizontally 
from the originally chosen point on 
the tephigram until it intercepts the 
line of saturation specific humidity 
passing through the corresponding 
point of the depegram (that is, 
through the specific humidity of the 
original particle). Thus the hori- 
zontal line from A would continue to 
the right until it meets a line drawn 
through A’ parallel to the 15 g/kg 
line of saturation specific humidity. 
Beyond this point the rising particle 
follows the curved pseudoadiabats. 
This process will be clarified by select- 
ing some other point from which a 
parcel of air would logically be more 
apt to rise through the air column. 
The ascent plotted in Fig. 13 was 
made in the early morning; thus the 
