WATER VAPOUR 
MB TEPHIGRAM 20-MARCH-45 1500 GMT FT KM 
Fig. 7a.—Ascent in an anticyclone, March 20, 1945. Ascent made 
over southern England at approximately 51°N 2°W. 
20° EAST 
Fre. 7¢—Contour chart for 500 mb at about 0600 GMT, 
March 20, 1945. Contour heights are given in feet and tempera- 
ture in degrees Fahrenheit. Figures in circles are wind speed 
in knots. Broken curves show isopleths of thickness of the 
layer 750-500 mb. 
IN THE UPPER AIR 
317 
was shallow and weak and the air above was quite dry, 
particularly at 550 to 600 mb, where the frost-point 
depression was 32C. On March 20th, the dry layer at 
the inversion was well marked and it was accentuated 
by the moistness of the air above. If the surface synop- 
tic charts are compared, the ascent of the 18th is seen 
to have been made in a weak warm sector with falling 
barometer, while the ascent of the 20th was made in a 
ridge. This would seem to contradict the relative dry- 
ness of the upper air on the 18th. On the 500-mb 
charts, however, the position is reversed. The dry air 
observed on the 18th between 700 and 500 mb is seen 
to be in an upper-air ridge, while the moister air of the 
20th is in an upper-air trough. 
Figures 10a and 106 give another example of an as- 
cent in an anticyclone. 
Intrusion of Moist Air Tongues into Dry Air. The 
ascent of June 7, 1943 (Fig. 8a with the surface synop- 
tic chart Fig. 8b) was made in a ridge in advance of a 
weak frontal system which is shown on the charts as 
having a double structure. The nature of the frost-point 
R 7 
PERSISTENT 
GONTRAILS NEAR 
MB TEPHIGRAM 7-JUNE-43 1200 GMT 
Fic. 8a.—Ascent showing moist air tongue intruding into 
dry air, 1200 GMT, June 7, 1943. Ascent made over southern 
England at approximately 51°N 2°W. 
WEST 30° 20° 1o° o° 
Fic. 8b.—Sea-level synoptic chart for approximately 0600 
GMT, June 7, 1943. 
