Explorer finding of adiabatic ascent in the cumulus congestus clouds of Colorado as shown in Fig. 20 was the second major discovery from Explorer sailplane which overturned prevailing thoughts. This finding was a result of reliable temperature measurements from the addition of the carefully evaluated reverse flow temperature probe to the instrument package on the sailplane (Table II at bottom of page). With the careful design and testing/evaluation of the housing and the slower airspeed of the sailplane we were able to make temperature measurements in cloud that did not exhibit wetting of the sensing diode and the resulting cooling. This can be seen in Fig. 4 which shows a couple of inches of ice on the front of the probe, but no evidence of ice on the rear of the probe. Prior to the discovery of adiabatic cores with Explorer, it was commonly thought that there was lateral mixing of air from outside the cloud into the interior and that adiabatic regions were rare. Although some previous measurements had hinted at the presence of adiabatic regions, the continuous, spiraling of the sailplane in the updraft provided convincing evidence that adiabatic regions did exist in the updraft core. See the papers by Johnson et al. (1977) and Heymsfield et al. (1978) for more information on this important finding. 

Note in Fig. 20 that as Explorer ascended the observed values of liquid water content (from the newly installed Johnson-Williams (JW) hot wire probe) gradually decreased after 1925 (~-10 C) while the observed total ice concentration and the concentration of ice >1 mm gradually increased. Panel 5 shows that there were relatively few ice particles from 1919 to 1920 (-1 to -3 C). It also shows that the liquid water content at times with greater than adiabatic values.¹

Over this 11 min period of ascent from 5.2 to 7.8 km (-1 to ~-19 C) the liquid water has mostly converted to ice particles as nucleation and growth of ice occurred in the updraft of this cloud. This is true even during the period 191920 to 191930 when the theta E measurement shows nearly adiabatic values (i.e., unmixed ascent). Most of the liquid water has converted to ice. Additionally, air with higher concentrations of ice from above the sailplane altitude might have mixed downward to increase the ice concentration of ice particles at the altitude of the sailplane.

¹Values greater than adiabatic were observed on some other days too and suggest that the large JW values may be instrumental artifacts since large drops that might have been accumulated in the updraft were not observed by the Cloud Particle Camera.