Microphysics of Clouds Initiated from a 1000 MW Dry Heat Source in Comparison with Environmental Clods—A Statistical Study

Abstract

To evaluate potential atmospheric impacts of wate heat released by dry cooling towers, studies have been made of an oil burning system (the “Météotron”), which emits sensible heat at a rate of ∼ 1000 MW and large quantities of aerosol particles into the atmosphere. Out of the 15 “burns” made during 1979, 12 times the rising column of smoke was capped with a cloud formation. The structures of these clouds were investigated with an instrumented aircraft. The clouds capping the Météotron (A) and the natural clouds unaffected by it (N) were compared by means of the Student's t applied to the mean liquid water content (LWC), droplet mean diameter (D_m) and droplet concentration (conc.) The N-clouds consisted essentially of stratus, cumulus and stratocumulus, developing sometimes up to 2000 m (AGL). Compared to the N-clouds, the volume of the A-clouds were similar or smaller, despite the fact that their condensation levels were sometimes lower and their tops generally higher. Generally, for both A- and N-clouds, the conc decreased with height while D_m and LWC increased; the increase of LWC is associated with the increase of D_m and the decrease of conc. In most cases, the A-clouds contained more droplets but with smaller mean diameter than the N-clouds (statistically significant at the 95% confidence level). This led to generally lower LWC in the A-clouds than in the N-clouds. This result is particularly noticeable when comparing cloud properties at the same height. The higher droplet concentration apparently did not result from a higher concentration of cloud condensation nuclei. The A-cloud characteristics were similar to those of freshly formed clouds. Their differences from N-clouds seem largely due to the heart released; the effect of the aerosol from Météotron is comparatively small.