Modification of the size distribution of falling raindrops by coalescence

✍ Scribed by B. J. Mason; R. Ramanadham

• Publisher: John Wiley and Sons
• Year: 1954
• Tongue: English
• Weight: 456 KB
• Volume: 80
• Category: Article
• ISSN: 0035-9009
• DOI: 10.1002/qj.49708034508

✦ Synopsis

Abstract

The manner in which the size distribution of raindrops is modified during their fall by mutual coalescence, accretion with cloud droplets, and by evaporation below cloud base is investigated. It is shown that if a constant flux of raindrops having an exponetial size distribution occurs at the level of origin (just below the melting level in a layer‐cloud) to give a steady‐state, this initial distribution will undergo considerable modification after a fall of 1 km, the smaller drops being seriously depleted and the larger ones increased. All three processes will cause a shift in the drop‐size spectrum towards larger diameters and produce an increase in the intensity of the radar echo at lower levels of the kind which is sometimes observed. Because of this modification of the drop‐size spectrum during fall and because of the rather rapid fluctuations which are frequently observed in the distribution at the ground, it is not often possible to correlate the latter with the intensity of the radar echo located higher up.