Open AccessEffects of Pressure on Collision, Coalescence, and Breakup of Raindrops. Part II: Parameterization and Spectra Evolution at 50 and 100 kPa
Author(s) -
Roland List,
R. Nissen,
C. Fung
Publication year - 2009
Publication title -
journal of the atmospheric sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.853
H-Index - 173
eISSN - 1520-0469
pISSN - 0022-4928
DOI - 10.1175/2009jas2875.1
Subject(s) - breakup , coalescence (physics) , drop (telecommunication) , collision , mechanics , spectral line , accretion (finance) , fragmentation (computing) , mass transfer , physics , materials science , meteorology , environmental science , astrophysics , computational physics , computer science , astronomy , telecommunications , computer security , operating system
Fragment size distributions, experimentally obtained for six drop pairs colliding at 50 kPa, are parameterized similarly to the 100-kPa drop pair experiments by Low and List. This information is then introduced into a box model to allow assessment of the spectra evolution and a comparison of the two datasets taken at the two pressures. The differences in breakup patterns include the following: The contributions to mass transfer by breakup and coalescence are very similar at the two pressures, with larger values at lower pressure; the overall mass evolution is not particularly sensitive to pressure; and disk breakup plays an “erratic” role. The situation for the number concentration, however, is totally different and develops gradually. At 50 kPa there is also no three-peak equilibrium developing as for 100 kPa. The times to reach equilibrium are ∼12 h. Note that the box model does not include accretion of cloud droplets—which may well be more important than growth by accretion of fragments. Application of the new parameterization is not beneficial for low rain rates, but it is strongly recommended for large rain rates (>50 mm h−1).