- Is virga rain that evaporates before reaching the ground?
Article
Bib No.:
- 400071
Authors:
- Fraser, A.B.
- Bohren, C.F.
Publication Date:
- 1992
Physical Description:
- pp.1565-1571
Subjects:
- METEOROLOGY - RADIATION - SCATTERING
- EMISSIONS
- METEOROLOGY - RADIATION - ABSORPTION
- PRECIPITATION - RAIN
- PRECIPITATION - RAINFALL
Citation:
- Monthly Weather Review, VOL. 120 NO. 8, 1992
Holding Location:
- See Parent Record
Link to Parent Record:
Parent Record:
- Monthly Weather Review.
Parent Details:
- VOL. 120 NO. 8, 1992
Media Type:
- Article
Collection:
- Library Collection
General Notes:
- Comment by SASSEN,K. and KREUGER,S.K.,121,No.8,
- 1993,pp.2426-2428.9 Refs.
- Reply by authors, pp.2429-2430.6 Refs.
Language:
- English
Abstract:
- The visual phenomenon called virga, a sudden change in the brightness of a precipitation shaft below a cloud, is commonly attributed to evaporation of raindrops. It is said to be rain that does not reach the ground. The optical thickness of an evaporating rain shaft, however, decreases gradually from cloud base to ground. Thus, it is more likely that virga results from snowflakes melting in descent. Horizontal optical-thickness decreases of more than ten can occur in the short distance over which a snowflake is transformed into a raindrop. This decrease is caused by two factors: a smaller number density of hydrometeors because of the greater fall velocity of raindrops than of equivolume snowflakes and a smaller scattering cross section: the first of these is dominant. An alternative explanation of virga is that it is precipitation that has not yet reached (rather than does not reach) the ground. This is a plausible explanation given the long time periods it may take hydrometeors, esp...