Some Recent Long-Range Diffusion Observations

Abstract

Recent atmospheric cloud-spreading (relative diffusion) data from a variety of sources are combined to show that the horizontal spreading rate is approximately linear over a time range from 1 to 10 or more hours (20?200 or more km) of downwind cloud travel. This result agrees with earlier observational studies, in which the horizontal cloud standard deviation σy has consistently been found to vary as tp, where t is the downwind travel time and p is in the range 1?1.2. For the present dataset, σy is found to vary as t1.1. A recent theoretical prediction, p = 7/6, valid over the entire range of t, is very close to these observed values.