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   Corona - Effects of droplet sizes

  Drop size distribution   Droplet diameter

When cloud droplets have a variety of sizes the corona is less distinct.  A 10%* variation reduces ring contrast and visibility. 20% is enough to make them disappear.

* In these simulations the cloud droplets are given a Normal distribution of diameters about their mean. The percentage figures are standard deviations expressed as a percentage of the mean value..


Smaller droplets produce larger coronae. Estimate the mean droplet size from the ratio of the diameter of the first ring to that of the moon.

  Red 1st ring (more reliable):
  Drop dia,µm = 250 / ring dia [in moon dia]

For the red outer edge of aureole:
  Drop dia,µm = 120 / aureole dia [in moon dia]