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When is a cloud too small to be considered a cloud? What is the largest cloud officially on record?

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closed as too broad by Spencer, Fred, Jan Doggen, Peter Jansson, trond hansen Mar 10 at 18:21

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    $\begingroup$ From meters to thousands of meters. $\endgroup$ – gansub Sep 2 '18 at 12:05
  • $\begingroup$ I don't think there is an official lower boundary. If it is visible you can describe it as a cloud. $\endgroup$ – Communisty Sep 3 '18 at 8:12
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    $\begingroup$ if you had asked this question over at astronomy the numbers had been impressive,but i guess you want to know about water clouds here on earth. $\endgroup$ – trond hansen Sep 3 '18 at 15:30
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    $\begingroup$ @Muze this is not a good question. Smallest cloud is pretty much meaningless. If you can see it - it's a cloud. The largest cloud could be interesting. How do you define a cloud? For example in thunderstorm clouds, how big can a convection cell be? In a single visible cloud mass, can there be several cells? Improve the question first. Make it detailed. $\endgroup$ – Gimelist Mar 4 at 3:35
  • $\begingroup$ This is tough, I'm not aware of defined limits on either end. As "clouds" are just defined by volumes of liquid water or ice particles there's no lower limit other than what's practical to see (as alluded to in a few comments). Distinct types of clouds may be classified based on observed characteristics but these all exist in a spectrum, ie they don't lose their "cloud" definition if a classification is not identifiable. Even beyond this, continuous clouds can exist in a storm system over thousands of square miles, how would these be quantified? This seems too ambiguous to have a good answer. $\endgroup$ – dplmmr Mar 4 at 4:50
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According to the peer reviewed reference The Distribution of Cloud Horizontal Sizes cloud horizontal sizes can vary from 100 meters - 8000 km based on sampling limitations. Globally clouds with horizontal length greater than 200 km constitute approximately 50 % of the total cloud cover on the earth.

The largest clouds i.e. those that have a horizontal scale of greater than 300 km are present over the mid latitude oceans during the summer and over the West Pacific and Indians ocean. Clouds of this size are also present over monsoonal land masses. The smallest cloud sizes (less than 10 kms) are found over trade wind areas and over desert areas.

Mention must also be made of super cloud clusters that are typically found in the Madden Julien Oscillation and these have a horizontal span of 3000 kms.

Vertically the tallest cumulonimbus clouds can span 12 km

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  • $\begingroup$ That reference appears to ARBITRARILY CHOOSE a minimum cloud size of 100m. The smaller the cloud, the harder it is to see at a distance -- but a teapot can easily produce a cloud with a scale of centimeters, and a cloud chamber produces clouds on a scale of millimeters. $\endgroup$ – jeffB Mar 7 at 17:26
  • $\begingroup$ @jeffB - "Samples at 1 Hz (≈100 m horizontal distance) are classified as either clear or cloudy using thresholds applied to data from cloud-detecting probes. " Why would you consider this arbitrary ? $\endgroup$ – gansub Mar 8 at 2:41
  • $\begingroup$ fair point, I'd reword to "chooses a minimum cloud size of 100m based on sampling limitations". While the data you have are much better than my complete lack of data, that still doesn't seem especially relevant to the question of "how small can a cloud be". If the paper had found no clouds smaller than (say) 200m given a 100m sample spacing, THAT would be relevant. Agree that the question doesn't give us very firm ground for supporting conclusions. $\endgroup$ – jeffB Mar 8 at 14:19
  • $\begingroup$ @jeffB I would be willing to accept an edit to my answer reflecting that statement. $\endgroup$ – gansub Mar 8 at 14:38

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