Funnel Cloud
Taken by Helio C. Vital on February 7, 2017 @ Rio de Janeiro, Brazil
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The photos show a very interesting funnel cloud over Rio de Janeiro half an hour before sunset (around 21:05 UTC). It was part of a thunderstorm cell that was approaching, announcing the arrival of a new weather system that would bring rain to the city several hours later. This type of funnel-shaped cloud is associated with a rotating column of wind (vortice or tuba) that extends from the base of a storm cloud. A Canon PowerShot SX60 HS camera at high zoom magnifications and (100-250 ISO) was used for the shots. Either 5/1 or 3/1 stacking was applied to the photos and the resulting images had their contrast enhanced with PhotoScape in order to bring out minor details in the cloud structures. Fortunately, in spite of their threatening appearance, the clouds did not produce any major storm and no damage was reported.
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Truely awesome!
Posted by markbuxton 2017-02-08 17:54:55
This is awesome!!!!
Dangerous...But Awesome!!!!
Posted by Lindavt 2017-02-09 18:44:59
The local ancient name for this phenomenon was *the tail of Lucifer* (here in South Italy on the Varano Lake coast).
Posted by iovane 2017-02-10 07:56:05
This funnel is noted as rotating. Was it observed that it was rotating clockwise? (typical for southern hemisphere low pressure as opposed to counter-clockwise funnel rotations we see often in Oklahoma, USA)
Posted by ObserverXL5 2017-02-10 10:01:26
Amazing image. When you say 3/1 stacking is that focus stacking you are using?
Posted by astrofud 2017-02-11 02:45:18
This is not a funnel cloud, please correct. Those are the undulatus clouds mixed with lenticular clouds which are never associated with thunderstorms are not dangerous to people on the ground. While they could be dangerous for airplanes as there is a lot of turbulence around them.
Posted by slochaser 2017-02-11 13:38:46
Thanks for your interesting remarks, ObserverXL5. As I was using multiple shooting (5 photos taken 0.1 second apart), as was able to make a coarse estimate of the rotation period of the tuba: 14+-5 seconds, indeed a very slow rotation, indicative of a low pressure formation. On the other hand, it was clearly counterclockwise (seen from above), contrarily to what one would expect for the Coriolis Effect in the Southern Hemisphere. So, I guess an alternative explanation lies in the fact that the Coriolis Effect mostly applies to large scale systems, such as hurricanes, while usually being too subtle in very small ones, that are much more likely to be influenced by the combination of other forces, such as landscape, prevailing wind patterns and many others, that can alter the angular momentum of air masses, giving rise to vortices. Thanks for bringing up that very interesting subject!

Thanks astrofud. I just meant that I stacked either 3 or 5 photos with Registax 6 (using its default options) in order to produce each image with less noise. The advantage is that I could then slightly enhance contrast using PhotoScape to highlight minor details in the clouds without turning the images grainy. Thanks again for the opportunity to clarify that point!

Glad you appreciated our contribution! Many thanks to all of you for your precious support!
Posted by hcvital 2017-02-11 13:46:09
175 thumbs up
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