Virga and Rainfall Traces

December 22, 2011

Virga 1200 (4)


Photographer: Top photo -  Stan Celestian; Bottom Photo - Alfred Herbel
Summary Author: Alfred Herbel; Stan Celestian; Jim Foster

The two photos above show examples of precipitation falling from clouds with most, but not all, of the rainfall evaporating before reaching the surface. In the top photo, taken in the White Tank Mountains near Waddell, Arizona, a column of rain is seen spilling out of a cumulonimbus cloud showing minimal vertical development. Nearly all of this is virga – the rain evaporated in the warm, dry air below the cloud. If you look closely you’ll note that some rain is reaching the surface. The cumulus cloud to the left shows a less remarkable virga shaft, but here the rain doesn’t make it all the way to the ground. Photo taken on September 24, 2011.

The bottom photo shows glaciated altocumulus clouds above the A8 highway near Stuttgart, Germany. Ice crystals, not raindrops, are falling from these comma-shaped clouds. No ice or snow reached the surface, since the air temperature was above freezing near the surface but still dry enough to evaporate most of what was falling. A few raindrops were observed to splatter on car windshields, though. Strong winds aloft are responsible for the curious curvature of the rain shafts. Photo taken on November 20, 2011.
Photo details: Top - Camera Maker: NIKON CORPORATION; Camera Model: NIKON D200; Focal Length: 35mm (35mm equivalent: 52mm); Aperture: f/9.0; Exposure Time: 0.0031 s (1/320); ISO equiv: 100; Exposure Bias: none; Metering Mode: Matrix; Exposure: program (Auto); White Balance: Manual; Light Source: Fine Weather; Flash Fired: No; Orientation: Normal; Software: Adobe Photoshop 7.0. - Bottom - Camera Model: CANON Digital IXUS 60; Aperture: f/2.8; Exposure Time: 1/125 sec.