Cumulonimbus Clouds (Cb)

The time series from CbCalvus1.jpg to CbCalvus21.jpg shows the development of a Cumulonimbus cloud over a period of about half an hour. At this cloud a flat top has been formed, but there is no Cirrus cover. In Cumulonimbus calvus clouds in a fraction of the upper swelling the cauliflower-like shape already disappeared. In the upper parts a white area mostly with vertical stripes appears. This can be well recognized in the series from CbCalvus32.jpg to CbCalvus35.jpg. In the front "hanging part" of the cloud also the development of "mammatus" can be noticed (see also Cu mammatus I, Cu mammatus II and mammatus view from an aircraft).

When the cloud begins to ice it will be named as "calvus". After the icing has initiated it mostly does not take a long time, until an anvil has been formed. However, this is under the assumption that (a) there is sufficient convective potential energy (CAPE) and (b) there is no strong horizontal wind shear disturbing the swelling. This was not the case for the clouds shown here. The clouds stayed in the "calvus" state until they collapsed again or were disrupted by wind shear.
On the pictures in the bottom row the observer can recognize a first sign of an anvil appearing in the front. It still consists of under-cooled water droplets, not of ice crystals.

This becomes apparent since the typical fibre structure is missing (and was also not formed later on). A "pileus" can be noticed on some of the images (CbCalvus4.jpg to CbCalvus14.jpg). More details about this can be found in chapter Cumulus pileus.

CbCalvus1- 21.jpg: S. Borrmann, Darwin, Northern Territory, Australia, SCOUT-O3 Field Campaign,
26 November 2005, 4:59 p.m. to
5:30 p.m.

CbCalvus32-35.jpg: S. Borrmann, Yellow Waters, Kakadu National Park, Northern Territory, Australia, SCOUT-O3 Field Campaign, 2 December 2005, 2:54 p.m.