Cumulus Clouds (Cu)

The series of images displays an approaching Cumulus congestus which resulted in a heavy rain shower for fifty minutes. Already before the first image was taken the virga below the cloud was noticed (look at CuPraecip1.jpg, CuPraecip2.jpg, CuPraecip11.jpg and CuPraecip18.jpg), so that the exact duration of the rain event cannot be estimated. During observation the cloud complex moved from the southern direction to the observer. At this stage two virgas were visible always occurring at the same spot of the cloud. In CuPraecip1.jpg one can derive from the cloud shape that this is a Cumulus congestus. The shape and extension of the cloud top remained nearly the same during observation. Especially there was not enough convection which might have influenced the cloud to develop to a Cumulonimbus.

Therefore this cloud stayed in the stage of Cumulus congestus praecipitatio. Having reached the observer (look at CuPraecip21.jpg) the precipitation decreased and shortly after it stopped completely. The rain droplets were so warm when they reached the ground that most probably there was no ice phase within the cloud. The main cloud base was extremely low (see CuPraecip13.jpg) so that despite of the warm ground air (32 deg C) the falling rain drops had no real chance to warm up. CuPraecip16.jpg shows the environment closely to the cloud. Besides the eight pictures presented here thirteen more exist which document this process.

CuPraecip1-21.jpg: S. Borrmann, Morro Branco near Fortaleza, Ceara, Brazil, 22 February 2004, 9:49 a.m. to 10:40 a.m.

Camera Parameters

Olympus E-1 SLR with a 14-54 mm objective. Exposure und ASA sensitivity choice are performed by the program automatic of the camera. The following images were all taken with a sensitivity of ASA 200, in a sRGB colour range with a resolution of 2560 x 1920 Pixel x 24 colours.

8

1/640

54

10

1/400

14

8

1/640

54

9

1/400

14

7.1

1/500

48

8

1/320

14

11

1/500

14