© Jan Knight
Serra de Alvorge, Portugal
Latitude: 39° 59' 5'' N
Longitude: 8° 27' 58'' W
18 September 2012 1635 (Local Time)
Image I.D.: P.9.16
CL = 2, CM = 0, CH = 0
Links in the image description will highlight features on the image. Mouse over the features for more detail.
This picture, taken from Serra de Alvorge in Portugal, shows a Cumulus congestus generated as a result of rising thermals from a wildfire. It is therefore classified as Cumulus congestus flammagenitus.
Light northwesterly low-level winds caused smoke from the wildfire to drift slowly to the southeast, and some smoke also rose vertically into the lower atmosphere. However, the atmosphere was deeply unstable above about 2300 m and the convective plume rose quickly to considerable height, resulting in the formation of a tower of Cumulus congestus flammagenitus.
The wildfire, located near Potamissa in the Limassol District of Cyprus, was approximately 20 km away from where the picture was taken near the village of Kivides. The base of the cloud is partially obscured by smoke rising directly from the fire and by a layer of smoke spreading in the lower atmosphere. Other Cumulus clouds of natural origin, on the right of the picture, are partially hidden by smoke.
The Cumulus flammagenitus cloud is identified as the species congestus by its relatively large extent, the bulging upper part resembling a cauliflower and by the towers sprouting from the cloud top. Observation over time showed that these towers rose from the main body of the cloud only to dissipate in the dry atmosphere above.
This cloud is Cumulus congestus flammagenitus, formed by the largest forest fire in history in Sweden.
The term flammagenitus refers to the cloud originating as a consequence of convective currents rising from the heat of a wildfire. The species is identified as congestus by its relatively large extent and bulging upper parts resembling a cauliflower (1, 2).
The cloud appears dark, in part because the cloud droplets are mixed with particulate matter resulting from combustion, and in part because the sun is behind it. Note the crepuscular rays (3, 4) across much of the sky, rendered visible by smoke haze in the atmosphere. The rays diverge from the position of the sun behind the cloud.
The cloud is being blown away from the heat source by a moderate southeasterly breeze.
This picture, taken towards the south from Vancouver, Canada, shows Cumulus flammagenitus generated as a result of rising thermals from a wildfire. The top of the cloud displays strong sproutings with sharp outlines and indicates the species congestus. Furthermore, the rising thermals have penetrated an elevated moist layer of air, generating a pileus accessory cloud. Southwesterly low-level winds caused a plume of smoke from the wildfire to drift to the northeast, obscuring the base of the Cumulus from the observer. The sky is otherwise largely clear with only a few Cumulus humilis clouds.
The accompanying time-lapse video shows the development of the various features noted in the this photograph.
Smoke originating from a gorse fire to the north (right of image) can be seen blowing towards the left. The heat produced by the fire was sufficient to induce the development of Cumulus which can be seen above the smoke layer. The Cumulus is transitioning from humilis into mediocris at 3, 4 as the sproutings indicate.
(NB. Hour of day not specified therefore estimated)
This huge convective cloud, caused by an eruption from a small volcanic island, is composed of a mixture of dust or grains of different sizes and of water drops thrown up by or condensing in the cooling column. The dark band at 1 is probably a "rain" of volcanic ash (dust or grains).