Cumulus Clouds (Cu)
Cu humilis
Smog BL Top Clouds
BL Top Clouds - Dust
Cu congestus I
Cu congestus II
Cu con praecipitatio
Con congestus IV
Con congestus V
Cu ´magritteus`
Cu mediocris
Cu pileus
Cu arcus
Tropical Cu
Marine BL



Pollution Boundary Layer Top Clouds


The panorama image shows the view from the tourist attraction Touchal, located at an altitude of 3800 m, to the South over Teheran that is approximately 15 km away. The (uppermost) inversion can be recognized as a sharp line between the blue sky and the layer of air pollution below. This inversion is located at an altitude of more than 3000 m. There are further inversions at lower altitudes.
These pictures were taken in the opposite direction, compared to the panorama view, i.e. towards North to North-east. The inversion climbs more and more to higher altitudes during noon-time and afternoon. The smog then spreads into the valleys from Teheran to the North passing the saddles of the mountains as if there were channels.

Therefore a brownish haze layer can be noticed at the bottom of BLTop1.jpg to BLTop17.jpg. Boundary layer clouds of the kind of Cumulus humilis which in this case are called boundary layer top clouds are formed at the upper limit of the haze layer (i.e. at the inversion).

Some of the pictures were taken right after each other. Sometimes a polarization filter was used (e.g. for the darker image BLTop15.jpg) and sometimes not (e.g. BLTop14.jpg). BLTop12.jpg and BLTop13.jpg, and also BLTop8.jpg and BLTop9.jpg are further examples. It can be clearly noticed that the clouds appear in higher contrast because of the attenuation of the blue sky (see also Skylight polarisation).

S. Borrmann, Touchal, 3800 m above sea level, Alborz mountains in north-western direction of Teheran, Iran, 17 August 2005, 0:02 p.m. to 0:37 local time