Wave Clouds
Stratospheric Clouds
Leewave Clouds I
Leewave Clouds II
Cap Cloud


Polar Stratospheric Clouds

The polar stratospheric clouds near Kiruna (Sweden) are mostly Leewave clouds. They are formed, when westerly flows pass the Scandinavian Alps. In the Lee-waves the air is adiabatically lifted and if the resulting cooling is sufficient, HNO3 and H2O condense onto the H2SO4-H2O liquid droplets of the stratospheric background aerosol. Thereby Leewave-PSC are generated which can stationary stay in the lee of the mountains.

PSC1.jpg shows a single polar stratospheric cloud of the kind of Lee-wave clouds which is embedded in a veil of thin PSCs.

PSC2.jpg presents also a single PSC with a tail at the leeside. The cloudless air is forced to the top by the mountains into the range of the PSC and cloud parts are formed. After the air has passed the stationary PSC the cloud particles evaporate again, when the air descends in the lee and is adiabatically heated. Sometimes PSC particles evaporate with a short delay so that they are transported out of the cloud by the fast flow. Then a visible tail is generated until the particles are evaporating.

PSC3.jpg shows a whole field of such individual stationary PSCs.

PSC4.jpg displays a scene above Kiruna, where the whole sky is covered with PSCs. The wave structure and with it the leewave character can be anyhow noticed. The colour effects are real and not artificially made by picture taking.

In PSC5.jpg a section of PSC4.jpg is enlarged. The optical effects of the PSC particles with a size of a few micrometers are clearly recognizable. However they are much more brilliant in real nature.

PSC6.jpg and PSC7.jpg show also special optical effects of the PSCs with the sun being low. Because of the iridescending optical appearance the PSCs are often also called "Mother of Pearl Clouds".

The images PSC8.jpg and PSW9.jpg were taken in January 2003. They show polar stratospheric clouds in an altitude above 22 km. PSC9.jpg which was taken with a telephoto clearly shows the iridescending colour effects.

In Brown Cloud and Leewave Clouds different kinds of Leewave clouds are presented. The generation of these cloud types is also described in detail in the latter chapter.


PSC1-5.jpg: Andreas Thomas, Stephan Borrmann, Kiruna (Sweden), POLSTAR Field Campaign, January 1997

PSC6+7.jpg: Cornelius Schiller, Kiruna, January 2000

PSC8+9.jpg: Ralf Weigel, Kiruna, EUPLEX Field Campaign, January 2003