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
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
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
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