Cirrostratus Clouds (Cs)

Cirrostratus Clouds

Cirrostratus.jpg: A Cirrostratus cloud layer coming from westerly directions in the evening is displayed here. Later it also trailed Altostratus clouds, yet without any precipitation. At the top left side dense Cirrus fibratus clouds already occur, in the centre of the image Cirrostratus fibratus and on the right side Altostratus are found.

Cirrostratus2.jpg: A Cirrosstratus layer which seems to consist of broad, merged contrails at first. But at the horizon one recognizes that it is a wide-spread Cirrostratus layer - most probably of natural origin.
The sun does not appear as a "round slice", but has a "washy" border. This indicates that the Cirrus clouds consist of non-spherical ice-crystals with solid crystal structure. If the cloud consisted of liquid, i.e. round water droplets, the sun would be seen as a clearly distinguished circle through the cloud layer. From the form and the appearance of the sun shining through the cloud layer one can directly make conclusions about the phase of the water in the clouds.

In chapter Sun through Clouds this is described in detail. The sizes of droplets and ice-particles in clouds are summarized in chapter Objects in Clouds.

Cirrostratus3-6.jpg: An upcoming Cirrostratus cover can be seen here. Except Cirrostratus5.jpg the images were taken using a circular-polarizing filter. It can be clearly recognized how the filter improves the contrast. Twisting manually polarizer versus analyzer results in the improvement of the contrast of the clouds. Also look at chapter Skylight polarization.

Cirrostratus7-14.jpg: During the APE-ENVISAT validation campaign a measurement flight was performed with the high-altitude research aircraft "Geophysica" on 3 August 2003. Right after departure at 7.30 a.m. this Cirrostratus layer was passed. The measurements show that wind velocities of 40 m/s occurred within this layer at the altitude of the tropopause (at 12 km). At the tropopause and within the cloud layer the temperature was 205 K = - 68 deg C. The number density of the ice particles with a diameter between 0.4 µm and 30 µm was 2 /cm3 of air. The observer on the ground saw that the clouds moved very fast over the sky without changing their visible structure. Also at the landing of the "Geophysica" - after four hours - high wind velocities occurred, because the contrail of the aircraft moved over ¼ of the sky within 1 minute.

CsTropics1-10.jpg: The sky above the tropics - the so-called "maritime continent" - shows often clouds of totally different kinds. The images of the Cirrostratus clouds which can reach altitudes up to 16 km were taken shortly after sunset.


Cirrostratus.jpg: S. Borrmann, Pulpit Rock, Carinthia, Austria, December 2001

Cirrostratus2.jpg: R. Weigel, S. Borrmann, Forli, North Italy, APE-Infra Field Campaign, October 2002

Cirrostratus3-6.jpg: S. Borrmann, Pulpit Rock, Carinthia, Austria, 3 January 2003, 2:10 p.m.

Cirrostratus7-14.jpg: S. Borrmann, Kiruna, North Sweden, during the EUPLEX Field Campaign, 8 February 2003, 8:07 p.m. to 8:15 p.m.

CsTropics1-10.jpg: S. Borrmann, Darwin (Fanny Beach), Northern Territory, Australia, during the SCOUT-O3 Field Campaign, 22 November 2005, 6:33 to 6:38 p.m. local time