query: How high can clouds reach in the atmosphere?
passage: Cumulonimbus cloud
Towering cumulonimbus clouds are typically accompanied by smaller cumulus clouds. The cumulonimbus base may extend several miles across and occupy low to middle altitudes - formed at altitude from approximately 200 to 4,000m (700 to 10,000ft). Peaks typically reach to as much as 12,000m (39,000ft), with extreme instances as high as 21,000m (69,000ft) or more.[2] Well-developed cumulonimbus clouds are characterized by a flat, anvil-like top (anvil dome), caused by wind shear or inversion near the tropopause. The shelf of the anvil may precede the main cloud's vertical component for many miles, and be accompanied by lightning. Occasionally, rising air parcels surpass the equilibrium level (due to momentum) and form an overshooting top culminating at the maximum parcel level. When vertically developed, this largest of all clouds usually extends through all three cloud regions. Even the smallest cumulonimbus cloud dwarfs its neighbors in comparison.
passage: Atmosphere of Venus
Odd structures known as polar vortices lie within the cold polar collars.[3] They are giant hurricane-like storms four times larger than their terrestrial analogs. Each vortex has two "eyes"—the centres of rotation, which are connected by distinct S-shaped cloud structures. Such double eyed structures are also called polar dipoles.[6] Vortices rotate with the period of about 3 days in the direction of general super-rotation of the atmosphere.[6] The linear wind speeds are 35–50m/s near their outer edges and zero at the poles.[6] The temperature at the cloud-tops in the each polar vortex is much higher than in the nearby polar collars reaching 250K (−23°C).[6] The conventional interpretation of the polar vortices is that they are anticyclones with downwelling in the centre and upwelling in the cold polar collars.[6] This type of circulation resembles a winter polar anticyclonic vortex on Earth, especially the one found over Antarctica. The observations in the various infrared atmospheric windows indicate that the anticyclonic circulation observed near the poles penetrates as deep as to 50km altitude, i.e. to the base of the clouds.[6] The polar upper troposphere and mesosphere are extremely dynamic; large bright clouds may appear and disappear over the space of a few hours. One such event was observed by Venus Express between 9 and 13 January 2007, when the south polar region became brighter by 30%.[24] This event was probably caused by an injection of sulfur dioxide into the mesosphere, which then condensed forming a bright haze.[24] The two eyes in the vortices have yet to be explained.[26]