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In aviation, ceiling is a measurement of the height of the base of the lowest clouds (not to be confused with cloud base which has a specific definition) that cover more than half of the sky (more than 4 oktas) relative to the ground.
Sky conditions are estimated in terms of how many eighths of the sky are covered in cloud, ranging from 0 oktas (completely clear sky) through to 8 oktas (completely overcast). In addition, in the SYNOP code there is an extra cloud cover indicator '9' indicating that the sky is totally obscured (i.e. hidden from view), usually due to dense fog ...
The boundary criteria between IMC and VMC are known as the VMC minima and are defined by: visibility, cloud ceilings (for takeoffs and landings), and cloud clearances. The exact requirements vary by type of airspace , whether it is day or night (for countries that permit night VFR), and from country to country.
BKN022 indicates a broken (over half the sky) cloud layer with its base at 2,200 ft (670 m) above ground level (AGL). The lowest "BKN" or "OVC" layer specifies the cloud ceiling . OVC050 indicates an unbroken cloud layer (overcast) with its base at 5,000 ft (1,500 m) above ground level (AGL).
Clouds of the genus nimbostratus tend to bring constant precipitation and low visibility. This cloud type normally forms above 2 kilometres (6,600 ft) [10] from altostratus cloud but tends to thicken into the lower levels during the occurrence of precipitation. The top of a nimbostratus deck is usually in the middle level of the troposphere.
A cloud base (or the base of the cloud) is the lowest altitude of the visible portion of a cloud. It is traditionally expressed either in metres or feet above mean sea level or above a planetary surface, or as the pressure level corresponding to this altitude in hectopascals (hPa, equivalent to the millibar ).
The scattering of direct sunlight on those clouds results in the same polarization pattern. In other words, the proportion of the sky that follows the Rayleigh Sky Model is high for both clear skies and cloudy skies. The pattern is also clearly visible in small visible patches of sky. The celestial angle of polarization is unaffected by clouds.
A ceilometer is a device that uses a laser or other light source to determine the height of a cloud ceiling or cloud base. [1] Ceilometers can also be used to measure the aerosol concentration within the atmosphere. [2] A ceilometer that uses laser light is a type of atmospheric lidar (light detection and ranging) instrument. [3] [4]