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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 ).
Cumulus clouds viewed from a plane flying above them. The liquid water density within a cumulus cloud has been found to change with height above the cloud base rather than being approximately constant throughout the cloud. In one particular study, the concentration was found to be zero at cloud base.
It marks where the cloud base begins when air is heated from below to the convective temperature, without mechanical lift. [ 1 ] Once the CCL is determined, the surface temperature necessary to raise a mass of air to that height can be found by using the Dry Adiabatic Lapse Rate (DALR) to determine the potential temperature.
The planetary boundary layer can have lower level clouds located around the capping inversion top. The two main types of clouds within the planetary boundary layer are fair-weather cumulus clouds and stratocumulus clouds. The underlying surface primarily determines the type of cloud produced within the planetary boundary layer.
A typical cumulus cloud has a scale of less than 1 kilometre (0.62 mi), and would require a grid even finer than this to be represented physically by the equations of fluid motion. Therefore, the processes that such clouds represent are parameterized, by processes of various sophistication. In the earliest models, if a column of air in a model ...
Soaring pilots refer to this near-base sucking as "cloud suck", a phenomenon known to generally be more intense the taller the cumulus cloud – and to thus be at maximum intensity with a cumulonimbus. Since the dynamic updraft is wide, the updraft velocity varies little laterally and thus the turbulence is minimised.
The cloud base will be somewhere within the layer bounded by these parameters. The difference between the dry adiabatic lapse rate and the rate at which the dew point drops is around 4.5 °C per 1,000 m. Given a difference in temperature and dew point readings on the ground, one can easily find the LCL by multiplying the difference by 125 m/°C.
the cloud IR emissivity, with values between 0 and 1, with a global average around 0.7; the effective cloud amount, the cloud amount weighted by the cloud IR emissivity, with a global average of 0.5; the cloud (visible) optical depth varies within a range of 4 and 10. the cloud water path for the liquid and solid (ice) phases of the cloud particles