The cloud top is where the snow, rain and sleet come from. Cloud top height can be estimated from the ground by triangulation. However, this is often inconvenient as this is practically feasible only for isolated clouds in full view of the observers. Ground-based radars can be used to derive this cloud property. An alternative approach is to acquire airborne observations either visually or using specific instruments such as a lidar. This technique is very appropriate to characterize individual clouds but becomes unmanageable to repetitively monitor clouds over large areas. Cloud top height may be derived from satellite measurements, either through stereophotogrammetry or by converting temperature measurements into estimations of height. An example of the stereo technique using the Multi-angle Imaging SpectroRadiometer instrument can be found , and using the Along Track Scanning Radiometer instruments . An example of the estimation of cloud top height from temperature measurements is available from . Cloud top pressure can also be used as an indicator of cloud top height. The Cooperative Institute for Meteorological Satellite Studies provides real-time cloud top pressure maps of the conterminous United States derived from data obtained from the GOES 11 and GOES 12satellites.
In convective clouds, the cloud top is largely influenced by the strength of the convection activity, which itself may depend on surface properties, in particular the supply of heat and water vapor below the cloud. Cloud top height is often much more variable than cloud base elevation. Clouds greatly affect the transfer of radiation in the atmosphere. In the solar spectral domain, cloud albedo is directly related to the nature, size and shape of cloud particles, which themselves are affected by the height of the cloud top. In the thermal domain, water is a strong absorber. Hence clouds cool downfrom the top through infrared radiation at the prevailing temperature: the higher the cloud top, the cooler the particles and the lower the rate of emission. For a synthetic discussion of the impact of clouds on the climate system, see the , in particular chapter 7.2.
