What is Cloud Liquid Water?
Cloud Liquid Water is a measure of the total liquid water contained in a cloud in a vertical column of atmosphere. It does NOT include solid water (snow, ice). Cloud water links the hydrological and radiative components of the climate system and are an interesting area of research. They function as both a warming greenhouse influence as well as a cooling factor as they increase the Earth's albedo, reflecting incoming solar energy back into space. Clouds can therefore provide both a positive and negative feedback to a changing climate. Less is known about clouds than many other measurements and researchers are now focusing on cloud change studies.
Cloud liquid water is a highly variable measure and depends on the type of clouds present at a given location. Complicating this measurement is the fact that different types of clouds can exist at different layers in the atmosphere. Some clouds have low density, such as cirrus clouds, others have higer density and are very wet, such as tropical cumulonimbus.
Cloud liquid water is reported as water per volume of air (g/m3) or per mass of air (g/kg). Using the density of water, cloud liquid water can also be reported as the depth of water in a column (mm).
Microwave Measurement of Cloud Liquid Water
Cloud water can be retrieved from passive microwave measurements because of its strong spectral signature and polarization signature (Wentz, 1997). Passive microwave observations provide a direct estimate of the total absorption along the sensor viewing path. At 18 and 37 GHz, clouds are semi-transparent allowing for measurement of the total columnar absorption. The absorption is related to the total amount of liquid water in the viewing path, after accounting for oxygen and water vapor absorption.
Validation of satellite measured columnar cloud liquid water is a difficult undertaking. The spatial variability of clouds makes comparisons between upward looking ground based radiometers and the large footprint size of the downward looking satellite retrievals problematic. The upward looking ground-based radiometers also have very limited geographic distribution, making meaningful validation over global ocean conditions impossible. Generally, validation is completed using a statistical histogram method (Wentz, 1997).
RSS Cloud Liquid Water Data Products
Individual radiometer gridded binary data files
Cloud liquid water is one of the ocean measurements simulataneously retrieved during radiometer data processing. This measurement is included in the individual satellite binary data files. See the Missions page for more information on each instrument and access to the data
|Instrument||Period of Operation||Version|
|SSM/I / SSMIS||1987 - present||V7|
|TMI||1997 - 2015||V7.1|
|AMSR-E||2002 - 2011||V7|
|WindSat||2003 - present||V7.0.1|
|AMSR2||2012 - present||V7.2|