The origin of cloud-base air: Mixed layer or surface layer?
Authors
David Romps — Lawrence Berkeley National Laboratory
Rusen Oktem — Lawrence Berkeley National Laboratory
Category
Warm low clouds, including aerosol interactions
Description
Cloud-base height is an important variable for a variety of applications, including air-traffic control, solar-power forecasting, and the parameterization of convection in global climate models. For the past 180 years, many different mathematical expressions have been proposed to estimate the cloud-base height from near-surface measurements of temperature, pressure, and humidity. None of these expressions are exact, and their errors range from tens of meters to hundreds of meters. Here, an exact expression is presented for cloud-base height assuming ideal gas behavior and constant heat capacities. This expression is then used, in conjunction with stereo photogrammetry and thermodynamic data from the ARM SGP site, to determine whether cloud-base air rises undiluted from the surface layer or is heavily diluted with mixed-layer air.
