The altitudes and properties of clouds are important to the earth's climate system because they affect the radiative balance, the abundance of water vapor, and the flux of water into the stratosphere, which in turn affects stratospheric temperature and ozone depletion. CloudSat and CALIPSO will measure global cloud altitude, microphysical properties, ice water content, and brightness temperature, as well as surrounding aerosol fields. In particular, CALIPSO will provide unprecedented global datasets for cloud height and aerosol vertical distribution, with far better accuracy than previously available. This work proposes to use these datasets, along with detailed aerosol and cloud microphysics models, to answer the following scientific questions. What governs the altitude of convection? How are stratospheric water vapor entry values regulated? To what degree are estimates of direct and indirect aerosol forcing biased by the assumption of the separability of albedo by haze and clouds?
Our recent work has shown that stratospheric water vapor is affected by both convective hydration and dehydration due to in situ generated clouds within the tropical tropopause layer (TTL), with the balance between the two depending on the absolute and relative altitudes of hydrating and dehydrating clouds - information that cannot be derived from currently available global measurements. This work will (1) use CALIPSO measurements to relate convective cloud altitude and temperature to quantities which are available globally on time scales of convective systems, such as hourly IR satellite imagery; (2) input the results of this convective analysis into microphysical models; and (3) compare the calculated in-situ subvisible cirrus cloud distributions to climatological distributions from CALIPSO measurements.
We also propose to investigate the environmental conditions controlling deep convection height using a combination of observational and modeling approaches. The observational approach will involve using CALIPSO and CloudSat aerosol, cloud height, and ice water content products, along with MODIS cloud products and NCEP meteorological fields. We will determine relationships between cloud height and other measured quantities (e.g., aerosol extinction, thermodynamic and humidity profiles, wind shear profile, convection structure). The modeling component of the proposed work will involve using a cloud-resolving model with detailed microphysics to understand the sensitivities of deep convection height to environmental conditions indicated by the satellite measurements.
The final component of the proposed work will address the direct and indirect aerosol forcings of boundary-layer clouds. The backscatter albedo measured by CALIPSO will provide a means to identify the respective roles of direct and indirect aerosol forcings. Our work with sub-orbital lidar albedo measurements indicates that in contrast to previous assumptions, there is an albedo continuum between haze and clouds, with the implication that the global aerosol radiative forcing is overestimated by assuming that the albedo of haze and clouds do not overlap. We will use large-eddy simulations of stratocumulus and trade cumulus clouds to understand the physical system underlying the CALIPSO lidar albedo measurements.
