MODIS_ACDNC Adiabatic Cloud Droplet Number Concentration daily value

Project: MODIS data - Cloud droplet number concentration is derived from MODerate Resolution Imager Spectroradiometer (MODIS) data from NASA's Terra platform. The MOD08_D3 daily data on a grid of 1x1 degrees is used, which can be downloaded from http://eosdata.gsfc.nasa.gov/daac-bin/MODIS/Data_order.pl NASA's data archive. From the joint histrogram of cloud optical thickness (COD) and cloud-top droplet effective radius (CDR) for liquid water clouds, CDNC is diagnosed assuming adiabatic clouds (Brenguier et al., J. Atmos. Sci., 2000; Quaas et al., Atmos. Chem. Phys., 2005) as CDNC = 1.37 e-5 * COD0.5 * CDR^-2.5 (CDR in m and CDNC in m^-3). Liquid water clouds only are used, and COD and CDR are restricted to their most reliable values (4 micrometer <= CDR <= 30 micrometer and 4 <= COD <= 70; Nakajima and King, J. Atmos. Sci., 1990). However, for MODIS-retrieved CDR, problems are known (Breon and Doutriaux-Boucher, IEEE Trans. Geosci. Remote Sens., 2005). The assumption of adiabacity may not necessarily be valid, even though large regions are considered. We recommend to use CDNC for statistical studies rather than to rely on absolute accuracy in single regions or short time-periods. Summary: Cloud droplet number concentration is derived from MODerate Resolution Imager Spectroradiometer (MODIS) data from NASA's Terra platform. The MOD08_D3 daily data (collection 4 processing stream) on a grid of 1x1 degrees is used, which can be downloaded from http://eosdata.gsfc.nasa.gov/daac-bin/MODIS/Data_order.pl. From the joint histrogram of cloud optical thickness (COD) and cloud-top droplet effective radius (CDR) for liquid water clouds, CDNC is diagnosed assuming adiabatic clouds.