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.