Available parameters are frequency of occurence, amount when present, and average cloud amount.
Units are percent. Various abbreviations are defined here ,and informal descriptions of the synoptic low cloud types are provided here . These grid box values were transferred to a regular 2.5 degree grid by assigning the irregular grid box value to all 2.5 degree grid boxes within it. Low cloud type over the ocean from surface observations. Journal of Climate ,11,383-403.