Layer Cloud Amounts for January and July 1979 from 3D-Nephanalysis

Abstract

Layer cloud amounts for the months of January and July 1979 have been extracted from a compressed version of the U.S. Air Force's 3D-nephanalysis. These layer cloud amounts are discussed in the context of the total cloud amount climatology described by Hughes and Henderson-Sellers. Low cloud (?2000 m) is the predominant cloud type in most regions. High cloud (?6000 m) amounts are generally less than ?10% and amounts are significantly smaller than the cirrus cloud amounts of London. It seems likely that some high level cloud has been incorrectly archived as middle level cloud as a result of: (i) the assumption of cloud emissivities of one in the retrieval algorithm and (ii) the latitudinally-invarient definition of the middle/high cloud boundary. There is a reasonable level of agreement between zonally averaged low level and total cloud amounts derived here and those of London. West coast stratus is correctly identified as low cloud but the polar cloud amounts exhibit a seasonal cycle opposite to that seen in traditional climatologies.