Measurements taken from the CCGS Pierre Radisson in the North Water Polynya
in spring and summer 1998, are used to study the effects of clouds on the
longwave and shortwave components of the Arctic surface radiation budget. T
he clear-sky baseline is provided by parametrizations taken from the litera
ture, tuned to the clear-sky measurements taken during the cruise. The effe
cts of clouds are examined in terms of cloud cover, cloud type, solar zenit
h angle and time of day. A diurnal signal in the cloud cover is found, with
minimum values at local noon. The cloud forcing of the surface radiation w
as found to be mostly negative (i.e., clouds predominantly cool the surface
when the sun is in the sky), with strong dependences on the solar zenith a
ngle, cloud amount and whether the sun is obscured by clouds or is in clear
sky; the influence of cloud type was secondary to these parameters.