Seasonal Variation of Cloud Radiative Forcing Over Young Sea Ice During the N-ICE2015 Experiment

There is a lack of comprehensive measurements of the seasonal variation of cloud and radiation properties over sea ice. The Norwegian Young Sea Ice experiment (N-ICE2015), conducted from January to June 2015, was the first experiment since SHEBA in 1997/1998 to measure cloud properties and all components of the surface energy balance. N-ICE2015 was also the first experiment that was focused on understanding the effects of the atmosphere specifically on thin, young sea ice near the edge of the Arctic ice pack. Here we present the variation of cloud radiative forcing (CRF) at the surface during the seasonal transition from winter to summer. Cloud macrophysical and microphysical properties were measured using a micropulse lidar and a ceilometer. Broadband radiometers were used to measure upwelling and downwelling shortwave and longwave radiative fluxes at the surface. These measurements are combined with radiative transfer calculations of clear-sky fluxes to determine cloud radiative forcing during the seasonal transition. During the winter, the CRF is determined by longwave radiation and averages about 20-30 W m^-2, with a range of 0 to 60 W m^-2. In spring, shortwave radiation creates a strong diurnal cycle in CRF with values ranging from about -40 to +60 W m^-2, the values of which depend strongly on the cloud fraction. In summer, the CRF averages to about 50-60 W m^-2 and is always positive with values ranging from 10 to 100 W m^-2. Two case studies, one in winter and one in spring, will be highlighted, as well as the dependence of CRF on cloud phase.