Cloud effect of persistent stratus nebulosus at the Payerne BSRN site

This analysis presents radiative transfer calculations of surface downwelling long-wave and short-wave radiation and the corresponding cloud radiative effect of single-layered, completely overcast stratus situations (stratus nebulosus) at the Baseline Surface Radiation Network (BSRN) site Payerne. We found an excellent agreement of 0.6 W m− 2 mean difference between modeled and observed downwelling long-wave radiation with a root mean squared error of 1.5 W m− 2 for 30 carefully selected cases. The discrepancies between modeled and observed diffuse downwelling short-wave radiation are with 2.8 ± 25.4 W m− 2 considerably higher. The net cloud radiative effect of the 30 cases shows a pronounced diurnal variation determined by the diurnal cycle of the short-wave cloud effect and the nearly constant positive long-wave cloud effect. Mean net cloud effect ranges from 80 ± 3 W m− 2 (min.: 75 W m− 2; max.: 85 W m− 2) during nighttime in the absence of solar radiation to − 197 ± 74 W m− 2 (min.: − 373 W m− 2; max.: − 91 W m− 2) around noon. Mean net cloud effect averaged over 24 h is 18 ± 20 W m− 2 (min.: − 28 W m− 2; max.: + 42 W m− 2) for the 30 cases assuming a persistent, completely overcast stratus cloud. This implies that stratus nebulosus can have a substantial positive radiative effect during the winter half year at this site.

► We model surface radiative fluxes of single-layered, overcast stratus situations. ► There is an excellent agreement between long-wave calculations and observations. ► The short-wave calculations show larger discrepancies. ► Instantaneous net cloud effect is strongly negative around noon. ► The net cloud effect averaged over 24 hours is slightly positive.