A one-dimensional model which has previously been tested against observational data is used to study the diurnal variation of a marine stratocumulus layer. The influence of the shortwave radiative heating during different seasons on the decoupling of the cloud layer from the subcloud layer is studied. Results for a typical winter and summer situation are presented. It is shown that the decoupling can strongly affect the surface energy balance, suggesting that it is important to resolve the diurnal variation. Finally, a sensitivity study of the model for initial and boundary conditions is presented. Abstract A one-dimensional model which has previously been tested against observational data is used to study the diurnal variation of a marine stratocumulus layer. The influence of the shortwave radiative heating during different seasons on the decoupling of the cloud layer from the subcloud layer is studied. Results for a typical winter and summer situation are presented. It is shown that the decoupling can strongly affect the surface energy balance, suggesting that it is important to resolve the diurnal variation. Finally, a sensitivity study of the model for initial and boundary conditions is presented.