A Global Perspective On The Diurnal Cycle Of Outgoing Radiation

The reflected solar radiation and emitted thermal radiation at the top of the atmosphere, referred to collectively as Earth Outgoing Radiation (EOR), exhibit strong diurnal signatures. Observing these diurnal signatures has proved challenging from current satellite observations at the global scale, yet a correct representation of diurnal variability is essential for a complete understanding of energy flows through the Earth system. It is clear that the diurnal variability is directly linked to the evolution of weather and climate processes. However, the relative importance of different processes in controlling the diurnal cycle of EOR is yet to be revealed at the global scale.

We seek to gain insight into what these processes are, and their relative importance, using global output at high temporal resolution from the Met Office numerical weather prediction model. We begin by presenting dominant patterns of diurnal variability in EOR, extracted via a principle component analysis. Next, we discuss the physical controls on these dominant patterns, such as surface heating, convective cloud development and marine stratocumulus cloud dissipation. Crucially, this will include examining the extent of coupling between the dominant EOR patterns and the diurnal variability in other relevant geophysical variables. Finally, we point out the significance of diurnal time lags that exist between EOR and the other relevant variables. The robustness of these results is assessed using geostationary satellite observations throughout.