Impact of Diurnal Warm Layers on Atmospheric Convection

Abstract

This manuscript presents a study of oceanic diurnal warm layers (DWLs) in kilometer-scale global coupled simulations and their impact on atmospheric convection in the tropics. With the implementation of thin vertical levels in the ocean, DWLs are directly resolved, and sea surface temperature (SST) fluctuations of up to several Kelvin appear in regions with low wind and high solar radiation. The increase of SST during the day causes an abrupt afternoon increase of atmospheric moisture due to enhanced latent heat flux (LHF), followed by an increase in cloud cover (CC) and cloud liquid water (CLW). However, although the diurnal SST amplitude is even exaggerated in comparison to reanalysis, this effect only lasts for 5–6 hr and leads to an absolute difference of 1% for CC and 0.01 kg m−2 for CLW. This can be explained by the fact that the low wind over the SST anomalies dampens their potential effect on the LHF and hence clouds. All in all, the impact of DWLs on convective CC is found to be negligible in the tropical mean.