Interannual variability in cloudiness, sea surface temperature, and atmospheric circulation over the midlatitude North Pacific during summer

Abstract

Large-scale interannual and interdecadal variability in surface-observed marine stratiform cloud (MSC) amount and sea surface temperature (SST) are closely coupled over the central North Pacific during summer. Increased (decreased) MSC amount occurs with decreased (increased) SST, resulting from coincident meridional shifts in the regions of strong SST gradient and cloud gradient between subtropics and midlatitudes. Investigation of variability in low cloud types indicates that a shift in the SST gradient region produces corresponding shifts in the transition from subtropical cumulus to midlatitude stratus and the transition from midlatitude stratocumulus to subtropical cumulus. Since MSC reduces the amount of radiation absorbed by the ocean, these processes create the potential for a positive MSC feedback on SST; however, estimated MSC radiative anomalies are observed to have little net impact on SST, probably due to the tendency for compensation by latent heat flux anomalies.Large-scale interannual and interdecadal variability in nimbostratus and SST are also coupled over the central North Pacific during summer, suggesting coincident meridional shifts in the storm track and region of strong SST gradient. This suggests synoptic activity also plays a role in MSC variability.