Observations and Models of Oceanic Diurnal Warming

Several recent studies have concluded that coupled climate models should utilize a diurnally varying SST to examine the details of the boundary layer response and ensuing air-sea interactions. The global distribution of diurnal warming is clearly linked to wind speed and will therefore respond to the climatic distributions and seasonal or anomalous changes in wind speed, as shown by the response to ENSO related wind speed anomalies. The Subtropical High regions in each ocean basin, and the Tropical Indian and Western Pacific Oceans have the largest averages of diurnal warming. The intra-day variability of surface warming has been related to the stability of the boundary layer and atmospheric convection. Since the tropical convection is an important driver of global atmospheric circulation, this example of ocean-atmospheric feedback underscores how diurnal warming of the ocean surface may influence larger scale weather patterns and climate.

The Zeng and Beljaars 2005 (ZB05) model has been widely adapted by the modeling community (ECMWF, GEOS-5, NOGAPS) because it conserves heat and is easily implemented. Here we evaluate the accuracy of ZB05 diurnal warming with GEOS-5 forcing and collocated SEVIRI SST data. As others have shown, our analysis showed that ZB05 does not retain sufficient heat in the afternoon; it diminishes far faster than both the empirically derived Gentemann 2003 model and collocated SEVIRI SST data. To diagnose discrepancies, we compared ZB05 profiles to General Ocean Turbulence Model (GOTM) profiles, developed a wind speed dependent parameterization of ZB05’s vertical profiles, and examine the influence of collocated ocean color data.