Modeled Diurnally Varying Sea Surface Temperatures and Their Influence on Surface Heat Fluxes

A diurnal warming model is used create a new data set of global, diurnally varying sea surface temperatures over a five year period from 2000 to 2004. The model is forced with atmospheric bulk variables, precipitation rate, and radiation fluxes from NASA's MERRA reanalysis whereas bulk SST is approximated by the Reynolds OI AVHRR-only SST dataset. The model simulates the diurnal warming magnitude (dSST) and sensible heat flux and latent heat flux computed with and without a diurnally varying skin temperature at every hour for each day. Differences between each of the fluxes with and without a diurnally varying SST are examined. Characteristics of the dataset are identified on a daily and semi-seasonal scale over the globe. Diurnal warming is concentrated in areas with climatologically low surface wind speed regimes, for example, in the low level convergence zones of the tropics, the Indian Ocean as a result from the Asian monsoon wind variability, the Mediterranean Sea in the summer months, the central Pacific coastlines near mountain ranges in the early months of the year, and the mid-Atlantic in association with the Bermuda High. Maximum averaged diurnal warming reaches roughly 0.3˚C and latent heat flux deficits of 15 W/m2 particularly in the Indian Ocean over a two-month period. With the exception of persistent diurnal warming in the central tropical Pacific just south of central Mexico, the duration of diurnal warming as a percentage of total daylight hours between the tropics and midlatitudes is quite comparable. In the mid-Atlantic, dSSTs can exceed roughly 0.7˚C up to 25% of the time in the two month period. Similarly, latent heat fluxes are underestimated by at least 10 W/m2 up to 25% of the time. Sensitivity of diurnal warming is specific to particular ranges of low wind speed and large solar radiation. Best guess bias corrections to the MERRA wind speeds results in increases as large as 1.5°C. Bimonthly averages, however, are generally less than 0.06°C and latent heat fluxes are less than 2 W/m2. While precipitation is the smallest contributor compared to winds and radiation, the model configurations allows conditions that are contrary to the underlying model physics in which precipitation increases diurnal warming.