Seasonal and Diurnal Variability of the Thermal Skin Layer Characteristics Based on a Comparison of Satellite Measurements by SEVIRI and Data from Temperature-Profiling Drifters

A comparative analysis of high time resolution data acquired by the SEVIRI scanner and temperature-profiling drifters during a multiyear period is carried out. The values of the correlation coefficients, standard deviation, regression coefficients, and mean value difference indicate quite a good agreement of the data. The dependence of temperature gradient dT across the near-surface layer on the season and time of day, as well as on the wind speed, heat fluxes, relative humidity, air temperature, and air–sea-surface temperature difference, is investigated. During the warm season, when the air temperatures are maximum (+18°C and above) and the total heat flux is directed seaward, dT reaches the maximum negative values (–0.8 to –0.9°C), which is primarily related to the presence of a skin layer (cool skin effect). As the wind speed increases, the absolute values of dT decrease due to the destruction of the skin layer. During the cold season, when the total heat flux is directed from the ocean to the atmosphere and the air temperature is at its minimum, dT reaches its maximum positive values. dT reaches the largest negative values in the second half of the day, the period of the greatest daytime warming. Night convection destroys the skin layer, and the dT absolute values decrease. A pronounced dependence of dT on the latent heat fluxes and relative humidity is obtained. The largest dT values are observed at minimum latent heat fluxes and a relative humidity of 85–90%.