Seasonal Variability of the Diurnal Cycle of the Black Sea Surface Temperature from the SEVIRI Satellite Measurements

Introduction. Heat and gas exchange between the ocean and the atmosphere, and stratification and vertical mixing in the sea upper layer are subjected to the diurnal variations of the sea surface temperature. Data and methods. The data obtained by the scanner SEVIRI in 2015 (time resolution is 1 hour) are used to study seasonal and spatial variability of the sea surface temperature diurnal cycle in the Black Sea. Results. During a day, the upper layer heats from 6:00 to 17:00 (the highest temperature) and then cools from 19:00 to 5:00 (the next morning) up to its minimum. The largest diurnal deviations of the sea surface temperature from the average seasonal ones are observed in spring-summer (+/- 0.8 degrees C), whereas the lowest deviations are typical of the autumn-winter period (+/- 0.1-0.2 degrees C). A few cases when the diurnal warming is high were detected and analyzed. In some regions, the amplitude of the sea surface temperature diurnal cycle exceeded 5 degrees C and reached its extreme values 7-7.2 degrees C. The low wind speed (less than 4 m/s) is an important reason of these extreme events. The most often intensive diurnal warming is due to the low wind conditions which are highly frequently observed in May. In winter the values of the sea surface temperature diurnal amplitude are minimum and do not exceed 1.5 degrees C. Since April, they sharply increase and reach their maximum 2.4 degrees C in May. The most significant sea surface temperature diurnal amplitude is observed in the Black Sea southeast region and in its southwest coastal part. Such spatial distribution is a result of the wind shadow zone which is formed by the Caucasian and Pontic mountains. Discussion and conclusion. The features of spatial and seasonal variability of the Black Sea surface temperature diurnal cycle, and its relation to the wind characteristics in different seasons are studied based on the SEVIRI scanner high-frequency measurements.