Thermic structure and intense internal waves on the narrow continental shelf of the Black Sea

Abstract

Measurements results of the thermic structure taken from the waters of the narrow continental shelf of the south coast of Crimea are discussed. Continuous observations were performed in July–August 1993, from a stationary oceanologic platform (depth 30 m) using an antenna with three temperature distribution sensors and two temperature gradient distribution sensors situated at the platform corners (in a 19×22 m plane) covering the thermocline completely. Probes were also made of the water layer down to the bottom using a CTD, and also the currents at 5, 10 and 20 m were observed. A continuous register of the sea level waves, wind and atmospheric pressure was taken. The thermic structure showed oscillations in three time-scales: synoptic, related to the surge phenomena (3–5 days); inertial (17–18 h) and short period (less than 1 h). The thermocline was completely extended with a strong negative setup, and was close to the bottom with a positive setup, possessing vertical gradients of up to 2°C/m. Inertial movements showed up in the current oscillations and also produced vertical displacements in the thermocline up to 8–10 m, happening constantly while the measurements were taken. These displacements were usually related to groups of intense internal short period waves with amplitudes of 4–9 m, periods of 14–28 min and wavelengths of 250–360 m. An intense movement, with diurnal period related to the breeze processes on the coast, was also found in the currents. The relationship between the parameters of the intense waves in groups and those of the medium dispersion and non-linearity as well as the parameters of the calculated solitons in the Korteweg and de Vries equation, are analyzed.