Seasonal Variability of Near-Inertial Internal Waves in the Deep Central Part of the Black Sea

Abstract

This observational study is concerned with the seasonal variability of near-inertial internal waves (NIWs) in the central part of the Black Sea. Rotary spectral analysis of the nearly year-long time series of the sea current velocity measurements at 100 m and 1700 m revealed the prevailing anticyclonic component of the motions near the local inertial frequency f. Both the rotary spectra and the visual exploration of the time series showed that the peaks of NIWs were blue-shifted to higher frequencies. The monthly average blue-shift was stronger up to 1.038f in the summer. It was found that the minimum intensification of the NIWs occurred in summertime and the maximum intensification was characteristic of the autumn-winter period when the NIW packets included up to 16 waves with pronounced clockwise rotation of the velocity vectors.

Observations of Near-Inertial Internal Waves over the Continental Slope in the Northeastern Black Sea

“…Therefore, the Black Sea basin could serve as a natural laboratory for the study of NIWs. The blue-shift phenomenon has been observed for NIW frequencies in the World Ocean [19,20], as well as for the Black Sea [14,15].…”

“…Observations of NIWs in the ocean are widespread [1,[3][4][5][6][7][8][9] and NIWs have been investigated in semi-enclosed seas, such as the Baltic Sea [10,11] and the Japan Sea [12,13]; observations of NIWs in the Black Sea are still rare [14][15][16][17]. The Black Sea is an almost tideless basin (the tides are less than several centimeters [18] in amplitude) so the inertial variability should dominate the energy spectra [14,15]. In other words, most of the energy in the sub-diurnal band in the Black Sea is due to near-inertial motions.…”

“…The measurements mostly refer to the coastal area and are extremely limited in time of observation during summer seasons. Recently, an attempt was made to identify the seasonality of NIWs in the central part of the Black Sea basin [15]. However, that observation was made for two fixed depths of 100 m and 1700 m.…”

Water Structure in the Utrish Nature Reserve (Black Sea) during 2020–2021 According to Thermistor Chain Data

“…Such oscillations are considered to be inertial internal waves with a period 10-20 h but, without additional information, the genesis of these is unclear. Previously, inertial waves with a period of about 17 h were observed and described in [79,80].…”

“…Such oscillations are considered to be inertial internal waves with a period 10-20 h but, without additional information, the genesis of these is unclear. Previously, inertial waves with a period of about 17 h were observed and described in [79,80]. Figure 15 shows an example of internal waves with a period of ~13 min, which were well manifested for 2 h at a horizon of 11.8 m. The amplitude of temperature fluctuations was up to 0.17 As a result of the analysis from the graphs, we found many manifestations of shortperiod internal waves at frequencies from 5 to 30 min and longer at periods of about 17 h. These results are generally consistent with the results from [77,79].…”