Short-period internal waves in tidal seas on various types of shelf according to in situ and satellite observations

The main source of generation of short-period internal waves (SIW’s) is the dissipation of the internal tide on the roughness of the bottom relief. Differences in the slope of the bottom and geographical latitude have an impact on the propagation of internal tide and on the generation of SIW’s. Based on the synthesis of the results of contact, remote observations, and modeling, the characteristics of the SIW’s in the Barents Sea on a wide shelf with small bottom slopes, and in the Avacha Bay with a narrow shelf and significant bottom slopes are considered.

In the Barents Sea, in situ observations were carried out in August 2016 near the Kharlov island. Measurements in the Avacha Bay were carried out in August – September 2018 near the Cape Shipunsky. The height and period of the SIW’s were estimated. The SIW’s spectrum was calculated and compared with the Garrett-Munk spectrum.

Sentinel-1A/B, ALOS-2 PALSAR-2, Sentinel-2A/B, and Landsat-8 images were used to analyze the manifestations of SIW’s. To identify the centers of internal tide generation, the tidal body force criterium for harmonics M2 and K1 was used, calculated using Copernicus reanalysis data and the OTIS tidal model.

On the records in the Avacha Bay, long-period fluctuations of isotherms due to semi-daily tidal dynamics are traced. Against the background of semi-daily fluctuations, SIW’s with a period of about 15 minutes and a height of up to 8 meters are distinguished. On the record, during the low tide period, a SIW’s train with heights of up to 15 meters was recorded. In the Barents Sea, the long-period variability of isotherms is less pronounced, short-period fluctuations with a period of about 10 minutes and a height of up to 5 meters are dominant.

The Ursell parameter demonstrates that waves about 8 meters high in the Barents Sea are weakly nonlinear, and waves about 15 meters high in the Avacha Bay are strongly nonlinear. Spectrum calculations show that the oscillation energy in the Barents Sea at all frequencies is lower than in the Avacha Bay, while it does not exceed the energy of the Garrett-Monk spectrum. In Avacha Bay, the oscillation energy at almost all frequencies is higher than the energy of the Garrett-Monk spectrum.

93 manifestations of SIW’s were detected in the Barents Sea, and 72 ones were detected in the Avacha Bay. Most of the manifestations are in the areas of high values of the tidal body force criterium, which may indicate the generation of SIW’s under the influence of the decay of the internal tide.

It was shown that both in the Barents Sea, close to the critical latitude for the semidiurnal tide, and in the Avacha Bay beyond the critical latitude for the diurnal tide, SIW’s are generated under the influence of an internal tide. However, the energy of short-period oscillations in the Avacha Bay is higher than in the Barents Sea.

The study was supported by RFBR grant No. 20-35-90054.