Physical Oceanography (Apr 2022)
Observations of the Second Mode Internal Waves in the White and Barents Seas
Abstract
Purpose. The purpose of the work is to describe a comprehensive technique for detecting the second mode internal waves, and to consider the cases of their record during the in situ measurements carried out in the coastal areas of the White and Barents seas in summer. Methods and Results. The initial data were formed based on the series of frequent many-hour CTD measurements performed in the coastal stratified areas in the summer seasons, 2009–2017. The waves, duration of which was 5–60 min and the heights exceeded 1 m, were considered. The observations were processed using the complex of wavelet- and mode-analyses. The cross-wavelet spectrum of the isotherms’ vertical displacements demonstrated a statistically significant increase in the cross-spectral power with a complete phase mismatch associated with the second mode of internal waves. The positions of the amplitude maxima of the second mode internal waves on the records of the isotherm oscillations were additionally checked by calculating the hydrostatic normal vertical modes. It is shown that in the near-surface seasonal pycnocline of the White Sea, the second mode internal waves were recorded as the single “convex” ones with average duration 10 min and amplitude 2 m. In the Barents Sea, such waves were observed both as the single “convex” waves, and as the “concave” and “convex” sequential ones with average duration 20 min and amplitude up to 1.5 m. It was established that in the considered areas of the White and Barents seas, the intermittency of the second mode internal waves did not exceed 1 %. Conclusions. Analysis of the archival data on the six-year-long in situ observations has resulted in first description of the cases when the second mode internal waves had been recorded in the White and Barents seas. Having been analyzed, more than 350-hour records of temperature fluctuations permitted to detect only 5 cases demonstrating the second mode internal waves in a form of the “convex” and “concave” ones with their total duration not exceeding 1.5 hours. This indicates that occurrence of such waves is extremely rare in the water areas under consideration.
