An extreme internal solitary wave event observed in the northern South China Sea
With characteristics of large amplitude and strong current, internal solitary wave (ISW) is a major hazard to marine engineering and submarine navigation; it also has significant impacts on marine ecosystems and fishery activity. Among the world oceans, ISWs are particular active in the northern South China Sea (SCS). In this spirit, the SCS Internal Wave Experiment has been conducted since March 2010 using subsurface mooring array. Here, we report an extreme ISW captured on 4 December 2013 with a maximum amplitude of 240 m and a peak westward current velocity of 2.55 m/s. To the authors’ best knowledge, this is the strongest ISW of the world oceans on record. Full-depth measurements also revealed notable impacts of the extreme ISW on deep-ocean currents and thermal structures. Concurrent mooring measurements near Batan Island showed that the powerful semidiurnal internal tide generation in the Luzon Strait was likely responsible for the occurrence of the extreme ISW event. Based on the HYCOM data-assimilation product, we speculate that the strong stratification around Batan Island related to the strengthening Kuroshio may have contributed to the formation of the extreme ISW.
Internal wave detection using the Moderate Resolution Imaging Spectroradiometer (MODIS)
[1] The Moderate Resolution Imaging Spectroradiometer (MODIS), with its combined attributes of fine spatial resolution, large swath area, and near-daily global coverage, has for the first time allowed sunglint (the near-specular reflectance pattern of sunlight off the ocean surface) to be used to analyze and survey high-frequency nonlinear internal solitary wave occurrences on a near-global scale. The sunglint area within the MODIS swath is large enough to cover an entire basin, and it's spatial resolution is fine enough to identify internal wave signatures whose wavelength is greater than a few hundred meters. This paper describes the use of MODIS for high-frequency nonlinear internal wave detection, presents the results of a survey that detected 3581 internal wave occurrences in MODIS imagery over the period between August 2002 through May 2004, and discusses ways MODIS imagery can be used to improve the study of internal waves.
Terdiurnal oscillations in OH Meinel rotational temperatures for fall conditions at northern mid‐latitude sites
High‐precision (∼0.5 K) measurements of OH Meinel (M) (6,2) rotational temperatures above the Bear Lake Observatory, UT (42°N, 112°W) during October 1996 have revealed an interesting and unexpected mean nocturnal pattern. Ten quality nights (>100 h) of data have been used to form a mean night for autumnal, near‐equinoctial conditions. The mean temperature and RMS variability associated with this mean night were 203 ± 5 K and 2.4 K, respectively, and compare very favorably with expectations based on Na‐lidar measurements of mean tidal temperature perturbations over Urbana, IL (40°N, 88°W) during the fall 1996. Furthermore, this comparison shows that the 8‐h tide was the dominant source of the mean nocturnal temperature variability in the OH M region during this period. Additional data, obtained at Fort Collins, CO (41°N, 105°W) in November 1997, illustrate the occurrence of an 8‐h component of OH temperature variability about two months after the equinox and show that daily amplitudes as high as ≅15 K are possible.