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.
First near‐global retrievals of OH rotational temperatures from satellite‐based Meinel band emission measurements
For the first time near‐global retrievals of mesopause OH rotational temperatures from satellite‐borne Meinel band emission measurements are presented. The measurements of the OH (3‐1) Meinel band near 1.5 micron were performed with the SCIAMACHY instrument on the European Space Agency's environmental satellite Envisat. The derived OH (3‐1) rotational temperatures are shown to be in reasonable agreement with the CIRA (1986) atmosphere temperatures for the seasons and latitudes considered. The derived temperatures are in good agreement with ground‐based measurements of the OH rotational temperature performed with a CEDAR Mesospheric Temperature Mapper (MTM) at Maui, Hawaii (21°N/204°E), with the GRound based Infrared P‐branch Spectrometer I (GRIPS‐I) at Hohenpeißenberg (47°N/11°E) and with GRIPS‐II at Wuppertal (51°N/7°E). The SCIAMACHY limb nighttime observations provide a unique data set of near‐global OH rotational temperature to study seasonal and geographical variations, dynamical processes and possibly long‐term temperature trends, if an extended data set becomes available in the future.
The forcing mechanism leading to the Kuroshio intrusion into the South China Sea
[1] We use a high-resolution numerical model to examine the forcing mechanism responsible for Kuroshio intrusion into the South China Sea (SCS). The collective wisdom is that variations in Kuroshio intrusion are closely related to the wind, inside or outside the SCS. A series of experiments was performed to identify the wind-related forcing regulating the intrusion. The experiments demonstrated that the importance of wind inside the SCS is greater than that outside the SCS. Furthermore, the northwestward Ekman drift due to northeasterly wind in winter intensifies the upstream Kuroshio in the Luzon Strait, enhancing the Kuroshio intrusion into the SCS. In particular, the wind stress curl (WSC) off southwest Taiwan is chiefly responsible for the Kuroshio intrusion. Both the WSC and intrusion show both seasonal and intraseasonal variation. As the negative WSC off southwest Taiwan becomes stronger, it contributes to anticyclonic circulation. The enhanced anticyclonic circulation helps the development of the Kuroshio intrusion. The consistency between WSC variability and the intrusion suggests that the WSC off southwest Taiwan is essential to the Kuroshio intrusion variability.