Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong Internal gravity waves are propagating disturbances of the ocean's density stratification. Their physics resembles that of surface gravity waves but with buoyancy rather than gravity providing their restoring force -making them much larger (10's to 100's of meters instead of 1 to 10 meters) and slower (hours instead of seconds). Generated primarily by tidal flow past seafloor topography and winds blowing on the sea surface, and typically having multi-kilometer-scale horizontal wavelengths, their estimated 1 TW of deep-sea dissipation is understood to play a crucial role in the ocean's global redistribution of heat and momentum 12 . A major challenge is to improve understanding of internal wave generation, propagation, steepening and dissipation, so that the role of internal waves can be more accurately incorporated in climate models.The internal waves that originate from the Luzon Strait on the eastern margin of the South China Sea (SCS) are the largest documented in the global oceans ( Figure 1).As the waves propagate west from the Luzon Strait they steepen dramatically ( Figure 1a), producing distinctive solitary wave fronts evident in sun glint and synthetic aperture radar (SAR) images from satellites ( Figure 1b). When they shoal onto the continental slope to the west, the downward displacement of the ocean's layers associated with these solitary waves can exceed 250 m in 5 minutes 8 . On such a scale, these waves pose hazards for underwater navigation and offshore drilling 4 , and supply nutrients from the deep ocean that nourish coral reefs 1 and pilot whale populations that forage in their wakes 13 .Over the past decade a number of field studies have been conducted in the region; this work has been comprehensively reviewed 10,11 . All of these studies, however, focused on the propagation of the internal waves across the SCS and their interactions with the continental shelf of China. Until the present study there had been no substantial in situ data gathered at the generation site of the Luzon Strait, in large part because of the extremely challenging operating conditions. A consequence has been persistent 5 confusion regarding the nature of the generation mechanism 11 ; an underlying cause being the sensitivity of the models employed to the system parameters, such as the chosen transect for a two-dimensional model, the linear internal wave speed or the assumed location of the waves' origin within the Luzon Strait. Furthermore, the lack of in situ data from the Luzon Strait has meant an inability to test numerical predictions of energy budgets 9 and no knowledge of the impact of the Kuroshio on the emergence of internal solitary waves 11 .The goal of IWISE is to obtain the first comprehensive in situ data set from the Luzon Strait, which in combination with high-resolution three-dimensional numerical modeling supports a cradle-to-grave picture ...

[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.

[1] A wide variety of oceanic and atmospheric phenomena are often observed in and around the sunglint region on optical images of the sea surface. The appearance of these phenomena depends strongly on the viewing geometry with areas on the sea surface that are rougher (or smoother) than the background appearing as either brighter or darker than the background depending on their position relative to the specular point. To understand these sea surface signature variations, this paper introduces the concept of a critical sensor viewing angle, defined as the sensor zenith angle at which different sea surface roughness variances produce identical sunglint radiance. It is when the imaging geometry transitions through the critical angle that a surface feature goes through a brightness reversal. Knowledge of where this transition takes place is important for properly interpreting the characteristics of the sea surface signature of these phenomena. The theory behind the concept of the critical angle is presented and then applied to sunglint imagery acquired over the ocean from space by the Moderate Resolution Imaging Spectroradiometer onboard NASA's Aqua and Terra satellites.Citation: Jackson, C. R., and W. Alpers (2010), The role of the critical angle in brightness reversals on sunglint images of the sea surface,

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[1] The nonhydrostatic Regional Ocean Modeling System is applied to study the effects of thermocline shoaling/deepening, bathymetry, and asymmetric modulated tides on the soliton growth to the west and east of Luzon Strait in the South China Sea and western Pacific Ocean. Luzon Strait comprises a shallow east ridge and a deep west ridge, and its interaction with barotropic tidal currents yields strong westward internal tides that disperse into solitons. Satellite imagery indicates that the westward solitons are more numerous and better defined than the eastward solitons. The model results show that the eastward solitons are 45%, 39%, 28%, and 23% smaller than the westward solitons due to asymmetric modulated barotropic tides at the east ridge, a deeper Pacific Ocean, westward thermocline shoaling related to the Kuroshio current, and internal tide resonance in a double ridge configuration, respectively. Due to the westward location of the Kuroshio, little thermocline deepening occurs east of the east ridge. Hence, the influence of thermocline deepening on counteracting eastward soliton growth is small. The Kuroshio mainly enhances westward soliton growth. The dispersion of internal tides into solitons is governed by the balance between the nonlinearity parameter on the one hand and the nonhydrostatic and Coriolis dispersions on the other. It is shown that this balance favors soliton growth for thermocline shoaling, while it counters it for a deeper ocean. A series of double ridge experiments is performed, in which the distance between the ridges and the height of the west ridge are varied. For a semidiurnal tidal forcing and two Gaussian ridges separated by 100 km, barotropic to baroclinic energy conversion is enhanced at both ridges, causing larger westward internal tides and solitons. The combination of Coriolis forcing, thermocline shoaling, and a double ridge configuration enhances the distinctiveness of the so-called type a and b solitons when a modulated tide occurs.