Generation of Internal Solitary Waves by Lateral Circulation in a Stratified Estuary

Abstract

Internal solitary waves are commonly observed in the coastal ocean where they are known to contribute to mass transport and turbulent mixing. While these waves are often generated by cross-isobath barotropic tidal currents, novel observations are presented suggesting that internal solitary waves result from along-isobath tidal flows over channel-shoal bathymetry. Mooring and ship-based velocity, temperature, and salinity data were collected over a cross-channel section in a stratified estuary. The data show that Ekman forcing on along-channel tidal currents drives lateral circulation, which interacts with the stratified water over the deep channel to generate a supercritical mode-2 internal lee wave. This lee wave propagates onto the shallow shoal and evolves into a group of internal solitary waves of elevation due to nonlinear steepening. These observations highlight the potential importance of three-dimensionality on the conversion of tidal flow to internal waves in the rotating ocean.

Breaking of internal solitary waves generated by an estuarine gravity current

“…High-resolution temperature and velocity data collected at the tower/M3 revealed frequent occurrences of high-frequency ISWs of elevation. Some of these waves appeared regularly during certain phases of a tidal cycle and were generated by the interaction between the tidally driven lateral circulation and channel-shore bathymetry [Xie et al, 2017b]. Here we report ISWs observed during wind events and generated by a different Geophysical Research Letters 10.1002/2017GL073824 mechanism.…”

“…Although the data analysis focused on the wind event on 20 October, the ISWs were observed on all down-estuary wind events during the mooring deployment period. Under weak wind conditions, internal waves occurred regularly Geophysical Research Letters 10.1002/2017GL073824 during certain phases of a tidal cycle and were generated by the interaction between the tidally driven lateral circulation and channel-shore bathymetry [Xie et al, 2017b], much like the ISWs generated by flowtopography interactions over a sill or on the continental shelf [Farmer and Armi, 1999;Klymak and Moum, 2003;Xie et al, 2015;Alford et al, 2015].…”

“…Our observations show that some large-amplitude ISWs broke and generated dissipation rate of order of 1 × 10 À4 m 2 s À3 , 3 orders of magnitude larger than the background level in the pycnocline. The ISWs were not only generated during wind events but also were generated by tidal currents [Xie et al, 2017b]. The waves lasted 0.5-2 h during a tidal cycle and produced elevated turbulence in the pycnocline.…”

“…This suggests that the ISWs propagated primarily in the lateral direction. Using the filtering method of Mirshak and Kelley [2009], we determined that the wave packets propagated in a westward direction within ±20°of the cross-channel direction [see Xie et al, 2017b].These waves can be described by the solution to a two-layer KdV equation for ISWs [Helfrich and Melville, 2006]:…”

Large Projected Decline in Dissolved Oxygen in a Eutrophic Estuary Due to Climate Change

“…V was selected to encompass all the waters below 10‐m depth in the main stem of Chesapeake Bay, ranging between the Rappahannock River in the south and the Patapsco River in the north (Figure d). The O 2 budget over the control volume is derived from the full conservation equation given by where x , y , and z stand for the longitudinal (along‐channel, namely, the major axis of the depth‐averaged tidal flows), lateral (cross‐channel), and vertical directions, respectively (see Xie et al, for a more detailed definition); u , v , and w represent the velocity components in these directions; K H and K V are the horizontal and vertical diffusivities, respectively; WCR is the water column O 2 uptake and includes algal respiration, organic matter oxidation, nitrification, and oxidation of sulfide/methane; SOD is the sediment oxygen demand; F air − sea is O 2 flux across the air‐sea interface; and P phyto is O 2 produced by phytoplankton in the euphotic layer.…”