Diurnal wind-driven processes on the northern Monterey Bay inner shelf

In the summer of 2007, a biophysical experiment was conducted to identify physical processes that determine the delivery of invertebrate larvae and juvenile rockfish to rocky intertidal and kelp forest communities in northern Monterey Bay, California. The experiment was sponsored by the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) and collected physical measurements including velocity from acoustic Doppler current profilers, surface gravity wave heights measured acoustically, and temperature from thermistor chain arrays both along- and across- the inner shelf in water depths of 10 – 60 m. The inner shelf is the transition between the nearshore and mid-shelf zones, and is defined where surface and bottom Ekman boundary layers overlap. Previous work has shown that the inner shelf in this region is rich in physical processes across many space and time scales. The goal here is to identify and quantify the dominant processes at the diurnal (24 hour) period. Diurnal tides contribute less than 10% of the observed currents. Thus the focus is on the oceanic response to a strong (8 - 15 m/s daily maximum) along-shelf sea breeze which forces offshore surface Ekman transport, drives average upwelling velocities of 26 m/day, and cools the water column 2 – 4 degrees/day. At 15 m (20 m) depth, measured diurnal surface transport is 36% ± 9% (77% ± 12%) of full theoretical Ekman transport. Examination of a diurnal heat budget shows that vertical advection is the dominant process during afternoon cooling (both horizontal advection and solar insolation are sources of heat during this period), and is needed to close the heat budget to within 5%. In contrast, during evening/early morning heating 92% of the observed heating is explained by along-shelf advection of a temperature gradient within the upwelling shadow, much greater than the heating attributed to either solar insolation (2%) or onshore motions (2%). Thus, the diurnal heat budget is closed to within a few percent and explained by two-dimensional processes: vertical advection by wind-driven upwelling during cooling and along-shelf advection during heating.Keywords: Inner shelf, Monterey Bay, coastal, wind-driven, physical oceanograph

Tidal-band and high-frequency internal variability on the central Oregon inner shelf

Analogous to ocean surface waves, waves in the ocean interior also experience steepening, breaking, and dissipation as they approach the coastline. Much less is known about this internal beach. In this work, extensive moored Acoustic Doppler Current Profiler and temperature/salinity data together with optical remote sensing are combined to describe and understand tidal-band and high-frequency internal wave propagation over the Oregon mid and inner shelf. Semidiurnal baroclinic velocity is dominated by the first mode at all locations, with larger velocities on the mid shelf and northern part of a large submarine bank. Mid-shelf sites have baroclinic ellipticity that is near the theoretical value for single, progressive internal tidal waves compared to more linearly polarized currents over the inner shelf. Temporal variability does not correspond to the spring-neap cycle and is overall uncorrelated between mooring locations due to variable along-shelf topography and stratification. An idealized model of two amplitude-modulated internal waves propagating from different directions reproduces some of the observed variability in inner-shelf semidiurnal ellipse parameters. Moored observations were combined with sea-surface imagery to describe the propagation of 11 bore-like internal waves across the inner shelf. The surface expression of these waves is identified by regions of increased pixel intensity during wind speeds between 2 - 5 m/s⁻¹. Optical measurements show that internal waves are refracted by bathymetry, and measured wave speed (~0.15 m/s) is higher than predicted by linear theory (< 0.1 m/s⁻¹). The number and strength of these high-frequency (15 minute period), highly nonlinear features are linked to regional-scale upwelling/downwelling as well as the phase of the mid-shelf internal tide. In general, both surface and bottom-trapped bores are observed on the inner shelf and their polarity can be predicted by the weakly nonlinear parameter of the Korteweg-de Vries wave propagation equation. These bores have different consequences for the amount of horizontal transport they accomplish and where in the water column this transport occurs. The transformation of the internal tide impacts the form of the nonlinear high-frequency oscillations observed on the inner shelf. The most efficient onshore transport of sub-thermocline water is observed during a shallow mid-shelf pycnocline with large mid-shelf semidiurnal displacement that results in only elevation waves onshore

The Inner-Shelf Dynamics Experiment

17 USC 105 interim-entered record; under review.The article of record as published may be found at http://dx.doi.org/10.1175/BAMS-D-19-0281.1The inner shelf, the transition zone between the surfzone and the midshelf, is a dynamically complex region with the evolution of circulation and stratification driven by multiple physical processes. Cross-shelf exchange through the inner shelf has important implications for coastal water quality, ecological connectivity, and lateral movement of sediment and heat. The Inner-Shelf Dynamics Experiment (ISDE) was an intensive, coordinated, multi-institution field experiment from September–October 2017, conducted from the midshelf, through the inner shelf, and into the surfzone near Point Sal, California. Satellite, airborne, shore- and ship-based remote sensing, in-water moorings and ship-based sampling, and numerical ocean circulation models forced by winds, waves, and tides were used to investigate the dynamics governing the circulation and transport in the inner shelf and the role of coastline variability on regional circulation dynamics. Here, the following physical processes are highlighted: internal wave dynamics from the midshelf to the inner shelf; flow separation and eddy shedding off Point Sal; offshore ejection of surfzone waters from rip currents; and wind-driven subtidal circulation dynamics. The extensive dataset from ISDE allows for unprecedented investigations into the role of physical processes in creating spatial heterogeneity, and nonlinear interactions between various inner-shelf physical processes. Overall, the highly spatially and temporally resolved oceanographic measurements and numerical simulations of ISDE provide a central framework for studies exploring this complex and fascinating region of the ocean.U.S. Office of Naval Research (ONR)ONR Departmental Research Initiative (DRI)Inner-Shelf Dynamics Experiment (ISDE

Developing an Integrated Ocean Observing System for New Zealand

New Zealand (NZ) is an island nation with stewardship of an ocean twenty times larger than its land area. While the challenges facing NZ’s ocean are similar to other maritime countries, no coherent national plan exists that meets the needs of scientists, stakeholders or kaitiakitanga (guardianship) of NZ’s ocean in a changing climate. The NZ marine science community used the OceanObs’19 white paper to establish a framework and implementation plan for a collaborative NZ ocean observing system (NZ-OOS). Co-production of ocean knowledge with Māori will be embedded in this national strategy for growing a sustainable, blue economy for NZ. The strengths of an observing system for a relatively small nation come from direct connections between the science impetus through to users and stakeholders of an NZ-OOS. The community will leverage off existing ocean observations to optimize effort and resources in a system that has historically made limited investment in ocean observing. The goal of the community paper will be achieved by bringing together oceanographers, data scientists and marine stakeholders to develop an NZ-OOS that provides best knowledge and tools to the sectors of society that use or are influenced by the ocean

SuandaSutaraCEOASShore-BasedVideo_SupplementalInformation.zip

Shore-based video remote sensing is used to observe and continually monitor nonlinear internal waves propagating across the inner shelf. Month-long measurements of velocity from bottom-mounted acoustic Doppler current profilers and temperature from thermistor chains at the 10- and 20-m isobaths are combined with sea surface imagery from a suite of cameras (Argus) to provide a kinematic description of 11 borelike internal waves as they propagate across the central Oregon inner shelf. The surface expression of these waves, commonly seen by eye as alternating rough and smooth bands, are identified by increased pixel intensity in Argus imagery (average width 39 ± 6 m), caused by the convergence of internal wave-driven surface currents. These features are tracked through time and space using 2-min time exposure images and then compared to wave propagation speed and direction from in situ measurements. Internal waves are refracted by bathymetry, and the measured wave speed (~0.15 m s⁻¹) is higher than predicted by linear theory (< 0.1 m s⁻¹). Propagating internal waves are also visible in subsampled Argus pixel time series (hourly collections of 17 min worth of 2-Hz pixel intensity from a subset of locations), thus extending the observational record to times without an in situ presence. Results from this 5-month record show that the preferred sea state for successful video observations occurs for wind speeds of 2–5 m s⁻¹. Continued video measurements and analysis of extensive existing Argus data will allow a statistical estimate of internal wave occurrence at a variety of inner-shelf locations.Keywords: Remote sensing, Internal waves, Continental shelf/slopeKeywords: Remote sensing, Internal waves, Continental shelf/slop

Statistics of internal tide bores and internal solitary waves observed on the inner continental shelf off Point Sal, California

Manuscript received 6 March 2017, in final form 31 July 2017The article of record as published may be located at http://journals.ametsoc.org/doi/full/10.1175/JPO-D-17-0045.1Moored observations of temperature and current were collected on the inner continental shelf off Point Sal, California, between 9 June and 8 August 2015. The measurements consist of 10 moorings in total: 4 moorings each on the 50- and 30-m isobaths covering a 10-km along-shelf distance and an across-shelf section of moorings on the 50-, 40-, 30-, and 20-m isobaths covering a 5-km distance. Energetic, highly variable, and strongly dissipating transient wave events termed internal tide bores and internal solitary waves (ISWs) dominate the records. Simple models of the bore and ISW space–time behavior are implemented as a temperature match filter to detect events and estimate wave packet parameters as a function of time and mooring position. Wave-derived quantities include 1) group speed and direction; 2) time of arrival, time duration, vertical displacement amplitude, and waves per day; and 3) energy density, energy flux, and propagation loss. In total, over 1000 bore events and over 9000 ISW events were detected providing well-sampled statistical distributions. Statistics of the waves are rather insensitive to position along shelf but change markedly in the across-shelf direction. Two compelling results are 1) that the probability density functions for bore and ISW energy flux are nearly exponential, suggesting the importance of interference and 2) that wave propagation loss is proportional to energy flux, thus giving an exponential decay of energy flux toward shore with an e-folding scale of 2–2.4 km and average dissipation rates for bores and ISWs of 144 and ¯ ¹, respectively.Office of Naval ResearchNational Science FoundationN0001417WX01136N00014-17-1-2890OCE-1521653N0017317WR0012