Transformation of wave energy across the fringing reef of Ipan, Guam

Ph.D. University of Hawaii at Manoa 2012.Includes bibliographical references.Measurements from a cross-shore array of pressure sensors and current-meters, deployed on the fringing reef of Ipan, Guam as part of the PILOT (Pacific Island Land-Ocean Typhoon) experiment, were analyzed to understand the processes driving the large water level oscillations observed at the shore during energetic wave events. Offshore, sea and swell (SS: 3 to 20 seconds period) energy is dominant, while on the reef flat, energetic oscillations are observed with periods in the infragravity (IG: 20 to 200 seconds) and far infragravity (fIG 200 to 1000 seconds) bands. The nonlinear processes that contribute to this low-pass transformation of wave energy across the reef are analyzed in terms of the energetics of the wave field in each frequency band. Wave transformation across the fringing reef is characterized by the strong breaking and dissipation of the incident SS energy which provides a driving force for the waves at lower frequencies. The SS energy on the reef flat is shown to be strongly dependent on the total reef flat water level that includes wave induced setup. The non linear transfer of energy between the SS and low frequency (LF: IG and fIG) bands is responsible for both the forcing and the loss of low frequency energy at the reef crest. In IG band, the low frequency oscillations resulting from the breaking SS envelope work against the incident bound waves and energy is transferred to the SS band similar to the nonlinear transfer observed on sandy beaches. The SS envelope oscillations at fIG frequencies force free fIG waves across the surfzone. Across the reef flat, low frequency oscillations at normal mode frequencies are preferentially excited. The development of standing waves on the reef flat is controlled by the strong depth dependent frictional dissipation of the LF waves reflected at the shoreline. During tropical storm Man-Yi, resonant standing modes in the fIG band were excited when a large increase in water level over the reef occurred due to wave setup that both reduced the effects of friction and the period of the fundamental mode

Numerical experiments on resonant wave amplification over a fringing reef

Waves are important drivers for reef hydrodynamics, and therefore strongly contribute to flooding over reef-lined coasts. While high-frequency waves are largely dissipated when they propagate over the reef flat due to breaking and friction, low-frequency (LF) waves are generally able to reach the back-reef beach. There, they can reflect and form (quasi-) standing wave patterns, which under resonant conditions can lead to disproportionally high run-up on the beach (e.g., Pequignet et al., 2009; Gawehn et al., 2016). The probability of this phenomenon is expected to increase due to sea-level rise (e.g., Pequignet et al., 2009). In this study, we numerically investigate long wave resonance and the processes enhancing or limiting the resonant amplification of long waves over the reef flat. Besides the role of frictional dissipation (e.g., Pomeroy et al. 2012), we investigate how the nonlinear transformation of long waves influences the amplification rate.Environmental Fluid MechanicsCoastal EngineeringHydraulic Structures and Flood Ris

Intercomparison of shipboard and moored CARIOCA buoy seawater fCO₂ measurements in the Sargasso Sea

The ocean is an important sink for carbon and heat, yet high-resolution measurements of biogeochemical properties relevant to global climate change are being made only sporadically in the ocean at present. There is a growing need for automated, real-time, long-term measurements of CO2 in the ocean using a network of sensors, strategically placed on ships, moorings, free-drifting buoys and autonomous remotely operated vehicles. The ground-truthing of new sensor technologies is a vital component of present and future efforts to monitor changes in the ocean carbon cycle and air–sea exchange of CO2.A comparison of a moored Carbon Interface Ocean Atmosphere (CARIOCA) buoy and shipboard fugacity of CO2 (fCO2) measurements was conducted in the western North Atlantic during two extended periods (>1 month) in 1997. The CARIOCA buoy was deployed on the Bermuda Testbed Mooring (BTM), which is located 5 km north of the site of the US Joint Global Ocean Flux Study (JGOFS) Bermuda Atlantic Time-series Study (BATS). The high frequency of sampling revealed that temperature and fCO2 responded to physical forcing by the atmosphere on timescales from diurnal to 4–8 days. Concurrent with the deployments of the CARIOCA buoy, frequent measurements of surface fCO2 were made from the R/V Weatherbird II during opportunistic visits to the BTM and BATS sites, providing a direct calibration of the CARIOCA buoy fCO2 data. Although, the in situ ground-truthing of the CARIOCA buoy was complicated by diurnal processes, sub-mesoscale and fine-scale variability, the CARIOCA buoy fCO2 data was accurate within 3±6 µatm of shipboard fCO2 data for periods up to 50 days. Longer-term assessments were not possible due to the CARIOCA buoy breaking free of the BTM and drifting into waters with different fCO2-temperature properties. Strategies are put forward for future calibration of other in situ sensors

LE NOUVEAU SYSTÈME MONDIAL DE PRÉVISIONS OCÉANIQUES DU MET OFFICE À UNE RÉSOLUTION DE 1/12°.

International audienceThe Met Offi ce has recently upgraded its operational Forecasting Ocean Assimilation Model (FOAM) from an eddy permitting 1/4° tripolar grid (ORCA025) to the eddy resolving 1/12° ORCA12 confi guration. FOAM-ORCA12 uses NEMOv3.6 (GO6 confi guration) coupled to CICE (GSI8.1 confi guration) for the ocean and sea-ice components, respectively. It assimilates observations of sea surface temperature (SST), temperature and salinity profi les, altimeter sea level anomaly and sea ice concentration, via NEMOVAR which is a multivariate incremental 3DVar scheme that runs over a 1-day time window. Qualitatively FOAM-ORCA12 better represents the details of mesoscale features in SST and surface currents. Traditional statistical verifi cation methods suggest that the new system performs similarly or slightly worse than the equivalent 1/4° system. However, it is known that comparisons of models running at different resolutions suffer from a double penalty effect, whereby higher-resolution models are penalised more than lower-resolution models for features that are offset in time and space. Results are shown from neighbourhood verifi cation methods which use common spatial scales for a fairer comparison between confi gurations of different resolutions, applied to SST. We show that, as neighbourhood sizes increase, ORCA12 consistently has lower Continuous Ranked Probability Scores than ORCA025

The Regional Coupled Suite (RCS-IND1): application of a flexible regional coupled modelling framework to the Indian region at kilometre scale

Abstract. A new regional coupled modelling framework is introduced – the Regional Coupled Suite (RCS). This provides a flexible research capability with which to study the interactions between atmosphere, land, ocean, and wave processes resolved at kilometre scale, and the effect of environmental feedbacks on the evolution and impacts of multi-hazard weather events. A configuration of the RCS focussed on the Indian region, termed RCS-IND1, is introduced. RCS-IND1 includes a regional configuration of the Unified Model (UM) atmosphere, directly coupled to the JULES land surface model, on a grid with horizontal spacing of 4.4 km, enabling convection to be explicitly simulated. These are coupled through OASIS3-MCT libraries to 2.2 km grid NEMO ocean and WAVEWATCH III wave model configurations. To examine a potential approach to reduce computation cost and simplify ocean initialization, the RCS includes an alternative approach to couple the atmosphere to a lower resolution Multi-Column K-Profile Parameterization (KPP) for the ocean. Through development of a flexible modelling framework, a variety of fully and partially coupled experiments can be defined, along with traceable uncoupled simulations and options to use external input forcing in place of missing coupled components. This offers a wide scope to researchers designing sensitivity and case study assessments. Case study results are presented and assessed to demonstrate the application of RCS-IND1 to simulate two tropical cyclone cases which developed in the Bay of Bengal, namely Titli in October 2018 and Fani in April 2019. Results show realistic cyclone simulations, and that coupling can improve the cyclone track and produces more realistic intensification than uncoupled simulations for Titli but prevents sufficient intensification for Fani. Atmosphere-only UM regional simulations omit the influence of frictional heating on the boundary layer to prevent cyclone over-intensification. However, it is shown that this term can improve coupled simulations, enabling a more rigorous treatment of the near-surface energy budget to be represented. For these cases, a 1D mixed layer scheme shows similar first-order SST cooling and feedback on the cyclones to a 3D ocean. Nevertheless, the 3D ocean generally shows stronger localized cooling than the 1D ocean. Coupling with the waves has limited feedback on the atmosphere for these cases. Priorities for future model development are discussed. </jats:p

The Regional Coupled Suite (RCS-IND1): application of a flexible regional coupled modelling framework to the Indian region at km scale

A new regional coupled modelling framework is introduced – the Regional Coupled Suite (RCS). This provides a flexible research capability with which to study the interactions between atmosphere, land, ocean and wave processes resolved at km-scale, and the effect of environmental feedbacks on the evolution and impacts of multi-hazard weather events. A configuration of the RCS focussed on the Indian region, termed RCS-IND1, is introduced. RCS-IND1 includes a regional configuration of the Unified Model (UM) atmosphere, directly coupled to the JULES land surface model, on a grid with horizontal spacing of 4.4 km, enabling convection to be explicitly simulated. These are coupled through OASIS3-MCT libraries to 2.2 km grid NEMO ocean and WAVEWATCH III wave model configurations. To examine a potential approach to reduce computation cost, and simplify ocean initialisation, the RCS includes an alternative approach to couple the atmosphere to a lower resolution Multi-Column K Profile Parameterization (KPP) for the ocean. Through development of a flexible modelling framework, a variety of fully and partially coupled experiments can be defined, along with traceable uncoupled simulations and options to use external input forcing in place of missing coupled components. This offers a wide scope to researchers designing sensitivity and case study assessments. Case study results are presented and assessed to demonstrate the application of RCS-IND1 to simulate two tropical cyclone cases which developed in the Bay of Bengal, namely Titli in October 2018 and Fani in April 2019. Results show realistic cyclone simulations, and that coupling can improve the cyclone track and produces more realistic intensification than uncoupled simulations for Titli but prevents sufficient intensification for Fani. Atmosphere-only UM regional simulations omit the influence of frictional heating on the boundary layer to prevent cyclone over-intensification. However, it is shown that this term can improve coupled simulations, enabling a more rigorous treatment of the near-surface energy budget to be represented. For these cases, a 1D mixed layer scheme shows similar first-order SST cooling and feedback on the cyclones as a 3D ocean. Nevertheless, the 3D ocean generally shows stronger localised cooling than the 1D ocean. Coupling with the waves have limited feedback on the atmosphere for these cases. Priorities for future model development are discussed

An Introduction to the ‘Oceans and Society: Blue Planet’ Initiative

We live on a blue planet, and Earth’s waters benefit many sectors of society. The future of our blue planet is increasingly reliant on the services delivered by marine, coastal and inland waters and on the advancement of effective, evidence-based decisions on sustainable development. ‘Oceans and Society: Blue Planet’ is an initiative of the Group on Earth Observations (GEO) that aims to ensure the sustained development and use of ocean and coastal observations for the benefit of society. The initiative works to advance and exploit synergies among the many observational programmes devoted to ocean and coastal waters; to improve engagement with a variety of stakeholders for enhancing the timeliness, quality and range of information delivered; and to raise awareness of the societal benefits of ocean observations at the public and policy levels. This paper summarises the role of the initiative, current activities and considerations for future directions