Jason McConochie

Bio: Jason McConochie is an academic researcher from Royal Dutch Shell. The author has contributed to research in topics: Tropical cyclone & Hindcast. The author has an hindex of 6, co-authored 18 publications receiving 142 citations. Previous affiliations of Jason McConochie include Woodside Petroleum.

The effect of wave‐induced turbulence on the ocean mixed layer during tropical cyclones: Field observations on the Australian North‐West Shelf

Abstract: [1] Field observations of water temperature on the Australian North-West Shelf (Eastern Indian Ocean) with the support of numerical simulations are used to demonstrate that the injection of turbulence generated by the wave orbital motion substantially contributes to the mixing of the upper ocean. Measurements also show that a considerable deepening of the mixed layer occurs during tropical cyclones, when the production of wave-induced turbulent kinetic energy overcomes the contribution of the current-generated shear turbulence. Despite a significant contribution to the deepening of the mixed layer, the effect of a background current and atmospheric forcing are not on their own capable of justifying the observed deepening of the mixed layer through most of the water column. Furthermore, variations of a normally shallow mixed layer depth are observed within a relatively short timescale of approximately 10 hours after the intensification of wave activity and vanish soon after the decay of storm surface waves. This rapid development tends also to exclude any significant contribution by wave breaking, as small rates of vertical diffusivity for wave breaking-induced turbulence would require longer timescales to influence the depth of the mixed layer.

Near-inertial ocean response to tropical cyclone forcing on the Australian North-West Shelf

Abstract: The Regional Ocean Modeling System (ROMS) was applied to the Australian North-West Shelf (NWS) to hindcast the ocean response to four intense historical tropical cyclones (TCs). While the four cyclones had very different trajectories across the NWS, all passed within 150 km of a long-term vertical mooring located on the continental shelf in 125 m depth. The observed ocean response at this relatively shallow, Southern Hemisphere shelf site was characterized by the development of a peak in the counter-clockwise (CCW) near-inertial kinetic energy, mixed layer deepening, and subsequent restratification. Strong near-inertial isotherm oscillations were also observed following two of the cyclones. ROMS reproduced these features and also showed that the peak in the near-inertial CCW kinetic energy was observed on the left side of each cyclone trajectory. The time rate of change of near-inertial kinetic energy depended strongly on the storm Rossby number, i.e., defined based on the storm speed, the storm length scale, and the Coriolis frequency. The shallow water depth on the NWS resulted in first, a more rapid decay of near-inertial oscillations than in the deep ocean, and second a generation efficiency (the ratio of near-inertial power to the rate of wind work) of up to 10%, smaller than found for cyclones propagating across deeper water. The total energy put into near-inertial motions is nevertheless large compared to the background tidal energy. The rapid decay of near-inertial motions emphasizes the importance of frictional effects in characterizing the response to cyclone forcing in shallow seas.

Source term balance in a severe storm in the Southern North Sea

Abstract: This paper presents the results of a wave hindcast of a severe storm in the Southern North Sea to verify recently developed deep and shallow water source terms. The work was carried out in the framework of the ONR funded NOPP project (Tolman et al. 2013) in which deep and shallow water source terms were developed for use in third-generation wave prediction models. These deep water source terms for whitecapping, wind input and nonlinear interactions were developed, implemented and tested primarily in the WAVEWATCH III model, whereas shallow water source terms for depth-limited wave breaking and triad interactions were developed, implemented and tested primarily in the SWAN wave model. So far, the new deep-water source terms for whitecapping were not fully tested in shallow environments. Similarly, the shallow water source terms were not yet tested in large inter-mediate depth areas like the North Sea. As a first step in assessing the performance of these newly developed source terms, the source term balance and the effect of different physical settings on the prediction of wave heights and wave periods in the relatively shallow North Sea was analysed. The December 2013 storm was hindcast with a SWAN model implementation for the North Sea. Spectral wave boundary conditions were obtained from an Atlantic Ocean WAVEWATCH III model implementation and the model was driven by hourly CFSR wind fields. In the southern part of the North Sea, current and water level effects were included. The hindcast was performed with five different settings for whitecapping, viz. three Komen type whitecapping formulations, the saturation-based whitecapping by Van der Westhuysen et al. (2007) and the recently developed ST6 whitecapping as described by Zieger et al. (2015). Results of the wave hindcast were compared with buoy measurements at location K13 collected by the Dutch Ministry of Transport and Public Works. An analysis was made of the source term balance at three locations, the deep water location North Cormorant, the inter-mediate depth location K13 and at location Wielingen, a shallow water location close to the Dutch coast. The results indicate that at deep water the source terms for wind input, whitecapping and nonlinear four-wave interactions are of the same magnitude. At the inter-mediate depth location K13, bottom friction plays a significant role, whereas at the shallow water location Wielingen also depth-limited wave breaking becomes important.

Winds near the Surface of Waves: Observations and Modeling

Abstract: The concept of a constant-flux layer is usually employed for vertical profiling of the wind measured at some elevation near the ocean surface. The surface waves, however, modify the balance...

15 priorities for wind-waves research: an Australian perspective

Abstract: The Australian marine research, industry, and stakeholder community has recently undertaken an extensive collaborative process to identify the highest national priorities for wind-waves res...

Robustness and uncertainties in global multivariate wind-wave climate projections

Abstract: Understanding climate-driven impacts on the multivariate global wind-wave climate is paramount to effective offshore/coastal climate adaptation planning. However, the use of single-method ensembles and variations arising from different methodologies has resulted in unquantified uncertainty amongst existing global wave climate projections. Here, assessing the first coherent, community-driven, multi-method ensemble of global wave climate projections, we demonstrate widespread ocean regions with robust changes in annual mean significant wave height and mean wave period of 5–15% and shifts in mean wave direction of 5–15°, under a high-emission scenario. Approximately 50% of the world’s coastline is at risk from wave climate change, with ~40% revealing robust changes in at least two variables. Furthermore, we find that uncertainty in current projections is dominated by climate model-driven uncertainty, and that single-method modelling studies are unable to capture up to ~50% of the total associated uncertainty.

Global changes of extreme coastal wave energy fluxes triggered by intensified teleconnection patterns

Abstract: In this study we conducted a comprehensive modeling analysis to identify global trends in extreme wave energy flux (WEF) along coastlines in the 21st century under a high emission pathway (Representative Concentration Pathways 8.5). For the end of the century, results show a significant increase up to 30% in 100 year return level WEF for the majority of the coastal areas of the southern temperate zone, while in the Northern Hemisphere large coastal areas are characterized by a significant negative trend. We show that the most significant long-term trends of extreme WEF can be explained by intensification of teleconnection patterns such as the Antarctic Oscillation, El Nino–Southern Oscillation, and North Atlantic Oscillation. The projected changes will have broad implications for ocean engineering applications and disaster risk management. Especially low-lying coastal countries in the Southern Hemisphere will be particularly vulnerable due to the combined effects of projected relative sea level rise and more extreme wave activities.

Upper ocean response to typhoon Kalmaegi (2014)

Abstract: Typhoon Kalmaegi passed over an array of buoys and moorings in the northern South China Sea in September 2014, leaving a rare set of observations on typhoon-induced dynamical and thermohaline responses in the upper ocean. The dynamical response was characterized by strong near-inertial currents with opposite phases in the surface mixed layer and in the thermocline, indicating the dominance of the response by the excitation of the first baroclinic mode. The thermohaline response showed considerable changes in the mean fields in addition to a near-inertial oscillation. In particular, temperature and salinity anomalies generally exhibited a three-layer vertical structure, with the surface layer becoming cooler and saltier, the subsurface layer warmer and fresher, and the lower layer cooler and saltier again. The response in the surface and subsurface layers was much stronger to the right of the typhoon track, while that in the lower layer was stronger along the track and to the left. These features of the upper ocean response were grossly reproduced by a three-dimensional numerical model. A model-based heat budget analysis suggests that vertical mixing was mainly responsible for the surface cooling and subsurface warming, while upwelling was the cause of cooling from below. Both observations and model results indicate that the whole upper ocean experienced an overall cooling in the wake of typhoon Kalmaegi.

Observation-Based Source Terms in the Third-Generation Wave Model WAVEWATCH III: Updates and Verification

Abstract: The observation-based source terms available in the third-generation wave model WAVEWATCH III (i.e., the ST6 package for parameterizations of wind input, wave breaking, and swell dissipatio...

Development and evaluation of an Earth System Model with surface gravity waves

Abstract: [1] The critical role of oceanic surface waves in climate system is attracting more and more attention. We set up an Earth System Model, which is named as the First Institute of Oceanography-Earth System Model (FIO-ESM), composed of a coupled physical climate model and a coupled carbon cycle model. A surface wave model is introduced through including the nonbreaking wave-induced vertical mixing, which can improve the performance of climate model especially in the simulation of upper ocean mixed layer depth in the southern ocean, into the ocean general circulation model. The FIO-ESM is employed to conduct Coupled Model Intercomparison Project Phase 5 (CMIP5) experiments. The historical simulation of FIO-ESM's physical climate model for 1850–2005 shows that the simulated patterns of surface air temperature (SAT), rainfall, and El Nino-Southern Oscillation (ENSO) match those of the observations. Future projections under the four scenarios of RCP2.6, RCP4.5, RCP6.0, and RCP8.5 are also conducted and the global averaged SAT in 2100 would be −0.007°C, 1.10°C, 1.85°C, and 3.92°C higher than that in 2005, respectively. The historical simulation and future projection under RCP8.5 with global carbon cycle show the SAT and atmospheric CO2 concentration are well reproduced in the historical period and the global averaged SAT would increase by 3.90°C in 2100, which is quite similar to the physical climate model's result. Further analysis shows surface wave makes projected SAT in RCP2.6 about 2°C cooler in the Arctic area and 2°C warmer in the southern ocean.