Coupled Ocean-atmosphere Modelling of Tropical Cyclones along the Western Australian SeasIn the project we simulated severe tropical cyclones (TCs), both in ocean and atmosphere, along the North Shelf of Australia. We used the latest developments in the 2-way coupled advanced ocean (hydrodynamic - ROMS and spectral waves -WW3) and the atmosphere (ARW-WRF) models. TCs genesis and dynamics are greatly dependent on available heat energy they draw from the ocean surface, hence there is obvious need to connect ocean and atmosphere models. Scenario for TC Olwyn showed full power of the system, predicting better ocean-atmosphere coupled system then each of the components alone.
Principal investigatorIvica Janekovic email@example.com
Area of scienceEarth Sciences, Geosciences, oceanography
Applications usedROMS, WRF, WW3, python-miniconda
Although, our understanding of dynamics and ability to predict paths of TCs has improved during recent years, our progress in modelling TCs intensities is still lacking correct interactions and feedbacks with the ocean. Small-scale processes and inner-core TCs dynamics are mostly influenced by fluxes and interactions between the ocean and are playing key roles responsible for TCs intensities. Without correct boundary layer dynamics, and ocean-atmosphere exchange of fluxes, TC intensity will stay poorly resolved and consequently predicted.
In this study we used modern ocean, wave and atmosphere models bound together into dynamically consistent complex system being capable of linking and exchanging important processes between them. At the same time, we managed to improve TC intensity and path if compared to traditionally uncoupled approach with better prediction of the ocean and wave states as well. Our modelling system is based on the COAWST model configured to use 2-way coupled atmospheric-ocean models: (i) WRF model capable of resolving TC processes using 57 vertical levels, 10 km horizontal resolution and advanced physics; (ii) 3D baroclinic ROMS ocean model using 30 vertically stretched “s” layers with increased resolution in the surface layers and 2 km horizontal resolution; (iii) WW3-spectral wave model sharing the same horizontal grid as the ocean model. All three models are providing realistic feedbacks at 10-minute intervals during the whole system integration with the ocean model sending information about sea surface temperature to the atmosphere model, surface ocean currents and sea level to the wave model and at the same time receiving feedbacks from the atmosphere model for updated surface heat and momentum flux, and from the wave model for wave induced stress and contribution to turbulent mixing. In parallel, wave model calculates wave dynamics and sends spectral parameters important for better representation of sea surface roughness to the atmosphere model which then adjusts air-sea boundary layer physics (important for TCs intensities) and sends surface winds back to the ocean and wave models.
This task would not be possible without HPC and Pawsey system. Each of the numerical models require significant resources and as fast as possible interconnections for information exchange between them. In that sense CRAY arch. provided realistic resources for the project. Further development on the numerical modelling system seems needed to include better physics in the atmosphere (i.e. ocean spray) as well in wave modelling (better dissipation terms). Those activities are planned for the future project(s).
Atmosphere modelling system producing realistic TC field of MCAPE (left) and humidity (right).
Case of TC Olwyn. Satellite image (left), and model results for atmosphere and waves (right).
List of Publications
1. 1. Mahjabin, T., Pattiaratchi, C., Hetzel, Y., Janekovic, I., 2019. Spatial and Temporal Variability of Dense Shelf Water Cascades along the Rottnest Continental Shelf in Southwest Australia, J. Mar. Sci. Eng., 7, 30, DOI:10.3390/jmse7020030.
2. Janeković, I., 2018. The importance of Ocean – Atmosphere – Wave interactions for tropical cyclones – example of cyclone Olwyn at the North Shelf region of Western Australia, Australian Coastal and Oceans Modelling and Observations Workshop (ACOMO) 2018, Canberra, Shine Dome, Australian Academy of Science.