Ocean circulation modeling in the 21st century (part-1)
Science generally evolves through methodical additions to previous theories and observations. I have seen so many improvements, developments, and inventions in the field of computer science like deep learning, machine learning, cloud computing, improved computational power supercomputer to quantum computing so many. But what about technologies and computational things in the field of oceanography?
The ocean covers about 70% of the earth’s surface and it produces over half of the world oxygen and absorbed 50 times more carbon dioxide than the atmosphere. The Ocean provides essential service to our planet. Ocean life and water quality are at the heart of the fisheries, tourism, industries that provides benefits to millions of people. The ocean provides renewable energy and is a major source of oil, gas, and other minerals. The First Global Planning Meeting for the UN Decade of Ocean Science for Sustainable Development 2021–2030 has set the stage for wide-ranging action and partnerships to strengthen scientific knowledge and innovation, increase resilience against marine and coastal hazards and reverse the decline in the health of the ocean.
The ocean decade is focused on 6 themes
1. A safe ocean
2. A sustainable and productive ocean
3. A transparent and accessible ocean
4. A clean ocean
5. A healthy and resilient ocean
6. And predicted ocean
I am going to write about the predicted ocean because there is a need more sophisticated and integrated system to tackle global challenges such as rising sea level, salinity intrusion, coastal inundation, frequent tropical cyclones, and ocean acidification as well as a predictable ocean where the society will have the capacity to understand current and future ocean conditions. Now, we are at the crossroad of deciding the relationship between the ocean and people.
Ocean modeling is a representation of the ocean in the form of an equation describing the physical processes of our understanding of how the ocean works. -Dr. Stephenie Waterman
Models provide an experimental tool for the scientific rationalization of ocean phenomena. Indeed during the past decade, large scale models have become the experimental tool of choice for many oceanographers and climate scientists. Ocean modeling is not an easy thing because the ocean interacts with a wide range of earth components including atmosphere, sea ice, land ice shelves, rivers, and the solid earth lower boundary and the simulation of the world ocean over time scales appropriate for climate involves extremely rich and complex arrays of flow regimes and interactions between components of the climate system. Additionally, the ocean is largely forced at its upper and lower boundaries. In particular, Tropical Ocean experiences intense equatorial currents with rapid adjustments to wind forcing associate with equatorial Kelvin, Rossby, and instability wave and a power interannual model of air-sea variability known as El Nino in the Pacific Ocean.
Several new codes for multi-level primitive equation modeling have been constructed since 1973. The codes were written mainly in the lower level computer programming languages like Fortran and C. in the late 1980s and early 1990s, more focused like coastal circulation models were developed.
Generally speaking, there are three kinds of models:
1: Mechanistic models: they are simplified models used and oriented for studying processes.
2: Simulation models: are used for calculating the realistic circulation of oceanic regions. The first simulation models were developed by Kirk Bryan and Michael Cox at the Geophysical Fluid Dynamics Laboratory in Princeton.
3: Coupled Atmosphere and Ocean numerical models: Ocean models run 30 times slower than atmosphere models of the same complexity.
Why do we need to Model Ocean?
Ocean models play a large role in aiding our understanding of the ocean’s influence on weather and climate. They are a repository for mechanistic theories of how the ocean works with numerical methods used to transform the mathematical expression of the theories into a computational tool for scientific investigations. In particular numerical models are for hypothesis-driven experimental and theoretical studies that make them an essential tool in the hierarchy of methods used by scientists to better understand the earth climate system.
Ocean Modeling has many important applications.
1: comparatively less expensive
2: the ability to forecast properties of the sweater as it moves and evolves through the ocean basin
3: help in understanding the dynamics of the ocean on a global or regional scale
4: a prerequisite to establishing a deeper and more predictive description of climate
5: interpretation of the paleoclimatic record
6: data assimilation and fisheries and other oceanic biosphere management
7: coupling models. Biogeochemical, bio-optical, sea ice, sediment, and other models can be embedded within other models.
General Steps of the ocean modeling
1: Discretizing equations and parameterizing: Present Ocean models tend to make the Boussinesq, traditional and hydrostatic approximations in addition to discretizing the continuum equations and parameterizing the unresolved processes.
1.1 Most common equations used in the modeling
From my experience, so many complexes and higher-order mathematical equations are used in the modeling but Naiver –stokes equation is the foundation of ocean modeling.
2: Generating grid: ocean models almost always employ a stretched grid in the vertical to allow better resolution of upper-ocean processes.
3: Set up parameters and boundary conditions.
Ocean models simulate several properties from the surface to the seafloor.
1: physical parameters: Temperature, salinity, currents, sea surface height, wave, and sea-ice, etc.
2: biogeochemical parameters: chlorophyll-a, primary production, dissolved oxygen, etc.
Accurate parameterizations are especially needed in long term integrations of coarse-resolution ocean models that are designed to understand the ocean variability within the climate system on seasonal to decadal time scales.
4: simulate the processes and analyze the simulated results : this is the final stage of the modeling .
Existing ocean some models
Scientists developed so many ocean models over the years with a focus on the properties of the ocean and their circulations.
1: MOM (modular ocean model) MOM is a three-dimensional ocean circulation model and the model was developed by National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory (NOAA/GFDL) in Princeton, NJ, USA.
2: POM (Princeton ocean model) is also a numerical model for ocean circulation. It was originally developed at Princeton University (G. Mellor and Alan Blumberg) in collaboration with Dynalysis of Princeton.
3: POP (parallel ocean program): POP is also a 3D ocean circulation model and it was developed by Los Alamos National Laboratory.
4: MITgcm (MIT general circulation model): MITgcm is a numerical model that solves the equations of motion governing the ocean using a finite volume method. It was developed at the Massachusetts Institute of Technology.
5: HYCOM (hybrid coordinate ocean model) HYCOM is a data-assimilative hybrid isopycnal-sigma-pressure (generalized) coordinate ocean model. It is a multi-institutional effort sponsored by the National Ocean Partnership Program (NOPP), as part of the U. S. Global Ocean Data Assimilation Experiment (GODAE)
6: ROMS (regional ocean modeling system): ROMS is a free surface, terrain-following that is based on primitive equations. The model was primarily developed and supported by researchers at the Rutgers University, University of California Los Angeles.
Conclusion
Knowledge of the current and future state of the ocean is so important to the development of sustainable ocean economic policies and management. An Advanced and integrated ocean model can help to improve climate prediction in a significant way. On the other hand, Studying ocean dynamics and climate ecosystem dynamics are quite challenging because the ocean is so interconnected and unstable as well as long time scales and large space involved of the complex marine food webs that span from viruses and bacteria to apex predators. The situation is improving with time but establishing and maintaining the long term observational records should be a top priority for ocean research.
References
1: https://coessing.files.wordpress.com/2016/08/ocean_modeling_joseph.pdf
2: https://pdfs.semanticscholar.org/ed30/24b084aa48ad6d91cba8e98f1a50f1043768.pdf
3: https://web.stanford.edu/~fringer/publications/obf-etal-om-2019.pdf
5: https://www.frontiersin.org/articles/10.3389/fmars.2019.00065/full
6: https://www.gfdl.noaa.gov/bibliography/related_files/smg0801.pdf
7: https://ccs.miami.edu/focus-area/climate-and-environmental-hazards/ocean-modeling/
8: https://link.springer.com/article/10.1007/s12562-018-1181-x
9: https://www.frontiersin.org/articles/10.3389/fmars.2019.00470/full
10: https://www.sciencedirect.com/science/article/pii/B9780128179451000010
