The MITgcm (MIT General Circulation Model) is a numerical model designed for study of the atmosphere, ocean, and climate. Its non-hydrostatic formulation enables it to simulate fluid phenomena over a wide range of scales; its adjoint capability enables it to be applied to parameter and state estimation problems. By employing fluid isomorphisms, one hydrodynamical kernel can be used to simulate flow in both the atmosphere and ocean.

You are welcome to download and use MITgcm.

Papers charting the development of MITgcm can be found here
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Planet-in-a-Bottle

Here we look at work by Sai Ravela, John Marshall, Chris Hill, Andrew Wong and Scott Stransky in which they use MITgcm to provide the virtual analogue for a fluid lab experiment in the physical laboratory, as part of an effort to demonstrate how to achieve real-time model-data synthesis, using measurements from a robotically controlled automated sensor system.

Figure 1. The components of the system: The laboratory observatory consists of a physical system: a rotating table on which a tank, camera and control system for illumination are mounted. The computational part consists of a measurement system for velocimetry, a numerical model (MITgcm), and an assimilation system.

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Modeling the Great Lakes

This month we focus on the work of Galen McKinley and Val Bennington at the University of Wisconsin, Madison.

With a view to developing a quantitative understanding of the role such bodies of water may play in the terrestrial carbon cycle, Galen and Val have been using the MITgcm to put together a comprehensive,  up-to-date description of the general circulation and temporal variability of Lake Superior. Figure 1 shows the summer-time mean circulation from their model.

Figure 1: Summer-time mean circulation from a simulation of Lake Superior using MITgcm.

Because of its large size (the lake is of order 500km long by 250km wide, with depths to 300 m) as well as difficulties associated with  fieldwork (particularly in winter), Lake Superior’s  general  circulation is rather poorly known. Believing the terrestrial ecosystem around the lake to be a substantial sink of CO₂ from the atmosphere, but not knowing to what degree carbon is being transferred to the lake and fluxed back to the atmosphere, Bennington and McKinley set out to build a holistic model of the system; step one being to build an up-to-date general circulation model. Read the rest of this entry »

Tidal Mixing Over Rough Topography

This month we focus on the work of recent doctoral graduate Maxim Nikurashin (now working at GFDL) who, in a collaboration with long time user Sonya Legg,  has  been using a non-hydrostatic, 2-D version of the MITgcm to explore tidal mixing over rough topography (Fig. 1). The MITgcm’s elegant non-hydrostatic and topography-representing capabilities  make it an ideal choice for this kind of high-resolution process study.

Figure 1: Snapshot of wave zonal velocity (ms-1) deviation from the barotropic tide from the control simulation in Nikurashin and Legg's high-resolution 2-D, MITgcm study of tidal mixing over rough topography.

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Population Competition in Action

As the Darwin project begins to bear fruit we focus here on the work of recent doctoral graduate Fanny Monteiro who together with Mick Follows and Stephanie Dutkiewicz have been using the MITgcm to probe the behaviour of self-assembling phytoplankton communities within a global ocean circulation (Follows et al. 2007). Figure 1 summarises the core ideas behind the teams work: Within this, many tens of phytoplankton “types” are initialized, each one having a randomly assigned sensitivity to light, temperature and nutrient requirements. In Fanny’s work, she additionally initialised this model with populations of “diazotrophs” – organisms that can fix their own nitrogen, but with the trade-off of correspondingly slow growth and high iron to phosphorus requirements.

Figure 1. Illustration of the key components in the self-assembling phytoplankton community model. After some years of interaction, the fittest "types" persist and occupy distinct habitats.

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