Documentation - CT2011_oi
To learn more about a CarbonTracker component, click on one of the above images.
Or download the full PDF version for convenience.
The link between observations of CO2 in the atmosphere and the
exchange of CO2 at the Earth's surface is transport in the atmosphere:
storm systems, cloud complexes, and weather of all sorts cause winds
that transport CO2 around the world. As a result, local events like
fires, forest growth, and ocean upwelling can have impacts at remote
locations. To simulate the winds and the weather, CarbonTracker uses
sophisticated numerical models that are driven by the daily weather
forecasts from the specialized meteorological centers of the world.
Since CO2 does not decay or react in the lower atmosphere, the
influence of emissions and uptake in locations such as North America
and Europe are ultimately seen in our measurements even at the South
Pole! Getting the transport of CO2 just right is an enormous
challenge, and costs us almost 90% of the computer resources for
CarbonTracker. To represent the atmospheric transport, we use the
Transport Model 5 (TM5). This is a community-supported model whose
development is shared among many scientific groups with different
areas of expertise. TM5 is used for many applications other than
CarbonTracker, including forecasting air-quality, studying the
dispersion of aerosols in the tropics, tracking biomass burning
plumes, and predicting pollution levels that future generations might
have to deal with.
2. Detailed Description
TM5 is a global model with two-way nested grids; regions for which
high-resolution simulations are desired can be nested in a coarser
grid spanning the global domain. The advantage to this approach is
that transport simulations can be performed with a regional focus
without the need for boundary conditions from other models. Further,
this approach allows measurements outside the "zoom" domain to
constrain regional fluxes in the data assimilation, and ensures that
regional estimates are consistent with global constraints. TM5 is
based on the predecessor model TM3, with improvements in the advection
scheme, vertical diffusion parameterization, and meteorological
preprocessing of the wind fields (Krol et al., 2005).
The model is developed and maintained jointly by the Institute for Marine and Atmospheric Research Utrecht (IMAU, The Netherlands), the Joint Research Centre (JRC, Italy), the Royal Netherlands Meteorological Institute (KNMI, The Netherlands), and NOAA ESRL (USA).
CarbonTracker, TM5 separately simulates advection, convection (deep
and shallow), and vertical diffusion in the planetary boundary layer
and free troposphere.
Figure 1. TM5 grids used in CarbonTracker. Figure shows the 1°x 1° nested regional grid over North America and a portion of the global 3°x 2° grid.
The winds which drive TM5 come from the European Center for Medium range Weather Forecast (ECMWF) operational forecast model. This
"parent" model currently runs with ~25 km horizontal resolution and 60
layers in the vertical prior to 2006 (and 91 layers layers in the
vertical from 2006 onwards). The carbon dioxide levels predicted by
CarbonTracker do not feed back onto these predictions of winds.
For use in TM5, the ECMWF meteorological data are preprocessed into
coarser grids. In CarbonTracker, TM5 is run at a global 3°x
2° resolution with a nested regional grid over North America at
1° x 1° resolution (Figure 1). TM5 runs at an external time
step of three hours, but due to the symmetrical operator splitting and
the refined resolution in nested grids, processes at the finest scale
are repeated every 10 minutes. The vertical resolution of TM5 in
CarbonTracker is 34 hybrid sigma-pressure levels (from 2006 onwards;
25 levels for 2000-2005), unevenly spaced with more levels near the
surface. Approximate heights of the mid-levels (in meters, with a
surface pressure of 1012 hPa) are:
|Level||Height (m)||Level||Height (m)
3. Further Reading