GEOS-Chem nested grid simulations
This page contains some basic information pertaining to the GEOS-Chem nested grid simulations. For more detailed information about met data availability for the various geographic regions, please see our Available met data for nested grid simulations wiki page. We also invite you to visit the wiki page of the Nested Model Working Group, which is responsible for coordinating nested-grid simulations within the GEOS-Chem user community.
Please also see our protocol for downloading and processing nested grid met data, which outlines the responsibilities for user groups using GEOS-Chem nested grid simulations.
Frequently asked questions
Can you save out boundary conditions for more than one nested grid in the same global run?
Yes, a single global simulation can output boundary conditions for multiple nested grid regions. In GEOS-Chem 12.3.2 and earlier, simply select multiple regions you would like to output boundary conditions for within the Nested Grid Menu of input.geos. In GEOS-Chem 12.4.0 and later, you can choose to either save out global boundary conditions that can be used for any region or you can create additional BoundaryCondition collections in HISTORY.rc.
Is it possible to run nested GEOS-Chem simulations on the AWS cloud?
Yes, you can run the nested grid simulations on AWS cloud. Please contact the GEOS-Chem Support Team for more information.
If we perform a nested grid simulation, is it possible to save out output in netcdf format?
Yes! You can output netcdf diagnostics for nested grid runs.
Can I run a nested grid simulation with GEOS-FP meteorology?
Yes! You can run GEOS-Chem nested grid simulations at the native GEOS-FP horizontal resolution of 0.25° x 0.3125° for the following regions:
--Melissa Sulprizio 16:17, 18 November 2014 (EST)
GEOS-FP nested-grid simulations for v10-01
Bastien Sauvage wrote:
I would be interested in running GC v11 in nested mode over Europe during summer 2013 (with GEOS_FP). However I am not sure this is possible as emissions and restart le seem not to be available in 0.3x0.2 over Europe? Is there a way to perform this simulation?
Lizzie Lundgren replied:
Starting in GEOS-Chem v10-01 you do not need to use separate emissions files with resolutions matching those of the European grid. The HEMCO emissions component can read global emissions and regrid them on-the-fly to the size of the nested grid. All you need to do is make sure you have the HEMCO data directories available. We do not have a European nested grid restart file available. However, you can contact the Nested Working Group to see if anyone has one to share. You could also try to use REGRIDH_RESTART in GAMAP to regrid from a coarser resolution. Alternatively, you can use the GAMAP routine called MAKE_EUR_DATA in the regridding directory of GAMAP.
--Bob Yantosca (talk) 15:40, 28 April 2017 (UTC)
How can I find which data are available for nested grid simulations?
Please see our Available met data for nested grid simulations wiki page. You can download the data from either the Harvard or Dalhousie data archives via FTP (or the wget utility).
--Bob Y. 14:09, 15 November 2010 (EST)
What if I can't find the GEOS-FP met data that I need?
If you cannot find the GEOS-FP nested grid met data for your particular geographic region of interest or time period of interest, then we invite you to download and process the met data yourself. Please see our GEOS-5 nested grid data protocol document for more information.
--Bob Y. 14:13, 15 November 2010 (EST)
Where can I find out more info about nested grid errors?
Please see the
posts on the Setting up GEOS-Chem nested grid simulations wiki page.
--Bob Y. 14:22, 15 November 2010 (EST)
I noticed abnormal concentrations at boundaries of the nested region. Is that normal?
If you see high tracer concentrations right at the boundary of your nested grid region, then this may be normal.
For nested grid simulations, we have to leave a “buffer zone” (i.e. typically 3 boxes along each boundary) in which the TPCORE advection is not applied. However, all other operations (chemistry, wetdep, drydep, convection, PBL mixing) will be applied. Therefore, in the “buffer zone”, the concentrations will not be realistic because the advection is not allowed to transport the tracer out of these boxes.
In any case, the tracer concentrations in the “buffer zone” will get overwritten by the 2° x 2.5° or 4° x 5° boundary conditions at the specified time (usually every 3h).
Therefore, you should exclude the boxes in the “buffer zone” from your scientific analysis.
The following diagram illustrates this:
<-------------------------------------- IGLOB ----------------------> +-------------------------------------------------------------------+ ^ | GLOBAL REGION | | | | | | <-------------- IIPAR -------------> | | | | | | +=================================[Y] ^ | | | | WINDOW REGION (met field size) | | | | | | | | | | | | <------- IM_W -------> | | | | | | +--------------------+ ^ | | | | | | | TPCORE REGION | | | | | | | | | (advection is | | | | | | |<------- I0 ---------->|<---->| done in this | JM_W | JJPAR | JGLOB | | I0_W | window!!!) | | | | | | | | | | | | | | | | | +--------------------+ V | | | | | | ^ | | | | | | | J0_W | | | | | | V | | | | | [X]=================================+ V | | | ^ | | | | J0 | | | V | | [1]------------------------------------------------------------------+ V
Diagram notes:
- The outermost box (GLOBAL REGION) is the global grid size. This region has IGLOB boxes in longitude and JGLOB boxes in latitude. The origin of the "Global Region" is at the south pole, at the lower left-hand corner (point [1]).
- The next innermost box (WINDOW REGION) is the nested-grid window. This region has IIPAR boxes in longitude and JJPAR boxes in latitude. This is the size of the trimmed met fields that will be used for a "nested-grid" simulation.
- The innermost region (TPCORE REGION) is the actual area in which TPCORE advection will be performed. Note that this region is smaller than the WINDOW REGION. It is set up this way since a cushion of grid boxes is needed TPCORE Region for boundary conditions.
- I0 is the longitude offset (# of boxes) and J0 is the latitude offset (# of boxes) which translate between the "Global Region" and the "Window Region".
- I0_W is the longitude offset (# of boxes), and J0_W is the latitude offset (# of boxes) which translate between the WINDOW REGION and the TPCORE REGION. These define the thickness of the Buffer zone mentioned above.
- The lower left-hand corner of the WINDOW REGION (point [X]) has longitude and latitude indices (I1_W, J1_W). Similarly, the upper right-hand corner (point [Y]) has longitude and latitude indices (I2_W, J2_W).
- Note that if I0=0, J0=0, I0_W=0, J0_W=0, IIPAR=IGLOB, JJPAR=JGLOB specifies a global simulation. In this case the WINDOW REGION totally coincides with the "Global Region".
- In order for the nested-grid to work we must save out concentrations over the WINDOW REGION from a coarse model (e.g. 2° x 2.5° or 4° x 5°) corresponding to the same fine-resolution WINDOW REGION. These concentrations are copied along the edges of the 1x1 WINDOW REGION and are thus used as boundary conditions for TPCORE.
Can I read nested grid met field files directly with GAMAP?
Yes, but you will have to call GAMAP with one of the following keywords:
gamap, ... /China ;; For China nested grid gamap, ... /NAmer ;; For N. America nested grid gamap, ... /Eur ;; For Europe nested grid
Otherwise you will get an error such as:
Attempt to read past end of FORTRAN unformatted file record. unit: 20.
You will also need to supply these keywords if you are using one of the lower-level GAMAP routines to read the data, for example:
ctm_get_data, ... /China success = ctm_get_datablock( ..., /China )
etc.
Setting up a 0.25 x 0.3125 nested-grid simulation for GEOS-FP
Visit our Setting up GEOS-Chem nested grid simulations wiki page for detailed instructions on how to set up a 0.25° x 0.3125° nested grid simulation with GEOS-FP meteorology.
--Melissa Sulprizio 16:17, 18 November 2014 (EST)