Ocean mask ____

setraseti123 · November 23, 2021, 12:07pm

Dear all,
I need to produce ocean mask file for running CMAQ-WRF two-way. But I am very new with CMAQ. May I ask you please advice me by details how can I produce ocean mask ?
Many thanks in advance,
Best regards,

foley.kristen · November 23, 2021, 4:06pm

Please take a look at this tutorial on the CMAQ GitHub repo:

github.com

USEPA/CMAQ/blob/main/DOCS/Users_Guide/Tutorials/CMAQ_UG_tutorial_oceanfile.md

## CMAQ Tutorial ##
### Creating an OCEAN file for input to CMAQ ###
Purpose: This tutorial describes how to create an ocean mask file that defines the fraction of each grid cell covered by open ocean or surf zone in the CMAQ modeling domain.


------------

The CMAQ sea spray emissions module requires the input of an ocean mask file (OCEAN). OCEAN is a time-independent I/O API file that identifies the fractional [0-1] coverage in each model grid cell allocated to open ocean (OPEN) or surf zone (SURF). The CCTM uses this coverage information to calculate sea spray emission fluxes from the model grid cells online during a CCTM run.

Additionally, CMAQ's gas-phase chemical mechanisms except cb6r3m_ae7_kmtbr contain an effective first order halogen mediated ozone loss  over the ocean (where OPEN + SURF > 0.0). The OCEAN file is also required for this process. The cb6r3m_ae7_kmtbr mechanism contains more explicit marine chemistry, but also requires the OCEAN file.

If your domain includes ocean, OPTION 1 is recommended. However, if your modeling domain does not contain any ocean, or you wish to bypass the CMAQ sea spray module and the reaction of ozone with oceanic halogens, follow OPTION 2 or 3.  

## OPTION 1: Create OCEAN file from shapefile of domain

### STEP 1: Download the Spatial Allocator</strong>

The Spatial Allocator (SA) tool can be downloaded from the CMAS Center at the following link: https://www.cmascenter.org/sa-tools/. Login and follow the download and installation instructions.

### STEP 2: Create the OCEAN file

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If your domain is outside the US and you want to be able to run CMAQ with ocean chemistry, you will need to a shapefile that is appropriate for your domain, but the approach should still be the same.

setraseti123 · November 23, 2021, 4:50pm

Dear Foley,
Many thanks for your help.I wonder if this is all the process I need to have an ocean file?
Because it was very short and quick.
Best wishes,

foley.kristen · November 23, 2021, 5:13pm

Greetings,
Were you able to run the script and create the file? That should be all that you need to do. In your run script you will then set the environment variable OCEAN_1 to the location of this file.

If you would like to see an example ocean file, there is one included in these 2016 CMAQ inputs for a domain over the contiguous US with 12km x 12km horizontal grid:
https://drive.google.com/drive/folders/1QyT1I4wgtvYufCKCtE6skfOSK_4KS9Vu

Look under the folder ‘surface’ at the file called ‘12US1_surf.ncf’.

setraseti123 · November 23, 2021, 6:25pm

Dear Foley,
I did not run it yet,but I read the run script you sent. And it is very short compare to the CMAQ and SMOKE. That is why I wondered!
Dose spatial allocator has only Shapefiles Run Script?

However regarding the run script, may I ask you please advice me about below setting :
setenv INPUT_FILE_MAP_PRJN "+proj=lcc,+lat_1=33,+lat_2=45,+lat_0=40,+lon_0=-97"

setenv INPUT_FILE_ELLIPSOID "+a=6370000.0,+b=6370000.0"

```what are the differences between lat_1 and lat_0? 
and what are +a and +b?
Many thanks,
Best wishes,

foley.kristen · December 1, 2021, 4:29pm

These environment variables are used to define the map projection based on the PROJ coordinate transformation software.

Here is a brief section on the map projections supported by CMAQ:

github.com

USEPA/CMAQ/blob/main/DOCS/Users_Guide/Appendix/CMAQ_UG_appendixC_spatial_data.md#c3-spatial-data-projection

<!-- BEGIN COMMENT -->

[<< Previous Appendix](CMAQ_UG_appendixB_emissions_control.md) - [Home](../README.md) - [Next Appendix >>](CMAQ_UG_appendixD_parallel_implementation.md)

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# Appendix C: Processing Spatial Data for CMAQ Inputs

## C.1 Geospatial Data

Air quality modeling requires many spatial data to generate anthropogenic,
biogenic, fire, sea salt, dust, and NH<sub>3</sub> emissions. In addition, land surface characteristics such as
land cover types with vegetation leaf area index (LAI) and fraction, albedo, and soil types are required in
modeling the exchanges of heat, moisture, and momentum between the land and atmosphere and dry deposition
of trace chemicals (e.g. O<sub>3</sub> and NH<sub>3</sub>). It is important to use a consistent coordinate system for all the
geospatial data used in emission, meteorology, and air quality modeling. Most of the geospatial data
required for the Sparse Matrix Operator Kernel Emissions (SMOKE)/Weather Research and Forecasting
(WRF)/CMAQ modeling can be generated using the Spatial Allocator (SA) that includes three components
developed for specific applications: Vector, Raster, and Surrogate Tools.

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Here is the PROJ documentation on the parameters for the Lambert Conformal Conic projection (LCC) that is used in the run script you are looking at.
https://proj.org/operations/projections/lcc.html

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Ocean mask ____

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