Questions about Top Boundary Conditions

CAMx has one optional input 2-D top boundary conditions file contains gridded and time-dependent concentration fields above the top of the master grid boundary. Top boundary conditions improve the
characterization of chemicals entering vertically across the model top, which is particularly
important for common stratospheric constituents such as ozone and nitrogen oxides according to some applications of CAMx. My top conditions-related questions are

  1. How CMAQ deal with exchanges between the top model layer and the
    environment above the model?
  2. Why CMAQ does not need top conditions? Is that because CMAQ keep the constant concentrations as initial conditions provided?
  3. How to create top conditions for CAMx using seasonal average hemispheric CMAQ output.
    Thank you.

In most applications, CMAQ inherits the dynamical state of the atmosphere from WRF. Thus, like WRF it assumes zero flux at the model top and so does not require a top boundary condition.

To represent potential impacts of stratosphere-troposphere exchange CMAQ includes an option to specify ozone mixing ratios in its UTLS based on space and time varying potential vorticity fields. To invoke the potential vorticity scaling of modeled O3 in the upper layers (100-50mb),
“set potvortO3” should be specified in the BuildScript. Also, potential vorticity fields must be available in the METCRO3D files generated by MCIP. This is enabled by setting LPV = 1 in the MCIP runscript. Additional information on this scheme can be found in Section 6.13 of the User’s Guide.


Hi Rohit Mathur,
Thank you very much for the updates with such a detail explanation. It seems easier for CMAQ to handle air mass exchange in its UTLS. I will conduct sensitivity analysis of w/o potvortO3 to lower level ozone model performance of CMAQ.
BTW, do you have any idea or a package to develop top boundary condition for CAMx from seasonal average hemispheric CMAQ output.
Thank you very much.