ADVECTION_DIFFUSION - 15 Sep 2005 1) Compiling for optional advection schemes You have a choice of using the Piecewise Parabolic Method (ppm) advection scheme or the new global mass-conserving scheme (yamo) that is similar to the one used in the air quality forecasting version of CMAQ. Inspired by discussions with Robert Yamartino, the method uses the ppm scheme for horizontal advection, deriving a vertical velocity component at each grid cell that satisfies the continuity equation using the driving meteorology model's density. This scheme (yamo) is the default specified in the release bldit script. To switch to the ppm advection scheme, you will need to make the following changes to the bldit script. 61,62c61,62 < #set ModDriver = ( module ctm $Revision; ) < set ModDriver = ( module ctm_yamo $Revision; ) --- > set ModDriver = ( module ctm $Revision; ) > #set ModDriver = ( module ctm_yamo $Revision; ) 70,71c70,71 < #set ModInit = ( module init $Revision; ) < set ModInit = ( module init_yamo $Revision; ) --- > set ModInit = ( module init $Revision; ) > #set ModInit = ( module init_yamo $Revision; ) 74,75c74,75 < #set ModAdjc = ( module denrate $Revision; ) < set ModAdjc = ( // yamo option does not need denrate ) --- > set ModAdjc = ( module denrate $Revision; ) > #set ModAdjc = ( // yamo option does not need denrate ) 80,81c80,81 < #set ModHadv = ( module hppm $Revision; ) < set ModHadv = ( module hyamo $Revision; ) --- > set ModHadv = ( module hppm $Revision; ) > #set ModHadv = ( module hyamo $Revision; ) 84,85c84,85 < #set ModVadv = ( module vppm $Revision; ) < set ModVadv = ( module vyamo $Revision; ) --- > set ModVadv = ( module vppm $Revision; ) > #set ModVadv = ( module vyamo $Revision; ) If you want to use no-op for horizontal or vertical advection or both you have to compile for ppm, modifying the bldit script as necessary. We have not developed no-ops for the yamo scheme. 2) Minimum Eddy Diffusivity Option (KZMIN) The minimum value for the eddy diffusivity (Kz) has an important impact on nighttime concentrations. Traditionally in CMAQ, the minimum value for Kz has been set to a somewhat high value (Kzmin = 1.0 m2/s). However, meteorology models generally use lower values for minimum Kz (often 0.1 - 0.5 m2/s). When CMAQ had been tested with minimum Kz values set similarly to what is used in the meteorology models, unrealistically high concentrations of primary species were simulated in areas of high emissions (e.g., urban areas). On the other hand, using a somewhat high Kzmin in CMAQ led to overpredictions of ozone at night in more rural areas. To allow the mixing to better respond to the land-use characteristics, a new option for the minimum eddy diffusivity (Kzmin) is introduced in CMAQv4.5. This option considers the fraction of urban area within a given grid cell, and it scales the Kzmin value in each cell according to: Kzmin = (0.5 * (1.0 - Furban)) + (2.0 * Furban) where "Furban" is the fraction of urban area in the grid cell (0.0 - 1.0). Using this formula, Kzmin can now vary between 0.5 m2/s (in grid cells with no urban area) to 2.0 m2/s (in grid cells that are 100% urban based on land-use classification). The new Kzmin formulation relies on a new 2D field that defines Furban. This field is called "PURB" (percentage of urban area), and it can appear in the MCIP output file GRIDCRO2D if users provide fractional land-use information as input to MCIP. Fractional land-use fields are not currently available in the "standard" MM5 or WRF output files. For MM5, the fractional land-use fields are found in output from the preprocessing programs (e.g., TERRAIN), and MCIP has been modified to read those files to make fractional land-use available in the output. At this time, no fractional land-use fields are available for WRF, and the new Kzmin formulation cannot be used with WRF output. Users who want to take advantage of the new Kzmin formulation but have already prepared meteorology with MCIP and emissions with SMOKE can do so by running MCIPv3.0 for one hour with the appropriate input files (MMOUT and TERRAIN) to create a new GRIDCRO2D file that contains PURB, which can be used with CMAQv4.5. CMAQv4.5 is set up to use the new Kzmin formulation as the default. Users can set up CMAQv4.5 to use the "old" Kzmin formulation (1.0 m2/s at all grid cells) by setting the environment variable "KZMIN" in the CMAQ script, run.cctm. setenv KZMIN T <--- use Kzmin formulation based on Furban in cell setenv KZMIN F <--- use Kzmin of 1.0 m2/s at all grid cells If the new Kzmin formulation is selected by the user (either as the default or by setting the KZMIN enviroment variable) and if PURB is not available in GRIDCRO2D, CMAQv4.5 will issue an error message and stop.