removing dxy from GOCART dust emission schemes. Code clean-up.

[saneku]

TYPE: enhancement

KEYWORDS: GOCART, dust emission, dust_opt, WRF-Chem

SOURCE: Alexander Ukhov (KAUST)

DESCRIPTION OF CHANGES:
This PR affects dust emission schemes (dust_opt=1,3,4) coupled with GOCART
aerosol module.

1. Current implementation of dust_opt=1,3 calculates air mass in the grid box using
   cell area and height, and air density, however a more elegant solution is now implemented
   (by analogy with dust_opt=4). This solution only requires height of the lowest model layer.
2. Another issue have been also resolved when using dust_opt=1. Due to incorrect
   indexing in the tile loop dust emissions diagnostics (variables EDUST1…5) were zero
   near the boundaries of the domain.
3. Each emission scheme (dust_opt=1,3,4) reported instantaneous dust emissions diagnostics
   (variables EDUST1…5) in different units: dust_opt=1 [kg/cell/dt], dust_opt=3 [gram/m^2/s],
   dust_opt=4 [ug/m^2/s]. For user convenience this discrepancy also has been fixed.
   now EDUST1..5 variables store accumulated dust emissions [kg/m^2] for dust_opt=1,3,4.
   For example, this can be useful when is necessary to estimate dust mass balance. In this
   case accumulated dust emission needs to be multiplied by cell area (m^2), see Appendix of [1].
4. Code clean-up has been also done in dust_opt=1,3.

LIST OF MODIFIED FILES:
M Registry/registry.chem
M chem/emissions_driver.F
M chem/module_gocart_dust.F
M chem/module_gocart_dust_afwa.F
M chem/module_qf03.F
M chem/module_uoc_dust.F

TESTS CONDUCTED:

1. To demonstrate correctness of the implemented changes a numerical simulations of the dust
   over the Middle East (chem_opt=301 with dust_opt=1,3,4, 100km resolution) with and without changes has been run.

Produced results (total dust surface concentration, total dust column loadings, and
accumulated total dust emissions at the end of 3 day simulation) before and after changes
are Identical, which is expected. Except for the case, where total dust emissions are
compared for dust_opt=1 (see pt. 2 above).

[1] Ukhov, A., Ahmadov, R., Grell, G., and Stenchikov, G.:
Improving dust simulations in WRF-Chem v4.1.3 coupled with the GOCART
aerosol module, Geosci. Model Dev., 14, 473–493,
https://doi.org/10.5194/gmd-14-473-2021, 2021.

RELEASE NOTE: Dependency on cell area (dxy=dx*dx) is removed from calculation of dust emissions (dust_opt=1,3,4. GOCART aerosol module). Output diagnostics of dust emission were unified across dust_opt=1,3,4. Code clean-up is dust_opt=1,2.

2. Jenkins testing is all PASS.

[davegill]

jenkins is OK

Please find result of the WRF regression test cases in the attachment. This build is for Commit ID: 8fd180e2cdb9958481e27a04949f2edf5d363f6b, requested by: saneku for PR: https://github.com/wrf-model/WRF/pull/1431. For any query please send e-mail to David Gill.

    Test Type              | Expected  | Received |  Failed
    = = = = = = = = = = = = = = = = = = = = = = = =  = = = =
    Number of Tests        : 19           18
    Number of Builds       : 48           46
    Number of Simulations  : 163           161        0
    Number of Comparisons  : 103           102        0

    Failed Simulations are: 
    None
    Which comparisons are not bit-for-bit: 
    None

[jordanschnell]

Approved