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README.DA_chem
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Aerosol/Chemical Data Assimilation in WRFDA
------------------------------------------------
1. Introduction
-------------
Aerosol/Chemical data assimilation capability is introduced in version 4.3, which allows the assimilation
of 6 types of surface measurements (PM2.5, PM10, O3, CO, NO2, SO2) with 3DVAR and provides the analyzed
initial conditions for WRF-Chem. This new capability is documented by Sun et al. (2020).
Sun, W., Liu, Z., Chen, D., Zhao, P., and Chen, M., 2020: Development and application of the WRFDA-Chem
three-dimensional variational (3DVAR) system: aiming to improve air quality forecasting and diagnose
model deficiencies, Atmos. Chem. Phys., 20, 9311-9329.
Analysis variables includes the four gas-phase variables (O3, CO, NO2 and SO2) and aerosol variables
from different aerosol schemes in WRF-Chem. Version 4.3 works with GOCART (15 species) or 4-bin MOSAIC
(32 species) aerosol scheme. Version 4.4 added another aerosol scheme MADE/VBS (35 species)
(Ha, 2022).
Ha, S., 2022: Implementation of aerosol data assimilation in WRFDA (v4.0.3) for WRF-Chem (v3.9.1) using the
RACM/MADE-VBS scheme, Geosci. Model Dev., 15, 1769–1788, https://doi.org/10.5194/gmd-15-1769-2022.
2. Compilation
---------------
To compile 3DVAR with aerosol/chemical DA capability, following the commands below:
setenv WRF_CHEM 1
./configure wrfda
./compile all_wrfvar
The executable is still da_wrfvar.exe, but now it can take WRF-Chem’s initial condition file as the background
(i. e., the ‘fg’ file) and perform the aerosol/chemical analysis in addition to the usual function for
meteorological analysis.
3. Namelist setting
------------------
All related settings are in a new namelist section named "wrfvarchem". Each namelist
parameter is explained below.
&wrfvarchem
chem_cv_options= 0, # this parameter sets chem control variables. 0 is defulat, no chemical DA.
10, # control variables are 4 gas + 15 GOCART aerosol variables
20, # control variables are 4 gas + 32 MOSAIC aerosol variables.
108, # control variables are 4 gas + 35 MADE/VBS aerosol variables
chemicda_opt= 1, # set obs assimilated, default 1, assimilate pm2.5
2, # assimilate pm10
3, # assimilate pm2.5 and pm10
4, # assimilate co, o3, so2, and no2
5, # assimilate pm2.5, pm10, co, o3, so2, and no2
var_scaling12=1.0, 1.0, …, # array with a dimension of 45*max_outer_iterations,
# inflation factors of chemical background error variances
# of aerosol/gas analysis variables at different
# outer loops. Default values are 1 (no inflation).
len_scaling12=1.0, 1.0, …, # arrary with a dimension of 45*max_outer_iterations,
# inflation factors of chemical background error length scales.
# Default values is 1.
use_chemic_surfobs = .true., # Default is true, read in ob_chemsfc.ascii file that includes 6 types of
# observation that are assumed to be processed for each analysis time and provided in the unit and
# the format specified in var/da/da_obs_io/da_read_obs_chem_sfc.inc and da_scan_obs_chem_sfc.inc.
/
4. Chemical/Aerosols background error covariance statistics
-----------------------------------------------------------
The standard GEN_BE package included in WRFDA cannot obtain the background error statistics for
aerosol/chemical variables. Users will need to use https://github.com/wrf-model/GENBE_2.0 to
generate a be.dat file that contains the background errors of chemical variables. Please refer
to the online commit message for its use.
5. Test case
---------------
A testcase is provided in https://www2.mmm.ucar.edu/wrf/users/wrfda/chemda_testcase/.
We have no resource to provide the assistance of this capability for users’ own applications.