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Concentrations less than background

PostPosted: Mon Jul 29, 2013 2:30 am
by sru20
Dear WRF/Chem users,
I have been using the WRF-Chem's chem_opt=16 for CO2 passive tracer in WRF/Chem version 3.4.1 and have seen that I do get CO2 concentrations less than background in the domain even though i am using positive definite and monotonic advection options:

moist_adv_opt = 2, 2, 2,2,
scalar_adv_opt = 2, 2, 2,2,
chem_adv_opt = 2, 2, 2,2,
tke_adv_opt = 2, 2, 2,2,
time_step_sound = 4, 4, 4,4,
h_mom_adv_order = 5, 5, 5,5,
v_mom_adv_order = 3, 3, 3,3,
h_sca_adv_order = 5, 5, 5,5,
v_sca_adv_order = 3, 3, 3,3,

I initialise my 3 nested domains with CO2=380 ppm and have constant values of 380ppm at the boundaries.I emit CO2 in the model but there is no chemistry and no loss processes. After the the first couple of time steps, i can see concentrations less than 380 ppm throughout the domain (typically 379.xxx). For an 11 day simulation, i can see a minimum concentration of 379.043 ppm and 379.824 ppm in the innermost and outermost domains respectively. So how do i end up getting values in the domain less than 380 if i am using positive definite advection schemes?

The full namelist is attached.

Any thoughts on this will be highly appreciated!

Thanks for your help,

Steve