MOZART-3
The Model for OZone And Related chemical Tracers (MOZART) version 3 is an extension of
the MOZART2 version discussed in: Brasseur et al., 1998; Hauglustaine et al., 1998;
Horowitz et al., 2003. The numerical solution approach solves a system of time-dependent
ordinary differential equations, primarily by two methods: explicit Euler and implicit
backward Euler. Species with long lifetimes and weak forcing terms are solved with the
explicit method (e.g., N2O), while species that comprise a "stiff system" with short
lifetimes and strong forcings are solved via the more robust implicit method (e.g., OH).
There are two chemical mechanisms that have been developed. The first is a 50-species
mechanism that represents chemical and physical processes in the "middle atmosphere"
(Forkman et al, 2002; Park et al., 2004; Sassi et al., 2004; and Gettelman et al, 2004).
The species included within this mechanism are contained within the Ox, NOx, HOx, ClOx,
and BrOx chemical families, along with CH4 and its degradation products. There are no
non-methane hydrocarbons (NMHCs) included in this "middle atmosphere" mechanism. There
are a total of 118 gas-phase reaction plus 18 heterogeneous reactions (see below)
contained with in this mechanism. An additional mechanism has been developed that merges
the detailed representation of tropospheric chemistry contained in MOZART2 (see MOZART2
chemistry section) with the "middle atmosphere" mechanism discussed above. This "whole
atmosphere" mechanism contains 106 species; 260 thermal reactions plus 18 heterogeneous
reactions.
Surface boundary conditions for CH4, N2O, CO2, CH3Cl, CCl4, CH3CCl3, CFCl3, CF2Cl2,
CFC-113, HCFC-22, CH3Cl, CH3Br, CF3Br, and CF2ClBr are based on observations. The model
accounts for surface emissions of NOX, CO, and NMHCs based on the emission inventories
described in Horowitz et al. (2003). The NOx source from lightning is distributed
according to the location of convective clouds based on Price et al. (1997) with a
vertical profile following Pickering et al. (1998). Aircraft emissions of NOX and CO are
included in the model based on Friedl (1997). MOZART3 contains a detailed representation
of both wet and dry deposition.
MOZART3 derives the photolysis coefficients for 50 and 66 photolytic reactions for the
"middle atmosphere" and "whole atmosphere" respectively. The photolysis calculation is
currently divided into two regions: (1) 120 nm to 200 nm (34 wavelength intervals); (2)
200 nm to 750 nm (122 wavelength intervals). The total photolytic rate constant (J) for
each absorbing species is derived during model execution by integrating the product of
the wavelength dependent exoatmospheric flux; the normalized actinic flux, which is
unity at the top of atmosphere; the molecular absorption cross-section; and the quantum
yield. The exo-atmospheric flux over these wavelength intervals can be specified from
observations and varied over the 11-year solar sunspot cycle. For wavelengths > 200 nm a
flux lookup table (LUT) approach is used, based on the Stratosphere, Troposphere,
Ultraviolet (STUV) radiative transfer model (S. Madronich, personal communication). The
normalized radiative flux is interpolated from the LUT as a function of altitude, column
ozone, surface albedo, and zenith angle. The temperature and pressure dependences of the
molecular cross sections and quantum yields for each photolytic process are also
represented by a LUT in this wavelength region. At wavelengths < 200 nm, the
wavelength-dependent cross section and quantum yields for each species are specified
(i.e., no temperature dependence is currently included). There are two exceptions to
this approach for J(NO) and J(O2). In these cases the detailed photolysis
parameterizations are included inline. In the Schumann-Runge Bands (SRBs), the J(NO)
parameterization is based on Minschwaner and Siskind (1993). This parameterization
includes the effect of self-absorption and subsequent attenuation of atmospheric
transmission by the model-derived NO concentration. For J(O2), the SRB and Lyman-alpha
parameterization are based on Koppers and Murtagh (1996) and Chabrillat and Kockarts
(1997), respectively. The wavelength-dependent normalized actinic flux is derived based
on the reduction in transmission due to the model abundance of ozone and molecular
oxygen. The wavelength dependent photolysis approach is also used in the solar heating
calculation (see below).
Heterogeneous processes on sulfate aerosols and polar stratospheric clouds (Type 1a, 1b,
and 2) are included following the approach of Considine et al. (2000).
Auroral production of NO can then be determined from the reaction of molecular oxygen
and N(2D); the latter distribution is taken from the TIME-GCM (Roble et al).
Results
A comparison of MOZART-3 simulations using different meteorological analyses was
presented at the Quadrennial Ozone Symposiumn, June 1-8, 2004, Kos, Greece: Sensitivity
of Ozone to Specification of Meteorological Parameters in a 3D Chemical Transport Model
(poster).
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