Fall 2003 GMI Strat/Trop combined model working group summary

Combined model issues:

-   **Meteorological fields:**

    -   Big issue for combined model due to fact that primary focus of
        combined model is a "seamless" representation of the UT/LS
        region.

    -   Primary need is a good met field which gives reasonable flux
        into the troposphere.

    -   Testing at GSFC (Mark Olson) suggests fvgcm met field does this
        well, although convective mass fluxes in fvgcm are weak.

        -   Anne Douglass will use "persuasive powers" to convince Steve
            Pawson (GMAO) to generate an updated fvgcm met field with
            improved convection (2/1/2004 target date)

        -   Implementation into combined model (2/2004)

        -   Issue: All "combined model" development at LLNL (Connell,
            Bergmann) with subsequent hand-off to GSFC after
            development????

-   **Hydrologic cycle:**

    -   Current strategy for H2O in GMI strat is monthly-varying
        climatology, inappropriate for combined model.

    -   Proposed H2O mechanism:

        -   H2O transported in strat and trop.

        -   H2O constrained by (set equal to) met field specific
            humidity in troposphere.

        -   H2O will be removed in stratosphere where mixing ratios
            exceed saturation vapor pressure or by PSC parameterization.

        -   PSC parameterization will be modified to eliminate "dehyd"
            species (note -- a working version of such a
            parameterization exists and is incorporated into GSFC CTM).
            David Considine (1/2004)

        -   Approach Andy Dessler, who has been working on H2O in TTL:

            -   Any better approaches?

            -   Can he provide a set of tests to evaluate H2O
                distributions in TTL?

        -   Considine, Connell, Bergmann, Steenrod, Core Group

-   **Photolysis:**

    -   Need a photolysis scheme that works both in stratosphere and
        troposphere that is efficient.

    -   Fast-J 2 is a good candidate, but does not work at zenith angles
        \> 85 degrees.

    -   Fast-J 2 can be tweaked in relatively short time to treat high
        solar zenith angles properly

        -   Michael Prather will provide a tweaked parameterization
            (11/13/2003).

        -   Peter Connell will incorporate in test version of combined
            model (12/1/2003).

        -   Evaluation???

-   **Chemical mechanisms:**

    -   More extensive box model intercomparison would be useful:

        -   LaRC vs SMVGEAR combined mechanism

        -   Scenarios to test isoprene, boreal biomass burning plume,
            alkoxy radicals at low temps and pressures, heterogeneous
            fates of compounds

        -   Mechanism efficiency comparisons

        -   Considine/Olson/Chatfield

    -   Testing and refinement of SMVGEAR mechanism:

        -   What matters and what doesn't in UT/LS region of interest
            for combined model?

        -   Can simplifications to current scheme be made to eliminate
            reactions and decrease necessary computational resources?

        -   Connell

    -   LaRC combined mechanism

        -   continued testing and refinement at LaRC using in-house
            tools

        -   module revisions to comply with GMI coding standards

        -   LaRC personnell

        -   May, 2004 due date

-   **Very short-lived species**

    -   Modify current Rn/Pb simulations to quantify stratospheric
        source of Pb-210 due to stratospheric Rn-222 decay vs. direct
        injection.

        -   implement 2 Pb-210 "flavors," 1 from decay of tropospheric
            Rn-222, 1 from decay of stratospheric Rn-222, otherwise
            identical.

        -   Turn off Pb-210 gravitational settling parameterization

        -   analyze new simulations

        -   Conduct modified simulations based on analysis results.

        -   repeat simulations with improved fvgcm met field when
            available.

        -   Considine/Ko/Core

    -   CH3I: Investigate product gas loss rates in box model to be
        consistent with range of solubilities of CH3I decay products --
        need some reasonable assumptions to design simple Source
        gas/Product gas system (Chatfield).