A new linearized ozone photochemistry scheme for high altitude NWP and climate models

We present results from a newly developed linearized ozone photochemistry parameterization based on output from the zonally averaged NRL-CHEM2D middle atmosphere photochemical-transport model. This CHEM2D-based linearized ozone photochemistry parameterization is part of the new prognostic ozone capability in NOGAPS-ALPHA, the Navy's prototype global high altitude numerical weather prediction (NWP) model. The upward extension of NWP models such as NOGAPS-ALPHA to include the stratosphere and lower mesosphere requires a fast, accurate representation of ozone photochemical production and loss. To reduce computational overhead, current operational NWP models generally parameterize these processes in terms of odd oxygen production and loss rates computed offline with a zonally averaged photochemical model of the middle atmosphere, expressing the local ozone photochemical tendency in terms of model ozone mixing ratio, temperature, and overlying ozone column abundance using a linearized, truncated Taylor-series type expansion about a mean reference state. A recent study of NOGAPS-ALPHA ozone simulations comparing the performance of three different ozone photochemistry schemes has shown that a preliminary version of the CHEM2D-based parameterization (with no temperature and overhead ozone column dependences) generally performed better than two earlier photochemistry schemes that are widely used for both NWP and climate applications. Here we present new NOGAPS-ALPHA ozone simulations using the full CHEM2D-based ozone photochemistry parameterization (including temperature and column terms), and evaluate its performance in both shorter 5-10 day forecasts and longer seasonal to inter-annual climate simulations. The impact of the new 3D prognostic ozone fields generated with the CHEM2D-based ozone photochemistry scheme on NOGAPS-ALPHA stratospheric heating rates and the development of a new "cold tracer" term to represent high-latitude catalytic ozone loss will also be discussed.