Formulation and evaluation of IMS, an interactive three-dimensional tropospheric chemical transport model 1. Model emission schemes and transport processes

In part one of this series of papers on a new integrated modelling system ( IMS), the interactive three-dimensional chemical transport model (CTM), we present a detailed description of the interactive emission scheme for bioge nic species and outline the datasets used for anthropogenic species. In add ition, we describe the transport scheme employed in this model. The biogeni c emission schemes incorporate the high-resolution Olson World Ecosystem da ta (Olson, 1992), the satellite-sensed terrestrial vegetation data from AVH RR (A Very High Resolution Radiometer) (Brown et al., 1985), and the CZCS ( Coastal Zone Color Scanner) data (Erickson and Eaton, 1993). These datasets provide seasonal variations in surface biogenic emissions. The emission sc hemes are tested against other estimates (e.g., GEIA) and equilibrium emiss ions. A comparison of terrestrial biogenic fluxes, both the spatial and tem poral (seasonal) variation of modelled surface net primary production, is c onsistent with the geographical variations of the global vegetation index ( GVI) distribution derived from AVHRR. The annual net primary production is 76000 Tg C yr(-1), which compares well with the 40500-78000 Tg C yr(-1) est imated by Melillo et al. (1993). This indicates that the model works well i n capturing spatial and seasonal variations in the terrestrial vegetation. The modelled surface vegetation fluxes are verified against data from Guent her et al. (1995). While the comparison shows a generally good agreement in terms of the temporal and spatial distributions of isoprene (530 Tg yr(-1) ), large discrepancies are seen over the tropical locations which often exh ibit strong seasonality in rainfall and very small variation in temperature . These differences indicate that a large difference in the estimation betw een an empirical relation and an LSM calculation occurs if an area in which seasonal distribution of rainfall is the main factor which determines the type of vegetation. In this paper, we assess (results are discussed in foll owing papers) the role of changing surface biogenic distributions in surfac e-to-atmosphere biogenic fluxes (both ocean-to-atmosphere and land-to-atmos phere).