3-DIMENSIONAL RADON 222 CALCULATIONS USING ASSIMILATED METEOROLOGICALDATA AND A CONVECTIVE MIXING ALGORITHM

The distribution of Rn-222 is simulated using a three-dimensional chem istry and transport model driven by assimilated data. The multiyear ca lculation is the first to use meteorological data from the Goddard Ear th Observing System data assimilation system (GEOS-1 DAS). In addition , this calculation is the first to use moist convection and boundary l ayer parameters directly from a DAS to calculate mixing via moist conv ection and turbulence. Previously, these quantities have been derived after the assimilation procedure. Model output and data are compared a t sites selected to evaluate model performance in a range of dynamic e nvironments. Simulated afternoon boundary layer concentrations are wit hin 30% of observed concentrations. Simulated nighttime concentrations are approximate to 50% of measured values although the bias is greatl y reduced (and even disappears at Socorro, New Mexico) when nocturnal sub-grid-scale turbulent mixing is suppressed. Continental profiles ar e ''C-like''; a result that is consistent with the moist convective al gorithm's tendency to move material from the planetary boundary layer (PBL) to the upper troposphere directly. CTM-calculated Rn-222 at Berm uda closely matches observations even during periods of frontal passag e showing that the atmospheric circulation is accurate and that ventil ation of the continental PBL is realistic. Model-calculated Rn-222 con centrations in the marine upper troposphere are consistent with observ ations in the eastern Pacific and near Darvin.