Implementation of aerosol assimilation in Gridpoint Statistical Interpolation (v. 3.2) and WRF-Chem (v. 3.4.1)

摘要

Gridpoint Statistical Interpolation (GSI) is an assimilation tool that isused at the National Centers for Environmental Prediction (NCEP) inoperational weather forecasting in the USA. In this article, we describeimplementation of an extension to the GSI for assimilating surfacemeasurements of PM_2.5, PM₁₀, and MODIS aerosol optical depth at550 nm with WRF-Chem (Weather Research and Forecasting model coupled with Chemistry). We also present illustrative results. In the past, theaerosol assimilation system has been employed to issue daily PM_2.5forecasts at NOAA/ESRL (Earth System Research Laboratory) and, we believe, it is well tested and mature enoughto be made available for wider use. We provide a package that, in addition toaugmented GSI, consists of software for calculating background errorcovariance statistics and for converting in situ and satellite data to BUFR (BinaryUniversal Form for the Representation of meteorological data)format, and sample input files for an assimilation exercise. Thanks toflexibility in the GSI and coupled meteorology–chemistry of WRF-Chem,assimilating aerosol observations can be carried out simultaneously withmeteorological data assimilation. Both GSI and WRF-Chem are well documentedwith user guides available online. This article is primarily intended to be atechnical note on the implementation of the aerosol assimilation. Its purposeis also to provide guidance for prospective users of the computer code.Scientific aspects of aerosol assimilation are also briefly discussed.