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

Abstract

Abstract. Gridpoint Statistical Interpolation (GSI) is an assimilation tool that is used at the National Centers for Environmental Prediction (NCEP) in operational weather forecasting in the USA. In this article, we describe implementation of an extension to the GSI for assimilating surface measurements of PM 2.5 , PM 10 , and MODIS aerosol optical depth at 550 nm with WRF-Chem (Weather Research and Forecasting model coupled with Chemistry). We also present illustrative results. In the past, the aerosol assimilation system has been employed to issue daily PM 2.5 forecasts at NOAA/ESRL (Earth System Research Laboratory) and, we believe, it is well tested and mature enough to be made available for wider use. We provide a package that, in addition to augmented GSI, consists of software for calculating background error covariance statistics and for converting in situ and satellite data to BUFR (Binary Universal Form for the Representation of meteorological data) format, and sample input files for an assimilation exercise. Thanks to flexibility in the GSI and coupled meteorology-chemistry of WRFChem, assimilating aerosol observations can be carried out simultaneously with meteorological data assimilation. Both GSI and WRF-Chem are well documented with user guides available online. This article is primarily intended to be a technical note on the implementation of the aerosol assimilation. Its purpose is also to provide guidance for prospective users of the computer code. Scientific aspects of aerosol assimilation are also briefly discussed.

A case study of aerosol data assimilation with the Community Multi-scale Air Quality Model over the contiguous United States using 3D-Var and optimal interpolation methods

“…The GSI's 3D-Var uses a similar approach (Pagowski et al, 2014;Liu et al, 2011) for its cost function…”

“…In this study, the PM 2.5 observations are located at 674 surface sites over CONUS, and all of them are used in data assimilations. The settings of GSI are similar to Pagowski et al (2014), in which the background error and length scales have vertical variance. Figure 1 shows that the vertical profiles of background errors and length scales for PM 2.5 (for PM 2.5 assimilation) and accumulation-mode sulfate (ASO4J, for AOD assimilation), which can be calculated using the GSI NMC (National Meteorological Center) method (Parrish and Derber, 1992) through the use of a tool called GEN_BE (Descombes et al, 2015).…”

“…A more complex method is using Gridpoint Statistical Interpolation (GSI) (Wu et al, 2002;Purser et al, 2003a, b), a 3D-Var method, developed by NOAA/NCEP. It has been applied to assimilate the Goddard Chemistry Aerosol Radiation and Transport (GOCART) aerosols in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) with its 3D-Var method (Pagowski et al, 2014;Liu et al, 2011). In the next sections, we describe the method that extends the GSI to assimilate CMAQ aerosols, comparing it to OI correction.…”

Evaluation of the high resolution WRF-Chem (v3.4.1) air quality forecast and its comparison with statistical ozone predictions

“…Chemical data assimilation, although currently still in its infancy for online coupled meteorology-chemistry models (Bocquet et al, 2015), could in future also be used as an efficient method for improving prediction of chemical concentration fields. For the WRF-Chem model, a technical note on the implementation of the aerosol assimilation and a guide for prospective users has been recently published by Pagowski et al (2014). Mean absolute error:…”

Limitations of ozone data assimilation with adjustment of NO<sub><i>x</i></sub> emissions: mixed effects on NO<sub>2</sub> forecasts over Beijing and surrounding areas

“…The role of CDA in optimizing initial and boundary conditions has been explored in several applications to improve forecasts of ozone and aerosol (Gaubert et al, 2014;Pagowski et al, 2014). Nevertheless, significant challenges persist in CDA.…”