An aerosol climatology for global models based on the tropospheric aerosol scheme in the Integrated Forecasting System of ECMWF

Abstract

Abstract. An aerosol climatology to represent aerosols in the radiation schemes of Global Atmospheric Models was recently developed. We derived the climatology from a reanalysis of atmospheric composition produced by the Copernicus Atmosphere Monitoring Service (CAMS). As an example of application into a global atmospheric model, we discuss the technical aspects of the implementation in the Integrated Forecasting System of European Centre for Medium Range Weather Forecasts (ECMWF-IFS) and the impact of the new climatology on the medium-range weather forecasts and one-year simulations. The new aerosol climatology was derived by combining a set of model simulation with constrained meteorological conditions and an atmospheric composition reanalysis for the period 2003–2014 produced by the IFS. The aerosol fields of the re-analysis are constrained by assimilating Aerosol optical thickness (AOT) retrievals product by the MODIS instruments. In a further step, we used modelled aerosol fields to correct the aerosol speciation and the vertical profiles of the aerosol reanalysis fields. The new climatology provides the monthly-mean mass mixing ratio of five aerosol species constrained by assimilated MODIS AOT. Using the new climatology in the ECMWF-IFS leads to changes in direct aerosol radiative effect compared to the climatology previously implemented, which have a small, but non-negligible impact on the forecast skill of large-scale weather patterns in the medium-range. However, details of the regional distribution of aerosol radiative forcing can have a large local impact. This is the case for the area of the Arabian Peninsula and the northern Indian Ocean. Here changes in the radiative forcing of the mineral dust significantly improve the Summer Monsoon circulation.

Present‐Day and Historical Aerosol and Ozone Characteristics in CNRM CMIP6 Simulations

“…This vertical distribution in CNRM‐CM6‐1 depends only on the aerosol type and is therefore unchanged in time and space. It is calculated from a pressure‐dependent function using a scale height specific to each aerosol type as described in Bozzo et al (). Other aerosol optical properties used as input in the radiative transfer scheme, both in CNRM‐CM6‐1 and CNRM‐ESM2‐1, namely, the single scattering albedo (SSA; 0 to 1 range) and the asymmetry parameter (ASY; 1 to 1 range), are prescribed depending on the aerosol type, relative humidity (except for DD and BC), and wavelength.…”

Sensitivity of Radiative Fluxes to Aerosols in the ALADIN-HIRLAM Numerical Weather Prediction System

“…In addition, stratospheric sulfates and volcanic dust are accounted for using assumed constant background values. The six AOD550 fields are distributed vertically using the assumed exponential profiles of Tanré [31] in the same way as described by [9]. Aerosol IOPs, namely the relation of AOD to AOD550, the SSA and ASY, of the 6 aerosol species are prescribed for 6 SW and 6 LW intervals in the default IFSRADIA radiation scheme.…”

“…SS approximately corresponds to the Tegen 'sea' aerosol category, DD to 'desert', OM to 'land' without sulfates and BC to 'urban' aerosols. Updated exponential functions [9] were applied to distribute the 2D MMR data vertically on model levels. The CAMS data and ECMWF IOPs are described in more detail in Appendix A.3.…”

“…The Copernicus Atmosphere Monitoring Service (CAMS) global reanalysis of atmospheric composition [7] has resulted in an extensive historical aerosol dataset. They also produce global forecasts of aerosols and atmospheric chemical constituents in near-real time [8].In the European Centre for Medium-Range Weather Forecast (ECMWF) model the use of a new global 3D aerosol climatology based on [7], combined with updated aerosol inherent optical properties (IOPs), led to a systematic improvement in lower troposphere temperature and wind forecasts over certain regions of the globe [9]. However, during wildfires, desert dust intrusions, volcanic eruptions and enhanced anthropogenic emissions aerosol concentrations in the atmosphere may significantly exceed climatological values, which can influence the weather on local to global scales.…”

“…By default, the system uses Tegen climatologies [23] of AOD550 of land, sea, desert, urban and sulfate aerosols and the following aerosol IOPs: AOD wavelength-scaling factor, SSA and ASY based on [24,25]. Our upgrades involve the combination of updated IOPs (ME, SSA and ASY for 11 aerosol species at 30 wavelengths) from ECMWF [9,26] and aerosol concentrations from the CAMS reanalysis [7] or CAMS n.r.t. data [8].…”