Aerosol analysis and forecast in the European Centre for Medium‐Range Weather Forecasts Integrated Forecast System: 2. Data assimilation

TLDR

The paper is the second in a series describing the GEMS aerosol effort. The study aims to produce aerosol forecasts and reanalyses using satellite optical depth data, focusing on the architecture and implementation of a new aerosol assimilation system. The aerosol modeling and analysis system is fully integrated into the operational four‑dimensional assimilation apparatus, with a theoretical architecture and practical implementation designed for the GEMS project. Results from a two‑year reanalysis (2003–2004) show that, despite compromises in control variables and error characteristics, the analysis skillfully assimilates observations and improves aerosol optical depth forecasts.

Abstract

This study presents the new aerosol assimilation system, developed at the European Centre for Medium‐Range Weather Forecasts, for the Global and regional Earth‐system Monitoring using Satellite and in‐situ data (GEMS) project. The aerosol modeling and analysis system is fully integrated in the operational four‐dimensional assimilation apparatus. Its purpose is to produce aerosol forecasts and reanalyses of aerosol fields using optical depth data from satellite sensors. This paper is the second of a series which describes the GEMS aerosol effort. It focuses on the theoretical architecture and practical implementation of the aerosol assimilation system. It also provides a discussion of the background errors and observations errors for the aerosol fields, and presents a subset of results from the 2‐year reanalysis which has been run for 2003 and 2004 using data from the Moderate Resolution Imaging Spectroradiometer on the Aqua and Terra satellites. Independent data sets are used to show that despite some compromises that have been made for feasibility reasons in regards to the choice of control variable and error characteristics, the analysis is very skillful in drawing to the observations and in improving the forecasts of aerosol optical depth.