Evaluation of multiple satellite aerosol optical depth within the Copernicus Atmospheric Monitoring Service (CAMS) data assimilation system.

Abstract:

Global monitoring and forecasting of aerosols are required to analyse and predict the impacts of aerosols on air quality and their role in modulating the climate variability. To achieve this, the Copernicus Atmosphere Monitoring Service (CAMS, http://www.copernicus-atmosphere.eu) provides reanalysis records and 5-day forecasts of aerosols using the Integrated Forecasting System (IFS) which combines state-of-the-art meteorological and atmospheric composition modelling together with the data assimilation of satellite products. The current CAMS aerosol monitoring system relies on the assimilation of Aerosol Optical Depth (AOD) at 550 nm observations derived from MODIS (TERRA and AQUA satellites) and PMAp (synergy between GOME-2, IASI, AVHRR onboard METOP-A,B,C satellites) datasets. Implementing new observational data streams is of great importance in order to enhance the accuracy of the observations, to increase their spatial and temporal coverage and to increase the resilience of the data assimilation system to the failure of instruments. However, prior to their use in the data assimilation system, new AOD observations must be properly evaluated to check their consistency with both the modelled AOD and the other satellite AOD observations used in the IFS. The IFS data assimilation system provides continuous global coverage, allows to build up global and regional statistics quickly and can help to identify deficiencies in satellite AOD retrievals. The goal of this work is to use the IFS to assess and intercompare new satellite AOD products, namely the SENTINEL3-A and -B/SLSTR AOD product (v2.0) and the VIIRS EPS AOD product from S-NPP and NOAA-20 satellites. A three month experiment was designed to passively monitor the observations and assess their consistency across geographic regions and seasons. The outcomes of this work are discussed to identify shortcomings in current AOD satellite products, to provide recommendations for their improvements and to design a strategy for the assimilation of multiple satellite AOD products within global atmospheric composition models.