the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Impact of assimilating NOAA VIIRS Aerosol Optical Depth (AOD) observations on global AOD analysis from the Copernicus Atmosphere Monitoring Service (CAMS)
Sebastien Garrigues
Melanie Ades
Samuel Remy
Johannes Flemming
Zak Kipling
Istvan laszlo
Mark Parrington
Antje Inness
Roberto Ribas
Luke Jones
Richard Engelen
Vincent-Henri Peuch
Abstract. Global monitoring of aerosols is required to analyse the impacts of aerosols on air quality and to understand their role in modulating the climate variability. The Copernicus Atmosphere Monitoring Service (CAMS) provides near real time forecasts and reanalyses of aerosols using the ECMWF Integrated Forecasting System (IFS), constrained by the assimilation of MODIS and PMAp Aerosol Optical Depth (AOD). Given the potential end-of-lifetime of MODIS AOD, implementing new AOD observations in the CAMS operational suite is a priority to ensure the continuity of the CAMS forecast performances. The objective of this work is to test the assimilation of the NOAA VIIRS AOD product from S-NPP and NOAA20 satellites in the IFS model. Simulation experiments assimilating VIIRS on top or in place of MODIS were carried out from June 2021 to November 2021 to evaluate the impacts on the AOD analysis.
For maritime aerosol background, the assimilation of VIIRS and the use of VIIRS from NOAA20 as an anchor reduce the analysis AOD values compared to MODIS-based experiments, in which the analysis values were too high due to the positive bias of MODIS/TERRA over ocean. Over land, the assimilation of VIIRS induces a large increase in the analysis over biomass burning regions where VIIRS shows larger AOD than MODIS. For dust source regions, the analysis is reduced when VIIRS is assimilated on top of or in place of MODIS, particularly over the Sahara, Arabian Peninsula and few places in Asia in the July-August period. The assimilation of VIIRS leads to an overall reduction of the bias in AOD analysis evaluated against AERONET measurements with the largest bias reduction over Europe, desert, and maritime sites.
Sebastien Garrigues et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2023-398', Anonymous Referee #1, 12 Apr 2023
The authors describe the assimilation of NOAA-VIIRS AOD in CAMS atmospheric model. This is an important study due to the drifting of MODIS Terra and Aqua satellites that will soon need to be replaced by VIIRS. The assimilation methodology is clearly defined, and the modeling results are clearly presented and explained. Overall, I recommend publication in ACP with two minor suggestions that might be taken into account by the authors: (1) I would encourage the authors to further extend the discussion on the sensitivity of the assimilation method towards specific aerosol types. This could be done for example by the evaluation of model performance at specific events when the dominant atmospheric composition is known (e.g. strong biomass burning or dust outbreaks). (2) I suggest that the discussion in Session 5 (especially 5.2 and 5.3) is based on bias improvement considerations (i.e. where and when the model performs better) rather than on the differences between the model runs.
Citation: https://doi.org/10.5194/egusphere-2023-398-RC1 -
RC2: 'Comment on egusphere-2023-398', Anonymous Referee #2, 18 Apr 2023
In this manuscript, the authors present a study showing the impact of assimilating VIIRS AOD observations alone and jointly with MODIS AOD in CAMS. The paper is well written and is scientifically interesting, regarding that MODIS instruments are going to retire eventually. I recommend accepting it for publication.
I have minor comments:
Abstract l19-20: I think the dates of your experiments need to be checked: The year is 2020 in your following text while in the conclusion it is 2021-2022.
L23-24: “Over land, the assimilation of VIIRS induces a large increase in the analysis over biomass burning regions where VIIRS shows larger AOD than MODIS.”: You may want to provide reasons on why VIIRS has larger AOD than MODIS?
L109-114: Any references about VIIRS NOAA algorithm should be provided.
L155: You are assimilating total AOD at 550nm, however AOD distribution is non-gaussian. Do you take it into account in your assimilation system? Do you perform any quality control of your data using filters?
Section 3.3: You may want to revise your title to include VIIRS as well.
Citation: https://doi.org/10.5194/egusphere-2023-398-RC2
Sebastien Garrigues et al.
Sebastien Garrigues et al.
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