Arctic spring and summertime aerosol optical depth baseline from long-term observations and model reanalyses, with implications for the impact of regional biomass burning processes
- 1Naval Research Laboratory, Monterey, CA, USA
- 2Department of Atmospheric Sciences, University of North Dakota, Grand Forks, ND
- 3NASA Langley Research Center, Hampton, Virginia, USA
- 4NASA Goddard Space Flight Center, Greenbelt, MD, USA
- 5European Centre for Medium-Range Weather Forecasts, Reading, UK
- 6Département de géomatique appliqué, Université de Sherbrooke, Sherbrooke, Québec, Canada
- 1Naval Research Laboratory, Monterey, CA, USA
- 2Department of Atmospheric Sciences, University of North Dakota, Grand Forks, ND
- 3NASA Langley Research Center, Hampton, Virginia, USA
- 4NASA Goddard Space Flight Center, Greenbelt, MD, USA
- 5European Centre for Medium-Range Weather Forecasts, Reading, UK
- 6Département de géomatique appliqué, Université de Sherbrooke, Sherbrooke, Québec, Canada
Abstract. We present an Arctic aerosol optical depth (AOD) climatology and trend analysis for 2003–2019 spring and summertime periods derived from a combination of multi-agency aerosol reanalyses, remote sensing retrievals, and ground observations. This includes the U.S. Navy Aerosol Analysis and Prediction System ReAnalysis version 1 (NAAPS-RA v1), the NASA Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), and the Copernicus Atmosphere Monitoring Service ReAnalysis (CAMSRA). Space-borne remote sensing retrievals of AOD are considered from the Moderate Resolution Imaging Spectroradiometer (MODIS), the Multi-angle Imaging SpectroRadiometer (MISR), and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Ground-based data include sun photometer data from Aerosol Robotic Network (AERONET) sites and oceanic Maritime Aerosol Network (MAN) measurements. Aerosol reanalysis AODs and space-borne retrievals show consistent climatological spatial patterns and trends for both spring and summer seasons over the sub-Arctic (60–70° N). Consistent signs in the AOD trend are also found for the high Arctic (north of 70° N) from reanalyses. The aerosol reanalyses yield more consistent AOD results than climate models, verify well with AERONET, and corroborate complementary climatological and trend analysis. Speciated AODs are more variable than total AOD among the three reanalyses, and a little more so for March–May (MAM) than for June–August (JJA). Black Carbon (BC) AOD in the Arctic comes predominantly from biomass burning sources in both MAM and JJA, and biomass burning overwhelms anthropogenic sources in JJA for the study period.
AOD exhibits a negative trend in the Arctic in MAM, and a positive trend in JJA during 2003–2019, due to an overall decrease in sulfate/anthropogenic pollutions, and a significant increase in biomass burning smoke in JJA. Interannual Arctic AOD variability is significantly large, driven by fine-mode, and specifically, biomass burning (BB) smoke, though more so in JJA than in MAM. Extreme AOD events during spring and summer in the Arctic, defined as AOD greater than the 95th percentile value, are mainly attributed to BB smoke transport events. Extreme AOD cases tend to occur later in the season (i.e., July and August, in the latter decade rather than spreading over April–August in the early decade during 2003–2019) corresponding to a shift to a later time in extreme boreal BB activities.
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Peng Xian et al.
Status: closed
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RC1: 'Comment on acp-2021-805', Anonymous Referee #2, 13 Nov 2021
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AC1: 'Reply on RC2', P. Xian, 21 Dec 2021
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-805/acp-2021-805-AC1-supplement.pdf
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AC1: 'Reply on RC2', P. Xian, 21 Dec 2021
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RC2: 'Comment on acp-2021-805', Anonymous Referee #1, 21 Dec 2021
The paper entitled "Arctic spring and summertime aerosol optical depth baseline from long-term observations and model reanalyses, with implications for the impact of regional biomass burning processes" by Peng Xian and coauthors presents a comprehensive view on long-term measurements and modelling of aerosol optical depth (AOD) in the Arctic. They consider ground-based AERONET sun photometer measurements, observations by three spaceborne instruments, and results from three aerosol reanalyses as well as their composite to investigate (i) the consitency of the different data sets, (ii) the annual and seasonal variation as well as the long-term trend in AOD together with the importance of biomass-burning smoke, and (iii) statistics on the occurrence of extreme AOD events.
While the work is of interest to the readers of ACP, it is far to much material for one publication. This review is late, also because it is impossible to read the manuscript in one sitting. In fact, the content could be split in as much as three papers according to the list of topics provided above. Such an approach would lead to very good papers that could be much more reader-friendly than the current submission. This reviewer therefore recommends to reject the paper in its current form and to re-submit after a thorough revision of content and readibility. Alternatively, the work requires major revisions, shortening, and a decision on which of the three topics to focus in this particular submission.
Please find some more specific comments below:
- The paper is rather lengthy and would benefit from trimming the text and content to what's really needed. A start would be a shorter title such as, e.g. to Arctic spring and summertime aerosol optical depth baseline from long-term observations and model reanalyses.
- Entire paragraphs could be omitted as they are repeating points made earlier or are just redundant, e.g. lines 24-31 (not needed in the Abstract), 141-148, 176-182, 299-303 (why mention if the statement end with "is not used here"),...
- The entire part about FLAMBE (description and results) could be omited. In fact, the point made here could be condensed down to something along the lines of "findings are also supported by burning emissions from FLAMBE" later in the discussion.
- There are way too many figures for one publication. In addition, some information in these figures could be moved to the supplement to improve the discussion of the findings. For instance, the main figures could stick to the Multi-Reanalysis Concensus and their discussion could link to more detailed figures including the specific findings of the three models in the supplement. The authors should re-evaluate if a figure that isn't thoroughly discussed in the text is needed in the manuscript.
- The study makes use of height-resolved measurements from CALIOP and considers detailed aerosol re-analyses fields. The work would be even stronger of this information was to be used to also investigate the vertical distibution of Arctic aerosols. Such an attempt would partly compensate for the disadvantage of AOD to refer to column aerosol load.
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AC2: 'Reply on RC1', P. Xian, 16 Mar 2022
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-805/acp-2021-805-AC2-supplement.pdf
-
AC2: 'Reply on RC1', P. Xian, 16 Mar 2022
Status: closed
-
RC1: 'Comment on acp-2021-805', Anonymous Referee #2, 13 Nov 2021
-
AC1: 'Reply on RC2', P. Xian, 21 Dec 2021
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-805/acp-2021-805-AC1-supplement.pdf
-
AC1: 'Reply on RC2', P. Xian, 21 Dec 2021
-
RC2: 'Comment on acp-2021-805', Anonymous Referee #1, 21 Dec 2021
The paper entitled "Arctic spring and summertime aerosol optical depth baseline from long-term observations and model reanalyses, with implications for the impact of regional biomass burning processes" by Peng Xian and coauthors presents a comprehensive view on long-term measurements and modelling of aerosol optical depth (AOD) in the Arctic. They consider ground-based AERONET sun photometer measurements, observations by three spaceborne instruments, and results from three aerosol reanalyses as well as their composite to investigate (i) the consitency of the different data sets, (ii) the annual and seasonal variation as well as the long-term trend in AOD together with the importance of biomass-burning smoke, and (iii) statistics on the occurrence of extreme AOD events.
While the work is of interest to the readers of ACP, it is far to much material for one publication. This review is late, also because it is impossible to read the manuscript in one sitting. In fact, the content could be split in as much as three papers according to the list of topics provided above. Such an approach would lead to very good papers that could be much more reader-friendly than the current submission. This reviewer therefore recommends to reject the paper in its current form and to re-submit after a thorough revision of content and readibility. Alternatively, the work requires major revisions, shortening, and a decision on which of the three topics to focus in this particular submission.
Please find some more specific comments below:
- The paper is rather lengthy and would benefit from trimming the text and content to what's really needed. A start would be a shorter title such as, e.g. to Arctic spring and summertime aerosol optical depth baseline from long-term observations and model reanalyses.
- Entire paragraphs could be omitted as they are repeating points made earlier or are just redundant, e.g. lines 24-31 (not needed in the Abstract), 141-148, 176-182, 299-303 (why mention if the statement end with "is not used here"),...
- The entire part about FLAMBE (description and results) could be omited. In fact, the point made here could be condensed down to something along the lines of "findings are also supported by burning emissions from FLAMBE" later in the discussion.
- There are way too many figures for one publication. In addition, some information in these figures could be moved to the supplement to improve the discussion of the findings. For instance, the main figures could stick to the Multi-Reanalysis Concensus and their discussion could link to more detailed figures including the specific findings of the three models in the supplement. The authors should re-evaluate if a figure that isn't thoroughly discussed in the text is needed in the manuscript.
- The study makes use of height-resolved measurements from CALIOP and considers detailed aerosol re-analyses fields. The work would be even stronger of this information was to be used to also investigate the vertical distibution of Arctic aerosols. Such an attempt would partly compensate for the disadvantage of AOD to refer to column aerosol load.
-
AC2: 'Reply on RC1', P. Xian, 16 Mar 2022
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-805/acp-2021-805-AC2-supplement.pdf
-
AC2: 'Reply on RC1', P. Xian, 16 Mar 2022
Peng Xian et al.
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