the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Aug 2025
PISTON and CAMP2Ex observations of the fundamental modes of aerosol vertical variability in the Northwest Tropical Pacific and Maritime Continent’s Monsoon
Abstract. While most large-scale smoke advection occurs within the free troposphere, Maritime Continent smoke transport is suspected to be unique in its long-range, near-surface transport. Such a pathway likely creates strong gradients and uncertainties in interpreting satellite and model data on light extinction, air pollution, and cloud condensation nuclei. This paper documents High Spectral Resolution Lidar (HSRL) data from the 2019 ONR PISTON cruise and NASA CAMP2Ex flights that revealed Maritime Continent smoke and pollution transport pathways and heterogeneity around the Marine Atmospheric Boundary Layer (MABL) over thousands of kilometers. Observations showed that 95 % of integrated aerosol backscatter occurred below 2500 m altitude. The R/V Sally Ride observed 50th and 84th percentile aerosol backscatter altitudes at ~600 and ~1500 m respectively, regardless of aerosol loading. Peak backscatter values occurred within or near the MABL top, diminishing as we approached 2–3 km altitude, but with occasional plumes reaching the melting level at 4800 m. At monsoonal scales, aerosol models largely account for the observed directional wind shear that causes altitude-dependent particle transport: near-surface particles remain in the core monsoon flow around the MABL, while at lower latitudes, aerosol layers aloft advect more eastwardly. Around the MABL, however, significant cloud-scale variability exists due to fine-scale flow, halo-entrainment-detrainment, and cold pool phenomena. Backscatter enhancements beneath individual clouds, extending to the ocean surface, likely relate to MABL-free troposphere exchange and air-sea interaction. So while aerosol transport occurs near the surface, particle extinction heterogeneity must still be considered for in situ observations and satellite retrievals.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 10 Oct 2025)
- RC1: 'Comment on egusphere-2025-2605', Anonymous Referee #1, 08 Sep 2025 reply
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This paper contains a lot of information that will be useful for researchers applying further analysis. The manuscript did read more like a Measurement Report than a scientific analysis aiming to move the research frontier forward, and I would suggest that the manuscript be reclassified as a Measurement Report. From a science point of view, I would have wished for more assessment of why the aerosol remains as low in the atmosphere as the authors found, and, how common that is. I did not see much discussion of other campaigns, including those associated with NASA, that also have documented long-range boundary layer aerosol transport. NASA ORACLES/DOE LASIC certainly did (see ACP/AMT special issue on the southeast Atlantic), and perhaps NASA SEAC4RS did too. I had trouble taking away what new scientific insights were gleaned. But just reframing the document as a Measurement Report would remove this additional weight from the authors and that would be fine as the collected data should be published to better familiarize the larger world with it. I would also suggest the authors read through the manuscript and look for ways to condense the language, as at 50 pages for the main text, it is quite long.
smaller comments:
1. URLs sprinkled throughout the manuscript belong in the data availability section I believe, not in the main text.
2. A larger map outlining the campaign location would be nice. Not everyone knows where Luzon or Manila are, or the various Seas.
3. The Hilario et al paper is referenced so often that it would be nice to see it briefly summarized in the Intro. I presume it did not include any HSRL analysis.