Preprints
https://doi.org/10.5194/egusphere-2024-3397
https://doi.org/10.5194/egusphere-2024-3397
16 Dec 2024
 | 16 Dec 2024

Adiabatic and radiative cooling are both important causes of aerosol activation in simulated fog events in Europe

Pratapaditya Ghosh, Ian Boutle, Paul Field, Adrian Hill, Marie Mazoyer, Katherine J. Evans, Salil Mahajan, Hyun-Gyu Kang, Min Xu, Wei Zhang, and Hamish Gordon

Abstract. Aerosol-fog interactions affect the visibility in, and life cycle of, fog and are difficult to represent in weather and climate models. Here we explore processes that impact the simulation of fog droplet number concentrations (Nd) at sub-kilometer scale horizontal grid resolutions in the UK Met Office Unified Model. We modify the parameterization of aerosol activation to include droplet activation by radiative cooling in addition to adiabatic cooling, and determine the relative importance of the two cooling mechanisms. We further test the sensitivity of simulated Nd to: (a) interception of droplets by trees and buildings, (b) overestimation of updrafts in temperature inversions, which leads to artificially high Nd values; and (c) potential mechanisms for droplet deactivation due to downward fluctuations in supersaturation.

We evaluate our model against observations from the ParisFog and LANFEX field campaigns, building on evaluation described in the companion paper. Including radiative cooling in the activation mechanism improves how accurately we represent the liquid water path and the vertical structure of the fog in our LANFEX case study. However, with radiative cooling the Nd are overestimated for most of the ParisFog cases, and the LANFEX case. The time-averaged overestimate exceeds a factor of four (the normalized mean bias factor exceeds 3.0) in four out of eleven ParisFog cases. Our sensitivity studies demonstrate how these overestimates can be mitigated. Assuming the overestimate affects both radiative and adiabatic cooling, we find that although radiative cooling is more often the dominant source, both cooling sources can sometimes dominate activation.

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.
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Journal article(s) based on this preprint

24 Sep 2025
Adiabatic and radiative cooling are both important causes of aerosol activation in simulated fog events in Europe
Pratapaditya Ghosh, Ian Boutle, Paul Field, Adrian Hill, Marie Mazoyer, Katherine J. Evans, Salil Mahajan, Hyun-Gyu Kang, Min Xu, Wei Zhang, and Hamish Gordon
Atmos. Chem. Phys., 25, 11157–11182, https://doi.org/10.5194/acp-25-11157-2025,https://doi.org/10.5194/acp-25-11157-2025, 2025
Short summary
Pratapaditya Ghosh, Ian Boutle, Paul Field, Adrian Hill, Marie Mazoyer, Katherine J. Evans, Salil Mahajan, Hyun-Gyu Kang, Min Xu, Wei Zhang, and Hamish Gordon

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-3397', Anonymous Referee #3, 31 Dec 2024
  • RC2: 'Comment on egusphere-2024-3397', Anonymous Referee #1, 06 Jan 2025
  • RC3: 'Comment on egusphere-2024-3397', Anonymous Referee #2, 25 Feb 2025
  • AC1: 'Comment on egusphere-2024-3397', Pratapaditya Ghosh, 16 Jun 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-3397', Anonymous Referee #3, 31 Dec 2024
  • RC2: 'Comment on egusphere-2024-3397', Anonymous Referee #1, 06 Jan 2025
  • RC3: 'Comment on egusphere-2024-3397', Anonymous Referee #2, 25 Feb 2025
  • AC1: 'Comment on egusphere-2024-3397', Pratapaditya Ghosh, 16 Jun 2025

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
AR by Pratapaditya Ghosh on behalf of the Authors (16 Jun 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (18 Jun 2025) by Pablo Saide
AR by Pratapaditya Ghosh on behalf of the Authors (23 Jun 2025)  Manuscript 

Journal article(s) based on this preprint

24 Sep 2025
Adiabatic and radiative cooling are both important causes of aerosol activation in simulated fog events in Europe
Pratapaditya Ghosh, Ian Boutle, Paul Field, Adrian Hill, Marie Mazoyer, Katherine J. Evans, Salil Mahajan, Hyun-Gyu Kang, Min Xu, Wei Zhang, and Hamish Gordon
Atmos. Chem. Phys., 25, 11157–11182, https://doi.org/10.5194/acp-25-11157-2025,https://doi.org/10.5194/acp-25-11157-2025, 2025
Short summary
Pratapaditya Ghosh, Ian Boutle, Paul Field, Adrian Hill, Marie Mazoyer, Katherine J. Evans, Salil Mahajan, Hyun-Gyu Kang, Min Xu, Wei Zhang, and Hamish Gordon

Data sets

Adiabatic and radiative cooling are both important causes of aerosol activation in simulated fog events in Europe Pratapaditya Ghosh, Ian Boutle, Paul Field, Adrian Hill, Marie Mazoyer, Katherine J. Evans, Salil Mahjan, Hyun-Gyu Kang, Min Xu, Wei Zhang, and Hamish Gordon https://doi.org/10.5281/zenodo.14005081

Pratapaditya Ghosh, Ian Boutle, Paul Field, Adrian Hill, Marie Mazoyer, Katherine J. Evans, Salil Mahajan, Hyun-Gyu Kang, Min Xu, Wei Zhang, and Hamish Gordon

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Short summary
We study the lifecycle of fog events in Europe using a weather and climate model. By incorporating droplet formation and growth driven by radiative cooling, our model better simulates the total liquid water in foggy atmospheric columns. We show that both adiabatic and radiative cooling play significant, often equally important roles in driving droplet formation and growth. We discuss strategies to address droplet number overpredictions, by improving model physics and addressing model artifacts.
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