A closed-to-open cell mixed-phase cloud transition observed over the Nordic Seas under high aerosol loading and strong surface fluxes
- 1University of Miami (Coral Gables, United States of America)
Abstract
Closed-to-open cell mixed-phase cloud transitions within marine cold air outbreaks remain poorly understood despite their importance to high-latitude climate. The Cold-Air outbreak Experiment in the Sub-Arctic Region (CAESAR) research aircraft sampled a cold and polluted closed-to-open cell transition with cloud-top temperatures below −20 °C and upstream cloud condensation nuclei concentrations surpassing 600 cm ⁻³ . The aerosol likely originates from Siberian industrial emissions. As the boundary layer deepens prior to and across the transition, driven by strong turbulent surface fluxes and aided by a weakening cloud-top inversion, aerosol number concentrations decrease and supercooled droplet sizes increase, causing ice particles to shift from primarily vapor depositional growth towards riming. Precipitation shafts within open-cells contain abundant large graupel (>5 mm diameter) with liquid-equivalent precipitation intensities reaching 3 mm h ⁻¹ . Ice precipitation co-exists with lidar-observed surface cold pools, modulated by entrainment events, juxtaposed with surface-based plumes of warm moist air. Updrafts support liquid water production along convergence boundaries at the upwind cold pool edge. Nonetheless, strong buoyancy fluxes exceeding 200 W m ⁻² prevent sub-cloud decoupling. Ice particle number concentrations increase tenfold across the transition, surpassing 10 L ⁻¹ within open-cells, more than 1000× ice nucleating particle number concentrations. Given that cloud temperatures are too cold for Hallett-Mossop rime splintering, this indicates the importance of other secondary ice production mechanisms. This case expands the observations needed to better understand mixed-phase Arctic cloud processes.
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BibTeX
@article{ephraim2026closedtoopen,
title = {{A closed-to-open cell mixed-phase cloud transition observed over the Nordic Seas under high aerosol loading and strong surface fluxes}},
author = {Samuel Ephraim and Paquita Zuidema and Aaron Bansemer and Lintong Cai and Markus Petters and Elise Rosky and Jefferson R. Snider and Zhien Wang and Sarah Woods and Kevin Barry and Theresa Campos and Owen Cruikshank and Sabine Eckhardt and Nikolaos Evangeliou and Romanos Foskinis and Jeffrey R. French and Bart Geerts and Coltin Grasmick and Silvia Henning and Varun Kumar and Andreas Massling and Camille Mavis and Greg M. McFarquhar and Athanasios Nenes and Gunnar Noer and Ryan Patnaude and Russell Perkins and Lise Lotte Sørensen and Henrik Skov and Tyler Tatro and Florian Tornow and Lu Zhang},
journal = {Atmospheric Chemistry and Physics},
year = {2026},
month = nov,
doi = {10.5194/acp-26-15375-2026},
url = {https://doi.org/10.5194/acp-26-15375-2026},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - A closed-to-open cell mixed-phase cloud transition observed over the Nordic Seas under high aerosol loading and strong surface fluxes
AU - Samuel Ephraim
AU - Paquita Zuidema
AU - Aaron Bansemer
AU - Lintong Cai
AU - Markus Petters
AU - Elise Rosky
AU - Jefferson R. Snider
AU - Zhien Wang
AU - Sarah Woods
AU - Kevin Barry
AU - Theresa Campos
AU - Owen Cruikshank
AU - Sabine Eckhardt
AU - Nikolaos Evangeliou
AU - Romanos Foskinis
AU - Jeffrey R. French
AU - Bart Geerts
AU - Coltin Grasmick
AU - Silvia Henning
AU - Varun Kumar
AU - Andreas Massling
AU - Camille Mavis
AU - Greg M. McFarquhar
AU - Athanasios Nenes
AU - Gunnar Noer
AU - Ryan Patnaude
AU - Russell Perkins
AU - Lise Lotte Sørensen
AU - Henrik Skov
AU - Tyler Tatro
AU - Florian Tornow
AU - Lu Zhang
PY - 2026
DA - 2026/11/03
JO - Atmospheric Chemistry and Physics
DO - 10.5194/acp-26-15375-2026
UR - https://doi.org/10.5194/acp-26-15375-2026
AB - Closed-to-open cell mixed-phase cloud transitions within marine cold air outbreaks remain poorly understood despite their importance to high-latitude climate. The Cold-Air outbreak Experiment in the Sub-Arctic Region (CAESAR) research aircraft sampled a cold and polluted closed-to-open cell transition with cloud-top temperatures below −20 °C and upstream cloud condensation nuclei concentrations surpassing 600 cm ⁻³ . The aerosol likely originates from Siberian industrial emissions. As the boundary layer deepens prior to and across the transition, driven by strong turbulent surface fluxes and aided by a weakening cloud-top inversion, aerosol number concentrations decrease and supercooled droplet sizes increase, causing ice particles to shift from primarily vapor depositional growth towards riming. Precipitation shafts within open-cells contain abundant large graupel (>5 mm diameter) with liquid-equivalent precipitation intensities reaching 3 mm h ⁻¹ . Ice precipitation co-exists with lidar-observed surface cold pools, modulated by entrainment events, juxtaposed with surface-based plumes of warm moist air. Updrafts support liquid water production along convergence boundaries at the upwind cold pool edge. Nonetheless, strong buoyancy fluxes exceeding 200 W m ⁻² prevent sub-cloud decoupling. Ice particle number concentrations increase tenfold across the transition, surpassing 10 L ⁻¹ within open-cells, more than 1000× ice nucleating particle number concentrations. Given that cloud temperatures are too cold for Hallett-Mossop rime splintering, this indicates the importance of other secondary ice production mechanisms. This case expands the observations needed to better understand mixed-phase Arctic cloud processes.
SN - 1680-7324
ER -