Cloud Dynamics Over the Southern Ocean: Unravelling Nature’s Marine Cloud Brightening

2025-01-01

In the pristine waters of the Southern Ocean surrounding Antarctica, scientists have discovered fascinating patterns in cloud formation that could have major implications for understanding Earth’s climate. Recent research conducted by Dr Gerald Mace from the University of Utah and colleagues reveals how air masses passing over the Antarctic continent naturally boost cloud brightness through a complex chain of chemical and physical processes. This natural phenomenon may hold important clues for improving climate models and predicting future climate change.

Supplementary material to "Impact on Cloud Properties of Reduced-Sulphur Shipping Fuel in the Eastern North Atlantic"

2025-06-05

Table S1.Statistics of the MERRA Reanalysis data within 500 km of the ARM ENA site for the pre and post periods.The column P indicates the probability that the distributions of a quantity as indicated in Figure 1 are drawn from the same sample population (null hypothesis) according to the Kolmogorv-Smirnov test using the unique average number of days in each period (500) as the number of independent samples.When P exceeds 0.99, we can be confident at the 99% level that the null hypothesis cannot be rejected, and the data appear drawn from the same sample population.

Comment on egusphere-2025-3735

2025-10-06

<strong class="journal-contentHeaderColor">Abstract.</strong> Starting in November 2023, the Houthi militia occupying northeastern Yemen has attacked ships passing through the Bab al-Mandab Strait, a chokepoint on the Europe-Asia route via the Suez Canal. Cargo ship traffic through the Red Sea has since plummeted, with ships instead taking the longer route around the Cape of Good Hope. The increase in traffic in the southeastern Atlantic Ocean is readily apparent in satellite retrievals of nitrogen dioxide. Within the stratocumulus deck covering much of the southeastern Atlantic, a previously detectible cloud microphysical perturbation due to ship pollution had largely disappeared following the International Maritime Organization's sulfur-limiting regulations in 2020 but returns during 2024 due to the increase in ship traffic despite the lower cloud brightening efficacy per ship. Because nitrogen dioxide pollution per unit of fuel oil burned is not affected by switching to low-sulfur fuel, quantifying the ratio of shipping-enhanced cloud droplet number and nitrogen dioxide concentrations before and after the fuel sulfur limits went into effect provides a constraint on the cloud changes from the regulations. We find that the ~80 % reduction in sulfur emissions leads to a ~66 % reduction in the increase in cloud droplet number concentration per unit marine fuel oil burned.

Comment on egusphere-2025-2075

2025-10-27

<strong class="journal-contentHeaderColor">Abstract.</strong> The global reduction in shipping fuel sulphur that culminated in 2020 with an ~80&thinsp;% reduction has enabled an inadvertent experiment on the role of aerosol-cloud interaction (ACI) in the climate system. We compare observations collected at the Atmospheric Radiation Measurement program's (ARM) Eastern North Atlantic site (ARM-ENA, 39.1 N, 28.0 W) during two June to September periods: 2016&ndash;2018 (pre-2020) and 2021&ndash;2023 (post-2020). We find a significant (~15&thinsp;%) decrease in cloud condensation nuclei concentrations post-2020, which resulted in a decrease in cloud droplet number (<em>N_d</em>) and an increase in effective radius (<em>r_e</em>) of marine boundary layer clouds. However, cloud liquid water path (LWP) increased post-2020. The increase in LWP offset the increase in <em>r_e</em>, resulting in insignificant changes to the optical depth distribution. MODIS and CERES data in the vicinity of ENA during these periods produce similar results also with negligible change in the albedo and optical depth distributions. Regional cloud occurrence declined in line with changes in the large-scale meteorology. Our results point to a complicated interplay among the factors that modulate cloud feedback in the Eastern North Atlantic.

Biological enhancement of cloud droplet concentrations observed off East Antarctica

npj Climate and Atmospheric Science · 2025-03-20 · 9 citations

Abstract The impact that biogenic emissions have on aerosol-cloud interactions across the Southern Ocean is poorly quantified. Here we use satellite and ship observations during austral summer to study these interactions. We present observational evidence that biogenic aerosols increase cloud condensation nuclei and cloud droplet number concentrations over the Southern Ocean off East Antarctica, coinciding with very low concentrations of ice-nucleating particles and higher occurrences of supercooled liquid-containing low-level clouds.

Simulation of Cloud Processes Over Offshore Coastal Antarctica Using the High‐Resolution Regional UK Met Office Unified Model With Interactive Aerosols

Journal of Geophysical Research Atmospheres · 2025-02-14 · 2 citations

Abstract The Southern Ocean and offshore coastal Antarctica are key regions for global climate. Low level mixed‐phase clouds strongly control the surface radiation budget of this region but remain challenging for climate models because of the complex processes controlling the sources and sinks of cloud liquid water, including both cloud liquid water and ice crystals. Here, we examine these interactions using the Unified Model (UM) regional climate model, with the Cloud AeroSol Interacting Microphysics (CASIM) and UK Chemistry and Aerosol (UKCA) models included for interactive aerosol and cloud microphysics. We simulate two case studies from the second field campaign of Clouds Aerosols Precipitation Radiation and atmospheric Composition over the Southern Ocean Phase 2 (CAPRICORN‐2), which represent the open ocean and the offshore coastal region of Antarctica. Compared with these observations, we find that the UM underestimates surface aerosol concentration by up to an order of magnitude and investigate the effect of this bias on the simulated cloud microphysical and radiative properties. We find that the cloud liquid water path (LWP) and surface radiative fluxes are also biased in the offshore coastal Antarctic case study, with a 32% mean underestimation of LWP and 76% mean overestimation of downwelling surface shortwave flux. Sensitivity tests show that the cloud liquid water bias is largely caused by deficiencies in the representation of the meteorology, and less by aerosol or cloud microphysical properties. Our results provide key insights on the modeling of cloud processes in high southern latitudes.

Storm Peak Laboratory: A Research and Training Facility for the Atmospheric Sciences

Bulletin of the American Meteorological Society · 2025-01-27 · 2 citations

Abstract Storm Peak Laboratory, located on the Steamboat Springs Ski Resort in Colorado on the west summit of Mount Werner at 10 532 ft (3220 m) MSL, is an internationally recognized high-elevation atmospheric research station that has been in use for over 40 years. This article provides a brief history of the Storm Peak Laboratory and the major research themes it has supported and discusses opportunities to leverage mountain observatory measurements to advance our understanding of the atmospheric processes. This facility provides long-term measurements of meteorology, clouds, aerosols, snow hydrology, and atmospheric gases, and it serves as a “proving ground” for instrument development and testing. Storm Peak Laboratory is part of multiple national and international observational networks. Due to the unique capabilities of Storm Peak Laboratory, there is a long history of targeted field campaigns primarily within the following research areas: mixed-phase cloud microphysics; atmospheric chemistry pertaining to the formation, characterization, and hygroscopicity of aerosols; and the transport and transformation of atmospheric mercury. Research training has been central to the mission of Storm Peak Laboratory (SPL) over the last 40 years. Currently, SPL hosts both undergraduate- and graduate-level courses in atmospheric science and snow hydrology organized by numerous institutions. Examples of these unique research training opportunities are provided. Significance Statement This article provides a brief history of the Storm Peak Laboratory and the major research themes it has supported. Furthermore, this article discusses opportunities to leverage mountain observatory measurements to advance our understanding of the atmospheric processes. Located on the Steamboat Springs Ski Resort in northwestern Colorado, Storm Peak Laboratory has been in use for over 40 years and is an internationally recognized high-elevation atmospheric research station. Due to the unique capabilities of Storm Peak Laboratory, there is a long history of targeted field campaigns primarily within the following research areas: mixed-phase cloud microphysics; atmospheric chemistry pertaining to the formation, characterization, and hygroscopicity of aerosols; and the transport and transformation of atmospheric mercury. Research training has been central to the mission of Storm Peak Laboratory (SPL) over the last 40 years. Currently, SPL hosts both undergraduate- and graduate-level courses in atmospheric science and snow hydrology organized by numerous institutions.

Impact on Cloud Properties of Reduced-Sulphur Shipping Fuel in the Eastern North Atlantic

2025-06-05

Abstract. The global reduction in shipping fuel sulphur that culminated in 2020 with an ~80 % reduction has enabled an inadvertent experiment on the role of aerosol-cloud interaction (ACI) in the climate system. We compare observations collected at the Atmospheric Radiation Measurement program's (ARM) Eastern North Atlantic site (ARM-ENA, 39.1 N, 28.0 W) during two June to September periods: 2016–2018 (pre-2020) and 2021–2023 (post-2020). We find a significant (~15 %) decrease in cloud condensation nuclei concentrations post-2020, which resulted in a decrease in cloud droplet number (Nd) and an increase in effective radius (re) of marine boundary layer clouds. However, cloud liquid water path (LWP) increased post-2020. The increase in LWP offset the increase in re, resulting in insignificant changes to the optical depth distribution. MODIS and CERES data in the vicinity of ENA during these periods produce similar results also with negligible change in the albedo and optical depth distributions. Regional cloud occurrence declined in line with changes in the large-scale meteorology. Our results point to a complicated interplay among the factors that modulate cloud feedback in the Eastern North Atlantic.

Storm Chasing with the INCUS Mission

2025-01-07

The overarching goal of the NASA INvestigation of Convective UpdraftS (INCUS) mission is to enhance our understanding of why, when and where tropical convective storms form, and why only some of these storms produce extreme weather. Convective storms transport air and water between Earth's surface and the upper troposphere. This vertical transport of air and water - often referred to as convective mass flux (CMF) - plays a critical role in Earth's weather and climate system through its impacts on large-scale atmospheric circulations, upper tropospheric moistening and high cloud-radiative feedbacks, precipitation rates, and extreme weather. Potential changes to CMF with changing climates may significantly impact these processes. In spite of the critical role of this vertical transport of water and air, representation of CMF remains a major source of error in weather and climate models, thereby limiting our ability to accurately predict convective storms and their impacts in current and future climates. The observations obtained from INCUS will enhance our understanding of tropical convective storm processes and provide guidance for representing these processes in weather and climate models.

Simulation of Southern Ocean cloud processes using the high-resolution regional UK Met Office Unified Model with interactive aerosols

2024-08-04

The Southern Ocean and coastal Antarctica are key regions for global climate. Low level mixed-phase clouds strongly control the surface radiation budget of this region but remain challenging for climate models because of the complex interactions between cloud liquid water and ice crystals. Here we examine these interactions using the Unified Model (UM) regional climate model, with the Cloud AeroSol Interacting Microphysics (CASIM) and UK Chemistry and Aerosol (UKCA) models included for interactive aerosol and cloud microphysics. We simulate case studies from the second field campaign of Clouds Aerosols Precipitation Radiation and atmospheric Composition over the Southern Ocean Phase 2 (CAPRICORN-2). Compared to these observations, we find that the UM underestimates surface aerosol concentration by up to an order of magnitude and investigate the effect of this bias on the simulated cloud microphysical and radiative properties. We find that the cloud liquid water path and surface radiative fluxes are also biased in the model, with a 32% mean underestimation of liquid water path and 76% mean overestimation of downwelling surface shortwave flux in one case study. Sensitivity tests show that the cloud liquid water bias is largely caused by deficiencies in the representation of the meteorology, and less by aerosol or cloud microphysical properties. Our results provide key insights on the modeling of cloud processes in high southern latitudes.