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Climate intervention using marine cloud brightening (MCB) compared with stratospheric aerosol injection (SAI) in the UKESM1 climate model

The difficulties in ameliorating global warming and the associated climate change via conventional mitigation are well documented, with all climate model scenarios exceeding 1.5 °C above the pre-industrial level in the near future. There is therefore a growing interest in geoengineering to reflect a greater proportion of sunlight back to space and offset some of the global warming. We use a state-of-the-art Earth-system model to investigate two of the most prominent geoengineering strategies.

MCB) compared with stratospheric aerosol injection (SAI) in the UKESM1 climate model">Read more

Opinion: The strength of long-term comprehensive observations to meet multiple grand challenges in different environments and in the atmosphere

To be able to meet global grand challenges, we need comprehensive open data with proper metadata. In this opinion paper, we describe the SMEAR (Station for Measuring Earth surface – Atmosphere Relations) concept and include several examples (cases), such as new particle formation and growth, feedback loops and the effect of COVID-19, and what has been learned from these investigations. The future needs and the potential of comprehensive observations of the environment are summarized.

Opinion: A critical evaluation of the evidence for aerosol invigoration of deep convection

As atmospheric particles called aerosols increase in number, the number of droplets in clouds tends to increase, which has been theorized to increase storm intensity. We critically evaluate the evidence for this theory, showing that flaws and limitations of previous studies coupled with unaddressed cloud process complexities draw it into question. We provide recommendations for future observations and modelling to overcome current uncertainties.

Mechanisms controlling giant sea salt aerosol size distributions along a tropical orographic coastline

Sea salt aerosol is an important marine aerosol that may be produced in greater quantities in coastal regions than over the open ocean. This study observed these particles along the windward coastline of O’ahu, Hawai’i, to understand how wind and waves influence their production and dispersal. Overall, wave heights were the strongest variable correlated with changes in aerosol concentrations, while wind speeds played an important role in their horizontal dispersal and vertical mixing.

N2O as a regression proxy for dynamical variability in stratospheric trace gas trends

This paper presents a technique for understanding the causes of long-term changes in stratospheric composition. By using N2O as a proxy for stratospheric circulation in the model used to calculated trends, it is possible to separate the effects of dynamics and chemistry on observed trace gas trends. We find that observed HCl increases are due to changes in the stratospheric circulation, as are O3 decreases above 30 hPa in the Northern Hemisphere.

Opinion: Recent developments and future directions in studying the mesosphere and lower thermosphere

The mesosphere or lower thermosphere region of the atmosphere borders the edge of space. It is subject to extreme ultraviolet photons and charged particles from the Sun and atmospheric gravity waves from below, which tend to break in this region. The pressure is very low, which facilitates chemistry involving species in excited states, and this is also the region where cosmic dust ablates and injects various metals. The result is a unique and exotic chemistry.

Global observations of aerosol indirect effects from marine liquid clouds

Interactions between aerosol pollution and liquid clouds are one of the largest sources of uncertainty in the effective radiative forcing of climate over the industrial era. We use global satellite observations to decompose the forcing into components from changes in cloud-droplet number concentration, cloud water content, and cloud amount. Our results reduce uncertainty in these forcing components and clarify their relative importance.

The dehydration carousel of stratospheric water vapor in the Asian summer monsoon anticyclone

We studied water vapour in a critical region of the atmosphere, the Asian summer monsoon anticyclone, using rare in situ observations. Our study shows that extremely high water vapour values observed in the stratosphere within the Asian monsoon anticyclone still undergo significant freeze-drying and that water vapour concentrations set by the Lagrangian dry point are a better proxy for the stratospheric water vapour budget than rare observations of enhanced water mixing ratios.

Rapid saturation of cloud water adjustments to shipping emissions

Aerosol from burning fuel changes cloud properties, e.g., the number of droplets and the content of water. Here, we study how clouds respond to different amounts of shipping aerosol. Droplet numbers increase linearly with increasing aerosol over a broad range until they stop increasing, while the amount of liquid water always increases, independently of emission amount. These changes in cloud properties can make them reflect more or less sunlight, which is important for the earth’s climate.

Molecular simulations reveal that heterogeneous ice nucleation occurs at higher temperatures in water under capillary tension

Using computer simulations of water, we find that water under tension freezes more easily than under normal conditions. A linear equation describes how freezing temperature increases with tension. Accordingly, simulations show that naturally occurring tension in water capillary bridges leads to higher freezing temperatures. This work is an early step in determining if atmospheric cloud droplets freeze due to naturally occurring tension, for example, during processes such as droplet collisions.

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