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Extensive coverage of ultrathin tropical tropopause layer cirrus clouds revealed by balloon-borne lidar observations

Upper tropical clouds have a strong impact on Earth’s climate but are challenging to observe. We report the first long-duration observations of tropical clouds from lidars flying on board stratospheric balloons. Comparisons with spaceborne observations reveal the enhanced sensitivity of balloon-borne lidar to optically thin cirrus. These clouds, which have a significant coverage and lie in the uppermost troposphere, are linked with the dehydration of air masses on their way to the stratosphere.

Observations of cyanogen bromide (BrCN) in the global troposphere and their relation to polar surface O3 destruction

We measured cyanogen bromide (BrCN) in the troposphere for the first time. BrCN is a product of the same active bromine chemistry that destroys ozone and removes mercury in polar surface environments and is a previously unrecognized sink for active Br compounds. BrCN has an apparent lifetime against heterogeneous loss in the range 1–10 d, so it serves as a cumulative marker of Br-radical chemistry. Accounting for BrCN chemistry is an important part of understanding polar Br cycling.

Explaining the green volcanic sunsets after the 1883 eruption of Krakatoa

It is well known that volcanic eruptions strongly affect the colours of the twilight sky. Typically, volcanic eruptions lead to enhanced reddish and violet twilight colours. In rare cases, however, volcanic eruptions can also lead to green sunsets. This study provides an explanation for the occurrence of these unusual green sunsets based on simulations with a radiative transfer model. Green volcanic sunsets require a sufficient stratospheric aerosol optical depth and specific aerosol sizes.

Opinion: Aerosol remote sensing over the next 20 years

Aerosols are small liquid or solid particles suspended in the atmosphere, including smoke, particulate pollution, dust, and sea salt. Today, we rely on satellites viewing Earth’s atmosphere to learn about these particles. Here, we speculate on the future to imagine how satellite viewing of aerosols will change. We expect more public and private satellites with greater capabilities, better ways to infer information from satellites, and merging of data with models.

Opinion: The importance of historical and paleoclimate aerosol radiative effects

Estimating past aerosol radiative effects and their uncertainties is an important topic in climate science. Aerosol radiative effects propagate into large uncertainties in estimates of how present and future climate evolves with changing greenhouse gas emissions. A deeper understanding of how aerosols interacted with the atmospheric energy budget under past climates is hindered in part by a lack of relevant paleo-observations and in part because less attention has been paid to the problem.

Drivers controlling black carbon temporal variability in the lower troposphere of the European Arctic

Models still fail in reproducing black carbon (BC) temporal variability in the Arctic. Analysis of equivalent BC concentrations in the European Arctic shows that BC seasonal variability is modulated by the efficiency of removal by precipitation during transport towards high latitudes. Short-term variability is controlled by synoptic-scale circulation patterns. The advection of warm air from lower latitudes is an effective pollution transport pathway during summer.

Paul J. Crutzen – a pioneer in Earth system science and a founding member of the journal Atmospheric Chemistry and Physics

Paul J. Crutzen was a pioneer in atmospheric sciences and a kind-hearted, humorous person with empathy for the private lives of his colleagues and students. He made fundamental scientific contributions to a wide range of scientific topics in all parts of the atmosphere. Paul was among the founders of the journal Atmospheric Chemistry and Physics. His work will continue to be a guide for generations of scientists and environmental policymakers to come.

Opinion: Tropical cirrus – from micro-scale processes to climate-scale impacts

Tropical cirrus clouds are essential for climate, but our understanding of these clouds is limited due to their dependence on a wide range of small- and large-scale climate processes. In this opinion paper, we review recent advances in the study of tropical cirrus clouds, point out remaining open questions, and suggest ways to resolve them.

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.

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