| 1. |
- Chen, Deliang, 1961, et al.
(författare)
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Summary of a workshop on extreme weather events in a warming world organized by the Royal Swedish Academy of Sciences
- 2020
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Ingår i: Tellus Series B-Chemical and Physical Meteorology. - : Stockholm University Press. - 1600-0889 .- 0280-6509. ; 72:1
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is not only about changes in means of climatic variables such as temperature, precipitation and wind, but also their extreme values which are of critical importance to human society and ecosystems. To inspire the Swedish climate research community and to promote assessments of international research on past and future changes in extreme weather events against the global climate change background, the Earth Science Class of the Royal Swedish Academy of Sciences organized a workshop entitled 'Extreme weather events in a warming world' in 2019. This article summarizes and synthesizes the key points from the presentations and discussions of the workshop on changes in floods, droughts, heat waves, as well as on tropical cyclones and extratropical storms. In addition to reviewing past achievements in these research fields and identifying research gaps with a focus on Sweden, future challenges and opportunities for the Swedish climate research community are highlighted.
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| 2. |
- Blichner, Sara M., et al.
(författare)
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Implementing a sectional scheme for early aerosol growth from new particle formation in the Norwegian Earth System Model v2 : Comparison to observations and climate impacts
- 2021
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 14:6, s. 3335-3359
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol-cloud interactions contribute to a large portion of the spread in estimates of climate forcing, climate sensitivity and future projections. An important part of this uncertainty is how much new particle formation (NPF) contributes to cloud condensation nuclei (CCN) and, furthermore, how this changes with changes in anthropogenic emissions. Incorporating NPF and early growth in Earth system models (ESMs) is, however, challenging due to uncertain parameters (e.g. participating vapours), structural issues (numerical description of growth from ∼ 1 to ∼ 100 nm) and the large scale of an ESM grid compared to the NPF scale. A common approach in ESMs is to represent the particle size distribution by a certain number of log-normal modes. Sectional schemes, on the other hand, in which the size distribution is represented by bins, are considered closer to first principles because they do not make an a priori assumption about the size distribution. In order to improve the representation of early growth, we have implemented a sectional scheme for the smallest particles (5-39.6 nm diameter) in the Norwegian Earth System Model (NorESM), feeding particles into the original aerosol scheme. This is, to our knowledge, the first time such an approach has been tried. We find that including the sectional scheme for early growth improves the aerosol number concentration in the model when comparing against observations, particularly in the 50-100 nm diameter range. Furthermore, we find that the model with the sectional scheme produces much fewer particles than the original scheme in polluted regions, while it produces more in remote regions and the free troposphere, indicating a potential impact on the estimated aerosol forcing. Finally, we analyse the effect on cloud-aerosol interactions and find that the effect of changes in NPF efficiency on clouds is highly heterogeneous in space. While in remote regions, more efficient NPF leads to higher cloud droplet number concentration (CDNC), in polluted regions the opposite is in fact the case.
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| 3. |
- Sporre, M. K., et al.
(författare)
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Springtime Stratospheric Volcanic Aerosol Impact on Midlatitude Cirrus Clouds
- 2022
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 49:2
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Tidskriftsartikel (refereegranskat)abstract
- Explosive volcanic eruptions can reach the stratosphere and cause elevated concentrations of sulphate particles for months to years. When these particles descend into the troposphere, they can impact cirrus clouds though to what degree is unknown. In this study, we combine three satellite data sets to investigate the impact of downwelling sulphate aerosol on midlatitude cirrus clouds during springtime. The results show that cirrus clouds in the northern hemisphere (NH) have lower ice water content (IWC), ice crystal number concentrations, and cloud fraction (CF) when the aerosol load in the lowermost stratosphere is elevated by volcanism. These changes are largest for the coldest clouds at the highest altitudes. The cirrus clouds in the southern hemisphere on the other hand show no significant changes with downwelling aerosol levels. The reduction in cirrus IWC and CF in the NH implies that volcanic aerosol can cool the climate through reduced warming from cirrus clouds.
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| 4. |
- Svenhag, Carl, et al.
(författare)
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Implementing detailed nucleation predictions in the Earth system model EC-Earth3.3.4: sulfuric acid–ammonia nucleation
- 2024
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Ingår i: Geoscientific Model Development. - Malmö : IVL Svenska Miljöinstitutet. - 1991-959X .- 1991-9603. ; 17:12, s. 4923-4942
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Tidskriftsartikel (refereegranskat)abstract
- Representing detailed atmospheric aerosol processes in global Earth system models (ESMs) has proven to be challenging from both a computational and a parameterizationperspective. The representation of secondary organic aerosol (SOA) formation and new particle formation (NPF) in large ESMs is generally constructed with low detail to save computational costs. The simplification could result in losing the representation of some processes. In this study, we test and evaluate a new approach for improving the description of NPF processes in the ESM EC-Earth3 (ECE3) without significant additional computational burden.The current NPF scheme in EC-Earth3.3.4 is derived from the nucleation of low volatility organic vapors and sulfuric acid (H2SO4) together with a homogeneous water-H2SO4 nucleation scheme. We expand the existing schemes and introduce a new lookup table approach that incorporates detailed formation rate predictions through molecular modeling of sulfuric acid–ammonia nucleation (H2SO2–NH3). We apply tables of particle formation rates for H2SO2–NH3 nucleation, including dependence on temperature, atmospheric ion production rate, and molecular cluster scavenging sink.The resulting differences between using the H2SO4–NH3 nucleation in ECE3 and the original default ECE3 scheme are evaluated and compared with a focus on changes in the aerosol composition, cloud properties, and radiation balance. From this new nucleation scheme, EC-Earth3’s global average aerosol concentrations in the sub-100 nm sizes increased by 12 %–28 %. Aerosol concentrations above 100 nm and the direct radiative effect (in Wm?2) showed only minor differences upon changing of the nucleation scheme. However, the radiative effect from clouds affected by aerosols from the new nucleation scheme resulted in a global decrease (cooling effect) by 0.28–1Wm?2. The modeled aerosol concentrations were compared to observed measurements at various stations. In most cases, the new NPF predictions (H2SO2–NH3) performed better at stations where previous underestimations for aerosol concentrations occurred.
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