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Absorbing aerosols over Asia: An inter-model and model-observation comparison study using CAM5.3-Oslo
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
(English)Manuscript (preprint) (Other academic)
National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-168050OAI: oai:DiVA.org:su-168050DiVA, id: diva2:1307606
Available from: 2019-04-28 Created: 2019-04-28 Last updated: 2019-08-28Bibliographically approved
In thesis
1. Aerosol-cloud-radiation interactions in global climate models
Open this publication in new window or tab >>Aerosol-cloud-radiation interactions in global climate models
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Clouds can reflect, absorb and re-emit radiation, thereby inducing a cooling or warming effect on the climate. However, the response of clouds to a changing climate is highly uncertain and the representation of clouds in state-of-the-art climate models remains a key challenge for future climate projections. Factors contributing to this uncertainty include processes on the microphysical scale involving aerosol particles with the size of just a few nanometers to micrometers. This thesis focuses on the representation of aerosol-cloud-radiation interactions in global climate models. Using idealized experiments from a model-intercomparison project with different anthropogenic aerosol forcings, it was found that both sulfate and non-sulfate aerosols yield an increase in cloud albedo in five regions of subtropical marine stratocumulus clouds. The changes in cloud albedo in the models were driven by changes in the cloud droplet number concentration and liquid water content. Further, it was found that the microphysical coupling of underlying aerosol-cloud interactions in models seems to dominate on the monthly timescale in subtropical marine stratocumulus regions, which can not be confirmed in observations. Quantifying the effect of aerosols on cloud properties in observations remains challenging. In addition, comparisons with satellite retrievals and the global climate model NorESM showed that this model is not able to capture elevated aerosol above cloud, seen in observations in two regions of marine stratocumulus clouds. Sensitivity experiments revealed that the model is most sensitive to the aerosol emissions, convection and wet scavenging in terms of the vertical aerosol distribution. Finally, the representation of aerosol absorption in global climate models was investigated. It was found that most of the models underestimate absorption by aerosols in a focus domain in Asia. Sensitivity studies with NorESM give rise to variations that lie within the large inter-model diversity.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2019. p. 58
Keywords
Aerosols, clouds, global climate models
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-168266 (URN)978-91-7797-612-7 (ISBN)978-91-7797-613-4 (ISBN)
Public defence
2019-06-14, Ahlmannsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2019-05-22 Created: 2019-04-29 Last updated: 2019-05-23Bibliographically approved
2. Multiple perspectives on absorbing aerosols over the northern Indian Ocean and Asia
Open this publication in new window or tab >>Multiple perspectives on absorbing aerosols over the northern Indian Ocean and Asia
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aerosol particles in the atmosphere scatter and absorb solar radiation, and thereby affect the Earth's energy budget, but the magnitude of the overall radiative effect due to aerosol-radiation interactions is uncertain. In particular, the impact of absorbing aerosol particles, mainly black carbon (BC), organic carbon and dust, is not completely understood. A large variety of absorbing aerosols can be found in Asia and over adjacent oceans due to huge urban, biomass burning and desert areas. This thesis focuses on the investigation of atmospheric aerosols over the northern Indian Ocean and Asia from multiple perspectives. This includes surface and vertical observations of physical and chemical particle properties by in-situ and remote sensing instruments as well as an investigation of the representation of absorbing aerosols in general circulation models. One main focus is on the identification of BC-containing particles at the marine remote Maldives Climate Observatory in Hanimaadhoo (MCOH) which is frequently influenced by continental air masses containing anthropogenic aerosols. During an intensive field campaign, vertical measurements of aerosol particles were performed with a Lidar and unmanned aerial vehicles. Elevated layers of absorbing aerosol above the marine boundary layer were found frequently when air masses had their source over the northern Indian Peninsula. However, determining a complete profile of particle absorption only from Lidar measurements is linked to high uncertainties. Long-term surface measurements of particle absorption and scattering together with observations of aerosol chemical composition at MCOH are used to evaluate purely optical methods for aerosol characterization. These optical methods are found to give reasonable estimates of particle types but they can not replace detailed chemical measurements. An additional comparison study of various instruments for determination of BC mass give potentially very diverse results, highlighting the complexity of the quantification of BC-containing particles. The investigation of the representation of absorbing aerosols over Asia in general circulation models reveals firstly that the particle absorption is generally underestimated in global climate models, and secondly that the range in aerosol absorption determined from major changes of emissions, meteorology and particle optical properties can not reach the large inter-model diversity. 

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2019. p. 48
Keywords
aerosols, black carbon, air pollution, South Asia
National Category
Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-172375 (URN)978-91-7797-791-9 (ISBN)978-91-7797-792-6 (ISBN)
Public defence
2019-10-11, William-Olssonsalen, Geovetenskaps hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2019-09-18 Created: 2019-08-28 Last updated: 2019-09-12Bibliographically approved

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