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Can an influence of changing aerosol emissions be detected in thepattern of surface temperature change between 1970 and 2000?
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The general circulation model CAM-Oslo was used to examine the influence of varyingaerosol and greenhouse gas emissions on the pattern of surface temperature change betweenthe years 1970 and 2000, and whether the temperature response over different regions wasgoverned by local (due to changes in energy fluxes) or far-field (due to changes in large-scale circulation) processes. Circulation changes, originating from precipitation anomaliesmainly over the west/central Pacific and off the east coast of North America, influenced asubstantial part of the northern hemisphere temperature change pattern in CAM-Oslo, inparticular over southern North America, but also over Europe and Asia. The result highlightsthe importance of better understanding zonally asymmetric precipitation changes due todifferent forcing agents. A local response in surface temperature due to net surface radiativeflux (RF) anomalies could also be detected over Europe and Asia, where the differencein all-sky net surface RF was mainly driven by aerosol- or circulation-induced changes inliquid water path and cloud cover. A local anthropogenic aerosol effect on the cloud dropletsize and subsequent short-wave (SW) RF was found over Europe and Asia, but only whenexcluding a change in the greenhouse gas concentration. For clear skies, the SW RF patternwas well-correlated with the aerosol optical depth anomalies. However, this correlation wasat least partly governed by relative humidity fluctuations. Overall, the greenhouse andaerosol effects on surface temperature were in the simulations found to be non-linear with asignificant feedback on the aerosol population from a warming climate.

National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-93874OAI: oai:DiVA.org:su-93874DiVA: diva2:649430
Available from: 2013-09-18 Created: 2013-09-18 Last updated: 2013-09-18Bibliographically approved
In thesis
1. Interactions between aerosols and large-scale circulation systems in the atmosphere
Open this publication in new window or tab >>Interactions between aerosols and large-scale circulation systems in the atmosphere
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Anthropogenic aerosol emissions have increased during the last century. The higher atmospheric aerosol burden is believed to partly have masked the enhanced greenhouse gas warming during the same period. However, the many different types of aerosols, and the uncertainties regarding their effect on clouds, makes it difficult to estimate their total climate impact. With their strong effect on atmospheric radiation and their varying spatial and temporal distribution, aerosols may also affect the atmospheric circulation. This thesis focuses on aspects of aerosol-induced circulation changes as represented in general circulations models.

Anthropogenic aerosol forcing is believed to generally cool the earth system, but model simulations show that the strongest cooling is not necessarily co-located with the strongest aerosol radiative forcing. It is shown that aerosol forcing can cause anomalies in the stationary wave pattern, which affects surface temperatures far from the region of aerosol forcing. In absence of a substantial global mean aerosol-induced cooling, the anomalous stationary wave pattern has a large influence on the simulated temperature-response pattern. The waves are primarily generated by aerosol-induced precipitation changes in the tropics, showing an important connection between aerosol emissions at low latitudes and surface temperate changes in the extra-tropics.

It is also demonstrated that the aerosol climate response differs depending on how the ocean surface is represented in a model, i.e. if a sea surface temperature response is permitted or not. The anthropogenic aerosol forcing generates a stronger cooling of the northern hemisphere when the sea surface temperatures can change compared to when they are fixed. The stronger inter-hemispheric temperature gradient affects both the tropical and extra-tropical zonal mean circulation. Thus, aerosol-induced circulation changes are dependent on the simulated surface temperature response.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2013. 34 p.
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-93872 (URN)978-91-7447-763-4 (ISBN)
Public defence
2013-10-18, Föreläsningssalen, Institutionen för ekologi, miljö och botanik, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2013-09-26 Created: 2013-09-18 Last updated: 2013-09-19Bibliographically approved

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