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AEROSOL & CLIMATE ( IN THE ARCTIC) Pamela Lehr METEO 6030 Spring 2006

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Presentation on theme: "AEROSOL & CLIMATE ( IN THE ARCTIC) Pamela Lehr METEO 6030 Spring 2006"— Presentation transcript:

1 AEROSOL & CLIMATE ( IN THE ARCTIC) Pamela Lehr METEO 6030 Spring 2006 http://www.arctic.noaa.gov/images/polarbear

2 TALK OUTLINE 1.Aerosol Basics 2.The Arctic 3.Aerosol in the Arctic (Recent Studies) 4.Summary http://www.photolib.noaa.gov/corps/

3 AEROSOL REFRESHER COURSE Definition: liquid or solid particles suspended in the air Scatter and absorb radiation Aerosol distribution largely determines cloud droplet distribution Chemical composition is important: solubility, radiative properties

4 Things to keep in mind about aerosol: Spatial and temporal variability –Temporal: relatively short lifetime (hours to weeks) –Spatial: depends on emission location, transport, lifetime Sources –Emitted directly – dust, sea salt, organics, soot –New particle formation (such as gas-to-particle conversion) – sulfates, organics CLIMATE IMPACTS: cooling? warming? NEXT: 5 EFFECTS TO REMEMBER

5 Aerosol “____________” Effect Direct: clear sky scattering by aerosol → cooling 1 st Indirect: –Constant LWC –Increased CCN → increased cloud droplet concentration → increased cloud albedo → cooling 2 nd Indirect (Cloud Lifetime): –Increased CCN → increased cloud droplet concentration → decreased precipitation efficiency → cloud lasts longer → cooling Semi-Direct: –Absorbing aerosol (BC) → warm the cloud → decrease in life of cloud → warming LW Indirect: –Thin clouds, low emissivity –Increased CCN → increased emissivity → possible warming www.iac.ethz.ch/groups/lohmann

6 What’s going on in the Arctic? First we need to think about conditions and climate in the Arctic Climate change, aerosol effects, etc., are often talked about in global averages But conditions can vary greatly by region –Pollution sources (anthropogenic aerosol and aerosol precursors) –Regional Climate

7 Winter Polluted Dec – April/May Pollution mostly confined to lowest 5 km Low cloud frequency ~35% Clear skies 30-40% Pollution sources: mostly northern Europe and Asia SO 2 from burning of fossil fuels & smelting of sulfide ores Inversions not uncommon Summer Unpolluted Low cloud frequency ~75% Clear skies 5-8% The Arctic (Barrie, L. 1986)

8 Cloud Emissivity and Surface LW Heating in the Arctic – Role of Aerosol The Idea: Thin clouds tend to have emissivities < 1 (not BB) Increase in CN (decrease in effective radius (r e )) → increase in emissivity in thin clouds If cloud is warmer than surface & emissivity is increased → warmer surface and colder troposphere (and vice versa) Most effective during polar night and when there are low sun angles (i.e., common conditions in the Arctic) (Garrett, et al. 2002)

9 More from the emissivity study… Figure below shows the sensitivity of surface CRF LW due to a decrease in r e versus liquid water path (LWP) (x-axis): –Translation: shift to smaller r e in thin clouds leads to greater LW surface flux = surface warming Possibility of Arctic warming due to changes in emissivity in addition to GHG warming is noteworthy (Garrett, et al. 2002)

10 Indirect Effect in the Arctic? A Recent Study Low, thin clouds There is a wavenumber range sensitive to cloud droplet size More negative slope associated with higher CN concentrations (smaller r e ) Check for a significant increase in emissivity at same time Is it likely due to a shift in the distribution’s r e ? Conclusion: Yes! Increase on the order of 3.4 W m -2 (Lubin & Vogelmann, 2006)

11 SUMMARY 5 aerosol effects: –Direct –1 st Indirect –2 nd Indirect –Semi-direct –LW Indirect Aerosol effect in arctic: surface warming (not during summer months) Studies indicate warming could be of climatological significance, though more studies need to focus on the winter months when the LW effect dominates

12 QUESTIONS? http://www.arctic.noaa.gov/images/polarbear

13 REFERENCES Barrie, L. A. Arctic air pollution: an overview of current knowledge. Atmos. Environ. 20, 643-663 (1986). Garrett, T., Radke, L. F. & Hobbs, P. V. Aerosol effects on cloud emissivity and surface longwave heating in the Arctic. J. Atmos. Sci. 59, 769-778 (2002). Lubin, D. & Vogelmann, A. M. A climatologically significant aerosol longwave indirect effect in the Arctic. Nature 439, 453-456 (2006). IPCC Third Assessment 2001, Scientific Basis www.ipcc.ch


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