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AEROSOL & CLIMATE ( IN THE ARCTIC)

AEROSOL & CLIMATE ( IN THE ARCTIC). Pamela Lehr METEO 6030 Spring 2006. http://www.arctic.noaa.gov/images/polarbear. TALK OUTLINE. Aerosol Basics The Arctic Aerosol in the Arctic (Recent Studies) Summary. http://www.photolib.noaa.gov/corps/. AEROSOL REFRESHER COURSE.

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AEROSOL & CLIMATE ( IN THE ARCTIC)

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

  2. TALK OUTLINE • Aerosol Basics • The Arctic • Aerosol in the Arctic (Recent Studies) • 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 • 1st Indirect: • Constant LWC • Increased CCN → increased cloud droplet concentration → increased cloud albedo → cooling • 2nd 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. The Arctic Winter Summer • Unpolluted • Low cloud frequency ~75% • Clear skies 5-8% • 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 • SO2 from burning of fossil fuels & smelting of sulfide ores • Inversions not uncommon (Barrie, L. 1986)

  8. The Idea: Thin clouds tend to have emissivities < 1 (not BB) Increase in CN (decrease in effective radius (re)) → 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) Cloud Emissivity and Surface LW Heating in the Arctic – Role of Aerosol (Garrett, et al. 2002)

  9. More from the emissivity study… • Figure below shows the sensitivity of surface CRFLW due to a decrease in re versus liquid water path (LWP) (x-axis): • Translation: shift to smaller re 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) (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 re) • Check for a significant increase in emissivity at same time • Is it likely due to a shift in the distribution’s re ? • Conclusion: Yes! • Increase on the order of 3.4 W m-2 (Lubin & Vogelmann, 2006)

  11. SUMMARY • 5 aerosol effects: • Direct • 1st Indirect • 2nd 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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