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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. - PowerPoint PPT Presentation
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AEROSOL & CLIMATE(IN THE ARCTIC)
Pamela Lehr
METEO 6030
Spring 2006
http://www.arctic.noaa.gov/images/polarbear
TALK OUTLINE
1. Aerosol Basics
2. The Arctic
3. Aerosol in the Arctic (Recent Studies)
4. Summary
http://www.photolib.noaa.gov/corps/
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
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
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 warmingwww.iac.ethz.ch/groups/lohmann
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
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• SO2 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)
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 (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)
(Garrett, et al. 2002)
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)
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)
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
QUESTIONS?
http://www.arctic.noaa.gov/images/polarbear
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 Basiswww.ipcc.ch