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Investigating Transatlantic Dust Heating by Aerosol Absorption

This paper by Davidi et al. (2012) explores the atmospheric heating effects of transatlantic dust, examining the radiative signature and impact on temperature changes. Through observational data analysis and modeling, it delves into the intricate interactions between aerosol particles, cloud fraction, and temperature variations, shedding light on the complex dynamics in the Sahara Air Layer over the Atlantic Ocean. The study identifies key factors influencing dust heating patterns, while distinguishing between meteorological impacts and radiative effects. By elucidating the role of aerosol-cloud correlations and retrieval artifacts, the research provides valuable insights into the atmospheric processes driving dust-induced heating trends in the middle of the Atlantic.

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Investigating Transatlantic Dust Heating by Aerosol Absorption

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  1. Observational bounds on atmospheric heating by aerosol absorption: Radiative signature of transatlantic dust Paper by: Davidi et al, 2012 Adeyemi Adebiyi

  2. Abstract

  3. Sahara Air layer Dunion and Marron, 2008

  4. The problem • Is it the “hot dusty” Sahara air carried by the predominant winds and get preserved over a long distance? • OR • the SW radiation absorbed with the layer by the aerosol particles over the Atlantic ocean?

  5. What they do…? • Uses MODIS AOD and cloud fraction + AIRS temperature(obs) + GDAS temperature(model) • Data with AOD > 0.6 are not used – WHY? • Because of cloud contamination and MODIS misclassifications • Does it actually matter? – It does matter, because it could lead to possible aerosol-cloud correlations or random noise

  6. Note the scale 2005

  7. What they do…? • Uses MODIS AOD and cloud fraction + AIRS temperature(Obs.) + GDAS temperature(model) • Data with AOD > 0.6 are not used – WHY? • Because of cloud contamination and MODIS misclassifications • Does it actually matter? – It does matter, because it could lead to possible aerosol-cloud correlations or random noise • All data are interpolated to 13:30LT for June-August, 2009

  8. Introduce β(P) = δTP/δτ – Radiative heating Shows changes in temperature with AOD at different level Dusty layer gets warmer Boundary layer gets colder

  9. Introduce β(P) = δTP/δτ – Radiative heating Above dusty layer gets colder

  10. Could it be something else?

  11. Retrieval Artifacts? • If dust were associated with retrieval artifacts, then sign-alternation at different pressure level would rather be unlikely. • Previous studies using different methods and data also found similar features e.g. Wang, 2010

  12. 2010 Dusty-sky minus clear-sky temperature response -> Dusty layer also gets warmer

  13. Geography? Since the trends are similar in all the sub-regions, then geographical effect is not the dominant factor

  14. Meteorology? • To tackle this, they removed βmodlfrom βobsto have Δβ and set this as the lower bound. • If meteorology was responsible for β, • then βobs, dust > 0, βobs, above >0, • but βobs, below ≠< 0

  15. Meteorology? Why is the maximum in dust heating in the middle of the Atlantic Ocean?

  16. Why is there maximum in dust heating in the middle of the Atlantic Oceanbut small on the east- and west-most boxes? • Small in east because βmodl is large given that meteorology is important close to the source • Small in the west because aerosol are composed mostly of marine types

  17. Why is there maximum in dust heating in the middle of the Atlantic Oceanbut small on the east- and west-most boxes? • Small in east because βmodl is large given that meteorology is important close to the source • Small in the west because aerosol are composed mostly of marine types • …or maybe there is relatively little assimilation of data by GDAS in middle of Atlantic ocean compared to the coasts

  18. Other ways of separating meteorology from radiative effect • Statistical analysis -- • by assuming the meteorology doesn’t change within a small area box. E.g. Loeb and Schuster, 2008 • Lagrangian analysis – • By considering the evolution/history of the aerosol properties and its impact on the environment using back-trajectories. E.g. Mauger & Norris, 2007; 2010

  19. Effect of cloud?

  20. Over the southern Atlantic?

  21. Observational bounds on atmospheric heating by aerosol absorption: Radiative signature of transatlantic dust Paper by: Davidi et al, 2012

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