Paper by: Davidi et al, 2012

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?

22. 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

23. 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

24. 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

25. Effect of cloud?

27. Over the southern Atlantic?

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