Post on 23-Feb-2016
description
Observational bounds on atmospheric heating by aerosol absorption: Radiative signature of transatlantic dust
Paper by: Davidi et al, 2012
Adeyemi Adebiyi
Abstract
Sahara Air layer
Dunion and Marron, 2008
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?
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
Note the scale
2005
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
Introduce β(P) = δTP/δτ – Radiative heating
Shows changes in temperature with AOD at different level
Dusty layer gets warmerBoundary layer gets colder
Introduce β(P) = δTP/δτ – Radiative heating
Above dusty layer gets colder
Could it be something else?
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
Dusty-sky minus clear-sky temperature response
2010
-> Dusty layer also gets warmer
Geography?
Since the trends are similar in all the sub-regions, then geographical effect is not the dominant factor
Meteorology?
To tackle this, they removed βmodl from βobs to 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
Meteorology?
Why is the maximum in dust heating in the middle of the Atlantic Ocean?
Why is there maximum in dust heating in the middle of the Atlantic Ocean but 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
Why is there maximum in dust heating in the middle of the Atlantic Ocean but 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
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
Effect of cloud?
Over the southern Atlantic?
Observational bounds on atmospheric heating by aerosol absorption: Radiative signature of transatlantic dust
Paper by: Davidi et al, 2012