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