Rutherford Appleton Laboratory

5th ADIENT Meeting

2nd April 2009, Manchester University

WP4.3.1 Comparisons of model simulations with

global radiance measurements

 C. Poulsen ,R. Siddans

With contributions from Dave smith(RAL), Maria Frontoso(Leeds) and Gareth Thomas(Oxford)

Motivation

• Oxford-RAL Aerosol and Cloud (ORAC) scheme retrieves AOD, effective radius and some indication of aerosol type.

• These results to be compared directly to models in ADIENT (WP4.2)

• However it is important to complement this activity with radiance comparisons to test consistency between model & measurements:

– Retrievals make assumptions about aerosol optical properties (and surface) which will often be inconsistent with model

– “Measured” SW flux makes assumptions about angular distribution of radiation (phase fn + BRDF).

– Radiance is directly measured and can be directly computed from model fields

– A stringent test of understanding of the direct effect:

• Aerosol distribution + Aerosol & surface optical properties + RT modelling

ATSR-2 & AATSR

• ATSR-2 (ERS-2 1995-) and AATSR (Envisat 2002-) have produced a time-series of global data with unique characteristics to test the representation of shortwave (SW) radiation in climate models.

• Dual-view observations at 0.55, 0.67, 0.87 and 1.6, 11 & 12μm are sensitive to the amount, type and size distribution of aerosol

• Reflectances accurate to1% following ESA inter-calibration study

AATSR

ECMWF

Cloud Clearing

Average

Minimum

Winds/brdfMODIS

Profiles

Rad

iativ

e T

rans

fer

Mod

el(R

AL-

FM

2D)

Statistical Comparisons &Time-series analysis

Cox and Munk

GLOMAP/UKCA

Mie model

CP2OPAC/Globaer other

Speciated size distributions

Spectral ref indices

Phase function

Extinction coef

SSA

Observed radiance

Simulated radiance

GLOMAP wish list

• AOD at 0.55 µm (0.87 and 0.67 if at all possible)• Aerosol type• Aerosol size (either size distributions or effective

radius)• Surface reflectance/BRDF, if it exists!• The height distribution of the aerosol • Single scattering albedo• Phase function• Extinction coefficient

GLOMAP wish list

• AOD at 0.55 µm (0.87 and 0.67 if at all possible)• Aerosol type• Aerosol size (either size distributions or effective

radius)• Surface reflectance/BRDF (only if it exists!)• The height distribution• Single scattering albedo (profile) of the aerosol • Phase function – only asymmetry available ?• Extinction coefficient (profile)

Comparison so far

• GLOMAP and ATSR cloud cleared radiances regridded to 5 degree over Europe

– Only coincident radiances compared

• GLOMAP information on radius(profile) number concentration and aerosol optical depth used to simulate ATSR radiances.

• GLOBAER optical properties-Maritime Clean used

• ATSR and GLOMAP compared-currently only over sea.

ATSR and Simulated GLOMAP radiances

ATSR-GLOMAP October 2004

postive-red negative-blue

ATSR-GLOMAP May 2004

2004 monthly average comparison

Conclusions & Next steps

• Initial analysis indicates AATSR radiances underestimated by GLOMAP + RT model

• However this based on simplified use of GLOMAP AOD + size.

• Next, obtain global data and perform runs– With GLOMAP optical properties– With CP2 (ideally) or GlobAerosol optical

properties• Perform analysis for ATSR forward and nadir

view• Analyse results as function of region.