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A new perspective on aerosol direct radiative effects in South Atlantic and Southern Africa Ian Chang and Sundar A. Christopher Department of Atmospheric Science University of Alabama in Huntsville, U.S.A. 97th American Meteorological Society

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A new perspective on aerosol direct radiative effects in South Atlantic and Southern Africa

Ian Chang and Sundar A. Christopher

Department of Atmospheric Science University of Alabama in Huntsville, U.S.A. 97th American Meteorological Society Annual Meeting 25 January 2017 This research is supported by NASA Earth and Space Science Fellowship and NASA CALIPSO Program ian.chang@nsstc.uah.edu

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Outline

  • Motivation
  • Data and methods
  • Results
  • Summary

Biomass burning in Southern Africa

Zuidema et al. 2016, BAMS

Africa

  • S. Atlantic

Field experiments 2016-2018

http://research.metoffice.gov.uk/research/obr/ aerosol/safari.html

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Motivation

Ocean

Top of Atmosphere

Background-aerosol =Negative radiative effect Background-aerosol =Positive radiative effect

 Cloud Properties  Aerosol Properties  Surface properties

Land

  • Radiative effects of

aerosol above cloud differ in magnitude and sign when compared to cloud- free cases.

  • Current satellite

aerosol product still deficient for providing global picture of aerosols above all surfaces.

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Objectives

  • To develop an algorithm to retrieve aerosol properties

above different scenes (clouds, ocean, land) using MODIS multispectral sensor.

  • To estimate the combined direct radiative effects of all scenes

using radiative transfer calculations.

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Objectives: 4 scenes in a case study

Walvis Bay MODIS-Terra on 25 August 2016 Aerosol:

  • 1. Over ocean
  • 2. Over land
  • 3. Above cloud (ocean)
  • 4. Above cloud (Land)

1 2 4 3

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Nighttime 532nm Total Attenuated Backscatter Daytime 532nm Total Attenuated Backscatter

Aerosol cluster Aerosol cluster

AOD retrieval and DRE calculations within elevated aerosol clusters

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Spectral signatures

Aerosol above cloud (ocean) Cloud only

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Data and Methods

Supplementary data information

  • CALIOP L2 (night and day): Aerosol clusters (>50km)
  • OMI Aerosol index
  • AOD (MOD04_3K) in cloud-free conditions
  • COD>4, cloud fraction=1 (MOD06)
  • Visible spectral surface albedo (MCD43C) for land
  • SAFARI 2000 aerosol optical properties (SSA550nm=0.91)
  • 1. Scene Identification
  • CALIOP (aerosol)
  • OMI Aerosol Index
  • MODIS (cloud,

aerosol, surface type)

  • Pixel heterogeneity
  • 2. Input
  • Radiance
  • Solar zenith angles
  • View zenith angles
  • Relative azimuth angles
  • Spectral surface albedo (land only)
  • Aerosol properties
  • 4. Output
  • Instantaneous flux (Wm-2)
  • 3. Look-up table
  • AOD
  • COD
  • Cloud effective

radius (ocean only)

  • Aerosol properties

Radiative Transfer Model

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Results: AOD retrieval (cloud-free only)

MODIS true-color

cloud-free

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Results: More AOD retrieval from 4 scenes

cloud-free

How do their direct radiative effects differ?

 Cloud-free  Above-cloud

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Results: Aerosol direct radiative effects (Wm-2)

Ocean Land

Aerosol (cloud-free)

  • 10
  • 20

Aerosol (above cloud)

+50

+150

+25 Wm-2 combined

Direct radiative effect = Background – aerosol

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Direct radiative effects depend on sun angle

(Chang and Christopher 2017)

AOD : 0.6 COD : 9.0 Cloud Eff Rad : 12.8 µm SSA (550nm) = 0.91 5oS 15oE

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Conclusions

  • Retrieval for aerosol above 4 major scenes are conducted for

SE Atlantic and Southern Africa.

  • Over ocean
  • Over land
  • Above cloud (over ocean)
  • Above cloud (over land)
  • The combined aerosol direct radiative effects are affected by

underlying scenes.

  • In-situ measurements are necessary to refine satellite algorithms and

reduce uncertainties in radiative transfer calculations.

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Recent Publications

  • Chang, I. and S. A. Christopher, 2016: Identifying Absorbing Aerosols Above

Clouds From the Spinning Enhanced Visible and Infrared Imager Coupled With NASA A-Train Multiple Sensors. IEEE Trans. Geosci. Remote Sens., 54, 3163- 3173, doi:10.1109/TGRS.2015.2513015.

  • Chang, I. and S. A. Christopher, 2017: The impact of seasonalities on the direct

radiative effects and radiative heating rates of absorbing aerosols above clouds. (under revision) .ian.chang@nsstc.uah.edu www.nsstc.uah.edu/users/ian.chang

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SEVIRI cloud optical depth (Aug- Sep 2016)

09Z 15Z

Mean cloud optical depth decreases during the day

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MOD04 and this study

cloud-free MOD04  Cloud-free  Above-cloud