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Aerosol Radiative Forcing from combined MODIS and CERES measurements

Aerosol Radiative Forcing from combined MODIS and CERES measurements. Jianglong Zhang Lorraine A. Remer Yoram Kaufman. Introduction MODIS/CERES Aerosol effect Aerosol forcing Outstanding issues. sundar@nsstc.uah.edu. Research Objective : To use merged MODIS/CERES

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Aerosol Radiative Forcing from combined MODIS and CERES measurements

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  1. Aerosol Radiative Forcing from combined MODIS and CERES measurements Jianglong Zhang Lorraine A. Remer Yoram Kaufman • Introduction • MODIS/CERES • Aerosol effect • Aerosol forcing • Outstanding issues sundar@nsstc.uah.edu Research Objective : To use merged MODIS/CERES Data to examine aerosol effects on radiation Sundar A. Christopher University of Alabama - Huntsville Christopher and Zhang, GRL – September, 2004 Zhang, Christopher, Remer, Kaufman, JGR- Part 1 - 2005 Zhang, Christopher, Remer, Kaufman, JGR- Part 2 - 2005 Christopher, Zhang, Remer, Kaufman, GRL – submitted – 2005 Yu et al – ACPD – 2005 – CCSP Anderson et al – BAMS - 2005 MODIS Science Team meeting, January 2006

  2. Aerosol Direct Effects • Aerosol effects are being examined increasingly from measurement based approaches since Terra/Aqua (Yu et al. ACPD-CCSP, 2005, Anderson et al. BAMS, 2005) • Direct radiative effects include change in net radiative flux at TOA from all aerosols. • Aerosol Climate forcing is for anthropogenic aerosols.

  3. Aerosol Effects – Satellite AOT + RT model • Satellite derived AOT (e.g. MODIS) plus RT model. – e.g. Boucher et al • Satellite derived AOT with MODIS aerosol properties – Remer and Kaufman, 2005. • Mostly over oceans unless high AOT - regional • Chou et al - SeaWIFS, • Boucher et al – POLDER, • Christopher et al – GOES – Regional/land • Remer and Kaufman - MODIS MODIS AOT Satellite + CTM Yu et al (ACPD) Chung et al (JGR-2005)

  4. MODIS Imager Pixel CERES Footprint MODIS/CERES Fusion CERES - 20X20 km2 nadir MODIS AOT – 10X10 km2 Point spread function Weighted MODIS aerosol Within CERES footprint – CERES SSF ~ 1 year of data Cloud Fraction AOT at 550 nm Fine Mode fraction CERES radiance and flux Cloud free only DRE = Fclear – F aerosol CERES Broadband SW radiance Cross track scanner RAP mode : For Angular Models Ongoing work : Data fusion of MODIS/MISR/CERES for aerosol research Terra swath CERES MODIS MISR

  5. CERES SSF (Merged MODIS and CERES) • Recent progress • Sample bias accounted for • Using MODIS narrowband to • CERES broadband conversion • (Loeb and M-Smith 2005) • 2. Bulk sample bias adjustments • Using forcing efficiencies • (Christopher & Zhang 2004) • 3. Aerosol angular model using • CERES RAP data (Zhang et al.) as • function of AOT, aerosol fine • mode fraction, wind speed. • CERES SSF • Point spread function weighted aerosol and cloud properties from MODIS L2 within CERES footprint • Most studies focus on cloud-free pixels over near-global oceans

  6. Angular Models • ERBE : Over cloud free oceans • No aerosol aerosol properties • No wind speed • TRMM : Over cloud free oceans • Include ECMWF wind speed • Use theoretical calculation to account • for the effect of aerosol optical depth on TOA radiation fields • New Terra ADM : Over cloud free oceans • Use SSM/I wind speed • Use the fraction of small mode to total • AOT () • More coverage compared to TRMM • MODIS : more accurate for aerosol research Significant differences

  7. MODIS AOT and CERES derived SWARF for NDJF Uncertainties Measurements Cloud contamination Retrievals (AOT,) Methods (ADM, Clear sky characterization) CERES Forcing wm-2 MODIS AOT Instantaneous Forcing Efficiency ~ -60 Wm-2/AOT

  8. Aerosol Radiative Effect from Terra ~ 1 year spatial distribution Cloud-free CERES Forcing -5.31.7 Wm-2 NH forcing 1.5times greaterthan SH Global mean value over oceans compare Well among methods although regional differences exist. Christopher and Zhang, GRL, 2004 Zhang et al, JGR, 2005, Part 1 and Part 2

  9. Anthropogenic Dust Marine Fine Mode (Anthropogenic) Shortwave Aerosol Forcing f • Cloud free anthropogenic forcing : -1.4 Wm-2 • From MODIS/CERES – Compares well (same mean value!) with recent Kaufman et al (GRL, 2005) work. – Christopher et al (submitted, GRL, 2005). • 550 = anthropogenic + dust + marine • 550f550=faa+fmm +fdd fa =0.920.03, fd =0.510.03 fm =0.320.07 a =[(f550-fdust)550-(fm-fdust)m]/(fa-fd) Christopher and Zhang, 2002;2004, GRL

  10. Summary • Merged MODIS/CERES product is an excellent data set for studying aerosol radiative effects although proper Angular models required. • New angular models developed not only as a function of AOT and wind speed but fine mode fraction that facilitated study of anthropogenic aerosol forcing. • Global TOA aerosol direct effect of -5.3±1.7 Wm-2 is in good agreement with previous studies. • Anthropogenic (fine mode) aerosol forcing from CERES/MODIS data is -1.4 ±0.8 Wm-2 which is in agreement with recent estimates by Kaufman et al (2005)..

  11. Future Directions • Cloud Free to all sky conditions • Multi-year MODIS/CERES anthropogenic aerosol forcing • Aerosol over land MODIS/CERES • MODIS/MISR/CERES data fusion for aerosols over bright targets • CERES and CTM Fusion

  12. Multi sensor approach foraerosol research MODIS (MOD06) for cloud clearing MISR for AOT – Bright Targets CERES for LW fluxes Longwave forcing : +7 Wm-2.

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