Aerosol Radiative Forcing from combined MODIS and CERES

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

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.

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. MODIS AOT • Mostly over oceans unless high AOT - regional Satellite + CTM • • Chou et al - Sea. WIFS, Boucher et al – POLDER, Christopher et al – GOES – Regional/land Remer and Kaufman - MODIS Yu et al (ACPD) Chung et al (JGR-2005)

MODIS/CERES Fusion CERES - 20 X 20 km 2 nadir MODIS AOT – 10 X 10 km 2 MODIS Imager Pixel CERES Footprint Ongoing work : Data fusion of MODIS/MISR/CERES for aerosol research Terra swath CERES MODIS MISR 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

CERES SSF (Merged MODIS and CERES) • CERES SSF • Point spread function weighted aerosol and cloud properties from MODIS L 2 within CERES footprint • Most studies focus on cloud-free pixels over near-global oceans Recent progress 1. 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.

Angular Models ERBE : Over cloud free oceans • No 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 Significant differences 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

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

Aerosol Radiative Effect from Terra ~ 1 year spatial distribution Cloud-free CERES Forcing -5. 3 1. 7 Wm-2 NH forcing 1. 5 times greater than 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

f Fine Mode (Anthropogenic) Shortwave Aerosol Forcing 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 550 f 550=fa a+fm m +fd d fa =0. 92 0. 03, fd =0. 51 0. 03 fm =0. 32 0. 07 a =[(f 550 -fdust) 550 -(fm-fdust) m]/(fa-fd) Christopher and Zhang, 2002; 2004, GRL

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). .

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

Multi sensor approach for aerosol research MODIS (MOD 06) for cloud clearing MISR for AOT – Bright Targets CERES for LW fluxes Longwave forcing : +7 Wm-2.