Aerosol Radiative Forcing from combined MODIS and CERES measurements Sundar A. Christopher University of Alabama - Huntsville 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 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

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. 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)

MODIS/CERES Fusion CERES Footprint CERES - 20X20 km2 nadir Imager Pixel CERES Footprint 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

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

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

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

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

Fine Mode (Anthropogenic) Shortwave Aerosol Forcing Dust Anthropogenic Marine 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

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 (MOD06) for cloud clearing MISR for AOT – Bright Targets CERES for LW fluxes Longwave forcing : +7 Wm-2.