Influence of Clouds and Aerosols on the Earth s Radiation Budget Using Clouds and the Earth s Radiant Energy System (CERES) Measurements

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1 Influence of Clouds and Aerosols on the Earth s Radiation Budget Using Clouds and the Earth s Radiant Energy System (CERES) Measurements Norman G. Loeb Hampton University/NASA Langley Research Center Bruce A. Wielicki NASA Langley Research Center, Hampton, VA December 5, 2003

2 Global Radiation Budget

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4 Low Cloud Amount Cloud Optical Depth Indirect Aerosol Forcing Direct Anthropogenic Aerosol Forcing High Cloud Amount Cloud Height Particle Size (Low Clouds) Stratospheric Ozone Land Albedo Carbon Dioxide 20 Earth Warming 10 Radiative Effect (W/m 2 ) 0 Earth Cooling Climate Sensitivity Radiative Effect at the Top of the Atmosphere For a 50% Increase in Climate Parameter

5 Clear-sky and Cloud Sensitivity From 19 GCMs Climate models are inconsistent in predicting the effects of clouds on climate. Sensitivity Parameter All Sky Clear Sky Temperature (K) Model Number 0.8 (Cess et al., 1990)

6 CERES Objectives (1) For climate change analysis, provide a continuation of the ERBE record of radiative fluxes at the top of the atmosphere (TOA), analyzed using the same algorithms that produced the ERBE data. (2) Double the accuracy of estimates of radiative fluxes at TOA and the Earth's surface. (3) Provide cloud property estimates that are consistent with the radiative fluxes from surface to TOA. (4) Provide the first long-term global estimates of the radiative fluxes within the Earth's atmosphere.

7 CERES Instrument 5 instruments on 3 satellites (TRMM, Terra, Aqua) for diurnal and angular sampling. Narrow field-of-view scanning radiometer with nadir footprint size of 10 km (TRMM); 20 km (Terra & Aqua). Measures radiances in µm, µm and 8-12 µm. Capable of scanning in several azimuth plane scan modes: fixed (FAP) or crosstrack, rotating azimuth plane (RAP), programmable (PAP). Coincident Cloud and Aerosol Properties from MODIS/VIRS

8 Terra/Flight Model 1 Lifetime Radiometric Stability Determined with the Internal Calibration Module Normalized to Ground Calibration Data Absolute Calibration: 0.5% LW 1% SW 1% Window Feb-00 Aug-00 Feb-01 Aug-01 Feb-02 Aug-02 Feb-03 DATE Stability Goal: better than 0.5% per 5 years While changes accounted for in CERES processing, ideal situation is change < 0.1% per mission.

9 An overlapping Earth radiation climate record: 22 years from Nimbus 7 to Terra.

10 Jan/Feb 98 El Nino TOA LW Flux Anomalies (relative to ERBE average) CERES ERBE-Like LW Flux Observations NOAA GFDL Standard Climate Model NOAA GFDL Experimental Prediction Model

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12 uses CERES data only Aerosol 3-hourly 1-degree grid CERES is a Sensor Web: up to 11 instruments on 7 spacecraft all integrated to obtain climate accuracy in top to bottom fluxes

13 CERES Single Scanner Footprint (SSF) Product - Coincident CERES radiances and imager-based cloud and aerosol properties. - Use VIRS (TRMM) or MODIS (Terra, Aqua) to determine following parameters in up to 2 cloud layers over every CERES FOV: Macrophysical: Fractional coverage, Height, Radiating Temperature, Pressure Microphysical : Phase, Optical Depth, Particle Size, Water Path Clear Area : Albedo, Skin Temperature, Aerosol optical depth, Emissivity Layer 2 VIRS/MODIS Imager Pixel CERES Footprint Layer 1 Clear CERES Footprint

14 Instantaneous TOA Flux Error by Cloud Property

15 Estimated Instantaneous TOA Flux Error Region S o (W m -2 ) Terra ADMs W m -2 (%) TRMM ADMs W m -2 (%) Clear All-sky Clear All-sky Tropics (2.2) (5.1) (3.5) (5.8) Midlat (3.0) (3.9) (5.6) (4.1) Polar (4.3) (5.9) (11.7) (9.8)

16 Cloud Radiative Forcing By Cloud Type

17 Cloud Forcing by Cloud Type Cloud Type Single-Layer Low Phase - Effective Cloud Top Pressure (mb) > 680 Single-Layer Mid-Level Single-Layer High - < 440 Multilayer Cloud -Lower layer liquid water -Upper layer ice -

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19 Net CRF Contribution by Cloud Type DECEMBER, 2001 Low Mid-Level High Multilayer (W m -2 )

20 Cloud Forcing By Effective Cloud Top Pressure and Optical Depth (Dec 2001)

21 Cloud Forcing By Effective Cloud Top Pressure and Optical Depth (June 2001)

22 Summary - CERES provides a unique dataset for studying the influence of clouds and aerosols on the Earth s radiation budget: i) Measurement stability to better than 0.5% for monitoring radiative flux changes. ii) Combined radiative fluxes, cloud and aerosol properties for climate model validation and process studies. iii) Improved TOA flux accuracy by a factor of 2-5 over previous radiation budget datasets => Can now quantify how different cloud types influence the Earth s radiation budget. - New Global Radiation Budget (surface and TOA) for 3 years of Terra data released to the climate community by April 2004.

23 Future: Combine CERES+MISR to study radiative effect of clouds at different spatial scales. Merge measurements from CERES & MODIS (Aqua) with CALIPSO, CloudSat, PARASOL. Improved radiative forcing estimates, especially for thin and multilayer clouds, aerosols. Climate model use of global datasets, comparisons between models and observations.