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The Radiative Budget of an Atmospheric Column in Tropical Western Pacific

The Radiative Budget of an Atmospheric Column in Tropical Western Pacific. Zheng Liu 1 Thomas Ackerman 1,2 , Sally McFarlane 2 , Jim Mather 2 , 1 University of Washington 2 Pacific Northwest National Laboratory. Background. Motivation: Cloud and water vapor feed back → model sensitivity

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The Radiative Budget of an Atmospheric Column in Tropical Western Pacific

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  1. The Radiative Budget of an Atmospheric Column in Tropical Western Pacific Zheng Liu1Thomas Ackerman1,2, Sally McFarlane2, Jim Mather2, 1University of Washington 2 Pacific Northwest National Laboratory

  2. Background • Motivation: • Cloud and water vapor feed back → model sensitivity • Cloud and radiative parameterization → feed back ↓↓ • Model evaluation: • Need : Radiative budgets at TOA, surface Column absorption, • Limited measurements → start with some atmospheric columns:Manus and Nauru

  3. Data Set Description: Observational Dataset • TOA net SW and LW fluxes: • GMS hourly observations, 0.3o x 0.3o grid (about 30km x 30 km) • Surface SW&LW downward fluxes: • ARM surface measurements, daily averaged from 1-min data • Surface LW upward fluxes: • NOAA optimum interpolated SST, weekly averaged, 1o x 1o grid • Surface SW upward fluxes: • Assumed sea surface SW albedo (6%)

  4. Data Set Description: Radiative Model Calculations • Computed fluxes and heating rates from ARM column observations • Retrieve vertical profiles of cloud microphysical properties from ARM millimeter wave radar data • Temperature and water vapor profiles from radiosonde launches • Sample the cloud properties every 5 minutes and perform radiative transfer only on the sampled profiles. • Calculate broadband fluxes

  5. Data Set Description: Climate Model • NCAR Community Atmosphere Model (CAM) • T42 resolution • Prescribed SST • Compare values from box over Manus (280 km x 280 km) with observations • Multi-scale modeling framework (MMF) • Embedded 2D cloud system resolving model (64 columns each 4 km in horizontal dimension) • Prescribed SST • Average 64 column values within Manus gridbox

  6. Observation v.s. Radiative Model • Frequency distribution → day to day comparison • TOA → Surface → Column absorption • Page organization:

  7. Remarks • SW clearsky offset • SW allsky “cumulus” effects • Manus is convectively more active than Nauru.

  8. Observation v.s. Models • Observation: Jun 16, 1999 ~ May 21, 2003 • Climate models: Jan 1, 1999 ~ Dec 31, 1999 • Radiative model calculation: • Manus: Feb 25, 2000 ~ Jul 31, 2000 • Nauru: Mar 9, 1999 ~ Dec 19, 1999

  9. Conclusion • Evaluation of the radiative budget of atmospheric columns can help understand the convective tropics • Discrepancy between calculations from radiative model and observations is probably due to scene mismatch between TOA and the surface and some 3D effects • Column SW absorption: • Clear sky: around 90w/m2 • All sky: • almost unaffected by cloud for both radative model and climate models • much greater variation according to observational data and bias towards more absorption than clear sky

  10. Future work • Compare with other TOA satellite data sets: ISCCP, CERES • Compare budget results from CAM run in forecast mode with observational data and climate model version of CAM • Compare surface radiative budget from satellite with ARM surface measurement

  11. Acknowledgements • Professor Ackerman • Sally Mcfarlane, Professor Fu, Professor Wood • All my first year classmates • All the audience here

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