The Radiative Budget of an Atmospheric Column in Tropical Western Pacific Zheng Liu Department of Atmospheric Science University of Washington

Backgroud ► Cloud and cloud-radiation parameterization determines the cloud and water vapor feedback of climate model,which induce high sensitivity to the forcing variation ► Model evaluation: TOA, surface radiative budgets and the column absorption, heating rate profile ► Limited measurements: start with some atmospheric columns, Manus and Nauru

Data Set Description: Observational Dataset ► TOA SW net fluxes and LW fluxes: GMS hourly observations, 0.3 o x 0.3 o grid ► Surface SW&LW downward fluxes: ARM surface measurements, daily averaged from 1-min data ► Surface LW upward fluxes: NOAA Optimum Interpolated SST, weekly averaged, 1 o x 1 o grid ► Surface SW upward fluxes: assumed Sea Surface SW Albedo (6%)

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

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

Conversion to Daily Averaged Fluxes ► Diurnal integration for SW: integrate the fluxes from sunrise to sunset and averaged over the day ► Interpolation of missing data: SW & LW ► Discard days with more than four hours of missing data

Observation v.s. Radiative Model ► Comparison of frequency distribution ► Comparison of daily averaged fluxes ► SW & LW; clear sky & all sky; TOA, surface and column absorption ► Take the same time period for observations and radiative model calculations: about 110 days’ data for each site

Observation v.s. Climate Model ► Observation: Jun 16, 1999 ~ May 21, 2003 ► Climate Model: Jan 1, 1999 ~ Dec 31, 1999

Conclusion ► Column SW absorption:  Clear sky: around 90w/m 2  All sky: almost unaffected by cloud for both radation model and climate model almost unaffected by cloud for both radation model and climate model much greater variation according to observational data and bias towards more absorption than clear sky much greater variation according to observational data and bias towards more absorption than clear sky ► Discrepancy with observations probably due to scene mismatch between TOA and the surface and some 3D effects ► Evaluation of the radiative budget of atmospheric columns can help understand the convective tropics

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

Thanks to ► Professor Ackerman ► Sally Mcfarlane, Professor Fu, Professor Wood ► All my first year classmates ► All the audience here