CCSM Atmospheric Model CCSM Atmospheric Model Working Group ReportWorking Group Report

J. J. Hack, D. A RandallJ. J. Hack, D. A Randall

AMWG Co-ChairsAMWG Co-Chairs

CCSM 2001 Workshop, CCSM 2001 Workshop, BreckenridgeBreckenridge

What has been happening What has been happening since the last time we met?since the last time we met?

Indicated our intentions for a final model Indicated our intentions for a final model configurationconfiguration– two-time level semi-Lagrangian dynamics with reduced linear gridtwo-time level semi-Lagrangian dynamics with reduced linear grid– 26 levels26 levels– prognostic cloud waterprognostic cloud water– generalized cloud overlap (plus requisite changes to LW SW)generalized cloud overlap (plus requisite changes to LW SW)– updated long wave water vapor absorption formulationupdated long wave water vapor absorption formulation– new convection parameterizationnew convection parameterization– netCDF native outputnetCDF native output– improved topographic filterimproved topographic filter

Were planning to conduct initial coupled simulationsWere planning to conduct initial coupled simulations– new ocean, sea ice, land, and couplernew ocean, sea ice, land, and coupler

Cumulus Convection Cumulus Convection ParameterizationParameterization

Variant of Arakawa-SchubertVariant of Arakawa-Schubert– developed by Marat Khairoudinov (CSU)developed by Marat Khairoudinov (CSU)

– multiple cloud bases/cloud topsmultiple cloud bases/cloud tops

– simplified closure, computationally efficient simplified closure, computationally efficient equilibrium cumulus kinetic energy closureequilibrium cumulus kinetic energy closure

– can handle arbitrary tracer transportcan handle arbitrary tracer transport– framework can be directly coupled to stratiform framework can be directly coupled to stratiform

cloud and boundary layer parameterizationscloud and boundary layer parameterizations

Strengths/Weaknesses of Proposed Strengths/Weaknesses of Proposed ModelModel

Improvements in a number of simulation Improvements in a number of simulation

featuresfeatures– precipitable water, implied ocean heat transport, polar precipitable water, implied ocean heat transport, polar

thermal bias, variability, eastern ocean solar energy thermal bias, variability, eastern ocean solar energy budgetbudget

Degradations in several important areas Degradations in several important areas – Wintertime stationary wave structureWintertime stationary wave structure– Excessive precipitation maximaExcessive precipitation maxima– No improvement in Arctic Surface wind fieldNo improvement in Arctic Surface wind field– Cold tropical tropopauseCold tropical tropopause– Non-conservative advection of tracers Non-conservative advection of tracers

Tests of the proposed Tests of the proposed configurationconfiguration

Uncoupled climatological forcingUncoupled climatological forcing

17-year AMIP II simulations17-year AMIP II simulations

No coupled simulations to dateNo coupled simulations to date– immediate priority was to enable a coupled immediate priority was to enable a coupled

evaluationevaluation

Ongoing Diagnostic AnalysesOngoing Diagnostic Analyses

NCAR NCAR – standard WGNE diagnostic suitestandard WGNE diagnostic suite

Stevens and HackStevens and Hack

– variability and other mean propertiesvariability and other mean properties Hurrell and SheaHurrell and Shea

PCMDI PCMDI (Wehner, Taylor, Sperber, Boyles, Achutarao)(Wehner, Taylor, Sperber, Boyles, Achutarao)– performance portraits, mean state, variabilityperformance portraits, mean state, variability– comparison to other models and observationscomparison to other models and observations

Variability Analyses Variability Analyses (through intraseasonal)(through intraseasonal)– MJO (Demott, Waliser, Ricciardulli)MJO (Demott, Waliser, Ricciardulli)– diurnal characteristics (Dai)diurnal characteristics (Dai)

In late May we reconsidered In late May we reconsidered optionsoptions

Tested a modification to the current ZM schemeTested a modification to the current ZM scheme– incorporates a precipitation evaporation mechanismincorporates a precipitation evaporation mechanism

Proposed alternative configuration to AMWGProposed alternative configuration to AMWG– model was same except for followingmodel was same except for following

3-time level spectral dynamical core with reduced grid3-time level spectral dynamical core with reduced grid modified Zhang-McFarlane convectionmodified Zhang-McFarlane convection

Put this decision to a “vote” from the AMWG Put this decision to a “vote” from the AMWG – extensive diagnostic studies were completed and extensive diagnostic studies were completed and

availableavailable Comments favored alternative configurationComments favored alternative configuration

Strengths/Weaknesses of New ModelStrengths/Weaknesses of New Model

Clear improvements to several simulation Clear improvements to several simulation

featuresfeatures– precipitable waterprecipitable water– implied ocean heat transportimplied ocean heat transport– polar thermal biaspolar thermal bias– eastern ocean solar energy budgeteastern ocean solar energy budget– eastern Pacific surface stresseastern Pacific surface stress

Degradations in several important areas Degradations in several important areas – No improvement in Arctic Surface wind fieldNo improvement in Arctic Surface wind field– Cold tropical tropopauseCold tropical tropopause– Non-conservative advection of tracers (no different than Non-conservative advection of tracers (no different than

CCM3)CCM3)

SummarySummary

Development of new atmospheric component is Development of new atmospheric component is complete and undergoing continued testing!complete and undergoing continued testing!

Improvements to physical and dynamical frameworkImprovements to physical and dynamical framework

Improvements to the simulationImprovements to the simulation

Improvements to computational performanceImprovements to computational performance

Demonstrated the AMWG development process Demonstrated the AMWG development process

worksworks