ccsm simulations w/core forcing some preliminary results and a discussion of dataset issues
DESCRIPTION
CCSM Simulations w/CORE Forcing Some preliminary results and a discussion of dataset issues. Marika Holland With much input from Bill Large Steve Yeager. Experiments Using CORE Forcing. CORE I Results - Ocean-Ice Coupled Runs. MOC. Sea Ice equilibrates rapidly. - PowerPoint PPT PresentationTRANSCRIPT
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CCSM Simulations w/CORE ForcingSome preliminary results and a discussion of
dataset issues
Marika HollandWith much input from
Bill LargeSteve Yeager
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Experiments Using CORE Forcing
Configuration Forcing Years Case
Ocean alone NYF 129 gx1v3.302
Ocean-Ice NYF 400 (running out to 500)
gx1v3.411
Ocean alone IVF 4x43 gx1v3.210
Ice alone IVF 1x43 M_controlYL
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CORE I Results - Ocean-Ice Coupled Runs
Sea Ice equilibrates
rapidly
MOC
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CORE-II Ocn-Only Experiments• Purpose of experiments
– Attribution of upper ocean biases in CCSM3 (Large and Danabasoglu, ‘05)– Ocean variability and process studies (Yeager and Large, 2004; Capotondi et al., 2005)
• Protocol– Initialized with Levitus/PHC, no motion– 4x43 year cycles– Salinity Forcing
• Precipitation factor used• Weak restoring with piston velocity of 50m/4yrs globally• Specified ice-ocean flux from coupled run• Frazil ice formation salinity flux
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Attribution of Upper Ocean Biases in CCSM3
Large and Danabasoglu, 2005
Equatorial Pacific Zonal Velocity
Coupled run biases
• upper ocean shear in west
• westward surface flow at 140E
Absent in Ocean-only runs
Associated with the lack of westerly wind bursts that are present in the observations
OBS
OceanOnly
Coupled
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Attribution of Upper Ocean Biases in CCSM3
Large and Danabasoglu, 2005
Pacific Zonal Velocity at 140W
Coupled and Ocean-Only biases
• Westward SEC too weak
• Eastward NECC too weak
Coupled biases
• Too symmetric about equator
• Presence of a SECC
• Associated with symmetric atmospheric forcing
OBS
OceanOnly
Coupled
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Attribution of Upper Ocean Biases in CCSM3
Large and Danabasoglu, 2005
Equatorial Pacific (2S-2N mean) Potential Temperature
Coupled and Ocean-only biases
• Warm bias indicative of a reduced temperature gradient
Coupled bias
• Cold bias at 100-200m depth, 180E
• Boundary layer not penetrating deep enough - related to sfc buoyancy forcing
OBS
Ocean OnlyMinus OBS
Coupled-OBS
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Ice-Only ExperimentsCORE-II Forcing
• Purpose of Experiments– Examine issues/difficulties in validating sea ice models– Perform simulations with different forcing datasets, – Perform simulations with variations in parameter values – quantify uncertainty due to model forcing vs model
physics– Currently a single cycle of forcing performed with
NCEP and with Large-Yeager (43 years)• Protocol
– Initial ice conditions from a previous ice-only run– Ocean heat flux convergence specified (held fixed) from
a CCSM3 coupled integration
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Average Sept Arctic Ice Concentration
CORE-II ForcedIce Only Experiments
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Arctic Ice Variability
Winter Variability Very SimilarSummer Variability Quite Different. Associated with Mean Differences.
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Antarctic Sept Averaged Sea Ice
NCEPLarge-Yeager
• NCEP forcing results in thicker ice cover
• SH variability very similar between runs
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Discussion of Dataset Issues
Compiled by Bill Large with input from dataset users
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New/Extended Data Available• IVF data through 2004 available at NCAR. • Should be checked out early in the new year. • Future CCSM IVF runs will run through 2004. • No intention of recomputing NYF (with data to 2004)
– Should the GFDL IVF data base be extended?
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New/Extended Radiation Data• Radiation data has just arrived • Contains "replacements" for the previous data for
January ‘97 - June ‘01. • "replacements may have some minor effects in
terms of global means (up to a few tenths W/m2) but there are some large flux values changes (> 100 W/m2) for a few grid cells (primarily land areas) for a few flux components.”
– Should we use the "replacement" data?
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Dataset Issues - Tropical Humidity• Comparison of TOA and NCEP humidity (Jiang et al., 2005 ) fundamentally
different than earlier comparison (Wang and McPhaden, 2000) on which tropical corrections were based.
• In tropical E Pac, new study consistent with SOC (NOT in west). • New comparison and SOC suggest humidity corrections should NOT be
zonally uniform (as currently done). • Considering exploring an objective alternative SOC-based correction that
depends on both lat and lon. (ERA-40 consistency) – What should be done for CORE? Should we work with relative or
specific humidity ?
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• Elizabeth Hunke (LANL) believes that the corrected humidity is still too high over Arctic Sea ice.
• She is trying to gather some data sets to quantify the possible problem, so that the correction could be improved.– Are there Arctic humidity data available?
Dataset Issues - Arctic Humidity
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• Mean wind stress in NYF based on 1958-2000 • Southern ocean has trend in zonal wind stress to
increasing westerlies. • If ACC transport tuned to winds from later years, a
weaker ACC will result when forced with NYF.– Should mean NYF be based on 1958-2000, 1983-
2000, 1958-2004, 1983-2004 ?
Dataset Issues - Normal Year Winds
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Dataset Issues - Wind Direction• NCEP wind direction has been compared to QSCAT. • There are 2 small regions of systematic bias; in the ITCZ
regions of central N Pacific, along the Pacific coast of S America.
• Possible correction being considered to adjust the mean and standard deviation of the wind direction
• N’=Q + (Q(N-N)• So N’ (corrected NCEP direction) is a function of the mean
QSCAT direction and the ratio of the standard deviations – Should corrections be applied? How? Globally?
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• The 5% reduction made to the solar radiation is supported by measurements from TAO and PIRATA bouys in the tropical Pacific and Atlantic.– Has anyone else found a similar or different result?
Dataset Issues - Solar Radiation Corrections
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Dataset Issues - Heat Imbalance• Normal year forcing,
when used with obs SST has a global ocean heat flux imbalance of -5 W/m2, compared to -1 W/m2 for the IVF (1958-2000).– Is this a problem?– Will be looking into in
any case.
NYF
+5 W/m2
+10 W/m2
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Dataset Issues - Others?
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Antarctic Winter Ice Variability
Nearly identical for the different forcing runs