tropical atlantic studies with speedo
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Tropical Atlantic studies with SPEEDO. Wilco Hazeleger Rein Haarsma Camiel Severijns. - PowerPoint PPT PresentationTRANSCRIPT
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Tropical Atlantic studies with SPEEDO
Wilco HazelegerRein Haarsma
Camiel Severijns
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Last year: Mean state of tropical Atlantic in SPEEDO (coupled Speedy-MICOM)
This year: Variability in the tropical Atlantic:- What are the mechanisms of tropical Atlantic variability?- What are the teleconnections with Europe?
Other projects at KNMI
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Interannual variability: Tropical Atlantic VariabilityAtlantic Nino (T=2-10yrs)
Ruiz Barradaset al 2000
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Interannual variability: Tropical Atlantic VariabilityInterhemispheric mode (T=2-10yrs)
Ruiz-Barradas et al
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SPEEDO (SPEEDy-Ocean)
LBMLAND
FOCEANSEA
SLABG-MODELMICOM+
Sea ice
LAND PRESCRIBEDOCEAN
THERMODYNAMICOCEAN
DYNAMICOCEAN
ATMOSPHERE(Molteni, ICTP Trieste)
Hazeleger, et al TR-KNMI 2003New developments: upgrade physics package,dynamic vegatation model, atmospheric chemistry
atmsph. mixed layer
Speedy
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SpeedO-Atlantic
Atmosphere (Speedy, global):
T30 (3.5 degree) primitive equations
7 layers
Simplified parameterizations
Ocean (MICOM-Atlantic: 40S – 70N):
Isopycnic coordinate primitive equation model (MICOM)
22 layers
1 degree horizontal resolution
SST prescribed outside the Atlantic and nudging at lateral boundaries
Land:Prescribed
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MEAN STATE: SPEEDO-controlSST error Temperature along equator
first REOF SST and wind stress second REOF SST and wind stress
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The coupled model results
SST error in exp with enhanced wind mixing Temp along equator
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Rotated EOFsSST and associated wind stress
Cold tongue mode Interhemispheric mode
Cold tongue mode dominant in late summer, interhemispheric mode in spring
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Heat budget of cold tongue mode
Entrainment latent heat flux
Short wave radiation horizontal advection
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Heat budget of interhemispheric mode
Entrainment latent heat flux
Short wave radiation horizontal advection
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Zonally averaged SST anomalies(8 yr filtered)
Seasons
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Atlantic Subtropical Cell pathways
Schott, Stramma
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EUC at 35W
Time series of seasonal data: a) 2N-2S, 50-160m positive u averagedb) Principal component of REOF 1Positive lag, REOF leads
Equatorial Undercurrent correlationswith cold tongue mode (unfiltered seasonaldata and 4-year filtered)
Seasonal data
4-year filtered data
0.2
0
-0.2
0.6
0
-0.2
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North Brazil Current correlationswith cold tongue mode (seasonal data and 4-yearfiltered data)
NBC at 10S
Time series of seasonal data: a) 33W-36W, 40-250m, positive v averagedb) Principal component REOF 1Positive lag, principal component leads
Seasonal data
4-year filtered
0.2
0
0.4
0
-0.4
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Lagged SVD of SST (Jul-Aug-Sept) and GH-500 (Oct-Nov-Dec)
Expl variance: 33%Correlation: 0.44
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Other studies with MICOM at KNMI:
Process studies: Agulhas Ring decayrole southern oceans in THC (Drijfhout)
Impact diapycnal mixing on THC and sea levelrise (Katsman)
Mechanisms of tropical Pacific variability (Zelle,Oldenborgh)
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What causes skewness of ENSO?
Response of SPEEDY and MICOM to a periodic wind forcing withan ENSO pattern
Skewness in thermocline, not in SST! (El Nino state minus La Nina state
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Currently: using Lagrangian trajectory methodsTo trace sources of changes in Equatorial thermocline
(Roberto de Almeida, USP)
Impact of South Atlantic variability on tropical Atlanticcirculation in MICOM (ocean-only)
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Summary and conclusions
SPEEDO produces realistic patterns and amplitude of Tropical Atlanticclimate variability:
a) Cold tongue mode generated by thermocline-upwelling feedbacks
b) Interhemispheric mode generated by upwelling and short-wave feedbacks (in the east) and by latent heat flux (in the west, a wind-evaporation-SST feedback).
Small impact of TAV on Northern Hemisphere variability
NBC transport may be a predictor for decadal variations of cold-tonguevariations, but correlations are weak
NB!! Thermocline variations do not couple well to SST in the eastern parts of the basin (this is only apparent in coupled models, in ocean-onlymodels Tair will generate variability, but surface flux anomaly should damp variability)!!
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Heat budget of decadal variations(8yr filtered zonally averaged data)
SST anomalies
Entrainment latent heat flux
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Heat budget of decadal variations
SST anomalies
Horizonal advection short wave radiation
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Zonal velocity differences averaged between 50E and 20W in SPEEDO
Enhanced ocean wind mixing efficiency minus Control
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First rotated EOF of SST in coupled SPEEDO and related variables
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Second rotated EOF of SST in coupled SPEEDO and related variables
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Control Wind mixing efficiency enhanced Buoyancy mixing efficiency enhancedObservations
SST error along equator depth of 20 degree isotherm
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SST budget in MICOM ocean-only (1S,10W):
EntrainmentRadiationLatent heat fluxSensible heat fluxHorizontal advection Diffusion(all in W/m^2)
Control Enhanced wind mixing
Dhc
Qw)TT(HvTuT
t
T
pesyx
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Heat budget from PIRATA
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Seasonal cycle Tropical Atlantic
Colors SPEEDOContours Da Silva
Seasonal cycle SST along equator(colors SPEEDO, contours Da Silva)
Change in winds and rain in JAS
Idem for JFM
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MEAN STATE: Observations
SST Temperature along equator
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Standard deviation of SST
: obs
:COLA model
: SPEEDO
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SST error along equator in coupled models
Davey et al 2001
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Dominant patterns of covariability betweenSST and early winter 500 hPa geopotential height when SST leads by 4 months. (Czaja and Frankignoul 2001)
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Users shell for MICOM developed by
Dutch Climate Research Center (CKO)
Camiel Severijns [email protected]
Can be downloaded from website: www.knmi.nl/onderzk/CKO
• NetCDF based
• Easy to use: basin, resolution, parameter choice.
• Coupling implemented as a library, using SCRIP tools for
interpolation
• Analysis tools (Bausteinen) for EOF, SVD, spectra etc.