tropical atlantic studies with speedo
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Tropical Atlantic studies with SPEEDO
Wilco HazelegerRein Haarsma
Camiel Severijns
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
Interannual variability: Tropical Atlantic VariabilityAtlantic Nino (T=2-10yrs)
Ruiz Barradaset al 2000
Interannual variability: Tropical Atlantic VariabilityInterhemispheric mode (T=2-10yrs)
Ruiz-Barradas et al
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
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
MEAN STATE: SPEEDO-controlSST error Temperature along equator
first REOF SST and wind stress second REOF SST and wind stress
The coupled model results
SST error in exp with enhanced wind mixing Temp along equator
Rotated EOFsSST and associated wind stress
Cold tongue mode Interhemispheric mode
Cold tongue mode dominant in late summer, interhemispheric mode in spring
Heat budget of cold tongue mode
Entrainment latent heat flux
Short wave radiation horizontal advection
Heat budget of interhemispheric mode
Entrainment latent heat flux
Short wave radiation horizontal advection
Zonally averaged SST anomalies(8 yr filtered)
Seasons
Atlantic Subtropical Cell pathways
Schott, Stramma
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
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
Lagged SVD of SST (Jul-Aug-Sept) and GH-500 (Oct-Nov-Dec)
Expl variance: 33%Correlation: 0.44
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)
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
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)
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)!!
Heat budget of decadal variations(8yr filtered zonally averaged data)
SST anomalies
Entrainment latent heat flux
Heat budget of decadal variations
SST anomalies
Horizonal advection short wave radiation
Zonal velocity differences averaged between 50E and 20W in SPEEDO
Enhanced ocean wind mixing efficiency minus Control
First rotated EOF of SST in coupled SPEEDO and related variables
Second rotated EOF of SST in coupled SPEEDO and related variables
Control Wind mixing efficiency enhanced Buoyancy mixing efficiency enhancedObservations
SST error along equator depth of 20 degree isotherm
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
Heat budget from PIRATA
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
MEAN STATE: Observations
SST Temperature along equator
Standard deviation of SST
: obs
:COLA model
: SPEEDO
SST error along equator in coupled models
Davey et al 2001
Dominant patterns of covariability betweenSST and early winter 500 hPa geopotential height when SST leads by 4 months. (Czaja and Frankignoul 2001)
Users shell for MICOM developed by
Dutch Climate Research Center (CKO)
Camiel Severijns severijn@knmi.nl
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.
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