Tropical Atlantic studies with SPEEDO Wilco Hazeleger Rein 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 Variability Atlantic Nino (T=2-10yrs) Ruiz Barradas et al 2000

Interannual variability: Tropical Atlantic Variability Interhemispheric mode (T=2-10yrs) Ruiz-Barradas et al

SPEEDO (SPEEDy-Ocean) LBM LAND FOCEAN SEA SLAB G-MODEL MICOM+ Sea ice LAND PRESCRIBED OCEAN THERMODYNAMIC OCEAN DYNAMIC OCEAN ATMOSPHERE (Molteni, ICTP Trieste) Hazeleger, et al TR-KNMI 2003 New 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-control SST errorTemperature 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 mixingTemp along equator

Rotated EOFs SST and associated wind stress Cold tongue modeInterhemispheric 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, m positive u averaged b)Principal component of REOF 1 Positive lag, REOF leads Equatorial Undercurrent correlations with cold tongue mode (unfiltered seasonal data and 4-year filtered) Seasonal data 4-year filtered data

North Brazil Current correlations with cold tongue mode (seasonal data and 4-year filtered data) NBC at 10S Time series of seasonal data: a)33W-36W, m, positive v averaged b)Principal component REOF 1 Positive lag, principal component leads Seasonal data 4-year filtered

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 decay role southern oceans in THC (Drijfhout) Impact diapycnal mixing on THC and sea level rise (Katsman) Mechanisms of tropical Pacific variability (Zelle, Oldenborgh)

What causes skewness of ENSO? Response of SPEEDY and MICOM to a periodic wind forcing with an ENSO pattern Skewness in thermocline, not in SST! (El Nino state minus La Nina state

Currently: using Lagrangian trajectory methods To trace sources of changes in Equatorial thermocline (Roberto de Almeida, USP) Impact of South Atlantic variability on tropical Atlantic circulation in MICOM (ocean-only)

Summary and conclusions SPEEDO produces realistic patterns and amplitude of Tropical Atlantic climate 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-tongue variations, 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-only models 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 advectionshort 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 enhanced Observations SST error along equator depth of 20 degree isotherm

SST budget in MICOM ocean-only (1S,10W): Entrainment Radiation Latent heat flux Sensible heat flux Horizontal advection Diffusion (all in W/m^2) ControlEnhanced wind mixing

Heat budget from PIRATA

Seasonal cycle Tropical Atlantic Colors SPEEDO Contours 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 SSTTemperature 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 Can be downloaded from website: 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.