Session 1. Climate events and anomalies in the Tropical Atlantic (TA) Abderrahim Bentamy Affiliation: IFREMER Address: BP 70 29280 Plouzan%E9 France email: abderrahim.bentamy@ifremer.fr title: Seasonal and Interannual Variability of Turbulent Fluxes over the Atlantic Tropical Ocean Coauthor: Abstract: This study aims to assess the consistencies and discrepancies of the seasonal and interannual variability of the ocean surface turbulent fluxes, including wind stress, latent and heat fluxes during the period 1993 -- 2008, over the Atlantic tropical basin. Data are derived from remotely sensed data and from the new ECMWF re-analysis ERA-Interim. Even tough some discrepancies are found, the results provide encouraging agreement on the spatial/temporal variations of the three turbulent flux components. Greg Foltz Affiliation: University of Washington JISAO Address: NOAA/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115 email: gregory.foltz@noaa.gov title: Interaction between the Atlantic meridional and Nino modes during 2009 Coauthor: Abstract: During the first half of 2009 sea surface temperatures (SSTs) were anomalously cold in the northeastern tropical Atlantic and anomalously warm in the central and eastern equatorial Atlantic. Associated with this anomalous meridional dipole in SST was a southward displacement of the ITCZ and extreme flooding in Northeast Brazil. In this study a combination of observations and a linear equatorial wave model is used to investigate the mechanisms responsible for the evolution of anomalous conditions in the equatorial Atlantic during 2009. It is found that anomalous cooling in the northeastern tropical Atlantic began in January, driven by stronger than normal wind-induced latent heat loss. The atmospheric response to anomalously cold SSTs included anomalous northwesterly surface winds along the equator and Ekman pumping to the north (3N-5N). The Ekman pumping in turn led to further anomalous cooling in the 3N-5N band and further strengthening of the meridional SST dipole during boreal spring. Along the equator, weaker than normal westward winds led to an anomalously deep thermocline and surface warming during boreal spring and early summer. The transient response to the anomalous equatorial wind forcing was a downwelling equatorial Kelvin wave and an upwelling equatorial Rossby wave. The Rossby wave reflected off the western boundary and propagated eastward along the equator as a Kelvin wave in June-July, raising the thermocline and putting an abrupt end to the developing equatorial warm event. These results highlight the role of ocean dynamics and air-sea coupling in the development of SST anomalies in the eastern ITCZ region and identify the equatorial Rossby wave as a potential link between the boreal spring meridional mode and the boreal summer Nino. Semyon Grodsky Affiliation: University of Maryland Address: AOSC/Computer and Space Sci. Bldg., University of maryland, College Park, MD 20742 email: senya@atmos.umd.edu title: Interannual near-surface salinity variability from PIRATA and Argo observations Coauthor: Abstract: We focus on 8S30W PIRATA location where both PIRATA and Argo have consistent time series indicating gradual salinification during 2000-2007 and rapid freshening in the two recent years. We compare these changes in salinity with the surface freshwater forcing. Julien Jouanno Affiliation: LEGOS Address: 18 Avenue Edouard Belin 31401 Toulouse cedex 9, FRANCE email: Julien.Jouanno@legos.obs-mip.fr title: The equatorial cold tongue in November-December in the Tropical Atlantic -- mechanisms and variability Coauthor: Abstract: The equatorial Atlantic is characterized by a seasonal cooling of surface temperatures from April to August. This cooling generally extends from 35°W to the African coast. Three months later, during November-December (ND), a secondary cooling occurs in the central equatorial Atlantic. The extent and intensity of this cold tongue shows a significant interannual variability. In comparison with its summer counterpart, it does not necessarily extend into the Gulf of Guinea. In this preliminary study, observations from PIRATA moorings, satellites and numerical simulations at 1/4° resolution based on global OGCM NEMO, are used to describe the characteristics and the variability of this cooling during the period 2001 to 2007. Interannual variability of the ND cold tongue in the model is in good agreement with observations and allows to explore the processes which drive its occurrence and characteristics. A special attention is given to the respective roles of thermocline shoaling, windstress and intraseasonal variability. Ingo Richter Affiliation: RIGC JAMSTEC Japan Address: 3173-25 Show-machi, Kanazawa-ku, Yokohama, 236-0001 Japan email: richter@jamstec.go.jp title: On the triggering of Benguela Ninos - equatorial vs. local forcing Coauthor: Abstract: Several studies have highlighted the importance of equatorial wind forcing on the development of Benguela Ninos, suggesting that downwelling Kelvin waves propagate the signal along the equator and southwest African coast in a time span of about 1-2 months. The influence of local along shore winds, on the other hand, has received less attention. The present study compares the relative importance of remote and local effects in the development of Benguela Ninos using a 120-year simulation of the coupled GCM for the Earth Simulator (CFES). Compared to many current GCMs, CFES achieves a rather realistic simulation of the tropical Atlantic. In addition to capturing the mean seasonal cycle the model also simulates Atlantic and Benguela Ninos with realistic amplitude and phase locking. Analysis of CFES output suggests that anomalous along shore winds in the Angola Benguela Area (ABA) are an important component in the development of Benguela Ninos. These wind variations induce SST anomalies through both increased latent heat flux and reduced upwelling and form part of a large-scale weakening of the South Atlantic subtropical anticyclone that appears to originate from the midlatitudes. Forcing by anomalous winds in the equatorial region also plays a role by preconditioning the ABA, but it is found that the local forcing is dominant. The large spatial extent of the wind anomalies may explain the high correlation between Benguela and Atlantic Ninos, which exists in both CFES and observations. The possible influence of Benguela Ninos on the formation of Atlantic Ninos will also be discussed. Mathieu Rouault Affiliation: University of Cape Town Address: Oceanography Dept, University of Cape Town, 7701 Rondebosch, South Africa email: Mathieu.Rouault@uct.ac.za title: Intrusion of tropical water in the Benguela upwelling, a numerical study. Coauthor: Abstract: Benguela Ninos are warmer than normal events in the Benguela upwelling system that have a negative impact on the ecosystem of region. They are also linked to above average rainfall at the coast. We are using a numerical model that reproduces quite well the observed sea surface temperature of the last 25 years to infer various properties such as poleward transport of Angolan water into the Benguela upwelling. This model indicates that Benguela Ninos are an exageration of the seasonal cycle at the Angola Benguela front leading to above normal poleward transport of warm, low salinity Angolan water into the Benguela upwelling. Fabrice Hernandez Affiliation: IRD Mercator Ocean Address: Mercator Ocean. 8-10 rue Hermes. Parc Technologique du Canal. 31520 Ramonville St Agne. France email: fabrice.hernandez@mercator-ocean.fr title: Tropical Atlantic Analysis Using Mercator Reanalysis Coauthor: Abstract: A global 20-year reanalysis based on ORCA2 configuration is analysed together with the GLORYS1V1 2002-2009 reanalysis. The interannual variability of the Gulf of Guinea cold tongue is examined and discussed. Session 2a. TA teleconnections Chunzai Wang Affiliation: NOAA AOML Address: 4301 Rickenbacker Causeway email: Chunzai.Wang@noaa.gov title: Teleconnected Influence of the Tropical Atlantic on the Tropical Indian and Pacific Oceans Coauthor: Abstract: Recent studies found that tropical Atlantic variability may affect the climate in both the tropical Pacific and Indian Ocean basins, possibly modulating the Indian summer monsoon and Pacific ENSO events. A warm tropical Atlantic Ocean forces a Gill-Matsuno-type quadrupole response with a low-level anticyclone located over India that weakens the Indian monsoon circulation, and vice versa for a cold tropical Atlantic Ocean. The tropical Atlantic Ocean can also induce changes in the Indian Ocean sea surface temperatures (SSTs), especially along the coast of Africa and in the western side of the Indian basin. Additionally, tropical Atlantic variability can influence the tropical Pacific Ocean via an atmospheric teleconnection that is associated with the Atlantic Walker circulation. Although the Pacific El Nino does not contemporaneously correlate with the Atlantic Nino, anomalous warming or cooling of the two equatorial oceans can form an inter-basin SST gradie! nt that induces surface zonal wind anomalies over equatorial South America and other regions in both ocean basins. The zonal wind anomalies act as a bridge linking the two ocean basins, and in turn reinforce the inter-basin SST gradient through the atmospheric Walker circulation and oceanic processes. Thus, a positive feedback seems to exist for climate variability of the tropical Pacific-Atlantic Oceans and atmospheric system, in which the inter-basin SST gradient is coupled to the overlying atmospheric wind. Regina Rodrigues Affiliation: Oceanographic Institute - University of Sao Paulo Address: Universidade de Sao Paulo - Instituto Oceanografico, Praca do Oceanografico 191, Sao Paulo, SP, Brazil, 05508-120 email: regina.rodrigues@usp.br title: The impacts of inter-El Nino event on the Tropical Atlantic variability and the Northeast Brazil climate Coauthor: Abstract: In this study, observations are used to investigate how differences in El Nino events affect the Brazilian Northeast (NE) precipitation and how this relates to the development of SST anomalies in the Atlantic. Our results show that El Nino telecommunication occurs not only in the tropical North Atlantic as previously thought, but also in the South Atlantic. This is due to the fact that different types of El Nino have different impacts on the SST anomalies over the equatorial and tropical South Atlantic but similar SST responses in the tropical North Atlantic. Strong and long (weak and short) El Nino events are followed by dry (wet) conditions in NE and cold (warm) anomalies in the equatorial Atlantic and Benguela Current region from December to May. Our results suggest that the SST anomalies over the equatorial and tropical South Atlantic are preconditioned by the characteristics of the El Nino event via an indirect extra-tropical route. Preliminary results from an atmosphere-ocean coupled model will also be presented. Yochanan Kushnir Affiliation: Lamont-Doherty Earth Observatory Address: 61 Route 9W, Palisades, NY 10964 email: kushnir@ldeo.columbia.edu title: The role of tropical Atlantic SST anomalies in forcing global circulation anomalies Coauthor: Abstract: The tropical Atlantic exhibits rather small amplitude SST anomalies in comparison to its Pacific counterpart. However, these SST anomalies force important teleconnections that affect global circulation patterns with impact on hydrological cycle variability worldwide. These impacts are felt in North and South America, in Africa, Europe, and Asia. We propose that it is through the tropical Atlantic that the much-discussed Tropical Atlantic Multidecadal Variability (a.k.a., Atlantic Multidecadal Oscillation) can influence global climate variability. In this work we review the patterns and time scales of climate fluctuations associated with tropical Atlantic SST variability and some of the mechanisms by which they operate. We also address the ability of general circulation models to correctly simulate these impacts. Session 2b. Dynamics and impacts of intraseasonal variability Anne Marie Treguier Affiliation: CNRS/ LPO Address: ifremer, BP 70, 29280 Plouzane, France email: treguier@ifremer.fr title: Biweekly ocillations in the Gulf of Guinea-- a case of strong currents on an eastern boundary. Coauthor: Abstract: Current data on the continental slope off Angola show very energetic biweekly oscillations at 1300 m depth (peak-to-peak amplitude reaching 20-30 cm/s at 30 meters above the bottom). Here we present a synthesis of recent modelling work and observations aimed at understanding the dynamics of these currents. A high resolution primitive equation model demonstrates that this deep variability is forced by equatorial winds, through the generation of equatorial Yanai waves that propagate eastward and at depth, and then poleward as coastal-trapped waves upon reaching the coast of Africa. We have used both the three-dimensional, nonlinear model and a linear model to investigate the kinetic energy at intraseasonal frequencies in the Gulf of Guinea, and the role of equatorial and coastal-trapped waves in its spatial distribution and temporal intermittency. Additional current meter data on the continental slope north of the equator display an energy profile in the 10-20 day period band that is strikingly different from the our previous observations, with surface intensification rather than bottom intensification and a secondary maximum near 800 m. The model reproduces these features and explains them-- the surface intensification in the north is due to the regional wind forcing, and the north-south dissymetry of the deep signal is due to shape of the African coast. Renellys C. Perez Affiliation: UM CIMAS Address: 4301 Rickenbacker Causeway, Miami, FL 33149, USA email: renellys.c.perez@noaa.gov title: Interannual variations of Tropical Instability Waves and their influence on the equatorial Atlantic cold tongue Coauthor: Abstract: The equatorial Atlantic cold tongue can be dramatically modified by westward propagating tropical instability waves (TIWs). TIWs have strong interannual variations, and we explore whether anomalous sea surface temperatures or anomalous wind forcing have a greater influence on TIW activity using a combination of satellite measurements-- TMI SST, AVISO SLA, QuikSCAT wind stress. These waves were relatively weak in the central and eastern equatorial Atlantic for three successive years beginning in 2006. The intensification of TIWs in mid 2009 and their impact on the cold tongue during the relaxation of the warming event will be described using daily averaged fields from the high-resolution MERCATOR Ocean global ocean analysis products (PSY3V1 and PSY3V2). Session 2c. Physical-Biogeochemical Interactions in the TA Ajit Subramaniam Affiliation: LDEO Columbia University Address: 61 Rt 9 W, Palisades, NY 10964 email: ajit@ldeo.columbia.edu title: Spatial variability in optical and biogeochemical properties of the Equatorial Atlantic Coauthor: Abstract: Moacyr Araujo Affiliation: DOCEAN UFPE Address: Departamento de Oceanografia, Universidade Federal de Pernambuco, Recife-PE, Brazil. email: moa@ufpe.br Title: Coral bleaching analysis in the western tropical Atlantic Session 3. Results from recent/ongoing TA observational programs Peter Brandt Affiliation: IFM-GEOMAR Address: Dusternbrooker Weg 20, 24105 Kiel, Germany email: pbrandt@ifm-geomar.de title: Variability of the Equatorial Undercurrent in the central Atlantic Coauthor: Abstract: Easterly/westerly wind anomalies in the western equatorial Atlantic during boreal spring and early summer precondition boreal summer cold/warm events in the eastern equatorial Atlantic (EEA) that manifest in a strong interannual Atlantic cold tongue (ACT) variability. The onset of the ACT is closely linked to the onset of the West African monsoon and particularly to the rainfall in the countries surrounding the Gulf of Guinea. Model simulations suggest a negative correlation between boreal summer ACT sea surface temperature (SST) and the strength of the Equatorial Undercurrent (EUC) supplying the equatorial upwelling. Here we present results from current meter moorings deployed between 2002 and 2008 and from 16 meridional ship sections along 23°W in the central equatorial Atlantic that allow quantifying the mean and the intraseasonal to interannual EUC variability. From shipboard ADCP measurements, the leading modes of zonal velocity variability along 23°W are calculated. A linear regression of the moored ADCP time series onto the leading modes allows reconstructing a time series of meridional sections of zonal velocity in the latitudinal and depth range 1.2°S to 1.2°N and 30 to 300m, respectively. EUC transport variability on seasonal to interannual time scales is discussed with respect to the variability of wind and sea surface temperature in the tropical Atlantic. Bernard Bourles Affiliation: IRD/ LEGOS & CRHOB Address: IRD, Cocotiers, 08BP841 COTONOU BENIN email: bernard.bourles@ird.fr title: Analysis of the Equatorial Undercurrent in the Gulf of Guinea Coauthor: N. Kolodziejczyk, Y. Gouriou and F. Marin Abstract: The Atlantic Equatorial Undercurrent (EUC) remains still very poorly documented in the Gulf of Guinea. At 10°W, the EUC experiences a strong seasonal cycle, with two maxima of EUC transport, one weakest in boreal winter and one strongest in boreal summer when strong upward excursion of the equatorial thermocline is observed (Kolodziejczyk et al., 2009). Here, the EUC is described east of 10°W from both currents and hydrographic measurements carried out from late spring to fall between 2000 and 2007. The fate of saline enriched water coming from tropics and subtropics during the boreal summer is discussed. Bill Johns Affiliation: RSMAS/ Univ. of Miami Address: 4600 Rickenbacker Causeway Miami, FL 33149 email: bjohns@rsmas.miami.edu title: TACE observations of the Equatorial Undercurrent in the Gulf of Guinea Coauthor: Abstract: Recent observations conducted as part of TACE include a basinwide survey of the EUC at the onset of the 2009 summer cold tongue season, and moored ADCP observations of the EUC at 10°W and 0°E in the Gulf of Guinea. The May-June 2009 shipboard survey showed that the intensity of the EUC decreased eastward across the basin, from a transport of 16.0 Sv at 23°W to 3.9 Sv at 5°E. The survey also revealed westward flow bands on either side of the equator between 10°W and 5°E extending from the surface to the level of the EUC core. In the thermocline layer these flows contained high salinity cores, indicating that EUC waters are being actively detrained into these westward flows and recirculated back toward the central basin. Near 10°W, a second, deeper, core of eastward flow was found on the equator between about 200-350 m, separated from the EUC by a thin layer of westward flow. Evidence from ADCP records suggests that this two-core structure precedes a summertime maximum in the EUC transport at 10°W, when these two cores merge into a thicker and stronger EUC extending through the themostad layer. Vestiges of this deep eastward core are seen all across the basin, but in the eastern basin it trends south of the equator to about 2°S and is no longer located below the upper EUC core. At 0°E the EUC appears to have a semiannual cycle, with the weakest transport occurring in late summer and fall, different from the behaviour at 10°W and 23°W. Roberto De Almeida Affiliation: CST INPE Address: Rod. Pres. Dutra km 40, 12.630-000, BRAZIL email: roberto@dealmeida.net title: Seasonal variability of the upper circulation of the southwestern Tropical Atlantic Coauthor: In this work we present an analysis of the seasonal variability of the upper circulation of the southwestern Tropical Atlantic, investigated using high-resolution near-surface (drifters + satellite altimeter) velocity measurements. Yves du Penhoat Affiliation: LEGOS IRD Address: 14 Av. Edouard Belin 31400 TOLOUSE FRANCE email: yves.du-penhoat@legos.obs-mip.fr title: Mixed layer heat budget in the eastern equatorial Atlantic derived from Argo floats during the AMMA/EGEE program Coauthor: Abstract: The mixed layer heat balance in the Eastern Equatorial Atlantic is examined in order to assess the contribution of the main processes, i.e. air-sea exchange, advection and entrainment, inside the oceanic upper layers from January 2005 to December 2007. This period coincides with the period of the AMMA-EGEE program during which the number of observations considerably increased in the basin. This study combines a set of in situ observations including Argo profiling floats, drifting MARISONDE buoys, CTD and XBT and profiles from PIRATA moorings, as well as remotely sensed retrievals --TMI AMSR-E SSTs and upper current analyses. Sea surface heat fluxes are derived from NWP models --ECMWF, ARPEGE and NCEP. Temperature and salinity profiles from in situ measurements are used to compute some terms of the mixed layer heat budget over the basin. We first diagnose the mixed-layer heat budget along the trajectory of some float trajectories. Results show that the tendency of the mixed layer temperature undergoes a strong seasonal cycle with contrasted inter-annual differences. This variability reflects the contribution of the seasonal cycle of sea surface heat fluxes. Oceanic advection and entrainment also experience a seasonal cycle, but less well marked than the surface fluxes. Advection and entrainment are seen to play an important role in the heat budget and can reach values as large as 100 W.m-2 in absolute value. In order to represent the spatial variability of the heat budget, some boxes are considered over which an average budget is computed. The domain-averaged terms of advection, entrainment, vertical diffusion, air sea flux and mixed layer temperature tendency are largely contrasted according to the considered box. Claudia Schmid Affiliation: NOAA/AOML/PHOD Address: 4301 Rickenbacker Causeway, Miami, FL 33149 E-mail: Claudia.Schmid@noaa.gov Title: Analysis of the variability of the Salinity in the eastern tropical Atlantic Abstract: Changes of the salinity in the tropical Atlantic are forced by a combination of atmosphere-ocean exchanges and oceanic fluxes. Data collected with profiling floats, CTDs and PIRATA moorings in conjunction with surface flux products are analyzed in an effort to improve our understanding of the seasonal variability and interannual changes. Rapid changes of the surface and subsurface salinity were observed along a hydrographic section at 23W (two realizations of this section were obtained within 2 weeks of each other). Data collected by the moorings help to analyze the causes of such rapid changes. Preliminary results will be presented in comparison with results from earlier studies. Monika Rhein Affiliation: University Bremen Address: Otto-Hahn-Allee 1, 28359 Bremen, Germany email: mrhein@physik.uni-bremen.de title: Upwelling and associated heat flux in the Equatorial Atlantic inferred from helium isotope disequilibrium Coauthor: Abstract: Upwelling velocities w in the equatorial band are too small to be directly observed. Here we apply a recently proposed indirect method, using the observed helium isotope (3He, 4He) disequilibria in the mixed layer. The helium data were sampled on three cruises in the eastern tropical Atlantic in September 2005 and June/July 2006. A one - dimensional two box model was applied, where the helium air-sea gas exchange is balanced by upwelling from 3He-rich water below the mixed layer and by vertical mixing. The mixing coefficients Kv were estimated from microstructure measurements, and on two of the cruises, Kv exceeded 1x10-4m2s-1, making the vertical mixing term of the same order of magnitude as the gas exchange and the upwelling term. In total, Helium disequilibrium was observed on 54 stations. 48% of the calculated upwelling velocities, were smaller than 1.0 x10-5 m/s, 19% were between 1.0 and 2.0 x10-5 m/s, 22% between 2.0 and 4.0 x10-5 m/s, and only 11% upwelling velocities exceeded this limit. The highest upwelling velocities were found in late June 2006. Meridional upwelling distribution indicated an equatorial asymmetry with higher vertical velocities between the equator and 1°-2° south compared to north of the equator, particularly at 10°W. Associated heat flux into the mixed layer could be as high as 138 W/m2, but depends strongly on the chosen depths where the upwelled water comes from. By combining upwelling velocities with SST and productivity distributions, a mean monthly equatorial upwelling rate of 19 Sv was estimated for June 2006, and a biweekly mean of 24 Sv for September 2005. Marcus Dengler Affiliation: Leibniz Institute for Marine Science (IFM-GEOMAR) Address: Kiel, Germany email: mdengler@ifm-geomar.de Title: On the parameterization of mixing processes at the equator Coauthors: M. Dengler, J. Schafstall, J. Toole, D. Banyte, B. Bourles Abstract: This contribution explores the skill of mixing parameterization in the upper and intermediate water column at the equatorial. Due to reduced wave-wave interaction, mixing in the deeper water column (>200m) of the tropical oceans is considered to be very low. Full depth microstructure profiles show that average eddy diffusivities rarely exceed 3x10-6m2s-1 throughout the deeper water column. However, dissipation rates calculated from internal wave-wave interaction parameterization underestimate observed dissipations rates by a factor of 5 within about 2° of the equator. In this region, the equatorial deep jets are pronounced and elevated dissipation rates are found in the high shear zones of the jets. A turbulence parameterization evaluated in unstable events overestimates dissipation rates directly on the equator but agrees well with observations away (>1°) from the equator. Domingos Urbano Affiliation: INPE Address: Rod. Pres. Dutra, KM40, Cachoeira Paulista, SP - Brazil email: domingos.urbano@cptec.inpe.br title: Upper ocean circulation in the southwestern tropical Atlantic Coauthor: Abstract: Most of the knowledge on the surface circulation in the southwestern tropical Atlantic off South America is based on geostrophic maps built on from sparse salinity/temperature profiles collected throughout the decades. Schematic pictures provided by previous researches have been important to elucidate the large scale circulation pattern, however uncertainties remains about the linkage in some regions. Almost none observation was collected between 10S and 15S in the eastern Atlantic. Recent direct velocity data collected by shipboard acoustic Doppler current profiler (S-ADCP) during the Brazilian PIRATA cruises, together with atmospheric data provided by radiosondes, reveal the existence of an eastward flow between 11S and 14S, probably generated by a feature in the wind field. Sverdrup transport computed from wind data also present eastward flow in the region. This recent feature can not be identified as the South Equatorial Countercurrent since it was described to be located between 7S and 9S (Molinari, 1982; 1983). How this eastward flow interacts with the sluggish South Equatorial Current system flowing eastward is of major curiosity due to the bifurcation process. High resolution ocean numeric models also present this eastward flow and need to be used to better understand its variability. Coupled ocean-atmospheric models are needed to better understand possible feedbacks that might be related with climate over South America. Session 4. Ocean, atmosphere, and coupled model simulations Paulo Nobre Affiliation: INPE Address: Rodovia Presidente Dutra, Km 40, Cachoeira Paulista, SP, BRAZIL email: paulo.nobre@cptec.inpe.br title: Uncoupled Variations of the Tropical Atlantic EUC in a fully coupled ocean-atmosphere model Coauthor: Abstract: A fully coupled ocean-atmosphere general circulation model (CGCM) is used to investigate the temporal variations of the Equatorial Undercurrent (EUC), which is compared to the EUC variability simulated by the ocean-component of the CGCM forced by prescribed winds. It is shown that the EUC depth variations on the CGCM simulations are seasonally dependent and liked to atmospheric climatological seasonal cycle. Herve Giordani Affiliation: CNRM Address: 42 Av. G. Coriolis 31057 Toulouse - France email: herve.giordani@meteo.fr title: Diagnosing Vertical Motion in the Equatorial Atlantic Coauthor: Abstract: Estimating vertical velocity in the oceanic upper-layers is a key issue for understanding the equatorial upwelling and thus the cold tongue development in the Eastern equatorial Atlantic. This paper aims to identify the physical sources of vertical velocity from a generalized w-equation valid at the equator. This w-equation is developed from the divergence equation of the primitive equation system and takes into account the turbulent buoyancy and momentum fluxes. An application of this diagnostic method is provided from a realistic ocean simulation of the Equatorial Atlantic. It is shown that the equatorial upwelling works to continuously adjust the density/pressure fields to the strongly sheared zonal current system formed by the superposition of the South Equatorial Current and the underlying Equatorial Under Current. This result supports the existence of an equatorial balance between the mass and the current fields which depends on the parameter b. As a consequence of this study, the upwelling along the equator appears to be an indirect response of the ocean to the Southeast surface wind-stress where the mass adjusts to the zonal circulation while the Angola upwelling results from dynamical forcings dominated by the stress-curl. Karthik Balaguru Affiliation: Texas A & M University Address: 401 University oaks blvd, # 1403, College Station, Texas - 77840 email: karthiknaidu@tamu.edu title: Barrier layers in the Atlantic warmpool-- Formation and influence on climate at various time-scales Coauthor: Abstract: The region to the east of the Caribbean and to the north of Latin America, is known as the Atlantic warm pool as the SSTs in this region are considerably higher than the rest of the basin. Barrier layer (BL)is an important feature of the Atlantic warm pool and may play a role in the maintenance of the warm SSTs, as the BL acts as a barrier to vertical mixing. We explored the formation mechanism of BLs in the Atlantic warm pool using the NCAR climate model CCSM 3.0 through a set of numerical sensitivity experiments. We find that the BL is maintained by not just advection of fresh-water from the Amazon but also through the remote mechanism of subduction. Formation of temperature inversions during boreal winter enhances the role of the BL in maintaining the warm SST. We also find that the BL-SST-ITCZ feedback, albeit weak, does appear to operate, at least in the model simulations. At shorter time scales, the BL can affect oceanic response to hurricane forcing. Using a high-resolution regional coupled climate model (ROMS-WRF)and satellite observations, we find that the BL causes less cooling at the ocean surface in the wake of hurricanes due to reduced vertical mixing. In the simulation, we even observe surface warming when a hurricane passes through a BL with a temperature inversion. This could act as a potential positive feedback for the hurricane intensity. Hailong Liu Affiliation: Address: RSMAS/CIMAS, 4600 Rickenbacker Causeway, Miami, FL 33149 email: hailong.liu@noaa.gov title: Diagnosing Atlantic warm pool and its climate impacts in IPCC-AR4 models Coauthor: Abstract: Earlier studies using models and observations have demonstrated the importance of the Atlantic warm pool (AWP) for summer climate and hurricanes. In specific, a large AWP weakens the southerly Great Plains low-level jet, which results in reduced northward moisture transport from the Gulf of Mexico to the U.S. east of the Rocky Mountains and thus decreases the summer rainfall over the central U.S. Decreased rainfall, if it persists, can cause drought in North America. A large AWP also reduces the tropospheric vertical wind shear in the hurricane main development region and increases the moist static instability of the troposphere, both of which help the intensification of tropical storms into major hurricanes. Despite these important findings from the earlier works, currently we do not have a clear understanding of AWP predictability. The main objective of this work to evaluate the performance of IPCC-AR4 models under 20C3M scenario in simulating AWP and associated atmosphere-ocean processes in the light of previous observational and diagnostic modeling studies. This work will provide a valuable guidance to understand and improve seasonal predictability of AWP. Kerstin Kirchner Affiliation: University of Bremen, Institute of Environmental Physics Address: Otto-Hahn-Allee 1, 28334 Bremen, Germany email: kkirchner@uni-bremen.de Title: An analysis of the formation, propagation and decay of North Brazil Current rings in the FLAME model Authors: K. Kirchner, M. Rhein, S. Hüttl-Kabus and C.W. Böning Abstract: Near the western boundary of the tropical North Atlantic, where the North Brazil Current (NBC) retroflects into the North Equatorial Countercurrent, large anticyclonic rings are shed. After separating from the retroflection region, the so-called NBC rings travel northwestward along the Brazilian coast, until they reach the island chain of the Lesser Antilles and disintegrate. These rings contribute substantially to the upper limb return flow of the Atlantic Meridional Overturning Circulation (AMOC) by carrying South Atlantic Water into the northern subtropical gyre. Their relevance for the northward transport of South Atlantic Water depends on the frequency of their generation as well as on their horizontal and vertical structure. Different types of rings are produced: they can be either confined to the surface layers or deep reaching, as well as only subsurface intensified with no surface signature. The ring shedding and propagation and the complex interaction of the rings with the Lesser Antilles are investigated in the 1/12° FLAME model. The ring properties simulated in FLAME reach the upper limit of the observed rings in diameter and agree with recent observations on seasonal variability, which indicates a maximum shedding during the first half of the year. When the rings reach the shallow topography of the Lesser Antilles, they are trapped by the island triangle of St. Lucia, Barbados and Tobago and interact with the island chain. The model provides a resolution which is capable of resolving the complex topographic conditions at the islands and illuminates various possible fates for the water contained in the rings. It also reproduces laboratory experiments, which indicate that both cyclones and anticyclones are formed after a ring passes through a topographic gap. We provide a detailed comparison with results from Garaffo et al. (2003), who used the isopycnic MICOM model with monthly climatological forcing to analyze the ring shedding and discuss the differences between both studies. Trajectories of artificial floats, which were inserted into the modeled velocity field, are used to investigate the pathways of the ring cores and their fate after they encounter the Lesser Antilles. The majority of the floats entered the Caribbean, while the northward, Atlantic pathway was found to be of minor importance. No prominent pathway was found east of Barbados, where a ring could avoid the interaction with the islands and migrate towards the northern Lesser Antilles undisturbed. Ben Kirtman Affiliation: University of Miami - RSMAS Address: 4600 Rickenbacker Causeway email: bkirtman@rsmas.miami.edu title: Impact of Ocean Model Resolution of CCSM4 Climate Variability Coauthor: Abstract: Several recent studies have focused on the importance of atmospheric model resolution in the simulations of climate (e.g.,Gent et al. 2009). The results include little or no change in the mean and variable climate (i.e., Hack et al. 2006) to significant differences in the ENSO cycle (Navarra et al. 2008) and in SST biases in the upwelling regions (i.e., Gent et al. 2009). The Gent et al. (2009; hereafter G09) study is of particular relevance here. First, both studies use the same version of the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM). The model used by G09 is identical to the control model used here. Third, where G09 focus on atmospheric model resolution (e.g., 2 degrees vs. 0.5 degrees horizontal resolution) our emphasis is on ocean model resolution. We enhance the 1 degree ocean model resolution used by G09 to 0.1 degree. The atmospheric component model resolution is identical (i.e., 0.5 degrees) in all the experiments presented here. Ramalingam Saravanan Affiliation: Texas A&M University Address: 3150 TAMU, College Station, TX 77843 email: sarava@tamu.edu title: Hurricanes and Air-Sea Interaction in the Tropical Atlantic Coauthor: Abstract: The frequency and intensity of hurricanes show considerable variations from year to year. Of particular importance is to distinguish between natural and human influences responsible for these variations. It is difficult to make this attribution using global climate models because they do not currently have sufficient horizontal grid resolution to properly simulate tropical cyclones. Therefore, "time-slice" experiments are used to make this attribution, where a fine-resolution regional atmospheric model is embedded inside a coarser global climate model. In this talk, we focus on two factors affecting hurricane activity, vertical shear and air-sea coupling, in the context of this regional modeling approach. We investigate how well global general circulation models manage to simulate the observed vertical shear in this region, and show that coupling between the atmosphere and the ocean must be properly represented to simulate the large-scale influences on vertical shear. To properly represent the effects of air-sea coupling, it is necessary to develop regional climate models that incorporate ocean-atmosphere interaction. We present some preliminary results from a high-resolution coupled regional climate model (CRCM) that we have developed, consisting of a regional atmospheric model (NCAR WRF) coupled to a regional ocean model (ROMS). We compare the simulation of hurricanes in coupled and uncoupled integrations of the CRCM, to assess the sensitivity to air-sea interaction. Chidong Zhang Affiliation: RSMAS/ University of Miami Address: 4600 Rickbacker Causeway, MPO, Miami, FL 33149 email: czhang@rsmas.miami.edu title: A possible root cause of the surface westerly bias over the equatorial Atlantic in climate models Coauthor: Abstract: The notorious warm SST bias in the tropical Atlantic Ocean in coupled GCM has been a subject of active research. It has been suggested that this bias is at least partially produced by unrealistic surface westerly wind near the equator. The westerly bias itself has been attributed to erroneous zonal gradients in surface pressure and precipitation in the tropical Atlantic and over the adjacent land. In this study, we suggest that even if there was no systematic error in the zonal gradient in precipitation, many atmospheric GCMs (AGCM) may still produce the westerly bias and warm SST bias when coupled with an ocean GCM. This suggestion is based on an analysis of vertical diabatic heating profiles from sounding observations, TRMM observations, and from two AGCMs. In observations of both soundings and TRMM, there is a strong low-level heating maximum over the Amazon basin, which is missing in the AGCMs. A low-level heating maximum is much more effective than a upper-level maximum to generate surface wind responses. A lack of such low-level heating maximum over the Amazon basin in AGCMs can then lead to insufficient easterlies or a westerly bias over the tropical Atlantic. It is argued that the unrealistic heating profile in AGCMs is a consequence of deficient parameterizations of atmospheric convection and precipitation processes. Brian Mapes Affiliation: RSMAS Address: 4600 Rickenbacker email: mapes@miami.edu title: Trying not to rain over the IAS in summer-- largest analysis tendencies (model struggles) in the MERRA reanalysis Coauthor: Abstract: The new NASA atmospheric reanalysis (MERRA) includes datasets of analysis tendencies. These fields indicate where and how hard the assimilated observations are acting to resist the underlying model's erroneous tendencies or first guess errors. A climatology of analysis tendencies shows global extrema in the NW Atlantic in summer. The sense of these is that the model has a lot of convective heating over this warm pool area that it shouldn't. THU afternoon Plenary Discussion: (1) Planned Research Activities, (2) Research Priorities and Progress. Bernard Bourles Affiliation: IRD/ LEGOS & CRHOB Address: IRD, Cocotiers, 08BP841 COTONOU BENIN email: bernard.bourles@ird.fr title: status of Pirata in France Coauthor: Abstract: France is one of the three nations in charge of the PIRATA program, with specific commitments on the field. This presentation is dedicated to the different actions carried out in 2009 in the framework of Pirata by the french scientific community, to the organization and management of PIRATA in France and to new perspectives. Edmo Campos Affiliation: University of Sao Paulo Address: Pca. do Oceanografico 191, Cid. Universitaria, 05508-120 Sao Paulo, Brazil email: edmo@usp.br title: Developing an Atlas Buoy Prototype in Brazil Coauthor: Abstract: Efforts towards the construction of an Atlas Buoy prototype (ATLAS-B) has been started as part of the Brazilian PIRATA Program. A Pilot Project for monitoring the SW Atlantic has been approved by Brazilian funding agencies, based on the deployment of an ATLAS-B near 28S, 43W. This mooring site will complement the data from the PIRATA SW Extension, providing important information for studying the variability of the atmospheric South Atlantic Convergence Zone (SACZ). The enhancement of the Brazilian capacity of instrument callibration is also part of this project. PIRATA-15 Paulo Nobre Affiliation: INPE Address: Rodovia Presidente Dutra, Km 40, Cachoeira Paulista, SP, BRAZIL email: paulo.nobre@cptec.inpe.br title: PIRATA-BR Program, 2009 Coauthor: Abstract: Activities of the PIRATA Program in Brazil during 2009 are described. Michael J. McPhaden Affiliation: NOAA PMEL Address: 7600 Sand Point Way NE, Seattle, WA 98115 email: michael.j.mcphaden@noaa.gov title: PMEL PIRATA Update Coauthor: Abstract: This presentation will provide a PMEL update on 2009 progress and 2010 plans for PIRATA maintenance. A presentation on scientific analysis of PIRATA data at PMEL will be submitted as a separate abstract. Rick Lumpkin Affiliation: NOAA AOML Address: 4301 Rickenbacker Cswy., Miami FL 33149 email: Rick.Lumpkin@noaa.gov title: PIRATA Northeast Extension Coauthor: Abstract: Status of the PIRATA Northeast Extension and plans for 2010-2011, for PIRATA-15 meeting.