Search

The Gulf of Guinea (GoG) reports high vulnerability to coastal flooding caused by relative or climate-induced sea level rise, which is an example of how coastal sea level changes remain poorly understood, in contrast to the global and regional average sea levels measured by satellite altimetry missions. The relationship between equatorial Atlantic Ocean variability and the 1° coastal band off the coast of the GoG is investigated at interannual time scales from 29 years from recent altimetric products in order to understand its mitigation to sea level rise in a region where there is no reliable tide gauges data. The study focuses on the (extreme) warm and cold events that occur in both the GoG and the Atlantic Ninos and links them to the well-known Benguela Ninos occurrences that occur off the coast of Angola and Namibia. A correlation between signals observed along the GoG with significant events depicted along the Angola-Namibian coastlines as the extraordinary Equatorial Atlantic Warming in 2010, 2012, and 2021 with the 2019 events depicted as the warmest in the last 40 years, which has never been reported in this region, using both altimetric monthly Sea Level Anomalies and Sea Surface Temperature Anomalies. Interannual SLA along the equatorial domain are systematically analyzed, and it is found that they advance the West African coastal ones by 1 month, supporting the idea that equatorial wave dynamics are responsible for their creation and the northward propagation observed on the SLA attributed mainly to the Kelvin coastal trapped waves., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

High self-esteem, an overall positive evaluation of self-worth, is a cornerstone of mental health. Previously we showed that people with low self-esteem differentially construct beliefs about momentary self-worth derived from social feedback. However, it remains unknown whether these anomalies extend to constructing beliefs about self-performance in a non-social context, in the absence of external feedback. Here, we examined this question using a novel behavioral paradigm probing subjects’ self-performance estimates with or without external feedback. We analyzed data from young adults (N = 57) who were selected from a larger community sample (N = 2402) on the basis of occupying the bottom or top 10% of a reported self-esteem distribution. Participants performed a series of short blocks involving two perceptual decision-making tasks with varying degrees of difficulty, with or without feedback. At the end of each block, they had to decide on which task they thought they performed best, and gave subjective task ratings, providing two measures of self-performance estimates. We found no robust evidence of differences in objective performance between high and low self-esteem participants. Nevertheless, low self-esteem participants consistently underestimated their performance as expressed in lower subjective task ratings relative to high self-esteem participants. These results provide an initial window onto how cognitive processes underpinning the construction of self-performance estimates across different contexts map on to global dispositions relevant to mental health such as self-esteem.

The oceans have a profound influence on the weather and climate of South Africa. Not only, most rainfall comes from condensation of water vapor originating from the flux of moisture from ocean to atmosphere but the temperature of the remote and surrounding oceans have an impact of the interannual variability of rainfall. A good example of this remote effect is the impact of the ocean during El Nino when the temperature of the Pacific and Indian Ocean is higher than normal. This creates more rainfall above the higher sea surface temperature thus modifying the global Walker and Hadley circulation. Air usually rises in the equatorial regions, especially above the ocean creating rainfall which increases further the ascending motion of air. The air is eventually pushed poleward and then cools and sinks in the subtropical region where Southern Africa sits, creating high pressure and subsidence which is not favorable to rainfall. This is one of the teleconnection mechanisms linking remote oceanic region to South Africa. The aim of the project was to better understand the role of the ocean on weather, climate and rivers of Southern Africa. Little work has been done to connect streamflow to the El Nino Southern Oscillation previous to that project. We also looked at the tropical Atlantic Ocean, which is closer to us although but smaller where a similar phenomenon to El Nino occurs, the Benguela Nino. Closer to South Africa, the Agulhas Current was known to impact the atmosphere above it due to high turbulent flux of moisture from sea to atmosphere. In the past, due to low resolution reanalyzed climate data that did not integrate the Agulhas Current, it was not possible to study the impact of the Agulhas Current on local climate with reanalyzed climate dataset such as ERA or NCEP. This project made some important advance to that matter using new high resolution reanalyzed climate data and a model and offer some sounds evidence on the impact of the Agulhas Current on coastal rainfall. A list of publication originating directly from the project and a list of student and thesis supported by the project is found at the end of the executive summary.

Benguela Niños and Niñas are intermittent, extreme warm and cold events that develop near the border between Angola and Namibia. These extreme events have been intensively studied these past years because of their significant impacts on the regional rainfall and the local marine ecosystem. Recently, Imbol Koungue et al. [2017], evidenced the role played by the Interannual Equatorial Kelvin waves during the onset of Benguela Niños and Niñas over 15 years (1997-2012). The present study is an update of the recent paper by Imbol Koungue et al. [2017]. We aim to revisit most of the Benguela Niños and Niñas developing before 1998 along the Angolan and Namibian coastlines using monthly averaged from an Ocean General Circulation Model (OGCM) for the period 1958 - 2015 which has been validated using available observation datasets. Preliminary results show the occurrences of 55 anomalous coastal events (29 warm and 26 cold) over the period 1958 - 2015. In agreement with recent studies, most of these anomalous coastal events are remotely forced via Interannual Equatorial Kelvin Wave (IEKW) propagations at interannual timescales with equatorial variability leading coastal SST variability by 1 month. Meridional transport anomalies across the ABF seem to contribute to the development of these anomalous coastal warm events. We show that October to April appears to be the favourable season in which anomalously warm or cold coastal events in the South-east Atlantic Ocean peak and are also linked to the remote oceanic forcing (IEKW).

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018; The objective of this study is to describe the low-frequency modulation of the Equatorial Kelvin Wave (EKW) activity in the tropical Atlantic as well as the low-frequency modulation of the local stratification and coastal winds along the coast of south-western Africa. We aim at investigating the control of these forcings in modulating the oceanic interannual variability off the coasts of Angola/Namibia and the phenomenology of Benguela Niño/Niña events. The methodology is based on the development of a high resolution (1/12°) long-term (1958 - 2008) numerical simulation of the South-Atlantic Ocean using the Regional Ocean Modeling System (ROMS). The evaluation of the model performances show that the model is skilful in reproducing the mean state and the interannual variability. The evaluation of the equatorial forcing reveals a low-frequency modulation of the EKW activity with a significant reduction of the EKW energy from 1958 to 1990, then re-energized up to 2008. Variations are associated with change in EKW baroclinic mode contribution to interannual sea level anomalies: from 1958 the second baroclinic mode dominate, and is then balance by the third baroclinic mode after the late 1990's. Concomitantly, further analyses show a decrease of the wind stress forcing and a modulation of the magnitude of wind projection coefficients according to the oceanic baroclinic modes in the Guinea gulf with in particular a strong increase of the third EKW mode. Changes are associated with the increase (decrease) of the intensity (maximum depth) of the equatorial stratification. Our results suggest that the change in the remote equatorial forcing may play an important role in the modulation of the variability off the coasts of South-West Africa. These results will be confronted to the low frequency modulation of local wind variations and Coastal Trapped Waves (CTW) signature due to different stratification state along the south-eastern coast of Africa. Indeed, modulation of the coastal stratification will most likely impact the characteristics of CTW propagation and their efficiency to imprint the coastal interannual variability in the Benguela Upwelling System.

ICAWA : International Conference AWA, Lanzarote, ESP, 17-/04/2018 - 20/04/2018; The PREFACE program allowed the deployment and annual maintenance of an ATLAS mooring at 6° S, 8° E during PREFACE cruises. A first mooring was bought by South Africa in 2006 and was deployed successfully for a year during a pilot project. PREFACE allowed to buy a second mooring needed to establish a permanent location as one replaced a mooring by a complete calibrated one. This is an extension of the PIRATA array of moorings in the tropical South-East Atlantic and an African contribution to the global observing system. PREFACE acquired an ATLAS mooring which is equipped with an extra currentmeter at 10 m depth and an extra short wave radiation sensor which allows calculation of the radiative flux and the net heat budget at a 10 minute temporal resolution. Turbulent sensible and latent heat fluxes can also be calculated at a 10 minute resolution. Sensible and Daily average is available in real time. A CO2 sensor is also deployed on the mooring. The strategic location of the mooring in the stratocumulus deck which is a problem to coupled models, offshore of the Congo River plume and upstream of the Angola Current make this mooring a unique measuring platform which has continuously worked in real time since May 2013. Mooring data and satellite remote sensing estimates of salinity indicates numerous intrusions of low salinity water from the Congo River since 2013. While the air and sea surface temperature (SST) distribution is unimodal, the upper ocean subsurface temperature and dynamic height is bi-modal and seems to be a seasonal Rossby wave triggered by a seasonal kelvin waves along the equator. PIRATA mooring, altimetry and SST allow monitoring the passage of Rossby waves all the way to Brazil modifying the SST in a region that is known to impact the regional Brazilian climate.

Madagascar's southern coastal marine zone is a region of high biological productivity which supports a wide range of marine ecosystems, including fisheries. This high biological productivity is attributed to coastal up-welling. This paper provides new insights on the structure, variability and drivers of the coastal upwelling south of Madagascar. Satellite remote sensing is used to characterize the spatial extent and strength of the coastal upwelling. A front detection algorithm is applied to thirteen years of Multi-scale Ultra-high Resolution (MUR) Sea Surface Temperatures (SST) and an upwelling index is calculated. The influence of winds and ocean currents as drivers of the upwelling is investigated using satellite, in-situ observations, and a numerical model. Results reveal the presence of two well-defined upwelling cells. The first cell (Core 1) is located in the southeastern corner of Madagascar, and the second cell (Core 2) is west of the southern tip of Madagascar. These two cores are characterized by different seasonal variability, different intensities, different upwelled water mass origins, and distinct forcing mechanisms. Core 1 is associated with a dynamical upwelling forced by the detachment of the East Madagascar Current (EMC), which is reinforced by upwelling favourable winds. Core 2 appears to be primarily forced by upwelling favourable winds, but is also influenced by a poleward eastern boundary flow coming from the Mozambique Channel. The intrusion of Mozambique Channel warm waters could result in an asynchronicity in seasonality between upwelling surface signature and upwelling favourables winds.

A Benguela Nino developed in November 2010 and lasted for 5 months along the Angolan and Namibian coastlines. Maximum amplitude was reached in January 2011 with an interannual monthly Sea Surface Temperature anomaly larger than 4°C at the Angola Benguela Front. It was the warmest event since 1995. Consistent with previous Benguela Niños, this event was generated by a relaxation of the trade winds in the western equatorial Atlantic, which triggered a strong equatorial Kelvin wave propagating eastward along the equator and then southward along the southwest African coast. In the equatorial band, the associated ocean sub-surface temperature anomaly clearly shows up in data from the PIRATA mooring array. The dynamical signature is also detected by altimetry derived Sea Surface Height and is well reproduced by an Ocean Linear Model. In contrast to previous Benguela Niños, the initial propagation of sub-surface temperature anomalies along the equator started in October and the associated warming in the Angolan Benguela Front Zone followed on as early as November 2010. The warming was then advected further south in the Northern Benguela upwelling system as far as 25°S by an anomalously strong poleward sub-surface current. Demise of the event was triggered by stronger than normal easterly winds along the Equator in April and May 2011 leading to above normal shoaling of the thermocline along the Equator and the south-west African coastline off Angola and an associated abnormal equatorward current at the Angola Benguela Front in April and May 2011.

PIRATA (Brazil, France, USA) has deployed between 1997 and 2001, an array of 12 ATLAS buoys with the objective of monitoring, describing and understanding the evolution of sea surface temperature, upper ocean thermal and saline structure, net heat budget, air-sea fluxes of momentum, latent and sensible heat and fresh water in the tropical Atlantic. The oceanic and meteorological observations are transmitted to shore via satellite and are available in near real-time on the Internet. They are communicated to the Global Telecommunication System and readily available for ocean and weather prediction models. The ultimate objective of PIRATA is real-time ocean monitoring to enable resource prediction in the adjacent countries. Published

Rainfall variability and changes in Southern Africa over the 20th century areexamined and their potential links to the global warming discussed. After a shortreview of the main conclusions of various experiments with Global AtmosphericModels (GCM) forced by increased concentrations of greenhouse gases for SouthernAfrica, a study of various datasets documents the observed changes in rainfall featuresat both daily and seasonal time steps through the last century. Investigations of dailyrainfall parameters are so far limited to South Africa. They show that some regionshave experienced a shift toward more extreme rainfall events in recent decades.Investigations of cumulative rainfall anomalies over the summer season do notshow any trend to drier or moister conditions during the century. However, closeexamination reveals that rainfall variability in Southern Africa has experiencedsignificant modifications, especially in the recent decades. Interannual variabilityhas increased since the late 1960s. In particular, droughts became more intense andwidespread. More significantly, teleconnection patterns associated with SouthernAfrican rainfall variability changed from regional before the 70s to near global after,and an increased statistical association to the El Niño – Southern Oscillation (ENSO) phenomenon is observed. Numerical experiments with a French GCM indicate that these changes in teleconnections could be related to long-term variations in the Sea-Surface-Temperature background, which are part of the observed global warming signal.

Sea-surface temperatures (SSTs) have been measured at Marion and Gough islands for nearly 50 years. These are some of the longest records of their kind in the sub-Antarctic. We present the trend, the seasonal cycle, and the time-frequency characteristics of the SST for both islands, which rose by 1.4°C at Marion Island and by 0.5°C at Gough Island over the 50-year period. Intermittent temperature oscillations, with periods of between 1 and 5 years, were observed throughout the record. A 5-year periodicity, compatible with an Antarctic CircumpolarWave signature, dominated after 1990 in both records. We also observed a strong low-frequency component with a period varying from 9.3 to 11.4 years at Marion Island, and a much weaker component with a period varying from 9.9 to 11.8 years at Gough Island.

Sea-surface temperatures may give strong indications of the location of fronts, currents, eddies and other components of ocean circulation. This has been recognized in particular for the seas around southern Africa. Almost all studies using this property have employed measurements of thermal infrared radiation from orbiting satellites. This has distinct disadvantages due to the shading effect of persistent cloud cover. Another option is to use microwave observations, which are not affected by cloud cover. Until recently, however, the spatial resolution of microwave data was far too coarse for the purpose of studying ocean circulation in detail. We describe here a new set of microwave data that does not have this disadvantage, and show how useful it is by describing examples of local applications.

Intrusions of warm equatorial water in the South East Atlantic Ocean off Angola and Namibia may be linked with above average rainfall along the coast of those countries but sometimes also with inland areas of southern Africa e.g. Zambia. During the 1984, 1986, 1995 and 2001 warm events, above average rainfall occurred near the sea surface temperature (SST) anomalies and extended inland from the coast to an extent that appeared to depend on the intensity of the regional moisture convergence and atmospheric circulation anomalies. Rainfall over western Angola/Namibia is greatest for those events for which the local circulation anomalies act to strengthen the climatological westwards flux of Indian Ocean sourced moisture across low latitude southern Africa and which flow anticyclonically over the warmest SST off the coast thereby weakening the mean southeasterly moisture flux away from Africa over the SE Atlantic. The significance of the warm events occurring during the February to April period is that this is the time when SST reaches its maximum in the annual cycle (up to 28°C off northern Angola) and this favours more intense local evaporation and convection and a greater impact on late austral summer rainfall. Better understanding of these warm events is necessary for assessing impacts on regional rainfall, agriculture and fisheries and for improving seasonal forecasting in this region.