The roles of static stability and tropical – extratropical interactions in the summer interannual variability of the North Atlantic sector

Summer seasonal forecast skill in the North Atlantic sector is lower than winter skill. To identify potential controls on predictability, the sensitivity of North Atlantic baroclinicity to atmospheric drivers is quantified. Using ERA-INTERIM reanalysis data, North Atlantic storm-track baroclinicity is shown to be less sensitive to meridional temperature-gradient variability in summer. Static stability shapes the sector’s interannual variability by modulating the sensitivity of baroclinicity to variations in meridional temperature gradients and tropopause height and by modifying the baroclinicity itself. High static stability anomalies at upper levels result in more zonal extratropical cyclone tracks and higher eddy kinetic energy over the British Isles in the summertime. These static stability anomalies are not strongly related to the summer NAO; but they are correlated with the suppression of convection over the tropical Atlantic and with a poleward-shifted subtropical jet. These results suggest a non-local driver of North Atlantic variability. Furthermore, they imply that improved representations of convection over the south-eastern part of North America and the tropical Atlantic might improve summer seasonal forecast skill

Storm Track Response to Perturbations in Climate

This thesis advances our understanding of midlatitude storm tracks and how they respond to perturbations in the climate system. The midlatitude storm tracks are regions of maximal turbulent kinetic energy in the atmosphere. Through them, the bulk of the atmospheric transport of energy, water vapor, and angular momentum occurs in midlatitudes. Therefore, they are important regulators of climate, controlling basic features such as the distribution of surface temperatures, precipitation, and winds in midlatitudes. Storm tracks are robustly projected to shift poleward in global-warming simulations with current climate models. Yet the reasons for this shift have remained unclear. Here we show that this shift occurs even in extremely idealized (but still three-dimensional) simulations of dry atmospheres. We use these simulations to develop an understanding of the processes responsible for the shift and develop a conceptual model that accounts for it. We demonstrate that changes in the convective static stability in the deep tropics alone can drive remote shifts in the midlatitude storm tracks. Through simulations with a dry idealized general circulation model (GCM), midlatitude storm tracks are shown to be located where the mean available potential energy (MAPE, a measure of the potential energy available to be converted into kinetic energy) is maximal. As the climate varies, even if only driven by tropical static stability changes, the MAPE maximum shifts primarily because of shifts of the maximum of near-surface meridional temperature gradients. The temperature gradients shift in response to changes in the width of the tropical Hadley circulation, whose width is affected by the tropical static stability. Storm tracks generally shift in tandem with shifts of the subtropical terminus of the Hadley circulation. We develop a one-dimensional diffusive energy-balance model that links changes in the Hadley circulation to midlatitude temperature gradients and so to the storm tracks. It is the first conceptual model to incorporate a dynamical coupling between the tropical Hadley circulation and midlatitude turbulent energy transport. Numerical and analytical solutions of the model elucidate the circumstances of when and how the storm tracks shift in tandem with the terminus of the Hadley circulation. They illustrate how an increase of only the convective static stability in the deep tropics can lead to an expansion of the Hadley circulation and a poleward shift of storm tracks. The simulations with the idealized GCM and the conceptual energy-balance model demonstrate a clear link between Hadley circulation dynamics and midlatitude storm track position. With the help of the hierarchy of models presented in this thesis, we obtain a closed theory of storm track shifts in dry climates. The relevance of this theory for more realistic moist climates is discussed.</p

Moment de sensibilisation à l’entrepreneuriat de l’hospitalité, auto-efficacité entrepreneuriale et aspiration à l’identité de rôle d’entrepreneur

Dans le sillage des travaux mesurant l’impact de l’éducation à l’entrepreneuriat, cette recherche examine l’effet spécifique du moment de la sensibilisation à l’entrepreneuriat (MSE) sur l’auto-efficacité entrepreneuriale (AEE) et sur l’aspiration à l’identité de rôle d’entrepreneur (AIRE) considérée comme un marqueur de la transition vers le rôle d’entrepreneur. Une analyse conceptuelle approfondie et un test empirique auprès de 440 étudiants en hospitalité sensibilisés à l’entrepreneuriat en France et au Sénégal montrent que l’AEE est un médiateur d’une relation positive entre le MSE et l’AIRE. Plus le moment de sensibilisation est tardif, plus il accroît directement l’AEE et indirectement l’AIRE.In the vein of research measuring the impact of entrepreneurship education, this study examines the specific effect of the Moment of Entrepreneurship Awareness (MEA) on Entrepreneurial Self-Efficacy (ESE) and Entrepreneur Role Identity Aspiration (ERIA) considered as a marker for the transition to the role of entrepreneur. An in-depth conceptual analysis and an empirical test with 440 hospitality students initiated to entrepreneurship in France and Senegal show that ESE is a mediator of a positive relationship between MEA and ERIA. The later MEA, the more it directly increases ESE and indirectly ERIA.Esta investigación examina el efecto específico del momento de la sensibilización sobre el emprendimiento (MSE) en la autoeficacia empresarial (AE) y en la aspiración a la identidad del rol de emprendedor (AIRE) considerado como un marcador para la transición al rol de emprendedor. Un análisis conceptual en profundidad y una prueba empírica ante 440 estudiantes de hotelería sensibilizados con el espíritu empresarial en Francia y Senegal muestran que la AE es mediadora de una relación positiva entre la MSE y la AIRE. Cuando más tardío es el momento de sensibilización, más aumenta directamente la AE e indirectamente la AIRE

Cross-Reactivity of SARS-CoV-2 Laboratory Diagnostics to Endemic Diseases in Africa: A Diagnostic Accuracy Study

Background: Serology is a great tool to assess the level of immunity against SARS-CoV-2 in settings with limited access to molecular diagnostics. However, African populations displays a particular immunological profile with massive circulation of infectious agents from different aetiologies that can affect assays performance.Methods: We evaluated the OMEGA Diagnostics COVID-19 ELISA-IgG and the ID Screen® SARS-CoV-2-N IgG Indirect in Senegal using a panel of 636 blood samples covering several African-endemic diseases and healthy donors to determine test sensitivity and specificity. The sensitivity panel of sera includes 461 serum samples collected from 91 patients hospitalized for COVID-19 disease. COVID-19 cases were confirmed by qRT-PCR and samples were collected on an interval of three days until viral clearance. In addition, 272 sera obtained from COVID-19 negative individuals were selected from a well-documented biobank of sera collected before the COVID-19 outbreak.Finding: High-cross reactivity have been found in individuals with a history of exposure to Chikungunya, HIV, malaria (Plasmodium falciparum), rheumatoid factor as well as healthy donors with respective specificities of 55%, 41.8%, 70%, 70% and 75%. ELISA experiments with commercial assays targeting either SARS-CoV-2 Nucleocapsid protein and Spike 2 protein or nucleocapsid protein only suggest that cross-reactivity might be directed against Spike 2 protein and not Nucleocapsid protein. Further samples characterisation reveals that anti-malaria IgG is the leading cause of such poor specificities, but exposure to other diseases contributed as well.Interpretation: We anticipate that COVID-19 seroprevalence can be biased if assays are not contextualized. Since malaria is endemic in African settings, we propose that a particular attention must be given in serological surveillance of COVID-19 or anti-SARS-CoV-2 antibodies quantification as vaccines are being rolled out