Impact of Stratospheric Geoengineering on Sea Surface Temperature in the Northern Gulf of Guinea

Among techniques proposed to limit global warming, there is Stratospheric Aerosol Geoengineering (SAG) which is aiming to increase Earth-atmosphere albedo by injecting sulfur dioxide into the stratosphere in order to reduce the solar radiation that reaches the earth. This study aims to assess the potential impact of SAG on Sea Surface Temperature (SST) in the Northern Gulf of Guinea and its causes using GLENS (Geoengineering Large Ensemble) simulations performed under a high anthropogenic emission scenario (RCP8.5). Here, we focus on two dynamically different regions: Sassandra Upwelling in Côte d’Ivoire (SUC, located east of Cape Palmas) and Takoradi Upwelling in Ghana (TUG, located east of Cape Three Points). Results show that in the SUC region, under climate change, there is an increase in SST (referred to as the current climate) all year long (by 1.52 °C on average) mainly due to an increase in net heat flux (lead by the decrease in longwave radiation) and also in weak vertical mixing (caused by strong stratification which dominates the vertical shear). Under SAG, SST decreases all the seasonal cycle with its maximum in December (−0.4 °C) due to a reduction in the net heat flux (caused by a diminution of solar radiation) and an increase in vertical advection (due to an increase in vertical temperature gradient and vertical velocity). In the TUG region, under climate change, SST warming is a little more intense than in the SUC region and SST changes are driven by an increase in the net heat flux and strong stratification. The cooling of the SST in TUG is similar to the SUC region, but contrary to this region, the cooling under SAG is not only explained by a decrease in the net heat flux but also by the remote forcing of wind changes at the western equatorial Atlantic

Joint observation-model mixed-layer heat and salt budgets in the eastern tropical Atlantic

In this study, we use a joint observation-model approach to investigate the mixed-layer heat and salt annual mean and seasonal budgets in the eastern tropical Atlantic. The regional PREFCLIM observational climatology provides the budget terms with a relatively low spatial and temporal resolution compared to the online NEMO model, and this later is then re-sampled as in PREFCLIM climatology. In addition, advection terms are recomputed offline from the model as PREFCLIM gridded advection computation. In Senegal, Angola and Benguela regions, the seasonal cycle of mixed-layer temperature is mainly governed by surface heat fluxes; however, it is essentially driven by vertical heat diffusion in Equatorial region. The seasonal cycle of mixed-layer salinity is largely controlled by freshwater flux in Senegal and Benguela regions; however, it follows the variability of zonal and meridional salt advection in Equatorial and Angola regions respectively. Our results show that the time-averaged spatial distribution of NEMO offline heat/salt advection terms compares much better to PREFCLIM horizontal advection terms than the online heat/salt advection terms. However, the seasonal cycle of horizontal advection in selected regions shows that NEMO offline terms do not always compare well with PREFCLIM, sometimes less than online terms. Despite this difference, these results suggest the important role of small scale variability in mixed-layer heat and salt budgets.</p

[Première partie] : Méthode des paquets d'ondes pour le calcul des sections efficaces et constantes de vitesse dans les processus non adiabatiques ([deuxième partie] : paramétrisation de problèmes à N-corps en mécanique quantique non relativiste)

La thèse est subdivisée en deux grandes parties I. Méthodes de paquets d'ondes pour le calcul des sections efficaces et constantes de vitesse pour les processus non adiabatiques. II. Paramétrisation du problème à N-corps en mécanique quantique non relativiste. La partie consacrée à la paramétrisation du problème à N-corps traite des problèmes de coordonnées généralisées et de super-symétrie en mécanique quantique non relativiste avec applications sur le système de coordonnées hypersphériques d'axes principaux. Des propriétés d'opérateurs dits quasimoments ont été étudiés et une généralisation de relation de commutation est établie pour ces quasimoments. L'étude de la super-symétrie en mécanique quantique non relativiste constitue une approche de résolution d'équation aux valeurs propres et principalement celle de Schrodinger. L'ensemble de tous ces travaux a fait l'objet de trois publications: J. Math. Phys. 40 6133 (1999) -J. Phys. B 324823 (1999) -Mol. Phys. 98, 387 (2000). L'autre partie consacrée à la dynamique moléculaire porte sur deux aspects: le premier concerne l'élaboration d'une méthode de calcul basée sur des paquets d'ondes pour déterminer la constante de vitesse d'échange de charge dans une collision ion-atome. Ces travaux ont donné lieu à trois publications: Phys. Rev. A, 63 42704 (2001) -J. Chem. Phys. 114, 8741(2001) -International Journal of Molecular Sciences, (sous presse, 2002). Le second problème traité est le calcul de la probabilité cumulative de réaction pour un transfert d'hydrogène lors d'une isomérisation. Les conclusions de ce travail ont fait l'objet d'une publication au J. Chem. Phys. 117 (sous presse).The thesis is subdivided in two parts: I. Method of wave packets for calculation of the cross section and thermal rate constant for the non-adiabatic processes. II. Parametrization of N-body problem in non-relativistic quantum mechanics. The part devoted to parameterization of the N-body problem deals with curvilinear coordinates and supersymmetry in non-relativistic quantum mechanics with applications to the principal-axis hyperspherical coordinate. Operators known as quasimomenta properties have been studied and a generalization of commutation relation has been established for these quasimomenta. The supersymmetry studied in non-relativistic quantum mechanics constitutes an approach for resolving the eigenvalue problems mainly for the Schrödinger equation. These works have been presented in three publications: J. Math. Phys. 40 6133 (1999) ; J. Phys. B 32 4823 (1999) ; Mol. Phys. 98, 387 (2000). The other part devoted to molecular dynamics contains two applications: first, the development of a method of calculation based on wave packets to extract the rate constant speed charge exchange process in ion-atom collision. This work have been presented in three publications: Phys. Rev. A, 63 42704(2001); J Chem. Phys. 114, 8741(2001); International Journal of Molecular Sciences, (in press, 2002). The second application concerns the computation of the cumulative probability of reaction for an hydrogen transfer in isomerization process. The conclusions are published in J Chem. Phys. 117 (in press, 2002).ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Spatio-Temporal Trend of Past and Future Extreme Wave Climates in the Gulf of Guinea Driven by Climate Change

This study assessed the extremes of wave conditions for past (1979&ndash;2005) and future (2026&ndash;2045 and 2081&ndash;2100) time slices in the Gulf of Guinea (GoG). The ensemble produced from eight General Circulation Models under different Representative Concentration Pathway (RCP) emission scenarios (RCP4.5 and RCP8.5) was subjected to linear regression analysis and Mann&ndash;Kendal test for their trends and significance, respectively. Results showed an increase in the extreme of significant wave height (Hs) and mean wave period (Tm) between 1979&ndash;2005, 2026&ndash;2045, and 2081&ndash;2100 with few exceptions. The average values of annual and seasonal Hs and Tm range from 1.26&ndash;1.62 m and 10.37 s&ndash;10.86 s, respectively, for 1979&ndash;2005. These Hs values are projected to increase by 0.1 m (0.05 m) to 1.72 m (1.67 m) and the Tm will increase by 0.29 s (0.24 s) to 11.15 s (11.10 s) by the end of the century (mid-century) time slices, respectively. The mean wave direction (Dm) (201.89&deg;&ndash;206.27&deg;) showed an anticlockwise shift (&minus;29.2 &times; 10&minus;3 degrees per year) for 1979&ndash;2005 which is projected to become more southwesterly with an increase up to 2.2&deg; (0.5&deg;) by end (mid) century in 2100 (2045), respectively. Future work will be on the impacts of changing wave on longshore sediment transport along the GoG

Spatio-Temporal Trend of Past and Future Extreme Wave Climates in the Gulf of Guinea Driven by Climate Change

This study assessed the extremes of wave conditions for past (1979–2005) and future (2026–2045 and 2081–2100) time slices in the Gulf of Guinea (GoG). The ensemble produced from eight General Circulation Models under different Representative Concentration Pathway (RCP) emission scenarios (RCP4.5 and RCP8.5) was subjected to linear regression analysis and Mann–Kendal test for their trends and significance, respectively. Results showed an increase in the extreme of significant wave height (Hs) and mean wave period (Tm) between 1979–2005, 2026–2045, and 2081–2100 with few exceptions. The average values of annual and seasonal Hs and Tm range from 1.26–1.62 m and 10.37 s–10.86 s, respectively, for 1979–2005. These Hs values are projected to increase by 0.1 m (0.05 m) to 1.72 m (1.67 m) and the Tm will increase by 0.29 s (0.24 s) to 11.15 s (11.10 s) by the end of the century (mid-century) time slices, respectively. The mean wave direction (Dm) (201.89°–206.27°) showed an anticlockwise shift (−29.2 × 10−3 degrees per year) for 1979–2005 which is projected to become more southwesterly with an increase up to 2.2° (0.5°) by end (mid) century in 2100 (2045), respectively. Future work will be on the impacts of changing wave on longshore sediment transport along the GoG