The monthly averaged data time series of temperatures and rainfall without interruption of Conakry Airport (9.34° N 13.37° W, Guinea) from 1960 to 2016 were used. Inter-annual and annual changes in temperature and rainfall were investigated. Then, different models: Mann-Kendall Test, Multi-Linear-Regression analysis, Theil-Sen’s slope estimates and wavelet analysis where used for trend analysis and the dependency with these climate forcings. Results showed an increase in temperature with semi-annual and annual cycles. A sharp and abrupt rise in the temperature in 1998 was found. The results of study have shown increasing trends for temperature (about 0.21°/year). A decrease in rainfall (about −8.14 mm/year) is found since the end of 1960s and annual cycle with a maximum value of about 1118.3 mm recorded in August in average. The coherence between the two parameters and climate indices: El Niño 3.4, Atlantic Meridional Mode, Tropical Northern Atlantic and Atlantic Niño, were investigated. Thus, there is a clear need for increased and integrated research efforts in climate parameters variations to improve knowledge in climate change.

In this investigation a statistical analysis of the characteristics of mesospheric inversion layers (MILs) over tropical regions is presented. This study involves the analysis of 16 years of lidar observations recorded at Réunion (20.8° S, 55.5° E) and 21 years of lidar observations recorded at Mauna Loa (19.5° N, 155.6° W) together with SABER observations at these two locations. MILs appear in 10 and 9.3 % of the observed temperature profiles recorded by Rayleigh lidar at Réunion and Mauna Loa, respectively. The parameters defining MILs show a semi-annual cycle over the two selected sites with maxima occurring near the equinoxes and minima occurring during the solstices. Over both sites, the maximum mean amplitude is observed in April and October, and this corresponds to a value greater than 35 K. According to lidar observations, the maximum and minimum mean of the base height ranged from 79 to 80.5 km and from 76 to 77.5 km, respectively. The MILs at Réunion appear on average ∼ 1 km thinner and ∼ 1 km lower, with an amplitude of ∼ 2 K higher than Mauna Loa. Generally, the statistical results for these two tropical locations as presented in this investigation are in fairly good agreement with previous studies. When compared to lidar measurements, on average SABER observations show MILs with greater amplitude, thickness and base altitudes of 4 K, 0.75 and 1.1 km, respectively. Taking into account the temperature error by SABER in the mesosphere, it can therefore be concluded that the measurements obtained from lidar and SABER observations are in significant agreement. The frequency spectrum analysis based on the lidar profiles and the 60-day averaged profile from SABER confirms the presence of the semi-annual oscillation where the magnitude maximum is found to coincide with the height range of the temperature inversion zone. This connection between increases in the semi-annual component close to the inversion zone is in agreement with most previously reported studies over tropics based on satellite observations. Results presented in this study confirm through the use of the ground-based Rayleigh lidar at Réunion and Mauna Loa that the semi-annual oscillation contributes to the formation of MILs over the tropical region.

Space weather science has been a growing field in Africa since 2007. This growth in infrastructure and human capital development has been accompanied by the deployment of ground-based observing infrastructure, most of which was donated by foreign institutions or installed and operated by foreign establishments. However, some of this equipment is no longer operational due to several factors, which are examined in this paper. It was observed that there are considerable gaps in ground-based space-weather-observing infrastructure in many African countries, a situation that hampers the data acquisition necessary for space weather research, hence limiting possible development of space weather products and services that could help address socio-economic challenges. This paper presents the current status of space weather science in Africa from the point of view of some key leaders in this field, focusing on infrastructure, situation, human capital development, and the research landscape.

Trend-Run model was performed to estimate the trend in surface temperatures recorded at 12 sites in Guinea from 1960 to 2016 and to examine the contribution of each climate forcing. The coefficient of determination (R²) calculated varies between 0.60 and 0.90, it provides total information about the simulation capability of the model. The decadal trend values also calculated show an upward trend (between 0.04 °C ± 0.06 °C decade⁻¹ and 0.21 °C ± 0.06 °C decade⁻¹). In addition, forcings’ contributions were quantified, and the annual oscillation (AO) contribution is higher for most of the stations, followed by semiannual oscillation (SAO). Among the forcings, the tropical Northern Atlantic (TNA) contribution is greater than that of the sunspot number (SSN), Niño3.4 and Atlantic Niño (AN). Moreover, the Mann-Kendall test revealed a positive significant trend for all stations except at the Macenta site. Additionally, with sequential Mann-Kendall test, trend turning points were found only for the stations of Mamou, Koundara and Macenta at different dates. The temperature anomalies depict warming episodes (1970s, 1980s, 1984 and 1990s). Since then, the temperature is consistently increasing over the country. A significant warming has been shown, which might be further investigated using these models with additional contributing factors.

Dans un contexte de changement climatique, la variabilité des paramètres météorologiques demeure très sensible à notre environnement. Ce travail s’inscrit dans une perspective globale de l’analyse de la variabilité annuelle, interannuelle et spatiale des paramètres météorologiques en Guinée. Il est basé sur l’exploitation de longues séries d’observations (57ans) mesurées par 12 stations météorologiques réparties sur l’ensemble des régions de la Guinée. L’objectif de cette thèse est d’exploiter ces séries originales, afin d’améliorer la compréhension de la variabilité des paramètres météorologiques et contribuer à augmenter la documentation des processus géophysiques associés. La démarche développée est basée sur une analyse climatologique, puis l’estimation des tendances, en utilisant des méthodes numériques adaptées. Il ressort de cette étude que la variabilité de la température est dominée par les cycles saisonniers annuel et semi-annuel, tandis que celle de la pluviométrie se caractérise par un cycle annuel prépondérant. Les résultats ont montré une tendance à la hausse de la température et une tendance à la baisse des précipitations depuis la fin des années 1960. Il a été constaté par ailleurs que les distributions spatiales de température et pluviométrie présentent, respectivement, un gradient latitudinal négatif et positif, dans le sens nord-sud. La pluviométrie reste cependant très élevée dans la région côtière et dans le sud-est du pays. En plus des oscillations semi-annuelle et annuelle, les forçages analysés contribuent à la variabilité de la température et de la pluviométrie à des échelles spatiales et temporelles différentes. Parmi ces forçages, nous avons examiné et quantifié, pour l’ensemble des 12 stations, les contributions de l’Atlantique Niño, l’indice Niño 3.4, de l’indice AMM, de l’indice TNA et le Flux Solaire. En ce qui concerne l’analyse des tendances à long-terme, les résultats montrent que les températures ont globalement augmenté de +0,04 à +0,21 °C/décade. La moitié nord et la région sud de la Guinée enregistrent le plus fort réchauffement, suivies par la région côtière influencée par les effets de côte, de topographie et d'urbanisation.