Porotrichum saotomense sp. nov. (Neckeraceae) and other additions to the moss flora of São Tomé & Príncipe, Gulf of Guinea, West Africa

2011 ◽  
Vol 33 (1) ◽  
pp. 6 ◽  
Author(s):  
Johannes Enroth ◽  
James R. Shevock
Keyword(s):  
West Africa ◽  
Gulf Of Guinea

scholarly journals Understanding the variability of the rainfall dipole in West Africa using the EC-Earth last millennium simulation

2021 ◽  
Author(s):  
Qiong Zhang ◽  
Ellen Berntell ◽  
Qiang Li ◽  
Fredrik Charpentier Ljungqvist
Keyword(s):  
West Africa ◽  
Model Simulation ◽  
Rainfall Variability ◽  
Low Pressure ◽  
Last Millennium ◽  
Tropical Atlantic ◽  
Gulf Of Guinea ◽  
Dipole Pattern ◽  
Sahel Region ◽  
Heat Low

AbstractThere is a well-known mode of rainfall variability associating opposite hydrological conditions over the Sahel region and the Gulf of Guinea, forming a dipole pattern. Previous meteorological observations show that the dipole pattern varies at interannual timescales. Using an EC-Earth climate model simulation for last millennium (850–1850 CE), we investigate the rainfall variability in West Africa over longer timescales. The 1000-year-long simulation data show that this rainfall dipole presents at decadal to multidecadal and centennial variability and long-term trend. Using the singular value decomposition (SVD) analysis, we identified that the rainfall dipole present in the first SVD mode with 60% explained variance and associated with the variabilities in tropical Atlantic sea surface temperature (SST). The second SVD mode shows a monopole rainfall variability pattern centred over the Sahel, associated with the extra-tropical Atlantic SST variability. We conclude that the rainfall dipole-like pattern is a natural variability mode originated from the local ocean–atmosphere-land coupling in the tropical Atlantic basin. The warm SST anomalies in the equatorial Atlantic Ocean favour an anomalous low pressure at the tropics. This low pressure weakens the meridional pressure gradient between the Saharan Heat Low and the tropical Atlantic. It leads to anomalous northeasterly, reduces the southwesterly moisture flux into the Sahel and confines the Gulf of Guinea's moisture convergence. The influence from extra-tropical climate variability, such as Atlantic multidecadal oscillation, tends to modify the rainfall dipole pattern to a monopole pattern from the Gulf of Guinea to Sahara through influencing the Sahara heat low. External forcing—such as orbital forcing, solar radiation, volcanic and land-use—can amplify/dampen the dipole mode through thermal forcing and atmosphere dynamical feedback.

scholarly journals Local air pollution from oil rig emissions observed during the airborne DACCIWA campaign

2019 ◽  
Vol 19 (17) ◽  
pp. 11401-11411 ◽  
Author(s):  
Vanessa Brocchi ◽  
Gisèle Krysztofiak ◽  
Adrien Deroubaix ◽  
Greta Stratmann ◽  
Daniel Sauer ◽  
...  
Keyword(s):  
West Africa ◽  
Marine Boundary Layer ◽  
Dispersion Model ◽  
Particle Dispersion ◽  
Gulf Of Guinea ◽  
Aerosol Chemistry ◽  
Oil Platforms ◽  
Sensitivity Tests ◽  
Local Air Pollution ◽  
Oil Rig

Abstract. In the framework of the European DACCIWA (Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa) project, the airborne study APSOWA (Atmospheric Pollution from Shipping and Oil platforms of West Africa) was conducted in July 2016 to study oil rig emissions off the Gulf of Guinea. Two flights in the marine boundary layer were focused on the floating production storage and offloading (FPSO) vessel operating off the coast of Ghana. Those flights present simultaneous sudden increases in NO2 and aerosol concentrations. Unlike what can be found in flaring emission inventories, no increase in SO2 was detected, and an increase in CO is observed only during one of the two flights. Using FLEXPART (FLEXible PARTicle dispersion model) simulations with a regional NO2 satellite flaring inventory in forward-trajectory mode, our study reproduces the timing of the aircraft NO2 enhancements. Several sensitivity tests on the flux and the injection height are also performed, leading to the conclusion that a lower NO2 flux helps in better reproducing the measurements and that the modification of the injection height does not impact the results of the simulations significantly.

scholarly journals Identification of Potential Drought Areas in West Africa Under Climate Change and Variability

2019 ◽  
Vol 3 (3) ◽  
pp. 429-444 ◽  
Author(s):  
Gandome Mayeul L. D. Quenum ◽  
Nana A. B. Klutse ◽  
Diarra Dieng ◽  
Patrick Laux ◽  
Joël Arnault ◽  
...  
Keyword(s):  
West Africa ◽  
Climate Models ◽  
Potential Evapotranspiration ◽  
Standardized Precipitation Index ◽  
Global Climate Models ◽  
Spatiotemporal Pattern ◽  
Historical Period ◽  
Gulf Of Guinea ◽  
Precipitation Concentration ◽  
The Impact

Abstract The study investigates how the rising global temperature will affect the spatial pattern of rainfall and consequently drought in West Africa. The precipitation and potential evapotranspiration variables that are obtained from the Rossby Centre regional atmospheric model (RCA4) and driven by ten (10) global climate models under the RCP8.5 scenario were used. The model data were obtained from the Coordinated Regional Climate Downscaling Experiment (CORDEX) and analyzed at four specific global warming levels (GWLs) (i.e., 1.5 °C, 2.0 °C, 2.5 °C, and 3.0 °C) above the pre-industrial level. This study utilized four (4) indices: the standardized precipitation index, the precipitation concentration index, the precipitation concentration degree, and the precipitation concentration period over West Africa to explore the spatiotemporal variations in the characteristics of precipitation concentrations. Additionally, studying the impact of the four GWLs on consecutive dry days, consecutive wet days, and frequency of the intense rainfall events led to a better understanding of the spatiotemporal pattern of extreme precipitation. The results show that, at each GWL studied, the onset of rainfall comes 1 month earlier in the Gulf of Guinea compared to the historical period (1971–2000) with increasing rainfall intensity in the whole study domain, and the northeastern part of the study area becomes wetter. The rainfall concentration is uniformly distributed over the Gulf of Guinea and the Savanna zone for both the historical period and RCP8.5 scenario, while the Sahel zone which has shown an irregular concentration of rainfall for the historical period shows a uniform concentration of rainfall under all four GWLs.

scholarly journals Local air pollution from oil rig emissions observed during the airborne DACCIWA campaign

2019 ◽  
Author(s):  
Vanessa Brocchi ◽  
Gisèle Krysztofiak ◽  
Adrien Deroubaix ◽  
Greta Stratmann ◽  
Daniel Sauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
West Africa ◽  
Marine Boundary Layer ◽  
Emission Inventories ◽  
Gulf Of Guinea ◽  
Aerosol Chemistry ◽  
Oil Platforms ◽  
Sensitivity Tests ◽  
Local Air Pollution ◽  
Oil Rig

Abstract. In the framework of the European DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) project, the airborne study APSOWA (Atmospheric Pollution from Shipping and Oil platforms of West Africa) was conducted in July 2016 to study oil rig emissions off the Gulf of Guinea. Two flights in the marine boundary layer were focused on the floating production storage and offloading (FPSO) vessel operating off the coast of Ghana. Those flights present simultaneous sudden increases of NO2 and aerosols concentrations. Unlike what can be found in flaring emission inventories, no increase in SO2 was detected and an increase in CO is observed only during one of the two flights. Using FLEXPART simulations in forward trajectory mode, our study reproduced the timing of the aircraft NO2 enhancements. We used a regional NO2 satellite flaring inventory in the simulations, which showed an overall good estimate of flaring emission. Several sensitivity tests on the flux and the injection height were also performed to better reproduce the measurements.

scholarly journals Downward cloud venting of the central African biomass burning plume during the West Africa summer monsoon

2020 ◽  
Vol 20 (9) ◽  
pp. 5373-5390
Author(s):  
Alima Dajuma ◽  
Kehinde O. Ogunjobi ◽  
Heike Vogel ◽  
Peter Knippertz ◽  
Siélé Silué ◽  
...  
Keyword(s):  
West Africa ◽  
Biomass Burning ◽  
Large Scale ◽  
Robust Statistics ◽  
Vertical Mixing ◽  
Aerosol Deposition ◽  
Hadley Cell ◽  
Gulf Of Guinea ◽  
Model Simulations ◽  
Fire Emissions

Abstract. Between June and September large amounts of biomass burning aerosol are released into the atmosphere from agricultural fires in central and southern Africa. Recent studies have suggested that this plume is carried westward over the Atlantic Ocean at altitudes between 2 and 4 km and then northward with the monsoon flow at low levels to increase the atmospheric aerosol load over coastal cities in southern West Africa (SWA), thereby exacerbating air pollution problems. However, the processes by which these fire emissions are transported into the planetary boundary layer (PBL) are still unclear. One potential factor is the large-scale subsidence related to the southern branch of the monsoon Hadley cell over the tropical Atlantic. Here we use convection-permitting model simulations with COSMO-ART to investigate for the first time the contribution of downward mixing induced by clouds, a process we refer to as downward cloud venting in contrast to the more common process of upward transport from a polluted PBL. Based on a monthly climatology, model simulations compare satisfactory with wind fields from reanalysis data, cloud observations, and satellite-retrieved carbon monoxide (CO) mixing ratio. For a case study on 2 July 2016, modelled clouds and rainfall show overall good agreement with Spinning Enhanced Visible and InfraRed Imager (SEVIRI) cloud products and Global Precipitation Measurement Integrated Multi-satellitE Retrievals (GPM-IMERG) rainfall estimates. However, there is a tendency for the model to produce too much clouds and rainfall over the Gulf of Guinea. Using the CO dispersion as an indicator for the biomass burning plume, we identify individual mixing events south of the coast of Côte d'Ivoire due to midlevel convective clouds injecting parts of the biomass burning plume into the PBL. Idealized tracer experiments suggest that around 15 % of the CO mass from the 2–4 km layer is mixed below 1 km within 2 d over the Gulf of Guinea and that the magnitude of the cloud venting is modulated by the underlying sea surface temperatures. There is even stronger vertical mixing when the biomass burning plume reaches land due to daytime heating and a deeper PBL. In that case, the long-range-transported biomass burning plume is mixed with local anthropogenic emissions. Future work should provide more robust statistics on the downward cloud venting effect over the Gulf of Guinea and include aspects of aerosol deposition.

Squall Response Based Design of Floating Units in West Africa

2011 ◽  
Author(s):  
Juan Alvarez ◽  
Pierre Orsero ◽  
Valerie Quiniou-Ramus ◽  
Michel Franc¸ois ◽  
Anne-Gae¨lle Moysan ◽  
...  
Keyword(s):  
West Africa ◽  
Return Period ◽  
Relevant Information ◽  
Gulf Of Guinea ◽  
Mooring Lines ◽  
Design Procedures ◽  
Axial Tension ◽  
Classical Design ◽  
Extreme Responses ◽  
South Zone

Squalls are one of the main issues for the design of West Africa floating units mooring systems. At the present time and due to the lack of more relevant information and models, squalls are represented by on site time series of time varying wind speed and relative heading. The first FPSO units were designed on the basis of a reduced Squall database. Nowadays, the number of squall records has been significantly increased and a response based analysis can be carried out. The present paper is focused on the Gulf of Guinea environment. The area has been divided into two zones: North (Nigeria…) and South (Congo, Angola…). This approach enabled us to deal with 90 Squall events for North zone and 115 Squall events for South zone. Two different mooring systems, with quite different natural periods, have been investigated in order to cover the range of already installed spread moored FPSO’s. For every Squall of the database, time domain and modal simulations have been carried out in order to obtain the maximum values of the axial tension in mooring lines and of the offset of a standard spread moored unit. Then a statistical procedure is applied a) to estimate 100-year return period values for these parameters and b) to assess overall trends besides the differences between results from both zones and both mooring systems. A comparative study has also been carried out to relate the 100-year return period extrapolations with the values derived from classical design procedures in order to evaluate the potential design margins for extreme responses. Finally, areas needing further investigation are identified.

scholarly journals High Species Richness and Extremely Low Abundance of Cumacean Communities Along the Shelf and Slope of the Gulf of Guinea (West Africa)

2021 ◽  
Vol 8 ◽  
Author(s):  
Anna Stȩpień ◽  
Krzysztof Pabis ◽  
Robert Sobczyk ◽  
Bjorn Serigstad
Keyword(s):  
Species Richness ◽  
West Africa ◽  
Principal Component ◽  
Distribution Patterns ◽  
Sampling Effort ◽  
Gulf Of Guinea ◽  
Local Pollution ◽  
High Species Richness ◽  
Unique Species ◽  
Marine Basins

The Gulf of Guinea belongs to the most scarcely sampled marine basins in the oceans of the world. We have analyzed diversity and distribution patterns of cumacean communities on the shelf and slope, along the coast of Ghana. The material was collected in October and November of 2012 using a van Veen grab (0.1 m2) on nine transects. Six stations were located at each transect (25, 50, 100, 250, 500, and 1,000 m). Sixty-three species of Cumacea were recorded with Leucon and Eocuma as the most speciose genera, with 12 and eight species, respectively. Comparisons of species richness with literature data pointed that the Ghanaian coast hosts very diverse communities. About 95% of species were new to science, and the number of cumacean species known from the West Africa increased by over 100%. Nevertheless, most of the species had extremely low abundance, 13 singletons and 15 doubletons were found. Mean density of cumaceans was estimated at only 1.5 ind./0.1 m2. Species accumulation curve did not reach the asymptotic level, suggesting undersampling, despite the fact that sampling effort was high (250 samples). The highest species richness was recorded in the inner shelf (25–50 m) and on the slope (1,000 m). Cluster analysis separated shallow water communities from deeper regions on the shelf and upper slope. The most unique species composition was found at 1,000 m. Principal component analysis showed the importance of oxygen, sediments, and human-related disturbance for distribution of cumacean communities. In the shallows, oxygen content and presence of gravel were the most important factors structuring communities. In the deeper bottom areas (250–1,000 m), cumacean fauna was affected by local pollution, mainly by higher concentration of barium, other heavy metals, and THC.

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