Case Study of an Intense African Easterly Wave

2005 ◽  
Vol 133 (4) ◽  
pp. 752-766 ◽  
Author(s):  
Gareth J. Berry ◽  
Chris Thorncroft
Keyword(s):  
Life Cycle ◽  
North Africa ◽  
Multiple Scales ◽  
West African ◽  
Unstable State ◽  
The West ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
West African Coast ◽  
African Coast

The life cycle of an intense African easterly wave (AEW) over the African continent is examined using European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses, Meteosat satellite images, and synoptic observations. This system, the strongest AEW of 2000, can be tracked from central North Africa into the eastern Atlantic Ocean, where it is associated with the genesis of Hurricane Alberto. Synoptic analysis of the kinematic and thermodynamic fields is supplemented by analysis of potential vorticity (PV), allowing exploration at the role of multiple scales in the evolution of this AEW. The authors’ analysis promotes the division of the AEW life cycle into three distinctive phases. (i) Initiation: The AEW development is preceded by a large convective event composed of several mesoscale convective systems over elevated terrain in Sudan. This convection provides a forcing on the baroclinically and barotropically unstable state that exists over tropical North Africa. (ii) Baroclinic growth: A low-level warm anomaly, generated close to the initial convection, interacts with a midtropospheric strip of high PV that exists on the cyclonic shear side of the African easterly jet, which is consistent with baroclinic growth. This interaction is reinforced by the generation of subsynoptic-scale PV anomalies by deep convection that is embedded within the baroclinic AEW structure. (iii) West coast development: Near the West African coast, the baroclinic structure weakens, but convection is maintained. The midtropospheric PV anomalies embedded within the AEW merge with one another and with PV anomalies that are generated by convection over topography ahead of the system. These mergers result in the production of a significant PV feature that leaves the West African coast and rapidly undergoes tropical cyclogenesis.

Gerhard Rohlfs in Yorubaland

1994 ◽  
Vol 21 ◽  
pp. 251-268 ◽  
Author(s):  
Elisabeth de Veer ◽  
Ann O'Hear
Keyword(s):  
West Africa ◽  
North Africa ◽  
English Translation ◽  
West African ◽  
The West ◽  
West African Coast ◽  
African Coast ◽  
The Way

Gerhard Rohlfs was born in Vegesack near Bremen in 1831. He was a frequent traveler in Africa, and in 1865-67 he became the first European to travel from north Africa across the Sahara to the west African coast, from Tripoli to Borno, then through Bauchi and Keffi to Loko, thence down the Benue to its confluence with the Niger at Lokoja, which he reached on 28 March 1867. From there, he proceeded upstream along the Niger to Raba, delivering presents to Masaba of Nupe. From Raba, he traveled overland through Yorubaland to Lagos. In 1868 he published an account of the first half of this journey, from north Africa to Borno, in Petermann's Mitteilungen. In 1872 his account of the second half, “Gerhard Rohlfs' Reise durch Nord-Afrika vom Mittelländischen Meere bis zum Busen von Guinea, 1865 bis 1867, 2. Hälfte: von Kuka nach Lagos (Bornu, Bautschi, Saria, Nupe, Yoruba),” also appeared in Petermann's. A later publication, Quer durch Afrika, which appeared in 1874-75, covered the entire journey.Rohlfs' accounts of his travels in west Africa south of the Sahara have up to now been greatly neglected. The works mentioned above have never been published in English translation, which no doubt goes some way to explain this neglect. Rohlfs' information on his stay in Kuka (the capital of Borno) and his visits to Bauchi and Nupe have been cited by some scholars, at least. Very few, however, appear to have consulted his description of the last leg of his 1866-67 journey, in which he proceeded from the Niger south through Yorubaland to Lagos, visiting Share, Ilorin, Iwo, Ibadan, and parts of Ijebuland on the way.

Informed Consent: Ezenwa–Ohaeto between Past and Future Uses of Pidgin

Matatu ◽  
2006 ◽  
Vol 33 (1) ◽  
pp. 115-134 ◽  
Author(s):  
Chantal Zabus
Keyword(s):  
Informed Consent ◽  
First Language ◽  
West African ◽  
The Other ◽  
Wole Soyinka ◽  
The West ◽  
West African Coast ◽  
African Coast ◽  
The 1950S ◽  
The One

The essay shows how Ezenwa–Ohaeto's poetry in pidgin, particularly in his collection (1988), emblematizes a linguistic interface between, on the one hand, the pseudo-pidgin of Onitsha Market pamphleteers of the 1950s and 1960s (including in its gendered guise as in Cyprian Ekwensi) and, on the other, its quasicreolized form in contemporary news and television and radio dramas as well as a potential first language. While locating Nigerian Pidgin or EnPi in the wider context of the emergence of pidgins on the West African Coast, the essay also draws on examples from Joyce Cary, Frank Aig–Imoukhuede, Ogali A. Ogali, Ola Rotimi, Wole Soyinka, and Tunde Fatunde among others. It is not by default but out of choice and with their 'informed consent' that EnPi writers such as Ezenwa–Ohaeto contributed to the unfinished plot of the pidgin–creole continuum.

scholarly journals Trains of African Easterly Waves and Their Relationship to Tropical Cyclone Genesis in the Eastern Atlantic

2017 ◽  
Vol 145 (2) ◽  
pp. 599-616 ◽  
Author(s):  
Abdou L. Dieng ◽  
Saidou M. Sall ◽  
Laurence Eymard ◽  
Marion Leduc-Leballeur ◽  
Alban Lazar
Keyword(s):  
West African ◽  
Dynamical Structure ◽  
African Easterly Waves ◽  
The South ◽  
The West ◽  
Easterly Waves ◽  
West African Coast ◽  
African Coast ◽  
Tropical Depressions ◽  
The Relationship

In this study, the relationship between trains of African easterly waves (AEWs) and downstream tropical cyclogenesis is studied. Based on 19 summer seasons (July–September from 1990 to 2008) of ERA-Interim reanalysis fields and brightness temperature from the Cloud User Archive, the signature of AEW troughs and embedded convection are tracked from the West African coast to the central Atlantic. The tracked systems are separated into four groups: (i) systems originating from the north zone of the midtropospheric African easterly jet (AEJ), (ii) those coming from the south part of AEJ, (iii) systems that are associated with a downstream trough located around 2000 km westward (termed DUO systems), and (iv) those that are not associated with such a close downstream trough (termed SOLO systems). By monitoring the embedded 700-hPa-filtered relative vorticity and 850-hPa wind convergence anomaly associated with these families along their trajectories, it is shown that the DUO generally have stronger dynamical structure and statistically have a longer lifetime than the SOLO ones. It is suggested that the differences between them may be due to the presence of the previous intense downstream trough in DUO cases, enhancing the low-level convergence behind them. Moreover, a study of the relationship between system trajectories and tropical depressions occurring between the West African coast and 40°W showed that 90% of tropical depressions are identifiable from the West African coast in tracked systems, mostly in the DUO cases originating from the south zone of the AEJ.

A New Lautoconus Species Radiation from Gambia, West Africa

The Festivus ◽  
2018 ◽  
Vol 50 (3) ◽  
pp. 164-172
Author(s):  
Edward Petuch ◽  
David Berschauer
Keyword(s):  
New Species ◽  
West Africa ◽  
River Mouth ◽  
Sympatric Species ◽  
West African ◽  
The West ◽  
Species Radiation ◽  
West African Coast ◽  
African Coast ◽  
Reef Fauna

Six sympatric species of the cone shell genus Lautoconus Monterosato, 1923 have been discovered on an isolated rock reef near the Gambia River Mouth, Gambia, West Africa. Of these, four were found to be new to science and, together, they represent a previously unknown Gambian endemic species radiation. These include: Lautoconus fernandi new species, L. gambiensis new species, L. rikae new species, and L. wolof new species. The poorly-known Gambian endemic cone, Lautoconus orri (Ninomiya and da Motta, 1982) was also found to be a component of the rock reef fauna, as was the wide-ranging L. guinaicus (Hwass, 1792) (Senegal to Ghana). The Gambian cluster of sibling species represents the farthest-south separate radiation of Lautoconus known from the West African coast.

scholarly journals DESIGN AND REALIZATION OF A SANDBAR BREAKWATER, LEKKI, NIGERIA

2020 ◽  
pp. 7
Author(s):  
Bart-Jan van der Spek ◽  
Bas van de Sande ◽  
Eelco Bijl ◽  
Cypriaan Hendrikse ◽  
Sanne Poortman ◽  
...  
Keyword(s):  
Construction Material ◽  
West African ◽  
Gulf Of Guinea ◽  
Construction Time ◽  
The West ◽  
West African Coast ◽  
African Coast ◽  
Coastal Retreat ◽  
Natural Dynamics ◽  
Port Infrastructure

The nature-based concept of the Sandbar Breakwater was born based on the typical natural dynamics of the West African coast (Gulf of Guinea). Learning from the development and coastal impact of the existing port infrastructure in West Africa, the application of sand as a construction material for marine infrastructure seemed very obvious. Along this coast, ports experience heavy sedimentation at the western updrift side of the breakwaters, leading to the rapid burying of valuable armour rock. The Sandbar Breakwater concept is based on this principle by using natural accretion as the basis for the port protection. Such a concept is advantageous as a large sediment drift naturally supplements the sand lling works during construction and the required rock volumes are reduced signicantly, saving construction time and minimising the environmental impact. To counteract the downdrift coastal retreat, a replenishable sand engine completes the scheme. The realisation of a Sandbar Breakwater at Lekki, Nigeria, in 2018, with subsequent safe and continuous port operations, proves the feasibility of the concept. Sustainable future development is further pursued by integrated maintenance campaigns following the Building with Nature principles to guarantee the operability of the port while preserving the alongshore sediment balance and minimising the environmental impact.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/-1wCqqB9f8E

scholarly journals High-resolution measurements of atmospheric molecular hydrogen and its isotopic composition at the West African coast of Mauritania

2012 ◽  
Vol 9 (12) ◽  
pp. 18799-18829
Author(s):  
S. Walter ◽  
A. Kock ◽  
T. Röckmann
Keyword(s):  
High Resolution ◽  
Isotopic Composition ◽  
Molecular Hydrogen ◽  
H2 Production ◽  
West African ◽  
Mixing Ratio ◽  
The West ◽  
Isotopic Signatures ◽  
West African Coast ◽  
African Coast

Abstract. Oceans are a net source of molecular hydrogen (N2) to the atmosphere, where nitrogen (N2) fixation is assumed to be the main biological production pathway besides photochemical production from organic material. The sources can be distinguished using isotope measurements because of clearly differing isotopic signatures of the produced hydrogen. Here we present the first ship-borne measurements of atmospheric molecular H2 mixing ratio and isotopic composition at the West African coast of Mauritania (16–25° W, 17–24° N). This area is one of the biologically most active regions of the world's oceans with seasonal upwelling events and characterized by strongly differing hydrographical/biological properties and phytoplankton community structures. The aim of this study was to identify areas of H2 production and distinguish H2 sources by isotopic signatures of atmospheric H2. Besides this a diurnal cycle of atmospheric H2 was investigated. For this more than 100 air samples were taken during two cruises in February 2007 and 2008, respectively. During both cruises a transect from the Cape Verde Island towards the Mauritanian Coast was sampled. In 2007 additionally four days were sampled with a high resolution of one sample per hour. Our results clearly indicate the influence of local sources and suggest the Banc d'Arguin as a pool for precursors for photochemical H2 production, whereas N2 fixation could not be identified as a H2 source during these two cruises. With our experimental setup we could demonstrate that variability in diurnal cycles is probably influenced and biased by released precursors for photochemical H2 production and the origin of air masses. This means for further investigations that just measuring the mixing ratio of H2 is insufficient to explain the variability of a diurnal cycle and support is needed, e.g. by isotopic measurements. However, measurements of H2 mixing ratios, which are easy to conduct online during ship cruises could be a helpful tool to easily identify production areas of biological precursors such as VOC's for further investigations.

The Dahomean Middleman System, 1727–c. 1818

1987 ◽  
Vol 28 (3) ◽  
pp. 357-375 ◽  
Author(s):  
David Ross
Keyword(s):  
Nineteenth Century ◽  
Eighteenth Century ◽  
West African ◽  
The West ◽  
Large Numbers ◽  
Supply Problem ◽  
West African Coast ◽  
African Coast ◽  
Trading Partners

During the first quarter of the eighteenth century, European merchants bought more slaves in the Bight of Benin than on any other part of the West African coast. From c. 1720 until 1727 much of their buying was concentrated in Savi, the capital of a small Aja state called Whydah. When the Dahomeans overran Savi in 1727 they stopped the inland slave suppliers from travelling to the coast, prevented the local Hueda from going inland to collect slaves, and insisted that the Europeans bought slaves only from Dahomean dealers. In an attempt to make sure that the Europeans had nothing more to do with their former trading partners the Dahomeans burned the factories in Savi and forced their European occupants to retire to Grehue, Savi's port, a spot on the coast where the Europeans maintained a number of fortified warehouses.The middleman policy did not at first operate satisfactorily. There were two reasons for this. The first was that the Dahomeans were, in practice, unable to prevent the Europeans from continuing to trade with the Hueda. The second was that the inland suppliers refused to sell slaves to Savi's conquerors. The Dahomeans solved their ‘coastal’ problem in the 1740S by placing a garrison in Grehue. This garrison kept the exiled Hueda at bay and held the Europeans in what amounted to open captivity. The Dahomeans were never able completely to solve their ‘supply’ problem. In the 1730s and 1740S the inland merchants took their slaves to ports which opened up on the Bight to the east of Grehue. Only in the 1750s and 1760s did they channel substantial numbers of slaves through Dahomey. In the last decades of the century they again boycotted the Dahomean market. Dahomey therefore prospered as a middleman state only between c. 1748 and c. 1770.An examination of their eighteenth century trading suggests that the Dahomeans were a slave-raiding community whose members realised in 1727 that they would soon run out of fresh raiding grounds. They appear to have introduced their middleman policy in an attempt to ensure that they would continue to profit from slave trading even after they had ceased to be able to take large numbers of captives themselves. Although the policy was by no means a complete success, it was important in that it seems to have led the Dahomeans to begin placing garrisons in the territories they ravaged. It appears, in fact, to have been the pursuit of their middleman goals that led them to begin creating the often described nineteenth century ‘greater’ Dahomean state. The middleman programme ceased to be of much importance after c. 1818, when the fall of Oyo enabled the Dahomeans to resume raiding widely in unexploited territory.

The Royal Navy and West Africa, 1843-1857

2008 ◽  
pp. 133-168
Author(s):  
Mark C. Hunter
Keyword(s):  
West Africa ◽  
Free Trade ◽  
West African ◽  
Economic Interest ◽  
Royal Navy ◽  
The West ◽  
The North ◽  
West African Coast ◽  
African Coast ◽  
American Diplomacy

This chapter analyses the British naval policies concerning West Africa between 1843 and 1857. During this period, Britain sought to encourage legitimate commerce and curtail slavery for its own economic interest, while domestically America feared the British domination of the West African coast. As such, suspicion and mistrust was rife between the two nations, and is in great detail via the abolitionist activity in the North of England; the actions of free traders and slavers; Royal Navy operations; the competition for trade between Britain and France; Commodore Charles Hotham’s slavery suppressing naval strategy; British free trade treaties; and the naval methods of enforcing British goals. It concludes in 1857, with British interests torn between strategic naval aims and domestic pressures, and British and American diplomacy still tense over West African policies.

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