Convection in an African Easterly Wave over West Africa and the eastern Atlantic: A model case study of Helene (2006)

2010 ◽  
Vol 136 (S1) ◽  
pp. 364-396 ◽  
Author(s):  
Juliane Schwendike ◽  
Sarah C. Jones
Keyword(s):  
West Africa ◽  
Model Case ◽  
African Easterly Wave ◽  
Easterly Wave

scholarly journals Case Study of a Developing African Easterly Wave during NAMMA: An Energetic Point of View

2009 ◽  
Vol 66 (10) ◽  
pp. 2991-3020 ◽  
Author(s):  
Joël Arnault ◽  
Frank Roux
Keyword(s):  
West Africa ◽  
Point Of View ◽  
Finite Domain ◽  
African Easterly Wave ◽  
Easterly Wave ◽  
Multidisciplinary Analysis ◽  
Energy Cycle ◽  
Convective Scale ◽  
Energetic Point ◽  
Energy Equations

Abstract The West African perturbation that subsequently evolved into Hurricane Helene (2006) during NASA’s African Monsoon Multidisciplinary Analysis (NAMMA), 15 August–14 September 2006, and AMMA’s third special observing period (SOP-3), 15–29 September 2006, has been simulated with the nonhydrostatic Méso-NH model using parameterized convection. The simulated disturbance evolved over West Africa and the adjacent eastern tropical Atlantic through interactions between different processes at the convective scale, mesoscale, and synoptic scale. The aim of this paper is to quantify the energetics of the simulated disturbance. A set of energy equations is first developed in the hydrostatic case to solve the limitations of Lorenz’s analysis when applied to a finite domain. It is shown that this approach is also valid in the compressible and in the anelastic case in order to apply it to the Méso-NH results. Application to the simulated pre-Helene disturbance allows one to determine the most important terms in these equations. These simplifications are taken into account to derive an energy cycle including barotropic and baroclinic conversions of eddy kinetic energy. The development of the simulated system was found to result from barotropic–baroclinic growth over West Africa and barotropic growth over the tropical eastern Atlantic. It is suggested that most of these energy conversions were the result of an adjustment of the wind field in response to the pressure decrease, presumably caused by convective activity.

scholarly journals Atlantic Tropical Cyclogenesis: A Three-Way Interaction between an African Easterly Wave, Diurnally Varying Convection, and a Convectively Coupled Atmospheric Kelvin Wave

2012 ◽  
Vol 140 (4) ◽  
pp. 1108-1124 ◽  
Author(s):  
Michael J. Ventrice ◽  
Christopher D. Thorncroft ◽  
Matthew A. Janiga
Keyword(s):  
West Africa ◽  
Diurnal Cycle ◽  
Deep Convection ◽  
Active Phase ◽  
Boreal Summer ◽  
Tropical Cyclogenesis ◽  
Tropical Atlantic ◽  
Kelvin Wave ◽  
African Easterly Wave ◽  
Easterly Wave

This paper explores a three-way interaction between an African easterly wave (AEW), the diurnal cycle of convection over the Guinea Highlands (GHs), and a convectively coupled atmospheric equatorial Kelvin wave (CCKW). These interactions resulted in the genesis of Tropical Storm Debby over the eastern tropical Atlantic during late August 2006. The diurnal cycle of convection downstream of the GHs during the month of August is explored. Convection associated with the coherent diurnal cycle is observed off the coast of West Africa during the morning. Later, convection initiates over and downstream of the GHs during the afternoon. These convective features were pronounced during the passage of the pre-Debby AEW. The superposition between the convectively active phase of a strong CCKW and the pre-Debby AEW occurred shortly after merging with the diurnally varying convection downstream of the GHs. The CCKW–AEW interaction preceded tropical cyclogenesis by 18 h. The CCKW provided a favorable environment for deep convection. An analysis of high-amplitude CCKWs over the tropical Atlantic and West Africa during the Northern Hemisphere boreal summer (1979–2009) highlights a robust relationship between CCKWs and the frequency of tropical cyclogenesis. Tropical cyclogenesis is found to be less frequent immediately prior to the passage of the convectively active phase of the CCKW, more frequent during the passage, and most frequent just after the passage.

Characteristics of an African Easterly Wave Observed during NAMMA

2010 ◽  
Vol 67 (1) ◽  
pp. 3-25 ◽  
Author(s):  
Robert Cifelli ◽  
Timothy Lang ◽  
Steven A. Rutledge ◽  
Nick Guy ◽  
Edward J. Zipser ◽  
...  
Keyword(s):  
West Africa ◽  
Deep Convection ◽  
Extended Period ◽  
Appreciable Change ◽  
Low Level ◽  
Convective Systems ◽  
African Easterly Wave ◽  
Wave Trough ◽  
Easterly Wave ◽  
Mesoscale Convective

Abstract The evolution of an African easterly wave is described using ground-based radar and ancillary datasets from three locations in West Africa: Niamey, Niger (continental), Dakar, Senegal (coastal), and Praia, Republic of Cape Verde (oceanic). The data were collected during the combined African Monsoon Multidisciplinary Analyses (AMMA) and NASA AMMA (NAMMA) campaigns in August–September 2006. Two precipitation events originated within the wave circulation and propagated with the wave across West Africa. Mesoscale convective systems (MCSs) associated with these events were identified at all three sites ahead of, within, and behind the 700-mb wave trough. An additional propagating event was indentified that originated east of the wave and moved through the wave circulation. The MCS activity associated with this event did not show any appreciable change resulting from its interaction with the wave. The MCS characteristics at each site were different, likely due to a combination of life cycle effects and changes in relative phasing between the propagating systems and the position of low-level convergence and thermodynamic instability associated with the wave. At the ocean and coastal sites, the most intense convection occurred ahead of the wave trough where both high CAPE and low-level convergence were concentrated. At the continental site, convection was relatively weak owing to the fact that the wave dynamics and thermodynamics were not in sync when the systems passed through Niamey. The only apparent effect of the wave on MCS activity at the continental site was to extend the period of precipitation activity during one of the events that passed through coincident with the 700-mb wave trough. Convective organization at the land sites was primarily in the form of squall lines and linear MCSs oriented perpendicular to the low-level shear. The organization at the oceanic site was more complicated, transitioning from linear MCSs to widespread stratiform cloud with embedded convection. The precipitation activity was also much longer lived at the oceanic site due to the wave becoming nearly stationary near the Cape Verdes, providing an environment supportive of deep convection for an extended period.

scholarly journals An Analysis of the Environments of Intense Convective Systems in West Africa in 2003

2010 ◽  
Vol 138 (10) ◽  
pp. 3721-3739 ◽  
Author(s):  
Stephen D. Nicholls ◽  
Karen I. Mohr
Keyword(s):  
West Africa ◽  
Regional Scale ◽  
Convective Available Potential Energy ◽  
Potential Temperature ◽  
Saharan Dust ◽  
Convective System ◽  
Low Level ◽  
Convective Systems ◽  
African Easterly Wave ◽  
Easterly Wave

Abstract The local- and regional-scale environments associated with intense convective systems in West Africa during 2003 were diagnosed from soundings, operational analysis, and space-based datasets. Convective system cases were identified from the Tropical Rainfall Measuring Mission (TRMM) microwave imagery and classified by the system minimum 85-GHz brightness temperature and the estimated elapsed time of propagation from terrain greater than 500 m. The speed of the midlevel jet, the magnitude of the low-level shear, and the surface equivalent potential temperature θe were greater for the intense cases compared to the nonintense cases, although the differences between the means tended to be small: less than 3 K for surface θe and less than 2 × 10−3 s−1 for low-level wind shear. Hypothesis testing of a series of commonly used intensity prediction metrics resulted in significant results only for low-level metrics such as convective available potential energy and not for any of the mid- or upper-level metrics such as the 700-hPa θe. None of the environmental variables or intensity metrics by themselves or in combination appeared to be reliable direct predictors of intensity. In the regional-scale analysis, the majority of intense convective systems occurred in the surface baroclinic zone where surface θe exceeded 344 K and the 700-hPa zonal wind speeds were less than −6 m s−1. Fewer intense cases compared to nonintense cases were associated with African easterly wave troughs. Fewer than 25% of these cases occurred in environments with detectable Saharan dust loads, and the results for intense and nonintense cases were similar. Although the discrimination between the intense and nonintense environments was narrow, the results were robust and consistent with the seasonal movement of the West African monsoon, regional differences in topography, and African easterly wave energetics.

Improving food value chains for cereal doughs in West Africa: case study of mawè in Benin

Food Chain ◽  
2019 ◽  
Vol 8 (1) ◽  
pp. 18-38 ◽  
Author(s):  
Marcel Houngbédji ◽  
Sègla Wilfrid Padonou ◽  
Ana Maria d’Auchamp ◽  
Noël Akissoé ◽  
Moses Dachariga Mengu ◽  
...  
Keyword(s):  
West Africa ◽  
Value Chains ◽  
Food Value

The Influence of Wharfs on School Children: A Case Study of Portee Wharf in Freetown, Sierra Leone

2019 ◽  
Vol 2 (3) ◽  
pp. 128-140
Author(s):  
Alhaji Bakar Kamara
Keyword(s):  
West Africa ◽  
Sierra Leone ◽  
School Children ◽  
Research Area ◽  
Background Information ◽  
Control Problems

The focus of this research is to investigate the influence of wharfs on school children. Therefore it will report the findings of the result on the influences of wharfs on school children with specific case on Portee Wharf in Freetown, Sierra Leone in West Africa. In this regard, the introduction describes the research area, stating the statement of the problem, the overall goal and specific objectives that will be attained in this study, justification for selecting the topic, problems to be encountered during the course of carrying out this research and major influences. Besides, an indication of the methods used to investigate the topic will also be highlighted. Moreover, the studies will analyze the actual responses of the respondents of the activities of the wharf on school-going children. It will address the questionnaire in accordance with the following: Background information of respondents, this investigated areas such as sex, age, religion, occupation and tribe; It enquires about the activities of the wharfs, reasons and consequences of children engaged in wharfs and strategies to control problems that may emanate from the wharf. The paper will show the findings, gives the summary, conclusion and recommendations of problems identified while carrying out the research.

scholarly journals Enhancing Satellite Oceanography-Driven Research in West Africa: a Case Study of Capacity Development in an Underserved Region

2021 ◽  
Author(s):  
Ebenezer S. Nyadjro ◽  
Brian K. Arbic ◽  
Christian E. Buckingham ◽  
Paige E. Martin ◽  
Edem Mahu ◽  
...  
Keyword(s):  
West Africa ◽  
Capacity Development
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