scholarly journals Structure and dynamics of the Saharan atmospheric boundary layer during the West African monsoon onset: observations and analyses from the research flights of 14 and 17 July 2006

2009 ◽  
Vol 136 (S1) ◽  
pp. 107-124 ◽  
Author(s):  
Christophe Messager ◽  
Douglas J. Parker ◽  
O. Reitebuch ◽  
A. Agusti-Panareda ◽  
Christopher M. Taylor ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
West African Monsoon ◽  
Monsoon Onset ◽  
West African ◽  
The West ◽  
African Monsoon ◽  
Structure And Dynamics

scholarly journals Characterization of the Diurnal Cycle of the West African Monsoon around the Monsoon Onset

2007 ◽  
Vol 20 (15) ◽  
pp. 4014-4032 ◽  
Author(s):  
Benjamin Sultan ◽  
Serge Janicot ◽  
Philippe Drobinski
Keyword(s):  
Diurnal Cycle ◽  
Deep Convection ◽  
West African Monsoon ◽  
Monsoon Onset ◽  
West African ◽  
Onset Date ◽  
The West ◽  
African Monsoon ◽  
Nocturnal Jet ◽  
Heat Low

Abstract This study investigates the diurnal cycle of the West African monsoon and its seasonal modulation with particular focus on the monsoon onset period. A composite analysis around the monsoon onset date is applied to the 1979–2000 NCEP–DOE reanalysis and 40-yr ECMWF Re-Analysis (ERA-40) at 0000, 0600, 1200, and 1800 UTC. This study points out two independent modes describing the space–time variability of the diurnal cycle of low-level wind and temperature. While the first mode appears to belong to a gradual and seasonal pattern linked with the northward migration of the whole monsoon system, the second mode is characterized by more rapid time variations with a peak of both temperature and wind anomalies around the monsoon onset date. This latter mode is connected with the time pattern of a nocturnal jet reaching its highest values around the onset date. The diurnal cycle of dry and deep convection is also investigated through the same method. A distinct diurnal cycle of deep convection in the ITCZ is evidenced with a peak at 1200 UTC before the monsoon onset, and at 1800 UTC after the monsoon onset. Strong ascending motions associated with deep convection may generate a gravity wave that propagates northward and reaches the Saharan heat low region 12 h later. The diurnal cycle of the dry convection in the Saharan heat low is similar during the preonset and the postonset periods with a peak at night (0000 UTC) consistent with the nocturnal jet intensification. This convection is localized at 15° and 20°N before and after the monsoon onset, respectively. Both during the first rainy season in spring and the monsoon season in summer, the nocturnal jet brings moisture in the boundary layer north of the ITCZ favoring humidification and initiation of new convective cells, helping the northward progression of the ITCZ. At the end of the summer the southward return of the ITCZ is associated with the disappearance of the core of the monsoon jet. Despite a lot of similarities between the results obtained using NCEP–DOE and ERA-40 reanalyses, giving confidence in the significance of these results, some differences are identified, especially in the diurnal cycle of deep convection, which limit the interpretation of some of these results and highlight discrepancies in the reanalyses.

The role of the Indian monsoon onset in the West African monsoon onset: observations and AGCM nudged simulations

2011 ◽  
Vol 38 (5-6) ◽  
pp. 965-983 ◽  
Author(s):  
Emmanouil Flaounas ◽  
Serge Janicot ◽  
Sophie Bastin ◽  
Rémy Roca ◽  
Elsa Mohino
Keyword(s):  
Indian Monsoon ◽  
West African Monsoon ◽  
Monsoon Onset ◽  
West African ◽  
The West ◽  
African Monsoon

The diurnal cycle of lower boundary-layer wind in the West African monsoon

2009 ◽  
Vol 136 (S1) ◽  
pp. 66-76 ◽  
Author(s):  
Kassimou Abdou ◽  
Douglas J. Parker ◽  
Barbara Brooks ◽  
Norbert Kalthoff ◽  
Thierry Lebel
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Lower Boundary ◽  
West African Monsoon ◽  
West African ◽  
The West ◽  
African Monsoon ◽  
Lower Boundary Layer

scholarly journals Impact of Boundary-Layer Processes on Near-Surface Turbulence Within the West African Monsoon

2010 ◽  
Vol 136 (1) ◽  
pp. 1-23 ◽  
Author(s):  
Fabienne Lohou ◽  
Frédérique Saïd ◽  
Marie Lothon ◽  
Pierre Durand ◽  
Dominique Serça
Keyword(s):  
Boundary Layer ◽  
West African Monsoon ◽  
West African ◽  
The West ◽  
Near Surface ◽  
African Monsoon ◽  
Boundary Layer Processes ◽  
Surface Turbulence

scholarly journals The West African Monsoon Onset: A Concise Comparison of Definitions

2015 ◽  
Vol 28 (22) ◽  
pp. 8673-8694 ◽  
Author(s):  
Rory G. J. Fitzpatrick ◽  
Caroline L. Bain ◽  
Peter Knippertz ◽  
John H. Marsham ◽  
Douglas J. Parker
Keyword(s):  
West African Monsoon ◽  
Monsoon Onset ◽  
West African ◽  
Seasonal Forecasting ◽  
The West ◽  
African Monsoon ◽  
Multiple Datasets ◽  
Monsoon Winds ◽  
Work Done ◽  
Selection Of

Abstract The onset of the West African monsoon (WAM) marks a vital time for local and regional stakeholders. While the seasonal progression of monsoon winds and the related migration of precipitation from the Guinea Coast toward the Sudan/Sahel is apparent, there exist contrasting man-made definitions of what the WAM onset means. Broadly speaking, onset can be analyzed regionally, locally, or over a designated intermediate scale. There are at least 18 distinct definitions of the WAM onset in publication, with little work done on comparing observed onset from different definitions or comparing onset realizations across different datasets and resolutions. Here, nine definitions have been calculated using multiple datasets of different metrics at different resolutions. It is found that mean regional onset dates are consistent across multiple datasets and different definitions. There is low interannual variability in regional onset, suggesting that regional seasonal forecasting of the onset provides few benefits over climatology. In contrast, local onsets show high spatial, interannual, and interdefinition variability. Furthermore, it is found that there is little correlation between local onset dates and regional onset dates across West Africa, implying a disharmony between regional measures of onset and the experience on a local scale. The results of this study show that evaluation of seasonal monsoon onset forecasts is far from straightforward. Given a seasonal forecasting model, it is possible to simultaneously have a good and a bad prediction of monsoon onset simply through selection of the onset definition and observational dataset used for comparison.

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