The West African Monsoon Dynamics. Part II: The “Preonset” and “Onset” of the Summer Monsoon

Sultan, Benjamin; Janicot, Serge

doi:10.1175/1520-0442(2003)016<3407:twamdp>2.0.co;2

Cited by 485 publications

(540 citation statements)

References 24 publications

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“…In this work, it is used on daily CAPE time series over West Africa for the period 1979-2009 in order to evaluate the seasonality of the variance of the synoptic time scale and of the related AEW signal. Previous studies have shown that dominant modes of monsoon synoptic variability are characterized by strong and reproducible 3-5 day oscillations (Sultan and Janicot, 2003). Hence, CAPE spectra are calculated on each individual June-September period using wavelet analysis method.…”

Section: Methodsmentioning

confidence: 99%

Climatology of convective available potential energy (CAPE) inERA‐Interim reanalysis over West Africa

Meukaleuni

Lenouo

Monkam

2015

Atmospheric Science Letters

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Section: Methodsmentioning

confidence: 99%

Climatology of convective available potential energy (CAPE) inERA‐Interim reanalysis over West Africa

Meukaleuni

Lenouo

Monkam

2015

Atmospheric Science Letters

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“…This underestimation may be partly explained by the fact that July 2006 was particularly dry with respect to the climatological conditions as the monsoon onset (i.e. the occurrence of rainfall) over the Sahel occurred nearly 2 weeks after its climatological average (24 June ±8 days: Sultan and Janicot, 2003;Janicot et al, 2008). The vegetation cover and soil moisture were reduced in 2006 relative to the climatological mean, which was favourable for dust source activation.…”

Section: Evaluation Of the Simulated Dust Distributionmentioning

confidence: 99%

Dust impact on the West African heat low in summertime

Lavaysse

Chaboureau

Flamant

2011

Quart J Royal Meteoro Soc

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) is investigated, with convective rainfall and dust bursts being observed over the Sahel at the beginning and end of the episode. Three Meso-NH simulations were designed which differed in their dust representation. All the simulations capture the variation in the WAHL intensity well, including the simulation without any dust effects. This shows the primary role of largescale forcing on the WAHL pulsation. In spite of additional daytime heating and night-time cooling effects over the Sahara, the simulation with dust climatology resembles the simulation without any dust effects. In contrast, the simulation using a prognostic dust scheme enhances alternating northward advection of warm and dry air and southward advection of cold and wet air associated with the propagation of an African easterly wave, leading to a strengthening of the WAHL variabilities. This study highlights two effects of dust on the WAHL over the Sahara: a so-called direct effect associated with dust radiative heating, which increases the WAHL thickness, and a so-called indirect effect that intensifies both the African easterly jet and a related African easterly wave.

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“…Janicot et al (2008) give an overview of the summer monsoon conditions during the AMMA SOP in 2006. The 2006 season was relatively unusual as the dynamical monsoon onset was in line with climatology but the convective monsoon onset (defined by the first rains in the north and the shift in convection patterns; Sultan and Janicot, 2003) was a month later. There was therefore a dry period after the wind shift had initiated the monsoon circulation.…”

Section: Introductionmentioning

confidence: 99%

Anatomy of an observed African easterly wave in July 2006

Bain

Parker

Dixon

et al. 2011

Quart J Royal Meteoro Soc

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The detailed structure of an African easterly wave (AEW) observed during the AMMA field campaign is analysed. The wave was present from 25 to 29 July 2006. A complex circulation pattern was observed: the overall structure of convection and the positive vorticity of the trough region had an elongated inverted-V appearance, wrapped around an area of low winds and clear skies. Satellite imagery showed that the AEW was a significant influence on the modulation of convection on the large scale.The wave was identified initially through its strong signature on soil moisture and convection. The AEW structure observed was not anticipated and has not been discussed in previous literature. In addition, wave tracking using a Hovmöller diagram of meridional winds did not detect the wave, and a Hovmöller of vorticity showed the wave moved at a slower speed than other AEWs in July.New schematics explaining the structure are presented, describing the case as observed by satellites and analysed by a limited-area version of the Met Office Unified Model. It is proposed that the positive vorticity branches of the inverted-V can be regarded as analogous to atmospheric fronts, with characteristic gradients in winds and thermodynamic properties, acting as locations for enhanced convection. The implications of the new case are discussed in relation to previous theory and it is suggested that the accepted model of an idealised AEW is incomplete and should be extended to include more complex structures.

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The West African Monsoon Dynamics. Part II: The “Preonset” and “Onset” of the Summer Monsoon

Cited by 485 publications

References 24 publications

Climatology of convective available potential energy (CAPE) inERA‐Interim reanalysis over West Africa

Climatology of convective available potential energy (CAPE) inERA‐Interim reanalysis over West Africa

Dust impact on the West African heat low in summertime

Anatomy of an observed African easterly wave in July 2006

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