The Structure and Properties of African Wave Disturbances as Observed During Phase III of GATE

Reed, Richard J.; Norquist, Donald C.; Recker, Ernest E.

doi:10.1175/1520-0493(1977)105<0317:tsapoa>2.0.co;2

Cited by 487 publications

(422 citation statements)

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“…The zonal distributions of northern (ConNE, ConNW, Cos, MarN) and southern (ConSE, ConSW, MarS) regions correspond to two commonly identified AEW latitude tracks (Reed et al, 1977;Nitta et al, 1985;Diedhiou et al, 1999;Pytharoulis and Thorncroft, 1999;Thorncroft and Hodges, 2001;Fink and Reiner, 2003). The ConNE, Cos and MarN regions were contrasted for zonal variations and were chosen to correspond to ground-based radar locations used in Guy et al (2011).…”

Section: Methodsmentioning

confidence: 67%

“…As mentioned previously, MCSs often travel faster than AEWs, and therefore life-cycle characteristics could be aliased to wave regimes other than the formative and decay stages. Despite this limitation, occurrence frequency results were consistent with previous studies (most of which concentrated on genesis/lysis of MCS with respect to AEW phase) that have found that deep convection occurs east of AEW troughs near the continental sites and west of and in the trough near the coast and Atlantic (Carlson, 1969;Payne and McGarry, 1977;Reed et al, 1977;Diedhiou et al, 1999;Fink et al, 2006;Kiladis et al, 2006;Laing et al, 2008). Fink and Reiner (2003) and Laing et al (2008), primarily using microwave and infrared observations for squall line and deep convective tracking, respectively, found a large fraction of systems were not associated with any AEW phase.…”

Section: Precipitation Feature Characteristicsmentioning

confidence: 99%

“…The wave disturbances, which may be initiated east of 20 • E (Berry et al, 2005;Thorncroft et al, 2008), are maximized near the AEJ level and progress westward at ∼ 8 m s −1 , with a wavelength of 2000-4000 km. Deep convection has been observed behind AEW troughs inland and in the eastern Atlantic and ahead of and within AEW troughs near the coast (Payne and McGarry, 1977;Reed et al, 1977;Duvel, 1990;Machado et al, 1993;Diedhiou et al, 1999;Kiladis et al, 2006). Westward-propagating MCSs in West Africa often move faster than AEW troughs (Aspliden et al, 1976;Fortune, 1980;Fink et al, 2006), and interact with the larger-scale environment through the transport of momentum (Moncrieff, 1992) and moisture (Lafore et al, 1988) and can reinforce cyclonic rotation when embedded in an AEW trough (Barthe et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

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Regional comparison of West African convective characteristics: a TRMM‐based climatology

Guy

Rutledge

2011

Quart J Royal Meteoro Soc

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A 13-year (1998-2010) climatology of mesoscale convective characteristics associated with the West African monsoon are investigated using precipitation radar and passive microwave data from the NASA Tropical Rainfall Measuring Mission satellite. Seven regions defined as continental northeast and northwest, southeast and southwest, coastal, and maritime north and south are compared to analyse zonal and meridional differences. Data are categorized according to identified African easterly wave (AEW) phase and when no wave is present. While some enhancements are observed in association with AEW regimes, regional differences were generally more apparent than wave vs. no-wave differences. Convective intensity metrics confirm that land-based systems exhibit stronger characteristics, such as higher storm top and maximum 30 dBZ heights and significant 85 GHz brightness temperature depressions. Continental systems also contain a lower fraction of points identified as stratiform. Results suggest that precipitation processes also varied depending upon region and AEW regime, with warm-rain processes more apparent over the ocean and the southwest continental region and ice-based microphysics more dominant over land, including mixed-phase processes. AEW regimes did show variability in stratiform fraction and ice and liquid water content, suggesting modulation of mesoscale characteristics possibly through feedback with the synoptic environment.

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Section: Methodsmentioning

confidence: 67%

Section: Precipitation Feature Characteristicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Regional comparison of West African convective characteristics: a TRMM‐based climatology

Guy

Rutledge

2011

Quart J Royal Meteoro Soc

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“…Significant EKE values also appear around 200 mb. This is likely to be associated with the penetration of the deep vertical diabatic heating in the ITCZ into the upper troposphere as observed by Burpee (1974) and Reed et al (1977) and obtained in the regional climate model of Hseih and Cook (2007).…”

Section: The Moist Life Cyclementioning

confidence: 99%

“…Many of these were used for composite analyses (e.g. Reed et al, 1977) but the smoothed-out structures gave only poor information on the evolving AEW structures, with only a few case-studies which could be used to diagnose the scale interactions (e.g. Carlson, 1969;Burpee, 1974;Karyampudi and Carlson, 1988;Ross, 1991).…”

Section: Introductionmentioning

confidence: 99%

The impact of moist processes on the African easterly jet–African easterly wave system

Cornforth

Hoskins

Thorncroft

2009

Quart J Royal Meteoro Soc

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ABSTRACT:The African Easterly Jet-Easterly Wave (AEJ-AEW) system was explored in an idealised model. Prescribed zonally symmetric surface temperature and moisture profiles determine the AEJ which becomes established through meridional contrasts in dry and moist convection.As in previous studies, a realistic AEJ developed with only dry convection. Including moist processes, increased its development rate, but reduced its speed and meridional extent. AEWs grew through barotropic-baroclinic conversions. Negative meridional potential vorticity (PV) gradients arose in the zonally symmetric state through the intrusion of the low-PV Saharan boundary layer. Since moist processes strengthened this significantly through diabatically generated PV in the Intertropical Convergence Zone, moist AEWs were three times stronger. Larger barotropic conversions and faster AEJ development increased the moist wave growth-rate. Jet-level and northerly low-level amplitudes grew, but in the moist case the low-level amplitudes weakened as the AEW interacted with convection, consistent with their absence from observations during the peak monsoon. Striking dependencies between the AEJ, AEW and rainfall existed. Two time-scales governed their evolution, depending on the transfer coefficients: (1) the AEJ's replenishment rate influenced by heat fluxes, and (2) the wave growth-rate, by damping, and the slower jet development rate.Moist AEWs were characterized by intermittent growth/decay, with growth preceded by increased mean rainfall and later, weakening AEJs. These dependencies established an internal 8-10-day variability, consistent with intra-seasonal observations of 9-day rainy sequences. This internal variability offers an alternative explanation to the previously proposed external forcing and a new view of the moist AEW life cycle.

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Interannual variability of African wave activity in a general circulation model

Thorncroft

Rowell

1998

Int. J. Climatol.

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The Structure and Properties of African Wave Disturbances as Observed During Phase III of GATE

Cited by 487 publications

References 0 publications

Regional comparison of West African convective characteristics: a TRMM‐based climatology

Regional comparison of West African convective characteristics: a TRMM‐based climatology

The impact of moist processes on the African easterly jet–African easterly wave system

Interannual variability of African wave activity in a general circulation model

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