Topographic Influence on the African Easterly Jet and African Easterly Wave Energetics

Hamilton, Harry L.; Ocasio, Kelly M. Núñez; Evans, Jenni L.; Young, George S.; Fuentes, José D.

doi:10.1029/2019jd032138

Cited by 16 publications

(27 citation statements)

References 55 publications

(96 reference statements)

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“…Hamilton et al. (2020) attributed a decrease of surface potential temperature resulting from the reduced elevation to the reduced meridional gradient, which we also find in our R1 simulations. This indicates that R1 terrain helps maintain a strong meridional temperature gradient in the low troposphere, and this mechanism is likely what links the weakened AEW activity to the R1 terrain.…”

Section: Resultssupporting

confidence: 88%

“…Our terrain reduction experiments imply a connection between the AEW stormtracks, the WAM basic state, and the North African terrain. Unlike the broad terrain reductions in the simulations by Wu et al (2009) and Hamilton et al (2020), our reductions were more localized, allowing the basic state to stay closer to its observed state. Nonetheless, local changes to the terrain yield changes to the basic state, such as a weakened ITCZ or vertical wind shear.…”

Section: Discussionmentioning

confidence: 66%

“…Hamilton et al (2017) used numerical modeling to examine the topographic influence of the Guinea highlands in West Africa and found a reduction of rainfall when the terrain was reduced. Similar to Wu et al (2009), Hamilton et al (2020) reduced the topography across their entire simulation region and showed changes to the AEJ and associated meridional temperature gradient. These changes to the basic state therefore produced weakened AEWs and their energetics.…”

mentioning

confidence: 80%

“…(2009), Hamilton et al. (2020) reduced the topography across their entire simulation region and showed changes to the AEJ and associated meridional temperature gradient. These changes to the basic state therefore produced weakened AEWs and their energetics.…”

Section: Introductionmentioning

confidence: 99%

“…Recent studies have examined this connection of AEWs and orography (e.g., Hamilton et al, 2017Hamilton et al, , 2020. Hamilton et al (2017) used numerical modeling to examine the topographic influence of the Guinea highlands in West Africa and found a reduction of rainfall when the terrain was reduced.…”

mentioning

confidence: 99%

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The Impact of Orography on the African Easterly Wave Stormtrack

2021

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We examined the sensitivity of African easterly waves (AEWs) to elevated terrain over North Africa using a numerical weather prediction model. We formed five ensembles of simulated AEW activity with orographic features independently reduced in four key regions. The ensemble members consisted of 10 consecutive AEW seasons simulated separately. From the ensembles, the southern AEW stormtrack was most sensitive to the reduction of the Ethiopian highlands. Energy budgets showed that diminished diabatic heating associated with precipitating convection was the likely driver of the weaker AEWs. Baroclinic overturning was the dominant pathway for this response. The northern AEW stormtrack was most sensitive to the reduction of the Hoggar and Tibesti mountains. In this case, a reduction in the vertical shear and diminished baroclinic energy conversions from the background state was associated with weaker AEWs. Through terrain reduction, our results provide a view of thermodynamic and dynamic feedback in AEWs that is complementary to what has been shown in past studies.

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Section: Resultssupporting

confidence: 88%

Section: Discussionmentioning

confidence: 66%

mentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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The Impact of Orography on the African Easterly Wave Stormtrack

2021

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Future projection of the African easterly waves in a high-resolution atmospheric general circulation model

2023

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Simulating the features of the African Easterly Waves (AEWs), such as their westward propagation off the east Atlantic coast, is challenging for coarse-resolution climate models. In this study, we use High-Resolution Atmospheric Model (HiRAM) to simulate AEWs and analyze their future projections by the end of the twenty first century. The simulations are performed globally at a horizontal resolution of $$\sim $$ ∼ 25 km. The model uses shallow convective parameterization for moist convection and stratiform cloudiness. Future projections are conducted using representative concentration pathway 8.5. The AEWs are separated with respect to their periods as 3–5- and 6–9-day period AEWs, and bandpass filtering is used to filter the waves from the mean flow. HiRAM simulates structure and propagation of the waves well; however, it tends to overestimate the associated precipitation. In the future, the AEW precipitation and intensity of the circulation will considerably increase. The northward extent of the AEW track also shows a significant increase in the future. Enhanced baroclinic overturning and eddy available potential energy generated due to diabatic heating is also observed in the future.

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Statistical downscaling for precipitation projections in West Africa

Polasky,

Evans,

Fuentes

2023

Theor Appl Climatol

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The West Africa region (5 • to 20 • N and 10 • E to 20 • W) is particularly vulnerable to climate change due to a combination of unique geographic features, meteorological conditions, and socio-economic factors. Drastic changes in precipitation (e.g., droughts or floods) in the region can have dramatic impacts on rain-fed agriculture, water availability, and disease risks for the region's population. Quantifying these risks requires localized climate projections at a higher resolution than is generally available from global climate models. Using Self-Organizing Maps, we produce station-based downscaled precipitation projections for medium and high-emission climate scenarios for this region. We find slight increases in precipitation in the coastal areas, and decreases in the interior Sahel region by an average of 10% by 2100 under the high greenhouse gas-emission scenario of Shared Socioeonomic Pathway 5-8.5. Precipitation decreases in the Sahel are primarily driven by reductions in the number of rainy days during the wet season, rather than by consistent decreases in the magnitude of the precipitation amounts or decreases in the average length of the wet season.

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Topographic Influence on the African Easterly Jet and African Easterly Wave Energetics

Cited by 16 publications

References 55 publications

The Impact of Orography on the African Easterly Wave Stormtrack

The Impact of Orography on the African Easterly Wave Stormtrack

Future projection of the African easterly waves in a high-resolution atmospheric general circulation model

Statistical downscaling for precipitation projections in West Africa

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