Characteristics of the Turkana low-level jet stream and the associated rainfall in CMIP6 models

Lino Oscar; Mutemi J. Nzau; Dyer Ellen; Opijah Franklin; James Rachel; Washington Richard; Webb Tom

doi:10.1007/s00382-022-06499-4

Characteristics of the Turkana low-level jet stream and the associated rainfall in CMIP6 models

Lino Oscar, Mutemi J. Nzau, Dyer Ellen^*, Opijah Franklin, James Rachel, Washington Richard, Webb Tom

^*Corresponding author for this work

Research output: Contribution to journal › Article (Academic Journal) › peer-review

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Abstract

The Turkana low-level jet stream (TJ) is important to climatic conditions over northern Kenya and East Africa. The representation of the TJ in climate models varies due to the TJ interaction with Turkana channel that is influenced by model resolution and influences the model representation of the regional climate. This study compares features of the TJ in CMIP6 AMIP model simulations with ERA5. Models reveal climatological wind speeds that match those of the reanalysis from the ERA5 at the jet entrance (13 m/s) but lower magnitudes of wind speed and vertical shears compared to ERA5 within the Turkana channel. The models with slowest wind speeds, have a flattened Turkana channel and fail to exhibit the terrain constriction at 37° E which otherwise aids in accelerating winds to form a jet core. Furthermore, they fail to represent the narrowing of the channel as in ERA5, thereby forming blocking walls in the channel, forcing vertical ascent and mixing, and weakening shear. This boosting of ascent motion promotes rainfall formation and enhances wet anomalies at the exit of the TJ when the jet stream is weaker. By applying a new narrowing index, we demonstrate the need to improve topography details in the CMIP6 models, particularly those with resolution coarser than 1.5°, in order to properly simulate the TJ and the observed rainfall over the northwestern areas of eastern Africa.

Original language	English
Journal	Climate Dynamics
Early online date	30 Sept 2022
DOIs	https://doi.org/10.1007/s00382-022-06499-4
Publication status	E-pub ahead of print - 30 Sept 2022

Bibliographical note

Funding Information:
This work is part of outputs from the LaunchPAD (Priority on African Diagnostics) project, funded by the Foreign, Commonwealth and Development Office (FCDO) to create a Climate Model Evaluation Hub for Africa. The analysis in this work was done via JASMIN data cluster with datasets. We acknowledge the ECMWF for providing the ERA5 datasets, and the World Climate Research Programme Working Group on Coupled Modeling, for providing CMIP6 datasets to support this research.

Publisher Copyright:
© 2022, The Author(s).

Keywords

Atmospheric models
CMIP6
East Africa rainfall
ERA5
Turkana low-level Jet stream

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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Final published version, 9.1 MBLicence: CC BY

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title = "Characteristics of the Turkana low-level jet stream and the associated rainfall in CMIP6 models",

abstract = "The Turkana low-level jet stream (TJ) is important to climatic conditions over northern Kenya and East Africa. The representation of the TJ in climate models varies due to the TJ interaction with Turkana channel that is influenced by model resolution and influences the model representation of the regional climate. This study compares features of the TJ in CMIP6 AMIP model simulations with ERA5. Models reveal climatological wind speeds that match those of the reanalysis from the ERA5 at the jet entrance (13 m/s) but lower magnitudes of wind speed and vertical shears compared to ERA5 within the Turkana channel. The models with slowest wind speeds, have a flattened Turkana channel and fail to exhibit the terrain constriction at 37° E which otherwise aids in accelerating winds to form a jet core. Furthermore, they fail to represent the narrowing of the channel as in ERA5, thereby forming blocking walls in the channel, forcing vertical ascent and mixing, and weakening shear. This boosting of ascent motion promotes rainfall formation and enhances wet anomalies at the exit of the TJ when the jet stream is weaker. By applying a new narrowing index, we demonstrate the need to improve topography details in the CMIP6 models, particularly those with resolution coarser than 1.5°, in order to properly simulate the TJ and the observed rainfall over the northwestern areas of eastern Africa.",

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author = "Lino Oscar and Nzau, \{Mutemi J.\} and Dyer Ellen and Opijah Franklin and James Rachel and Washington Richard and Webb Tom",

note = "Funding Information: This work is part of outputs from the LaunchPAD (Priority on African Diagnostics) project, funded by the Foreign, Commonwealth and Development Office (FCDO) to create a Climate Model Evaluation Hub for Africa. The analysis in this work was done via JASMIN data cluster with datasets. We acknowledge the ECMWF for providing the ERA5 datasets, and the World Climate Research Programme Working Group on Coupled Modeling, for providing CMIP6 datasets to support this research. Publisher Copyright: {\textcopyright} 2022, The Author(s).",

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AU - Rachel, James

AU - Richard, Washington

AU - Tom, Webb

N1 - Funding Information: This work is part of outputs from the LaunchPAD (Priority on African Diagnostics) project, funded by the Foreign, Commonwealth and Development Office (FCDO) to create a Climate Model Evaluation Hub for Africa. The analysis in this work was done via JASMIN data cluster with datasets. We acknowledge the ECMWF for providing the ERA5 datasets, and the World Climate Research Programme Working Group on Coupled Modeling, for providing CMIP6 datasets to support this research. Publisher Copyright: © 2022, The Author(s).

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Y1 - 2022/9/30

N2 - The Turkana low-level jet stream (TJ) is important to climatic conditions over northern Kenya and East Africa. The representation of the TJ in climate models varies due to the TJ interaction with Turkana channel that is influenced by model resolution and influences the model representation of the regional climate. This study compares features of the TJ in CMIP6 AMIP model simulations with ERA5. Models reveal climatological wind speeds that match those of the reanalysis from the ERA5 at the jet entrance (13 m/s) but lower magnitudes of wind speed and vertical shears compared to ERA5 within the Turkana channel. The models with slowest wind speeds, have a flattened Turkana channel and fail to exhibit the terrain constriction at 37° E which otherwise aids in accelerating winds to form a jet core. Furthermore, they fail to represent the narrowing of the channel as in ERA5, thereby forming blocking walls in the channel, forcing vertical ascent and mixing, and weakening shear. This boosting of ascent motion promotes rainfall formation and enhances wet anomalies at the exit of the TJ when the jet stream is weaker. By applying a new narrowing index, we demonstrate the need to improve topography details in the CMIP6 models, particularly those with resolution coarser than 1.5°, in order to properly simulate the TJ and the observed rainfall over the northwestern areas of eastern Africa.

AB - The Turkana low-level jet stream (TJ) is important to climatic conditions over northern Kenya and East Africa. The representation of the TJ in climate models varies due to the TJ interaction with Turkana channel that is influenced by model resolution and influences the model representation of the regional climate. This study compares features of the TJ in CMIP6 AMIP model simulations with ERA5. Models reveal climatological wind speeds that match those of the reanalysis from the ERA5 at the jet entrance (13 m/s) but lower magnitudes of wind speed and vertical shears compared to ERA5 within the Turkana channel. The models with slowest wind speeds, have a flattened Turkana channel and fail to exhibit the terrain constriction at 37° E which otherwise aids in accelerating winds to form a jet core. Furthermore, they fail to represent the narrowing of the channel as in ERA5, thereby forming blocking walls in the channel, forcing vertical ascent and mixing, and weakening shear. This boosting of ascent motion promotes rainfall formation and enhances wet anomalies at the exit of the TJ when the jet stream is weaker. By applying a new narrowing index, we demonstrate the need to improve topography details in the CMIP6 models, particularly those with resolution coarser than 1.5°, in order to properly simulate the TJ and the observed rainfall over the northwestern areas of eastern Africa.

KW - Atmospheric models

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KW - East Africa rainfall

KW - ERA5

KW - Turkana low-level Jet stream

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DO - 10.1007/s00382-022-06499-4

M3 - Article (Academic Journal)

AN - SCOPUS:85139182882

SN - 0930-7575

JO - Climate Dynamics

JF - Climate Dynamics

ER -

Characteristics of the Turkana low-level jet stream and the associated rainfall in CMIP6 models

Abstract

Bibliographical note

Keywords

UN SDGs

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