The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability

Zephirin Yepdo-Djomou; David Monkam

doi:doi:10.11648/j.ijema.20251301.14

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The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability

Zephirin Yepdo-Djomou^*

, David Monkam

Published in International Journal of Environmental Monitoring and Analysis (Volume 13, Issue 1)

Received: 25 January 2025 Accepted: 13 February 2025 Published: 26 February 2025

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Abstract

The composite method is used to analyse 6-9 day waves and air temperature over North Africa during the summer of 1981-1990. Based on the daily outputs of the NCEP/NCAR reanalysis, the results of this study demonstrate that a large peak in the 6-9 days band (at 7.2 days) in the power spectra of the zonal wind component at 700 hPa during summer 1981 has been found. The waves were clearly visible in the filtered (around 7.2 days) and even in the unfiltered series of the zonal wind component. The structure of the 6-9 day waves shows two opposing circulation vortices on both sides of latitude 12.5N, with the maximum (minimum) temperature anomaly appearing around 15N - 25N above the equator. In addition, these vortices are associated with anomalies in the meridional component of the northerly (southerly) wind, which are respectively connected to the maximum (minimum) temperature anomalies. The spatial configuration of the waves also shows strong temperature modulations associated with the disturbed meridional component of the wind, mainly north of 20°N, and for summers when these waves are very active, there is an opposition of signs between the temperature anomalies to the north-east and to the north-west in the areas of the Libyan and Azores highs. Due to the strong influences of the Libyan and Azores highs, a distribution of opposite surface level pressure (SLP) values is also observed. On the contrary, when these waves were not active, this opposition of signs in the composite of the air temperature anomalies did not exist and the isopleths tended to be paralleled to the parallels of latitude, and the filtered SLP anomalies had the same sing in the two anticyclones areas. Thus, the appearance and/or activity of the 6 to 9 day waves could be linked to the existence of a phase opposition between these two anticyclones. This study reinforces our understanding of the involvement of atmospheric dynamic and thermodynamic processes in the variation and evolution of waves in North Africa.

Published in	International Journal of Environmental Monitoring and Analysis (Volume 13, Issue 1)
DOI	10.11648/j.ijema.20251301.14
Page(s)	39-48
Creative Commons	This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.
Copyright	Copyright © The Author(s), 2025. Published by Science Publishing Group

Keywords

Atmospheric Waves, Air Temperature Anomalies, Cyclonic, Anticyclonic Vortices

References

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[2]	Lenouo A., F Mkankam Kamga and Yepdjuo. Weak interation in the African easterly jet. Annales Geophysicae, 2005, 23, 1637-1643. https://doi.org/10.5194/angeo-23-1637-2005
[3]	Lenouo A., F Mkankam Kamga. Sensitivity of African easterly waves to boundary layer conditions, Ann. Geophys., 2008, 26, 1355–1363. https://doi.org/10.5194/angeo-26-1355-2008
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[5]	Enyew BD and Mekonnen A. The Interaction between African Easterly Waves and Different Types of Deep Convection and Its Influence on Atlantic Tropical Cyclones. Atmosphere, 2022, 13(1), 5. https://doi.org/10.3390/atmos13010005
[6]	De Felice, P., Viltard, A., Monkam, D., and Ouss C. Characteristics of North African 6-9 day wave during summer 1981. Mon. Wea. Rev., 1990, 118, 2624-2633. https://doi.org/10.1175/1520-0493(1990)118<2624:CONADW>2.0.CO;2
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[10]	Oubuih, J., de Felice, P., and Viltard, A. Influence of the 6 - 9-day wave disturbances on the temperature, vorticity and cloud cover over the tropical Atlantic during summer 1985. Meteorol. Atmos Phys, 1999, 69, 137-144. https://doi.org/10.1007/BF01030417
[11]	Diedhiou, A., Janicot, S., Viltard, A., and de Felice, P. Composite pattern of easterly wave disturbances over West Africa and tropical Atlantic: a climatology from 1979-95 NCEP/NCAR reanalyses, Clim. Dyn., 2001, 18, 241–253, https://doi.org/10.1007/s003820100173
[12]	Kalnay, E., Kanamitsu, M., Kistler, R., Collins, W., Deaven, D., Gandin, L., Iredell, M., Saha, S., White, G., Woolen, J., Zhu, Y., Chelliah, M., Ebisuzaki, W., Higgins, W., Janowiak, J., Mo, KC., Ropelewski, C., Wang, J., Leetma, A., Reynolds, R., Jenne, R., Joseph, D. The NCEP/NCAR 40-year reanalysis project. Bull. Am. Meteorol. Soc., 1996, 77, 437-471.
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[15]	Monkam, D. Tropospheric waves of synoptic scale in Africa: kinematic characterization, structure and spatio-temporal and comparative study of two systems of waves summer by using data of analysis. Ph. D. thesis, University Paris 6, 1990, 180 pp
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[17]	Burpee, R. W. Some features of synoptic-scale waves based on compositing analysis of GATE data. Mon. Wea. Rev., 1975, 103, 921–925. https://doi.org/10.1175/1520-0493(1975)103<0921:SFOSWB>2.0.CO;2
[18]	Wallace JM, Lim GH, Blackmon ML. Relationship between cyclone tracks, anticyclone tracks and baroclinic waveguides. J Atmos Sci, 1988, 45, 439-462. https://doi.org/10.1175/1520-0469(1988)045<0439:RBCTAT>2.0.CO;2
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[20]	Diedhiou, A., Janicot, S., Viltard, A., and de Felice, P. Energetics of easterly wave disturbances over West Africa and tropical Atlantic: a climatology from 1979-95 NCEP/NCAR reanalyses, Clim. Dyn., 2002, 18, 487–500. https://doi.org/10.1007/s00382-001-0195-7

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APA Style

Yepdo-Djomou, Z., Monkam, D. (2025). The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability. International Journal of Environmental Monitoring and Analysis, 13(1), 39-48. https://doi.org/10.11648/j.ijema.20251301.14

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ACS Style

Yepdo-Djomou, Z.; Monkam, D. The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability. Int. J. Environ. Monit. Anal. 2025, 13(1), 39-48. doi: 10.11648/j.ijema.20251301.14

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AMA Style

Yepdo-Djomou Z, Monkam D. The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability. Int J Environ Monit Anal. 2025;13(1):39-48. doi: 10.11648/j.ijema.20251301.14

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@article{10.11648/j.ijema.20251301.14,
  author = {Zephirin Yepdo-Djomou and David Monkam},
  title = {The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability
},
  journal = {International Journal of Environmental Monitoring and Analysis},
  volume = {13},
  number = {1},
  pages = {39-48},
  doi = {10.11648/j.ijema.20251301.14},
  url = {https://doi.org/10.11648/j.ijema.20251301.14},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.ijema.20251301.14},
  abstract = {The composite method is used to analyse 6-9 day waves and air temperature over North Africa during the summer of 1981-1990. Based on the daily outputs of the NCEP/NCAR reanalysis, the results of this study demonstrate that a large peak in the 6-9 days band (at 7.2 days) in the power spectra of the zonal wind component at 700 hPa during summer 1981 has been found. The waves were clearly visible in the filtered (around 7.2 days) and even in the unfiltered series of the zonal wind component. The structure of the 6-9 day waves shows two opposing circulation vortices on both sides of latitude 12.5N, with the maximum (minimum) temperature anomaly appearing around 15N - 25N above the equator. In addition, these vortices are associated with anomalies in the meridional component of the northerly (southerly) wind, which are respectively connected to the maximum (minimum) temperature anomalies. The spatial configuration of the waves also shows strong temperature modulations associated with the disturbed meridional component of the wind, mainly north of 20°N, and for summers when these waves are very active, there is an opposition of signs between the temperature anomalies to the north-east and to the north-west in the areas of the Libyan and Azores highs. Due to the strong influences of the Libyan and Azores highs, a distribution of opposite surface level pressure (SLP) values is also observed. On the contrary, when these waves were not active, this opposition of signs in the composite of the air temperature anomalies did not exist and the isopleths tended to be paralleled to the parallels of latitude, and the filtered SLP anomalies had the same sing in the two anticyclones areas. Thus, the appearance and/or activity of the 6 to 9 day waves could be linked to the existence of a phase opposition between these two anticyclones. This study reinforces our understanding of the involvement of atmospheric dynamic and thermodynamic processes in the variation and evolution of waves in North Africa.
},
 year = {2025}
}

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TY  - JOUR
T1  - The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability

AU  - Zephirin Yepdo-Djomou
AU  - David Monkam
Y1  - 2025/02/26
PY  - 2025
N1  - https://doi.org/10.11648/j.ijema.20251301.14
DO  - 10.11648/j.ijema.20251301.14
T2  - International Journal of Environmental Monitoring and Analysis
JF  - International Journal of Environmental Monitoring and Analysis
JO  - International Journal of Environmental Monitoring and Analysis
SP  - 39
EP  - 48
PB  - Science Publishing Group
SN  - 2328-7667
UR  - https://doi.org/10.11648/j.ijema.20251301.14
AB  - The composite method is used to analyse 6-9 day waves and air temperature over North Africa during the summer of 1981-1990. Based on the daily outputs of the NCEP/NCAR reanalysis, the results of this study demonstrate that a large peak in the 6-9 days band (at 7.2 days) in the power spectra of the zonal wind component at 700 hPa during summer 1981 has been found. The waves were clearly visible in the filtered (around 7.2 days) and even in the unfiltered series of the zonal wind component. The structure of the 6-9 day waves shows two opposing circulation vortices on both sides of latitude 12.5N, with the maximum (minimum) temperature anomaly appearing around 15N - 25N above the equator. In addition, these vortices are associated with anomalies in the meridional component of the northerly (southerly) wind, which are respectively connected to the maximum (minimum) temperature anomalies. The spatial configuration of the waves also shows strong temperature modulations associated with the disturbed meridional component of the wind, mainly north of 20°N, and for summers when these waves are very active, there is an opposition of signs between the temperature anomalies to the north-east and to the north-west in the areas of the Libyan and Azores highs. Due to the strong influences of the Libyan and Azores highs, a distribution of opposite surface level pressure (SLP) values is also observed. On the contrary, when these waves were not active, this opposition of signs in the composite of the air temperature anomalies did not exist and the isopleths tended to be paralleled to the parallels of latitude, and the filtered SLP anomalies had the same sing in the two anticyclones areas. Thus, the appearance and/or activity of the 6 to 9 day waves could be linked to the existence of a phase opposition between these two anticyclones. This study reinforces our understanding of the involvement of atmospheric dynamic and thermodynamic processes in the variation and evolution of waves in North Africa.

VL  - 13
IS  - 1
ER  -

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Author Information

Zephirin Yepdo-Djomou

Research Division, National Institute of Cartography, Yaoundé, Cameroon

Contact Email

http://orcid.org/0009-0006-1656-4910
David Monkam

Department of Physics, Faculty of Science, University of Douala, Douala, Cameroon

Contact Email

http://orcid.org/0009-0008-4889-9218

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Plain Text BibTeX RIS

APA Style

Yepdo-Djomou, Z., Monkam, D. (2025). The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability. International Journal of Environmental Monitoring and Analysis, 13(1), 39-48. https://doi.org/10.11648/j.ijema.20251301.14

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ACS Style

Yepdo-Djomou, Z.; Monkam, D. The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability. Int. J. Environ. Monit. Anal. 2025, 13(1), 39-48. doi: 10.11648/j.ijema.20251301.14

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AMA Style

Yepdo-Djomou Z, Monkam D. The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability. Int J Environ Monit Anal. 2025;13(1):39-48. doi: 10.11648/j.ijema.20251301.14

Copy | Download

@article{10.11648/j.ijema.20251301.14,
  author = {Zephirin Yepdo-Djomou and David Monkam},
  title = {The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability
},
  journal = {International Journal of Environmental Monitoring and Analysis},
  volume = {13},
  number = {1},
  pages = {39-48},
  doi = {10.11648/j.ijema.20251301.14},
  url = {https://doi.org/10.11648/j.ijema.20251301.14},
  eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.ijema.20251301.14},
  abstract = {The composite method is used to analyse 6-9 day waves and air temperature over North Africa during the summer of 1981-1990. Based on the daily outputs of the NCEP/NCAR reanalysis, the results of this study demonstrate that a large peak in the 6-9 days band (at 7.2 days) in the power spectra of the zonal wind component at 700 hPa during summer 1981 has been found. The waves were clearly visible in the filtered (around 7.2 days) and even in the unfiltered series of the zonal wind component. The structure of the 6-9 day waves shows two opposing circulation vortices on both sides of latitude 12.5N, with the maximum (minimum) temperature anomaly appearing around 15N - 25N above the equator. In addition, these vortices are associated with anomalies in the meridional component of the northerly (southerly) wind, which are respectively connected to the maximum (minimum) temperature anomalies. The spatial configuration of the waves also shows strong temperature modulations associated with the disturbed meridional component of the wind, mainly north of 20°N, and for summers when these waves are very active, there is an opposition of signs between the temperature anomalies to the north-east and to the north-west in the areas of the Libyan and Azores highs. Due to the strong influences of the Libyan and Azores highs, a distribution of opposite surface level pressure (SLP) values is also observed. On the contrary, when these waves were not active, this opposition of signs in the composite of the air temperature anomalies did not exist and the isopleths tended to be paralleled to the parallels of latitude, and the filtered SLP anomalies had the same sing in the two anticyclones areas. Thus, the appearance and/or activity of the 6 to 9 day waves could be linked to the existence of a phase opposition between these two anticyclones. This study reinforces our understanding of the involvement of atmospheric dynamic and thermodynamic processes in the variation and evolution of waves in North Africa.
},
 year = {2025}
}

Copy | Download

TY  - JOUR
T1  - The 6-9-Day Wave and the Spatial Distribution of Air Temperature in Northern Africa in Summer: Inter - Annual Variability

AU  - Zephirin Yepdo-Djomou
AU  - David Monkam
Y1  - 2025/02/26
PY  - 2025
N1  - https://doi.org/10.11648/j.ijema.20251301.14
DO  - 10.11648/j.ijema.20251301.14
T2  - International Journal of Environmental Monitoring and Analysis
JF  - International Journal of Environmental Monitoring and Analysis
JO  - International Journal of Environmental Monitoring and Analysis
SP  - 39
EP  - 48
PB  - Science Publishing Group
SN  - 2328-7667
UR  - https://doi.org/10.11648/j.ijema.20251301.14
AB  - The composite method is used to analyse 6-9 day waves and air temperature over North Africa during the summer of 1981-1990. Based on the daily outputs of the NCEP/NCAR reanalysis, the results of this study demonstrate that a large peak in the 6-9 days band (at 7.2 days) in the power spectra of the zonal wind component at 700 hPa during summer 1981 has been found. The waves were clearly visible in the filtered (around 7.2 days) and even in the unfiltered series of the zonal wind component. The structure of the 6-9 day waves shows two opposing circulation vortices on both sides of latitude 12.5N, with the maximum (minimum) temperature anomaly appearing around 15N - 25N above the equator. In addition, these vortices are associated with anomalies in the meridional component of the northerly (southerly) wind, which are respectively connected to the maximum (minimum) temperature anomalies. The spatial configuration of the waves also shows strong temperature modulations associated with the disturbed meridional component of the wind, mainly north of 20°N, and for summers when these waves are very active, there is an opposition of signs between the temperature anomalies to the north-east and to the north-west in the areas of the Libyan and Azores highs. Due to the strong influences of the Libyan and Azores highs, a distribution of opposite surface level pressure (SLP) values is also observed. On the contrary, when these waves were not active, this opposition of signs in the composite of the air temperature anomalies did not exist and the isopleths tended to be paralleled to the parallels of latitude, and the filtered SLP anomalies had the same sing in the two anticyclones areas. Thus, the appearance and/or activity of the 6 to 9 day waves could be linked to the existence of a phase opposition between these two anticyclones. This study reinforces our understanding of the involvement of atmospheric dynamic and thermodynamic processes in the variation and evolution of waves in North Africa.

VL  - 13
IS  - 1
ER  -

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