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Seasonal variations of surface duct conditions in Ngaoundere, North Cameroon

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Abstract

The seasonal variations of refractivity gradients from 104 to 3000 m above ground level in the troposphere layer are presented based on observations from the radiosonde station located in Ngaoundere (13.5°E, 7.3°N), a middle belt savannah region of Cameroon. Six years (2006–2011) of data from in situ measurements made by Agency for the Safety of Air Navigation in Africa and Madagascar (ASECNA) of the temperature, moisture, and pressure are used to determine the surface duct conditions over Ngaoundere region. Each time that a negative gradient from the Abel-retrieved refractivity profiles is seen, it implies the presence of a duct in this study. The occurrence of ducts strongly depends on the local climate and synoptic weather conditions which have an appreciable influence on the refractivity vertical profile, especially the seasonal north–south movement of the Inter Tropical Convergence Zone (ITCZ) which provides wet and dry seasons to the region. Monthly and seasonal variations of ducts were also determined from the measured data. The highest and the lowest occurrence rate of surface ducts were observed during the wet and the dry seasons, respectively. September appears as the month when most of the ducts occur at the rate of at least one duct per day. The median duct thickness and duct strength are high and strong during the wet season, whereas they are low and weak during the dry season. When the data are separated into stable and unstable atmospheric conditions, we noticed that surface duct characteristics show some seasonal differences. Surface ducts are found to be more frequent in a stable atmosphere than in an unstable atmosphere. Statistical results are discussed alongside with local meteorological conditions and weather systems affecting the town of Ngaoundere. Besides, comments are made on their prospective significance in the region.

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Acknowledgments

The authors are very grateful to ASECNA-Ngaoundere for making available the radiosonde data of the Ngaoundere airport used for the analysis. This work benefited from helpful discussions with Kamsu Tamo P. H. and Roméo Chamani (University of Douala).

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Authors and Affiliations

  1. LEMAP, Department of Physics, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon

    Samuel Kaissassou & D. A. Vondou

  2. Department of Physics, Faculty of Science, University of Douala, P.O. Box 24157, Douala, Cameroon

    André Lenouo

  3. Laboratory of Industrial Systems and Environmental Engineering, Fotso Victor Technology Institute, University of Dschang, Dschang, Cameroon

    Armand Nzeukou

  4. Laboratory of Mechanic, Department of Physics, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon

    Clément Tchawoua

Authors
  1. Samuel Kaissassou
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  2. André Lenouo
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  3. Armand Nzeukou
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  4. Clément Tchawoua
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  5. D. A. Vondou
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Correspondence to Samuel Kaissassou.

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Responsible Editor: R. Roebeling.

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Kaissassou, S., Lenouo, A., Nzeukou, A. et al. Seasonal variations of surface duct conditions in Ngaoundere, North Cameroon. Meteorol Atmos Phys 127, 659–674 (2015). https://doi.org/10.1007/s00703-015-0387-z

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