Climatology of super‐refraction and trapping layers conditions over Central and West Africa

Meteorological Applications - Tập 28 Số 4 - 2021
Samuel Kaïssassou1,2, Lucie A. Tchotchou Djiotang3, A. J. Komkoua Mbienda4, Brice Ekobo2, B. Ndzana2, Roméo S. Tanessong5, G. M. Guenang4, Derbetini A. Vondou3
1Department of Meteorology, Climatology, Hydrology and Soil Sciences, National Advanced School of Engineering, University of Maroua, Maroua, Cameroon
2Laboratory of Electric Mechatronic and Signal Processing, Department of Electric and Telecommunication Engineering, National Advanced School of Engineering, University of Yaoundé I, Yaoundé, Cameroon
3LEMAP, Department of Physics, Faculty of Science, University of Yaoundé I, Yaoundé, Cameroon
4Faculty of Science, University of Dschang, Dschang, Cameroon
5Faculty of Agronomy and Agricultural Sciences, School of Wood, Water and Natural Resources, University of Dschang, Ebolowa, Cameroon

Tóm tắt

AbstractThe propagation of radio electric waves emitted from ground‐based meteorological instruments is determined through stratification of the atmosphere. In super‐refractive cases characterized by strong temperature inversions or strong vertical moisture gradients, the radar beam can be deflected towards the ground (trapping). This phenomenon often results in spurious returned echoes and misinterpretation of radar images such as erroneous precipitation, wind, and temperature detection. In this study, a 5‐year Central and West Africa (CWA) climatology of the frequency of super‐refractive and trapping‐layer base height has been produced using refractivity computations from European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses at a 40‐km horizontal resolution and 60 levels in the vertical direction. The aim of this climatology is to improve the understanding on how frequent such anomalous propagations conditions are, which is a prerequisite for fully benefiting from radar data information for the multiple purposes of model validation, precipitation analysis, and data assimilation. First, the main climatological features are summarized for the whole CWA: Sahara and inlands seldom experience super‐refraction, whereas coastal areas are strongly affected, especially in regions where the temperature inversion and the trade winds are intense lying near the surface. Over land, seasonal averages of super‐refraction frequencies reach 80% (40%) over moist areas year‐round but remain below 40% (15%) in most other regions. Seasonal statistics exhibit a pronounced diurnal cycle of super‐refraction occurrences, with averaged frequencies peaking at 60% in summer late afternoon over the areas located on the Atlantic Ocean border but inlands region are less affected with super‐refractive cases by midday.

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Meteorological Applications

Tập 28 Số 4

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