Climatology of super-refraction and trapping layers conditions over Central and West Africa,Meteorological Applications

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Climatology of super-refraction and trapping layers conditions over Central and West Africa
Meteorological Applications ( IF 2.3 ) Pub Date : 2021-07-27 , DOI: 10.1002/met.2016
Samuel Kaissassou _{1,

2} , L. Djiotang ₃ , A. Komkoua ₄ , B. Ekobo ₁ , B. Ndzana ₁ , R. Tanessong ₅ , M. Guenang ₄ , A. Vondou ₃

Affiliation

The 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.

中文翻译：

中非和西非超折射和捕集层条件的气候学

地面气象仪器发射的无线电波的传播是通过大气分层来确定的。在以强烈逆温或强烈垂直湿度梯度为特征的超折射情况下，雷达波束可能会偏向地面（捕获）。这种现象通常会导致虚假的回波和对雷达图像的误解，例如错误的降水、风和温度检测。在这项研究中，使用欧洲中期天气预报中心 (ECMWF) 分析的折射率计算得出了 5 年中非和西非 (CWA) 超折射和捕获层基础高度频率的气候学。水平分辨率为 40 公里，垂直方向为 60 级。这种气候学的目的是提高对这种异常传播条件的频率的理解，这是充分利用雷达数据信息实现模型验证、降水分析和数据同化等多种目的的先决条件。首先，总结整个CWA的主要气候特征：撒哈拉和内陆很少经历超折射，而沿海地区受到强烈影响，特别是在靠近地表的逆温和信风强烈的地区。在陆地上，潮湿地区全年超折射频率的季节性平均值达到 80% (40%)，但在大多数其他地区仍低于 40% (15%)。季节性统计数据显示出明显的超折射发生的昼夜循环，

更新日期：2021-07-27

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