|Title||A 5-year 40km resolution global climatology of super-refraction for ground-based radar meteorology.|
|Publication Type||Technical memorandum|
|Year of Publication||2008|
|Secondary Title||ECMWF Technical Memorandum|
The propagation of electromagnetic beams emitted from ground-based meteorological radars is determined by the stratification of the atmosphere. In extreme super-refractive situations characterized by strong temperature inversions or strong vertical gradients of moisture, the radar beam can be deflected towards the ground (ducting or trapping). This often results in spurious returned echoes and mis-interpretation of radar images such as erroneous precipitation detection. In this work, a 5-year global climatology of the frequency of super-refractive and ducting conditions and of trapping layer base height has been produced using refractivity computations from ECMWF temperature, moisture and pressure analyses at a 40-km horizontal resolution. The aim of this climatology is to better document how frequent such events are, which is prerequisite to fully benefit 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 globe and a particular focus is then laid on Europe and the U.S.A., where extensive precipitation radar networks already exist. Finally, the sensitivity of ducting occurrence to radar height is assessed by initiating refractivity vertical gradient computations from either the lowest or the second lowest model level.