engleski

Impact of mesoscale meteorological processes on anomalous radar propagation conditions

The impact of mesoscale processes on the occurrence of anomalous propagation (AP) conditions for radio waves, including ducts, super refractive and subrefractive conditions were studied. The chosen meteorological situations are the bora wind and the sporadic sea/land breeze (SB/LB) during three selected cases over a large portion of the northern Adriatic. For this purpose, we used available radiosoundings and numerical WRF-ARW model simulations (of real cases and their sensitivity tests) at a horizontal resolution of 1.5 km. The model simulated the occurrences of AP conditions satisfactorily, although their intensities and frequency were underestimated at times. Certain difficulties appeared in reproducing the vertical profile of the modified refractive index, which is mainly dependent on the accuracy of the modeled relative humidity. The spatial distributions of summer AP conditions reveal that the surface layer above the sea (roughly between 30 and 100 m asl) is often covered by super refractive conditions and ducts. The SB is highly associated with the formations of AP conditions: (i) in the first 100 m asl, where super refractive conditions and ducts form because of the advection of colder and moister air, and (ii) inside the transition layer between the SB body and the anti-SB current in the form of subrefractive conditions. When deep convection occurs, all three types of AP conditions are caused by the downdraft beneath the cumulonimbus cloud base in its mature phase that creates smaller but significant pools of cold and dry air. The bora wind usually creates an AP conditions pattern associated with the hydraulic jump and influences AP conditions distribution over the sea surface.

anaprop; bora wind; sea breeze; convection; modified refractive index

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