Monday, 9 June 2014: 2:30 PM
John Charles Suite (Queens Hotel)
Here we study the impact of mesoscale processes (over the wider area of the northern Adriatic) on the occurrence of anomalous propagation (named anaprop) of radio waves: radioducts, superrefractions and subrefractions. The chosen formations are sea/land breeze, and the bora wind during one chosen summer case. For the purpose of the analysis we used radiosoundings in Udine and San Pietro, Italy, and numerical WRF-ARW model at the horizontal resolution of 1.5 km with output each hour. Results show that the model can successfully simulate the occurrence of anaprops, although the intensity is sometimes underestimated. The model has certain difficulties in reproducing the correct height and intensity of anaprops since the faithful vertical profile of the modified refractive index is most dependent on the accuracy of the modeled vertical changes of relative humidity. Spatial anaprop distributions show that the surface layer above the sea (roughly between 30 and 100 m a.s.l.) is mainly covered by superrefractions and radioducts during the entire period studied. Sea breezes (SB) are thoroughly associated with the anaprop formations: (i) in the first 100 m above the surface within the SB body where superrefractions and radioducts form due to advection of colder and moist air, (ii) in the upper region of the SB front which is usually related to elevated radioducts and superrefractions, (iii) inside transition layer between the SB body and the anti-SB current with subrefractions. When a deep convection occurs (either in combination with the SB or bora flow), we observe elevated superrefractions and subrefractions between 0.5 and 1 km above the surface. Subrefractions are also caused by downdraft beneath the cumulonimbus cloud base in its mature phase that creates smaller pools of cold and dry air. Below subrefractions in the lowermost 200 m, the type of anaprop is changed from superrefractions to radioducts. The bora wind usually creates radioducts and superrefractions (inside the hydraulic jump in the shallow surface layer) due to advection of colder and drier air. Bora is also associated with subrefractions over the sea surface along the edges of bora jets where a lateral exchange of air with different moisture content occur due to the convergence of flow and increased horizontal vorticity.
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