Monday, 9 June 2014
Palm Court (Queens Hotel)
The occurrence of anomalous propagation (named anaprop) of radio waves: radioducts, superrefractions and subrefractions is usually observed in the planetary boundary layer (PBL) due to large vertical variations in humidity and temperature. The anaprop formations and their spatial distributions were mainly dependent on (i) the PBL depth and its structure, (ii) sea surface temperature (SST) distributions and (iii) were highly associated with local wind circulations, particularly with sea/land breezes (SLB). Here the WRF-ARW model is used at high resolution to analyze propagation environment during the domination of certain mesoscale processes over the Adriatic sea. Typical bora wind, SLB regimes and accompanied changes in SST field are explored in order to assess potential influence on the anaprop occurrence. However, numerical models usually suffer from inadequate model parametrization of subgrid scale processes, such as mixing due to stratified turbulence. This parametrization issue is even more present in cases of coastal mountain airflow where various air masses interact over different underlying surfaces and over complex terrain. Therefore, a new generalized so-called z-less mixing length-scale (proposed by Grisogono (2010)) is deployed in WRF; it is uniformly valid for stably-stratified airflows. This modified PBL scheme takes an explicit care of existing local turbulence, mean wind-shear, buoyancy and turbulent Prandtl number; i.e., the length-scale formulation is uniformly valid for all non-negative gradient Richardson numbers, Ri, i.e., Ri ≥ 0, while it also includes local values of the Prandtl number. The related simulation of anaprops is compared to its counterpart using a standard WRF parametrization suite and to the regular near-surface and air-sounding data observed in the area.
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