Naslov
Impact of mesoscale meteorological processes on the anomalous propagation conditions

Autori
Telišman Prtenjak, Maja ; Horvat, Igor ; Viher, Mladen

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Skup
ICAM 2013 - International Conference on Alpine Meteorology

Mjesto i datum
Kranjska Gora, Slovenija, 03.06.2013. - 07.06.2013

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
anaprop; bora wind; thunderstorms; sea/land breeze; Adriatic

Sažetak
The occurrence of the anomalous propagation (so called anaprop) of radio waves: radioducts, superrefractions and subrefractions is created by the different properties of the atmosphere through the altitude difference in temperature, humidity and air pressure. Atmospheric variability is a result of large scale conditions, frequently modified by mesoscale structures that influence the height of boundary layer and produce local fronts with abrupt spatial changes in temperature and humidity. Here we study the impact of 3 mesoscale phenomena (over the wider area of the northern Adriatic) on the occurrence of anaprop conditions: sea/land breeze, the bora wind and cumulonimbus clouds. The selected period that unites them is 13 - 20 August 2000. For the purpose of the analysis we used radiosoundings in Udine, with a sampling period of every 6 hours and numerical WRF-ARW model at the horizontal resolution of 1.5 km every hour. Results show that the model can successfully simulate the occurrence of anaprops in Udine, although their 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 the most dependent on the accuracy of the modeled vertical changes of relative humidity. Spatial anaprop distributions show that the sea surface (between 30 and 100 m a.s.l.) is mainly covered by superrefractions and radioducts through the entire studied period. Sea breezes (SB) are continuously connected with the anaprop formations: (i) in the first 100 m above the ground within SB body where superrefractions and radioducts form due to advection of colder and moist air, (ii) in upper region of the SB front which are usually connected with elevated radioducts and superrefractions, (iii) inside transition layer between the SB body and anti-SB current with subrefractions. When a deep convection over land appears, we observe the elevated superrefractions and subrefractions between 0.5 and 1 km above ground. Subrefractions are 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 through by the advection of colder and drier air, in the shallow surface layer usually creates radioducts and superrefractions: over land and coast, inside the hydraulic jump, and over the sea and islands, in somewhat deeper layer. Bora is also associated with subrefractions: (i) over the sea surface along the edges of bora jets where a lateral exchange of air with various moisture content occur due to the convergence of flow and increased vorticity, and (ii) on the windward side of Dinaric Alps where the formation of the local vortices below the mountain top affect the moisture profile.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

Napomena
Rad je djelomično poduprt sredstvima s HRZZ projekta 09/151 (CATURBO)

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