The unexpected snowstorm of 13-14 January 2002 in Zagreb/Neocekivana snjezna oluja 13-14. sijecnja 2002. u zagrebu

The purpose of this paper is to present the causes of an unusual event of local snowstorm which lasted continuously for 28 hours resulting in 23 cm of snow. It was poorly forecasted since it occurred under a steady surface anticyclone in south-eastern Europe, east of the Alps. In the troposphere the...

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Veröffentlicht in:Geofizika (Zagreb, Croatia) Croatia), 2010-12, Vol.27 (2), p.127
Hauptverfasser: Jurcec, Vesna, Dragojlovic, Dragoslav
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Sprache:eng
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Zusammenfassung:The purpose of this paper is to present the causes of an unusual event of local snowstorm which lasted continuously for 28 hours resulting in 23 cm of snow. It was poorly forecasted since it occurred under a steady surface anticyclone in south-eastern Europe, east of the Alps. In the troposphere the most noteworthy feature was the middle-upper tropospheric front in an environment marked by sinking motion presented by the Q vectors field. It formed upstream from an intensifying cold trough in less than half a day. Another extraordinary feature was a low tropopause with a breaking region exchanging tropospheric and stratospheric air just above the area of Zagreb. The processes which mainly characterised this event in synoptic scale were advections of potential vorticity in the stratosphere and troposphere along the tropospheric cold trough. The interactions of orographically induced polar air upsloping clouds by synoptic scale in westerlies and the low level mesoscale saturated air, influenced by the terrain in the area of Zagreb by easterly flow, were considered the causes of the snowfall. Such an event leads to the "feeder-seeder" process in which large scale ascent generating higher level seeder clouds containing ice droplets large enough to efficiently washout precipitation to interact with the lower level (feeder) moisture area and cause precipitation. This is considered one of the few significant mesoscale precipitation processes that is essentially entirely microphysical in nature. Keywords: middle-upper tropospheric front, potential vorticity, tropopause break, "feeder-seeder" washout process Cilj je ovog rada da prikaze pojave koje prate snjeznu oluju u Zagrebu i kaos u prometu grada s kontinuiranim oborinom od 28 sati i 23 cm debljine snijega. Oluja nije dobro prognozirana jer je bila pod utjecajem dugotrajne prizemne anticiklone u jugoistocnoj Europi istocno od Alpa. U troposferi je najizrazitija bila visinska fronta srednje troposfere, karakterizirana silaznim gibanjima prikazanim poljem Q-vektora. Ova se fronta formirala uzlazno od hladne doline u troposferi, i ojacala u razdoblju manjem od pola dana. Druga izvanredna pojava je bio lom tropopauze iznad Zagreba, oznacen razmjenom troposferskog i stratosferskog zraka na tom podrucju. Pojava koja je najvise utjecala na razvoj ove situacije je bila advekcija potencijalne vrtloznosti duz troposferske hladne doline. Ovakav intenzivni razvoj sinopticke situacije vec ukazuje i na mogucnost obilnijih snj
ISSN:0352-3659