Why Did Danube River Freeze? / Zašto se Dunav zamrznuo?

Frozen Danube: a bench covered with snow facing the river

            Hundreds have died from exposure to the cold across Europe.

            The Danube's freezing is just one of many severe winter events in the continent this year. At least four Balkan nations suspended shipping on the Danube on February 14th because of heavy ice on the river.

            Keeping Europe frozen is a climate pattern called a "Russian Winter." In the coldest parts of the year, when the intense cooling of the surface layers of air over northeastern Siberia occurs, the time is right for the formation of a Siberian anticyclone. The Siberian anticyclone is one of the principal sources of polar air masses, and outbreaks of polar air westward from the high-pressure area can cause severe cold spells in the European continent. Earlier this month a strong such anticyclone formed, and with a low pressure system over Greenland, it worked to push frigid temperatures across Europe. That cold has lingered long enough to freeze the Danube, the second longest river in Europe.

            The Danube flows through 10 countries, so precise records of its last freezing are not easy to come by. But an obvious reason for this year's freeze is the teeth-chattering cold. Taking Belgrade, Serbia, as example, this year's cold streak is the worst in decades.

            Belgrade's present cold wave from January 29th to February 13th shows temperatures far below normal for each day. The worst of the stretch was a high of minus 12 C (10 F) and a low of minus 24 C (minus 11 F). 

Frozen Danube: trapped boats

            Više stotina ljudi je umrlo od hladnoće širom Evrope.

            Zamrzavanje Dunava je samo jedna od posledica oštre zime na kontinentu. Zbog leda, 14. februara su najmanje četiri balkanske zemlje obustavile rečnu plovidbu.

            Smrzavanje Evrope je posledica klimatskog obrasca poznatog pod nazivom “Ruska zima”. Tokom najhladnijeg perioda u godini, kad dođe do intenzivnog hlađenja površinskih slojeva vazduha nad severoistočnim Sibirom, formira se sibirski anticiklon. On je jedan od glavnih uzroka polarnih vazdušnih masa. Pomeranje polarnog vazduha iz područja visokog pritiska ka zapadu, može da izazove izuzetno hladne vremenske prilike na evropskom kontinentu. Početkom februara upravo se formirao jedan takav anticiklon, a sa sistemom niskog pritiska iznad Grenlanda, on je praktično “poguran” ka Evropi. Pored toga, prelazio je dovoljno sporo da se zamrzne Dunav, druga reka po veličini u Evropi.

            Dunav protiče kroz 10 zemalja, tako da nije lako doći do preciznih podataka kada se to poslednji put desilo. Ove godine, očigledan razlog za to je izuzetno jaka zima. U Beogradu, na primer, ovo je najgori hladan talas decenijama unazad. Trajao je od 29. januara do 13. februara i svakog dana je beležio temperature koje su daleko ispod proseka za to doba godine. Dobra ilustracija za izuzetno niske temperature su i zabeležene vrednosti u toku dana koje su se kretale u rasponu od -12 C do -24 C. 

Frozen Danube: Zemun's quay, frozen river on the left

Sources/Izvori: Live Science, Our Amazing Planet