Andrija Mohorovicic was an eponym. You may remember that I bored you in this column yesterday with the story of how he came to be his country's most celebrated meteorologist by discovering, almost en passant within his busy schedule, the geological feature now known as the "Mohorovicic discontinuity".
Similarly, Croatia's best known meteorological phenomenon involves an eponym. The Bora, a harsh north or north-easterly wind that blows down to the Adriatic at intervals between December and mid-March, is not so-called because some find it boring; it takes its name from Boreas, the ancient Greek personification of the North Wind.
The Bora is born in the mountains that surround the Adriatic Sea, from the Dolomites in Italy around to the Dinaric Alps. It is an unwelcome winter visitor from Trieste, right down the long Croatian coastline to Albania. It is a cousin of the Mistral, a similar wind which blows down the valley of the Rhone in France, and like the Mistral, it is a hybrid, a "fall" or "katabatic" wind exacerbated by the funnelling effect of the mountain valleys extending towards the coast.
A katabatic wind occurs when air at relatively high altitudes is cooled by contact with a cold snow-covered mountain surface underneath. As this air becomes colder than the free atmosphere surrounding it, it begins to slide down the mountain-side like a great invisible river. It flows downhill from little channels into larger gullies, and thence down deep ravines; the movement is gentle where the slope is slight, but in other places the air may plunge headlong over a precipice in the form of a turbulent cataract of wind, and its ferocity is enhanced by constriction as it is channelled down the narrow mountain passes towards the sea.
The icy Bora sets in very suddenly, triggered by a suitable configuration of barometric pressure. Indeed its onset is so sudden that in days gone by, would-be marauders approaching the Dalmatian coast were convinced that the savage wind was deliberately and instantaneously provoked by local inhabitants for their protection, and initiated by means of fires and palls of magic smoke.
Nowadays, the phenomenon are well known. It spills down from the mountains through well known Bora corridors, gathering speed as it descends from the snow-covered uplands to pound the coastal waters into waves, and then dissolve the waves themselves into massive clouds of spray. Renowned for its impetuosity and volatility, and feared and respected by Adriatic mariners, the Bora frequently reaches gale force and may gust at times to speeds approaching 100 m.p.h.