olelog

Today I am slowly moving from linguistics back to earth sciences - or at least to meteorology. Winds. Winds can have all sorts of weird names, but also more straight ones based on their direction, like the (mid-latitude) westerlies in my part of the world - although many of the more straight ones are rooted in local languages, or dialects. So let’s move from Santa Ana or the Devil's Breath to Northerners and Southerners.

Luckily I didn’t experience the Bora, when I was in Slovenia and Croatia. The Bora is known throughout the northern Adriatic. The name derives from the Ancient Greek word for north, “borea”, which we also find in boreal - boreal forest and so on. Or maybe rather from the Greek mythological figure of Boreas, the North Wind. In Croatian it is called bura and in Slovenian burja.

The bora is a strong, cold and gusty north-easterly wind which descends to the Adriatic Sea from the Dinaric Alps, the mountains behind the Dalmatian coast (the coast of Croatia). It is mainly a winter phenomenon that develops when a slow-moving depression is centred over the Plain of Hungary and western Balkans so that winds are blowing from the east towards the Dinaric Alps. These mountains form a barrier which trap the cold air to the east of them whilst the Adriatic coast remains comparatively mild. Gradually, though, the depth of the cold air increases until the air flows over passes and through valleys to reach the Adriatic Sea.

The bora begins suddenly and without warning and the cold air typically descends to the coast so rapidly that it has little time to warm up. The bora can reach speeds of more than 100 km/h and has been known to overturn vehicles and blow people off their feet. In the Trieste area the wind was even more powerful in the past, since the slopes of the Karst were barer than they are today, as a result of the great number of trees that were needed to build Venice.

Down-slope winds flowing from high elevations of mountains, plateaus, and hills down their slopes to the valleys, planes or sea below are called katabatic winds. Katabatic is another word derived from the Greek, namely from katabaino - to go down. An upslope wind is called anabatic. Kata means down and ana means up.

When a katabatic wind is warmed by compression during its descent into denser air, it is called a foehn.

Katabatic flows slumping down from uplands or mountains may be funneled and strengthened by the landscape and are then known as mountain gap wind such as the Santa Ana (the one that is causing wildfires in California).

Cold and usually dry katabatic winds, like the Bora, result from the downslope gravity flow of cold, dense air. A large-scale katabatic wind that descends too rapidly to warm up is called a fall wind. The Bora is such a fall wind.

Slovenia and Croatia also have their own name for a wind coming from the south, namely the jugo. Some of you may remember that Jugoslavia actually meant South Slavia - in fact called Südslavien in German. Jugo is the local name for the Sirocco. The Sirocco is a Mediterranean wind that comes from the Sahara and reaches hurricane speeds in North Africa and Southern Europe, but that is yet another story.

• http://www.istrianet.org/istria/geosciences/meteorology/winds-bora-adr.htm
• http://en.wikipedia.org/wiki/Burja
• http://www.weatheronline.net.nz/reports/wxfacts/Katabatic-winds.htm
• http://www.rmets.org/activities/schools/local_winds.php