Meltemi

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Fig. 1) Formation of the Meltemi ( enlarged / synoptic view )

The Meltemi ( Greek μελτέμι meltémi ) is the prevailing wind during the summer months in the Aegean Sea . It blows from April to October as a dry northwest, north and northeast wind from the Greek mainland towards Crete in the eastern Mediterranean. The Meltemi is perceived as pleasantly cool and always brings bright weather and a good, clear view. 
 

Surname

The word Meltemi is of Turkish origin: meltem for "breeze, gentle wind". The Greeks called the wind earlier ἐτησίαι , etēsíai "the annual Wind" (dt.  Etesian ; ἐτήσιος , etḗsios , "annual"; ἔτος , Étos , "Year"). In the Latin version of the Acts of the Apostles , it is called euroaquilo ; the wrong ancient Greek names εὐροκλύδων , euroklydōn , and εὐρακύλων , eurakylōn , are derived from this.

In modern Greek, the name derived from Turkish is used today for wind, Greek meltemi from Turkish meltem , which today means “light summer land wind ”. On the other hand, the word etezyen , used today in Turkish for this special wind, comes from ancient Greek and was conveyed via French.

Emergence

Every year, at the end of May and beginning of June, light north winds, the so-called prodromi, set in. A week later, the summer wind comes, which softens the heat of the glow of the sun.

The Meltemi is a regional wind system and is one of the synoptic winds , the creation of which is based on the complex interaction of global wind systems.

At the beginning of the summer half-year there are already large-scale pressure differences between the Azores high pressure area ( H ) * on the one hand and the low pressure area of ​​the summer monsoon ( t ) * over Southwest Asia on the other. The position of both pressure systems can be viewed as quasi-stationary and is one of the causes of the annually recurring flow behavior.

Since cold air flows south on the east flank of a high and on the west flank of a low, a current in the north-westerly direction forms in the northern hemisphere. Werner Rauh described this air mass transport as the etisial flow, Hermann Flohn as the summer north flow .

This current, and thus also the Meltemi, is part of the northeast trade wind that blows to the intertropical convergence zone (ITC) when the subtropical high pressure belt shifts between 35 ° and 45 ° north in northern summer.

Fig. 2) Wind strengths over the Balkans, Greece and the Aegean Sea.
Azimuthal polar stereographic projection,
map center at 51 ° East, 0 ° North. ( enlarged view )

The weather situation on August 11, 2011 can be used as an example of a continuous pressure gradient across the Mediterranean from the Azores high to the monsoon low (Fig. 2). The Meltemi was blowing with strong gusts of up to 8 Beaufort and extreme weather warnings were issued for central and northern Greece.

Over the Anatolian plateau ( Asia Minor ) and the Arabian Peninsula , with the seasonally increasing solar radiation, heat lows ( t ) form, which further intensify the low pressure influence and thus the pressure difference. Supporting, accelerating and in particular decisive for the strength of the Meltemi is the low temperature ( t ) over central Turkey.

Another important factor in the relationship between atmospheric circulation and the formation of the Meltemi is the presence of an anti-cyclonic center ( H ) over Italy , Central Europe or the Balkan Peninsula . When the Azores high pushes a wedge into this region in summer, it causes exactly this high pressure influence z. B. over the Balkans and Hungary with the so-called Balkan high.

However, the exact location of the high is of secondary importance; In any case, a Meltemi weather situation can arise over the Aegean Sea and relatively cool continental air flows in succession from the region of southern Russia , the Ukraine and the Caspian Sea . These air masses then flow into the heat depression ( t ) over the Persian Gulf and further towards the ITC (see Fig. 1 / synoptic view ).

In addition to the meteorological parameters, the Meltemi is influenced by the special topographical features of the terrain. High mountains on the Greek mainland, the southern Balkans and Turkey create a canalization effect and, when crossing, the air dries out, which gives Greece the well-known bright blue and cloudless sky.

Further channeling effects occur between the large number of islands of different sizes in the Aegean Sea and the mainland. In addition, mountains that are at right angles to the Meltemi flow (e.g. the mountains of Crete ) can significantly slow down the wind flow on their windward side.

Information.svg* Dynamic pressure areas are shown in Figures 1 and 2 with capital letters H and T , thermal pressure areas, however, for methodological reasons with lower case letters h and t .

Occurrence

The Meltemi blows in the northern and central part of the Aegean Sea from the north and then fans out like a gigantic gust. In the east ( Dodecanese - Rhodes ) it blows from the northwest and then expires in the eastern Mediterranean . Near the Peloponnese the Meltemi is a little tamer and blows from the northeast. In the large bays of the Turkish west coast (Gökova-Golf, Güllük-Golf) it turns west. The Meltemi brings an average of 4–5 Bft. , but can also blow for days with eight or more winds. In particular, the southernmost part of the island of Karpathos is one of the safest Melteme areas for windsurfers. The Meltemi blows here in summer for weeks without a break, day and night, with winds between 5 and 7 Bft. and can even go up to 9 Bft on some days. turn up.

The Meltemi reaches its maximum in July / August. The probability is 70% from June to September. It usually starts in the morning and blows until sunset. But it can also be that during the day it is 6–8 Bft. blows and also stands through the night.

For sailors in the Aegean, caution is advised in the straits through which the Meltemi has to squeeze, such as between Tinos and Andros . There it can blow 1 to 2 winds stronger, with a correspondingly strong current. Then showing up is exhausting. The same goes for capes. Mountain ridges at right angles to the current generate weak winds in the lee side , but further out a storm. Strong down winds can occur when anchoring in the lee of the islands.

Signs

Opinions differ as to whether one can predict the wind. However, there are signs of increased meltemi:

  • Rising air pressure in the Balkans
  • Dry air, deep blue sky
  • Small balls of clouds on the mountain peaks of the mainland
  • Fields of high fleecy clouds come from southwest to west

See also

Web links

Wiktionary: Etesien  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ New Testament , Acts 27:14 ( Actus_Apostolorum text at Wikisource ).
  2. ↑ Thomas Abel Brimage Spratt : Sailing Directions For The Island Of Candia Or Crete . London 1866, p. 25 . ( different versions ), English
  3. ^ Adolf Kaegi : Benseler's Greek-German school dictionary . 13th edition. Leipzig and Berlin 1911, p. 367 .
  4. ^ Karl Steuerwald, Turkish-German dictionary , keyword meltem .
  5. ↑ http://www.wetter3.de/antriebe.html
  6. ↑ http://www.goruma.de/Wissen/Naturwissenschaft/Meteorologie/hoch_und_tiefdruckgebiete.html
  7. ↑ Werner Rauh: 'Climatology and vegetation conditions of the Athos peninsula and the East Aegean islands Lemnos, Evstratios, Mytiline and Chios' ISBN 978-3-540-01428-7 , p. 14 ff.
  8. ↑ Dr. Hermann Flohn: 'To the knowledge of the annual course of the weather in the Mediterranean area' Geofisica pura e applicata 1948, p. 183
  9. ↑ Markus-Hermann Schertenleib, Helena Egli-Broz: 'Globale Klimatologie: Meteorologie, Wetterinformation und Klimatologie' p. 55
  10. ↑ On the website of Wetter3 , the development of the storm can be called up in a review of the weather in 6-hour steps.
  11. ↑ I. Koletsis, K. Lagouvardos, V. Kotroni and A. Bartzokas: 'The interaction of northern wind flow with the complex topography of Crete Iceland - Part 1: Observational study', Nat. Hazards Earth Syst. Sci. 2009, p. 1851 ff.