Two earth-spanning air pressure belts determine wind and weather in the marginal tropics of the southern hemisphere as well as the northern hemisphere of the planet. The marginal tropics are the zone between the subtropics and the equatorial tropics.
One air pressure belt is the subtropical high pressure belt on the pole side, to which our Azores high also belongs. The other air pressure zone (the tropical counterpart, so to speak) is the low pressure zone of the inner tropics, often referred to as the equatorial low pressure trough.
Steady winds blow between the two air pressure belts. Here, there are none of the volatile high-pressure-follows-low-pressure and warm-air-follows-cold-air cycles that we know from our mid-latitudes. The winds are also much more predictable here, they largely only blow in one direction: from the east - in the northern hemisphere from the north-east (north-east trade winds) and in the southern hemisphere from the south-east (south-east trade winds). An exception to this is the central and northern Indian Ocean, which has its very own wind system (monsoon).
The technical term for this zone of very constant easterly winds is the trade wind zone. The trade winds of both hemispheres are called "trade winds" in Anglo-Saxon. The root of the word lies in the Old Saxon "trada", which means comfortable footpath. The trade winds fuelled overseas trade in the 17th to 19th centuries - at a time when the course and sailing time of tall ships were still largely determined by the wind. The zone of constant trade winds, which is located between ten and 30 degrees north and south latitude, became a trade route for tall ships. The Spanish sailors gave the tropical part of the Atlantic the name "el golfo de las damas". Translated, this means that it was so easy to navigate in the trade winds that even a woman could have taken the helm - typically Spanish.
Nowadays, it is mainly blue water sailors and surfers who have discovered this wind zone for themselves. It offers very predictable winds in terms of direction and strength, as well as often friendly and warm weather. If you want to get your girlfriend interested in surfing, you should let her have a go at a trade wind spot - many of the most popular surf spots are in the trade wind region.
Everything about the trade winds:
The trade wind zone is a giant cream cake - surf spots with cherries on top
If you take a closer look, not all trade winds are the same. There is the core trade wind: we often find this area between 15 and 25 degrees latitude. Here, the trade winds are extremely stable in both summer and winter - both in terms of winds and with regard to the beautiful weather; Cape Verde, for example, is located in this zone.
Then there is the root zone of the trade winds further polewards: here, the trade winds can usually only be relied upon in the summer of the respective hemisphere. In winter, on the other hand, the winds are more erratic, sometimes stronger and then weaker, sometimes from the easterly trade wind direction, then again from other directions - sometimes low pressure systems from the westerly wind zone appear with their rainfall. Cool ocean currents often prevail in the eastern section of the large oceans, so the air here is also cooler than would be possible at this latitude. The Canary Islands also belong to this root zone of the trade winds.
Finally, the third type of trade wind is the trade wind outflow zone. It is often found on the western sides of the marginal tropical oceans and near the equator. Here, the trade winds are often weaker - and are not quite as directional as in the core trade wind zone. The dryness of the core trade winds is also unknown here; localised showers with brief strong gusts are commonplace in some months. In summer and autumn, there are also bad weather disturbances embedded in the easterly flow - with prolonged and thundery rainfall. Some of them develop into tropical cyclones such as hurricanes. Large parts of the Caribbean belong to the outlet zone of the trade winds.
All parts of the wind special:
- The west wind
- The east wind on the Baltic Sea
- Ora and Vento on Lake Garda
- The foehn in the Alps
- The Meltemi in Greece
- The bora in Croatia
- The sirocco in the central Mediterranean
- The mistral in the south of France
- The Tramontana in the northern Mediterranean
- The Levante in southern Spain
- The trade wind zone
- The roots of the trade winds
- Core trade wind - In the centre of the trade wind
- Passat run-off zone - The end of the Passat
- Interview: Climate researcher Dr Michael Sachweh - "Chasing storms is my passion"
- Windfinder: How wind forecasts are created, the difference between forecast and super-forecast
