Climbing up the north face of Mount Teide, it is quite common to see a flat layer of white clouds that seems to divide the island into two levels; it is the so-called “sea of clouds” generated by the trade winds.
Trade winds play a crucial role -along with the cushioning effect the sea has on temperatures- on the climate of the Canary Islands. It helps create subtropical-like conditions of remarkable thermal stability, resulting in benign winters and summers. Coming from the northeast and blowing almost all year round, although more intensely so during the summer months, they sweep and stir the coastal waters of the eastern sectors of the islands. These winds come loaded with moisture after travelling big distances over the sea, so that, upon contact with the north and northeast faces of the highest islands, the air rises up the slope and cools down, producing an intense process of condensation in the form of clouds. This layer of clouds is slowed down by the full force of warmer air in the upper layers of the atmosphere -the widely known thermal inversion layer- and, therefore, if we look down from upland areas, the sea of clouds can be seen, clinging onto the slopes. In areas where the mountains do not reach as much height, the mass of clouds slides down the mountain on the faces opposite to the direction of the wind and evaporates and vanishes as a result of the higher temperature in these slopes; this phenomenon is technically referred to as Foehn effect, generating a rather attractive formation known as the “waterfalls of waves”. Both phenomena are especially spectacular on the island of Tenerife.
As noted above, trade winds are also of great importance on the weather; this way, the north and northeast areas of the island are more humid and cooler around the coast and midlands, while the south is remarkably drier and hotter. This is due to the fact that Tenerife is ultimately a very large mountain with three slopes surrounded by these winds, but they cannot cover the entire altitude of the mountain. Therefore a large area in the south is sheltered from them. Such climatic differences have an impact on the vegetation that grows naturally as well as the choice in crops, as they give rise to a wide diversity of microclimates, and specific plant formations depending on direction and altitude. This way, the mass of laurel forest, also known as “green forest”, mainly shows in the Teno and Anaga mountain ranges, where fog condensation of the trade winds in the tree leaves contributes to the amount of water found on the grounds during the dry summer months.