Air

Winds at ground level

Winds can be divided into ground level winds, that blow in the lower strata of the troposphere, and high altitude winds. As far as winds at ground level are concerned, different types can be distinguished: local periodical winds, such as coastal and valley breezes, that form as a result of the unequal heating caused by unequal solar radiation, and global winds, whose direction and intensity depend on the distribution of the big pressure cells in the world. The trade winds blow from the subtropical anticyclonic cells towards the equatorial low pressure areas. These winds are very steady and their direction is E-NE in our hemisphere and E-SE in the Southern Hemisphere. From the northern flank of the same anticyclonic cells the westerlies blow, flowing from SW in the northern hemisphere and from NW in the southern hemisphere. The easterlies, instead, come from the internal Polar regions and meet the westerlies in the subpolar low pressure areas. As the seasons change, the pressure systems change and so do the winds. In addition to the global wind systems there are local systems, even on a vast scale, such as the monsoon winds (from the Indian word mausin that means season) that are seasonal winds caused by the unequal heating of continental and oceanic areas. The winter monsoon winds that are cold and dry blow from the Asian continent towards the Indian Ocean, while the summer monsoon winds blow from the ocean towards the continent carrying humid, warm air accompanied by particularly intense, at times catastrophic, precipitations.