The flow of air around the planet – together with the oceans and their currents – determines how thermal energy and moisture are redistributed around Earth. Although influenced by various factors from one year to the next, these large-scale air movements are consistent in structure and are important factors in determining the climate at any location in the world. This is especially true for Namibia which straddles the Tropic of Capricorn and is bounded by the Atlantic Ocean with its powerful Benguela Current. Namibia's arid nature results from the persistent presence of dry air for most of the year and high rates of evaporation. Moist, warm air that can fall as rain reaches Namibia infrequently. This aridity is the product of the three major circulation systems discussed below.

Namibia's geographical position spans a zone roughly between 17 and 29 degrees south of the equator, along the southwestern coast of Africa. This places Namibia in an area where it is exposed to air movements in three major circulation systems or belts:

1. The Intertropical Convergence Zone – or ITCZ as it is often referred to – near the equator is where the air masses from the northern and southern hemisphere come together. Air in the Intertropical Convergence Zone is moist and warm and it spirals upwards creating a belt of low pressure. As it rises, the air cools and the moisture condenses forming the great band of cloud clearly visible in the images in figure 3.01. This zone shifts seasonally, southwards towards Namibia in the southern hemisphere's summer, retreating northwards in the southern winter. Its position follows that of the sun overhead, shifting annually between the Tropic of Cancer in the northern hemisphere and the Tropic of Capricorn in the southern hemisphere (just south of Rehoboth). The positions of these two imaginary lines of the tropics are equidistant from the equator and determined by the 23.5-degree angle of tilt of the earth on its axis.1
2. The middle belt is the Subtropical High-Pressure Zone. The air in the upper atmosphere, becoming cold and dry as it is forced out from equator towards the poles, subsides in the subtropics forming centres of high pressure. Two high-pressure centres – the South Atlantic Anticyclone and the Botswana Anticyclone dominate weather patterns over Namibia. In winter, the South Atlantic anticyclone is positioned off the west coast of Namibia while the Botswana anticyclone lies inland. The descending air from these highpressure centres inhibits the formation of clouds and results in dry, clear winter days. Their influence weakens when the centres of high pressure are pushed southwards in summer, making way for warm moist air to be drawn in from the north and east to form clouds and rain.
3. The southernmost Temperate Zone, extending from Antarctica to the Tropic of Capricorn, is characterised by cold, moist air. The influence this zone has on Namibia is greatest during the winter months when it moves northwards and prevailing winds carry a succession of low-pressure systems and cold fronts from west to east that sweep across southern Africa. Although the impacts of these fronts weaken as they move over the land, they are responsible for the small falls of rain over the southern parts of Namibia in winter. These frontal weather systems bring much more winter rain to the southern Cape in South Africa.

Earth's oceans have a much greater capacity to absorb and store energy from the sun than the atmosphere above the water surface. The natural flow of the oceans distributes this heat energy – cold dense water moves from the poles towards the equator, while warm lighter water is carried from the equator polewards. By distributing the heat in this way, these ocean currents regulate the temperature of the oceans and the temperature of the air above them, and have a major influence on the weather and climate. This is particularly true when the current that flows along the coast is much colder than the tropical air above it, as is the case with Namibia.