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Field guide training: Climate and weather – Part 5
Winds – nothing else but moving amounts of air. In the following blog you can acquire further knowledge on this topic for you future field guide training.
Winds are nothing else than moving air masses. The movement results from the pressure gradient between high and low pressure areas. So it happens that many different wind streams run around the globe. These are well documented in the age of modern weather recording and can be well predicted with regard to long-term weather conditions.
Particularly important in this context are the northeastern trade wind and the southeastern trade wind which are constantly spiralling on both sides of the equator. They are mainly caused by the rotation of the earth and the Coriolis force (see excursus). Local winds also occur along coastal areas and inland, which have a significant influence on day-night temperatures. These can be subdivided as follows:
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Mountain winds: Mountain winds are usually hot and dry and run from inland towards the sea.
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Anabatic winds: In the morning the air on mountain slopes warms up faster than the air masses at lower altitudes. As a result, the less dense, warm air moves up the mountain slopes. This phenomenon can be observed when hiking in the mountains in the early morning, when fog wafts up the mountain slopes.
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Catabatic winds: At night, air masses in higher altitudes cool down faster than the air in the valley. This results in an air flow downstream.
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Land and sea breezes: Depending on the time of day, offshore and onshore winds exist in coastal regions. During the day, the air heats up faster over land than over the sea. Balancing currents cause winds to blow from the sea towards the coast. At night, the air above the land cools down faster than above the sea. At the same time, warm sea air rises, resulting in an offshore air flow.
All these wind phenomena can be observed on the coasts of South Africa. As a field guide it is important to understand how “weather works” in order to be able to predict it if necessary.
Excursus into physics: The Coriolis force has already been mentioned in the context of the development of trade winds. This is an inertial force that deflects a moving body (the earth) transversely to its direction of movement when it is described relative to a rotating reference system and is not exactly parallel to its axis of rotation.
