The concept of 'fronts' arose after the 1914-18 war from the similarity of the interface between different air masses to the battle-front between opposing armies in France. The idea was introduced by a handful of meteorologists working in a spare room of the home of Vilhelm Bjerknes in Bergen (Norway). He developed the idea in co-operation with his son, Jacob, and Tor Bergeron, Carl-Gustav Rossby and others, who became known as the 'Bergen School'. No group in history has had a larger impact on the way we think about weather today.

It can be seen in Figure 13.1 that adjacent winds blow in contrary directions over the southeast of Australia; to the left, an mP air mass is advected from the south-west, and, to the right, much warmer mT air enters from the north. So a line with triangular protuberances has been drawn on the map at the boundary between the two air masses (Chapter 15). This line represents a cold front, advancing in the direction of the triangles.

Criteria for a front vary, but typically a meteorologist will look for a horizontal temperature gradient of at least 3 K/100 km in subtropical regions (more at higher latitudes), and a difference of wind direction by at least 60°. The whole pattern of temperatures, winds, uplift, humidity, clouds and precipitation around a front constitutes a frontal system, including a frontal (transition) zone, where the differences of temperature etc. are most abrupt. The frontal boundary is a 'cold front', when a cold air mass moves into a warmer area. A warm front arises when a warm air mass advances into a colder region, repelling and riding over the cooler air mass. Conventional symbols are shown in Figure 13.2.

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Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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