Winter

Minor Snow: Heaven’s essence rises, Earth’s essence sinks


May 31st, 2012
by Jo Law

The pentad when ‘heaven’s essence rose’ and ‘earth’s essence sank’, great winds swept across the Australian’s east coast. Bellambi AWS recorded wind gusts up to 94 km/h from a west northwest direction on Saturday June 26th. Elsewhere, a slow moving low pressure system brought heavy rain to Victoria causing flooding on city streets made worse by accumulation of autumn leaves near drainage areas. The precipitation also fell in the alpine region, amassing up to 300mm of fresh snow in some towns. The cold change swept across the continent bringing wintery conditions throughout, and to the delight of weather watchers, breaking records. Canberra is said to have experienced an overnight sub-zero average of -0.2º C, reportedly the coldest May in half a century. Darwin experienced a chilly 24.8ºC maximum on Tuesday June 29th, the coldest May day in 31 years.

The subsolar point, or solar noon, is where the sun is directly overhead in relation to the observer on the ground. In winter, the subsolar point moves away from the southern hemisphere towards the Tropic of Cancer (23.5ºN), the midday sun climbs lower in our sky, consequently, we receive less insolation. Asides from lowering the apparent air temperature, the differing amount of solar heating create changes in air movement in the atmosphere. For example, eastern Australia is particularly affected by the ‘east coast lows’ in the winter months when intense low pressure systems cause strong winds and heavy rainfalls like those experienced at the beginning of this pentad. Other pressure systems in the lower atmosphere such as the sub-tropical ridge is associated with dry winters and stable weather conditions in Australia’s north and wet winters in southern part of the continent.

According to paleoclimatological theory, the earth’s current atmosphere is in its third iteration. The nascent atmosphere when the planet was forming was constituted by abundant lighter elements, such as hydrogen and helium. This was soon dispersed by solar winds and the intense thermal activities of the earth. Greenhouse gases from earth’s volcanic activities were quick to replace this lost atmosphere. The oxygen in our current atmosphere is attributed to the presence of aerobic organisms like cyanobacteria. The point, when organisms and minerals became saturated with oxygen and the gas became free in the atmosphere for the first time, is known as the ‘Great Oxygenation Event’. Occurred about 2.4 billion years ago, it is also known as the ‘Oxygen Catastrophe’ when this newly freed gas, accumulating in the atmosphere, killed the anaerobic organisms inhabiting the early earth, resulting in mass extinction.

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