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 Subiectul mesajului: cate ceva despre moonsoon...At a glance
MesajScris: Mar Dec 13, 2011 6:15 am 

Membru din: Joi Sep 15, 2011 4:55 am
Mesaje: 580
Localitate: Darwin-Australia
Ca tot este aproape sa se formeze in Top End.....

The monsoon is part of the usual evolution of the seasons in northern Australia. Active phases of the monsoon bring heavy rainfall to northern Australia.

This climate influence is related to: Tropical Depressions ENSO MJO
What is it?

The term monsoon derives from the Arabic word mausam, meaning season. It is used to describe the seasonal reversal of winds that occurs over parts of the tropics. In northern Australia, southeasterly trade winds characterise the dry season, while the wet or monsoon season (October to April) is characterised by a northwesterly monsoonal flow. As the Australian summer approaches, the continent heats up. Low pressure is created, which effectively draws the monsoon trough - a zone of low pressure and rising air - over northern Australia. This trough draws in moist air from the surrounding oceans and this influx of moist air is referred to as the monsoon.

The monsoon can be in either an "active" or an "inactive" phase. The active phase is usually associated with broad areas of cloud and rain, with sustained moderate to fresh northwesterly winds on the north side of the trough. Widespread heavy rainfall can result if the trough is close to, or over, land. An inactive or "break" period occurs when the monsoon trough temporarily weakens or retreats north of Australia. It is characterised by light winds and isolated shower and thunderstorm activity, sometimes with gusty squall lines. Transitions from active to inactive monsoon phases may be associated with the Madden-Julian Oscillation, a large-scale slow-moving band of increased cloudiness that travels eastwards in the tropics.

The monsoon trough frequently spawns individual low pressure systems, sometimes called monsoon depressions, often moving from east to west across northern Australia, producing heavy rain and flooding.
Where, when and for how long does it occur?

The northern wet season extends from October to April. Active monsoon periods may occur at any time during this period, however the initial monsoon onset normally occurs in late December. Later than normal onsets are often associated with El Niño conditions in the Pacific, while La Niña is usually associated with an early onset.

A typical wet season consists of a prolonged inactive period during the buildup (period before initial onset), followed by two or three active/inactive cycles, each full cycle lasting from about four to eight weeks. Inactive periods are usually longer than active ones.
How does it affect Australia?

The monsoon is associated with cloudy conditions, lengthy periods of heavy rain, occasional thunderstorms and fresh to strong squally winds. This often causes flooding in affected areas.

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