The generally low relief of Australia and the arrangement of its major land forms are reflected in the patterns of distribution of many climatic features. The distribution of rainfall is strongly affected by the Eastern Highlands. Australia's small size among the continents permits even the most interior location to be only about 550 miles from one of the oceans. Isotherms extend principally in east-west directions and reflect normal latitudinal differences.
Australia's climatic characteristics are also fundamentally related to the fact that the entire continent lies between 10° and 40° south latitude. This position places portions of the continent in the belt of the southeast trade winds throughout the year, within the belt of tropical monsoon rainfall in the summer, and within the westerly wind system in the winter. The climates of Australia are as a consequence characterized by abundant heat and drought and by significant differences in the seasons of rainfall. Tasmania has a relatively cool and moist climate because of its position several degrees to the south of the mainland.
The traditional seasons of the northern hemisphere are, of course, reversed in Australia. Since the seasonal range of temperature is not great in most parts of the continent, the season of drought and the season of rain may be more significant divisions of the year, particularly in the lower latitudes. As the three major wind systems shift to the north and the south with the seasons, individual regions experience the annual sequence of weather conditions.
SUMMER PERIOD
During the warmer half of the year (November to April) most of Australia except the north coast is under the influence of the southeast trades. These winds bring considerable rainfall to the windward slopes of the Eastern Highlands, but they are drying winds to the great interior areas of low relief.
The north coast is dominated during this season by the northwest monsoon, which brings as much as 50 to 60 inches of rainfall to parts of the tropical coastal region. Tropical hurricanes bring heavy rainfall and destructive winds to the northwest coast near Broome and to the northeast coast near Cooktown in summer. The summer rainfall diminishes rapidly toward the interior desert regions. The southern coastal region receives little or no effective rainfall during the six warmer months, but the east coast usually receives considerable moisture from the southeast trades as they rise over the Eastern Highland. High temperatures are experienced throughout the continent, but Tasmania offers some relief from both heat and drought.
Because of the low absolute humidity that prevails over much of Australia during the hotter months, relatively few uncomfortable days occur each year despite the high temperatures. The combination of heat and humidity along the north coast and along the northeast coast, however, produces much uncomfortable weather for white inhabitants. On the other hand, the cooler season in tropical Australia is no more uncomfortable than the warmer season along the southern coast.
WINTER PERIOD
During the six cooler months (May to October) the north coast is dominated by the southeast trades, producing a long season of drought. The trades continue to bring moisture to the northern portion of the east coast and drought to the interior desert regions.
During the cooler half year the southern part of Australia is affected by the northward seasonal migration of the Antarctic cyclonic belt. During July and August the eastward-moving storms have reached their greatest intensity and also their deepest penetration of the continent. The intensity, position, and rate of movement of these storms largely explain the variable cooler season weather conditions that prevail over the southern third of the continent. Rainfall as great as 40 or 60 inches comes to parts of the southwest and southeast coast and to Tasmania during the winter months. The amount rapidly diminishes, however, toward the north. Thus it is seen that the interior desert regions receive little rainfall from any of the three major sources from which various portions of the continent are benefited.
Winter temperatures are comparatively mild in all parts of Australia except at higher altitudes. Snowfall does not occur in Perth, Adelaide, or Melbourne along the south coast. The Monaro and Tasmania uplands receive abundant snowfall and freezing temperatures every winter. Snow sometimes falls in the Blue Mountain, New England, Flinders, and Southwestern uplands. Frosts have occurred in practically all parts of the continent except the northern quarter. Even the sugar-growing districts of southeastern Queensland suffer frost damage occasionally.
Rainfall is most reliable along the southern and northern margins of Australia and least reliable in the central desert region. The wettest areas in Australia are on the Atherton Plateau and in Tasmania, and the driest area is in the vicinity of Lake Eyre. Evaporation exceeds rainfall in nearly all parts of Australia. South winds are usually cool and north winds are normally hot as experienced by most Australians. Sunshine is most abundant in central Australia and least abundant in Tasmania and in the southeastern and southwestern corners of the continent.
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