Geo 3B: Climatic cycles and variations in spacial patterns associated Flashcards
Account for climatic cycles and variations as a result of El Nino and La Nina
Spatially, El Nino and La Nina are climatic cycles that influence climate in the Pacific Ocean between eastern Australia and the west coast of South America, particularly Peru. The La Nina cycle is a strong normal pattern, whilst El Nino creates noticeable climatic changes every 3 to 7 years. Both cycles interact with the heat budget, hydrological cycle and atmospheric circulation to produce climatic changes.
A La Nina cycle will produce strong easterly trade winds across the Pacific between the two continents. These winds develop from high air pressure developing over the east coast of South America. This is a result of minimal convection from the cold Humboldt oceanic current. Precipitation is minimum and drought is common. Conversely, the warn Eastern Australian current influences the continents off shore waters. This causes lower air pressure, particularly during summer months. Heavy convectional precipitation and cyclones result, such as Cyclone Yasi in 2011, which coincided with a La Nina cycle. This air pressure is measured and expressed as the Southern Oscillation Index. When the index is strongly positive, then rainfall is high and above average.
An El Nino cycle sees a reverse in the ocean temperatures across the Pacific; initiating changes to air pressure and precipitation. El Nino cycles are noticeable when the air pressure in the central Pacific increases. This weakens the normally strong trade winds. Warmer water extends across the west coast of South America, reducing the upwelling associated with the Humboldt Current. Peru experiences high than normal precipitation due to the warmer water and lower air pressure. Cool water is replaced with warm in the western Pacific, lifting air pressure and dramatically reducing precipitation and producing severe droughts such as in 1997, a very strong El Nino event. The SOI is sternly negative and rainfall over eastern and northern australia will be below average.
Account for climatic cycles and variations as a result of solar output
Solar output accounts for long term change such as glacial and interglacial periods. Over 99% of the total energy of the earth’s climate system is from the sun. The solar output of energy(converted to heat at the Earth’s surface) is therefore a vital part of shaping the Earth’s climate. Solar energy received is known as the solar constant. Billions of years ago it was about 75% of it’s current intensity. Since then it has been increasing at a rate of 10% per 1 billion years. The gradual warming slowly changes/impacts the Earth’s atmosphere.
Recent time scales indicate there are a variety of solar variations that can occur. One example is the 11 year sunspot cycle. The theory is that wen the sun is active(e.g. magnetic storms, solar flares) it blows cosmic rays away from the Earth which results in fews clouds and a warmer world. A period of fewer sunspots is referred to as a minimum and can coincide with periods of cooling. This is thought to be the trigger for the ‘little ice age’ of 1650-1850 in which Europe, North America and much of the rest of the world experienced bitterly cold winters and very cool, or no summers.
The cyclic nature of the sun’s output is not fully understood by scientists and other factors need to be considered when accounting for the fluctuations in the Earth’s climate.
Account for climatic cycles and variations as a result of volcanoes
Large volcanic eruptions can cause shorter term periods of cooling for up to seven years. The cooling is mainly due to the sulphate aerosols that are thrown high into the upper atmosphere by large scale eruptions. These tiny droplets of sulphuric acid remain suspended in the stratosphere where they scatter incoming solar radiation, lowering the amount of energy reaching the surface of the Earth. e.g. The Mount Pinatubo(Phillipines) eruption in 1991 caused a reduction in insolation by 10% and cooled the Earth by half a degree.
Huge erupts called large igneous provinces occur infrequently(a few times every 100 years). They can reshape climate for much longer periods of time and cause mass extinctions. These igneous provinces contain very large volumes of magmatic rock and occur in the form of continental flood basalts like the Ethiopian Highlands in Africa or ocean plateaus. They release large volumes of sulphuric gas that forms sulphuric acid in the atmosphere, reflecting heat and resulting in substantial cooling.
Volcanoes are a component of the carbon cycle. Over geological time they release carbon dioxide from inside the Earth. This is often not significant enough to cause climate change by an interaction with other cycles. The end of the snowball ice age(650 million years ago) is linked with the slow build up of carbon dioxide from volcanic activity.
