water Flashcards
explain normal years of climate
in normal years, pacific winds travel around the walker cell. The Walker cell is whereby atmospheric air moves eastwards and surface air west across Pacific, causing trade winds.
Now back to Normal years, as the winds travel westwards along the surface of the Pacific, they take warm surface water with them. The cold Peruvian current that flows northwards along the west coast of South America is drawn into the circulation and also flows westwards. As it flows, it is heated by the sun and by the time it is in Indonesia, warm, moist air rises over Indonesia, creating low-pressure area and heavy rain. The air then circulates east in the upper atmosphere, sinking into the cooler high-pressure area over western South America, giving dry conditions that that create Peru’s Atacama Desert.
explain La Nina
MORE SIMPLY - the normal walker loop intensifies / gets stronger with stronger trade winds. This means increased warm water being pushed towards SouthEast Asia and Australia leading to a low pressure system and heavy rain, flooding can occurs (as surface runoff less infiltration etc.)
MORE DETAILED- At times, the normal situation intensifies / gets stronger . Here, during this La Nina, low pressure over the western Pacific becomes even lower and high pressure over the eastern Pacific higher. As a result, rainfall increases over Southeast Asia, and South America suffers drought. Trade winds strengthen due to the increased pressure difference between the two areas….La Nina can occur just before or after El Nino.
explain El Nino
MORE SIMPLY - Trade winds weaken, meaning warm water does not get pushed towards Australia, leaving them with only high pressure and no rainfall so droughts. ( Precipitation levels will drop in well i wrote Australia from sheet but markscheme apparently said north east Brazil or something during an El Nino
event (1). This reduction will lead to lower river flows (1) as well
as lower soil moisture levels (1). )
Instead, South America well mark scheme says calfornia? now receives more warm water so has increased precipitation due to the low pressure associated with rising warm air. (. This will lead to higher levels of surface runoff (1) - and
possibility of flood events as river flow exceeds bankful capacity)
MORE DETAILED-During El Nino years, pressure systems and weather patterns reverse. Warmer waters develop in the eastern Pacific, with temperatures rising by up to 8 degrees Celsius. Warm, moist air rises, creating heavy rainfall over the eastern Pacific too. The air then circulates west in the atmosphere. The descending air then creates drier conditions which lead to drought in Northern Australia and Indonesia.
what is the Southern Oscillation Index
It is the change in air pressure between ‘normal’ years and El Nino. Its strength, direction and speed is called the Southern Oscillation Index (SOI).
To calculate this, meteorologists record air pressure at Easter Island (west of South America) and subtract that at Darwin in northern Australia.
A sharp drop indicates that El Nino is imminent….most droughts affecting easting and northern Australia result from ENSO and El Nino.
