Climate scale
1 day (diurnal cycle) - Weather occurs on an hourly or daily basis. The primary cause is the rotation of the Earth on it's axis.
1 year (yearly cycles) - Equinoxes and solstices occur twice a year due to the 23.5 degree tilt of the Earth's axis
10 years (decadal scale) - Longer-term variabilities begin to appear, such as El Niño & La Niña, and rapid climatic shifts can occur.
- Low pressure system = lots of rain
- Warm water
- Downwelling common
- Deep thermocline
- High pressure system = dry contritions
- Cold water
- Upwelling common
- High pressure system = dry contritions
- Cold water replaces warm
- Upwelling develops
- Low pressure system = lots of rain
- Warm water replaces cold
- Downwelling develops
- Deep thermocline
- Low pressure system = lots of rain
- Warm water
- Downwelling common
- Deep thermocline
- High pressure system = dry contritions
- Cold water
- Upwelling common
El Niño
Normal conditions in the tropical Pacific Ocean
Surface winds move from east to west and form a high pressure system over S. America and a low pressure system over Australia. This movement of air from high to low pressure in this region is called the Walker Circulation Cell. Surface currents also move water westward, and together with the winds they concentrate the warm water in the western Pacific Ocean.
Western Pacific Ocean
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Eastern Pacific Ocean
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The ENSO - El Niño-Southern Oscillation
Every 3 – 8 years, the system reverses. Trade winds weaken or reverse and the warm water migrates from Australia to S. America. It arrives in time for Christmas. The people of South America call it the Corriente del Niño, and it's not a nice Christmas present. There are two phases: the Warm (El Niño) and cold (La Niña) phases.
Western Pacific Ocean
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Eastern Pacific Ocean
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What is El Niño?
Basically, it's a giant puddle (or pod) of heated water that sloshes across the Pacific Ocean. It's similar to an iceberg in that the warm pod extends deep below the surface.
Typically an El Niño event lasts 1 year but can last up to 3 years. In multi-year events, first year not as affected. Even though all of the action occurs in the southern hemispheres, El Niño has effects in both hemispheres.Effects of El Niño - Biology
Upwelling is typical off western S. America and is responsible for the great biologic productivity in the area. However, this reverses to downwelling during El Niño years. Fish, birds, etc. die or migrate away from area. This creates a loss of revenue from fishing, tourism, etc., which adversely affects the local economy.
Effects of El Niño - Oceans
Sea level rises as much as 20 cm (8 in) and the water temp increases up to 7º C in the eastern Pacific Ocean waters off the coast of South America. As the temperature increase, so does evaporation and the intensity of low pressure system. This results in increased rainfall amounts in normally dry areas and intensifies coastal storms
Recognizing an El Niño
Basically, scientists just check the Sea Surface Temperatures (SST). Normal: 6-8° C warmer in the western tropical Pacific than in the eastern tropical Pacific.
La Niña
La Niña is not the opposite of an El Niño. Rather, it is a return to “normal” conditions from an El Niño strong. La Niña produces strong currents, powerful upwelling, and chilly and stormy conditions along S. American coast. The Eastern Pacific cools rapidly, and the Western Pacific warms rapidly. The Trade Winds return to normal and spreads the cooler eastern Pacific waters westward.
Western Pacific Ocean
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Eastern Pacific Ocean
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Current El Niño Status
From: NOAA Center for Weather and Climate Prediction / Climate Prediction Center
100 years - Centennial scale
- Scientists use paleoclimatic data to track solar and ocean
l variability. Large scale climatic changes and variability can be tracked, such as Pacific Decadal Oscillation (PDO) & North Atlantic Oscillation (NAO) During the last 100 years, human population and CO2 levels rose exponentially and climate related events began to severely impact human populations.
The Pacific Decadal Oscillation (PDO) was first identified in 1996 and appears to have two return periods: 15 to 25 years and 50 to 70 years. In the positive phase, cooler than normal water is present in the North Pacific Ocean and a band of warmer than normal water is located along the western coast of North America. The negative phase is the opposite.
image source: Climate Science: Investigating Climatic and Environmental Processes - Decadal Processes
The North Atlantic Oscillation (NAO) has a period of about 12 years. During the positive phase, the Azores high is stronger than normal and the Icelandic Low is deeper than normal. This causes Europe to have warm and wet winters, mild and wet winters in the eastern US and cold and dry winters in Canada & Greenland. The negative phase results in weaker pressures in the Azores High and Icelandic Low, cold & snowy winters in the eastern US and moist air to the Mediterranean.
image source: Climate Science: Investigating Climatic and Environmental Processes - Decadal Processes
During the last 100 years we have seen an increase in CO2levels and a corresponding increase in global temperatures. Recently, CO2 levels measured at Mauna Loa Observatory in Hawai'i were over 400 ppm for the first time in human history.
Image from: Dr. Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/) and Dr. Ralph Keeling, Scripps Institution of Oceanography (scrippsco2.ucsd.edu/).
1,000 years - long term cycles begin to appear, including variability in the carbon cycles on land and sea and changes to the thermohaline current. During the last 1,000 years:
- Europe's "Little Ice Age"
- Large Volcanic Eruptions
- Multi-decadal droughts
- Ice cores
- Palynology
- Tree Rings
100,000 year cycles - Extreme long term trends appear
- Milankovitch cycles
- Last Ice Age cycle 60,000 to 20,000 years before present
- Ice Age Cycles began ~2.6 million years ago to present
- Decline of the Neanderthal, rise of Homo sapiens
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