Lecture 3: Megatrends Part I - Physical. Solar irradiance Measured by satellites since 1970s and proxy measurements. The sun has a well-known eleven-year irradiance (W · m -2 ) cycle that produces a ~0.08% variation in output.
Measured by satellites since 1970s and proxy measurements.
The sun has a well-known eleven-year irradiance (W·m-2) cycle that produces a ~0.08% variation in output.
Studies show that solar variability has played a role in past climate changes. For example, a decrease in solar activity is thought to have triggered the Little Ice Age between approximately 1650 and 1850.
As part of its 11-year cycle, the sun is now ramping up, after an unusually long lull.
Since 1750, the average amount of energy coming from the Sun either remained constant or increased slightly.
Climate models that include solar irradiance changes can’t reproduce the observed temperature trend over the past century or more without including a rise in greenhouse gases.
Warming is observed near the surface (greenhouse effect) rather than all layers of the atmosphere (which would indicate a contribution from solar activity).
Changes in the Earth’s, movement relative to the sun, have an effect upon climate.
The episodic behavior of glacial and interglacial periods have primarily been caused by these cycles.
sea-to-air heat transfer
Warm shallow current
Cold, salty deep current
Wind-driven surface currents (e.g. Gulf Stream) head polewards from the equatorial Atlantic Ocean
Pacific Decadal OscillationThe Pacific Decadal Oscillation (PDO) is a long-term ocean fluctuation of the Pacific Ocean. The PDO waxes and wanes approximately every 20 to 30 years.During a "warm", or "positive", phase, the west Pacific becomes cool and part of the eastern ocean warms; during a "cool" or "negative“ phase, the opposite pattern occurs
Anomaly patterns in Wintertime SST
ENSO- and PDO-related climate anomalies share very similar spatial patterns over North America and the North Pacific Ocean.
Note that the main center of warming for the PDO (left) is in the north Pacific, while the main warming of action for ENSO is in the equatorial Pacific (right).
latest images from the OSTM/Jason-2 satellite
Eastward progression of a strong wave of warm water, known as a Kelvin wave
Latest weekly SST departures are:
Niño 4 1.3ºC
Niño 3.4 1.2ºC
Niño 3 0.7ºC
Niño 1+2 0.4ºC
The trade winds normally pile up warm surface water in the western Pacific while upwelling colder water in the east from below the surface along the equator and off the west coast of South America.
During El Niño, the trade winds weaken along the equator as atmospheric pressure rises in the western Pacific and falls in the eastern Pacific.
Anomalous warming in the central and
eastern Pacific ensues as warm water in the western Pacific migrates eastward and upwelling is reduced
Nino 3.4 Sea Surface Temperature Index (departure from average)
The Southern Oscillation Index (Tahiti - Darwin)
In recent decades, indices based on sea surface temperature have come into common usage because satellites and an observing network of buoys in the equatorial Pacific now allow for collection real time, high quality data. The network of buoys referred to is the Tropical Atmosphere Ocean (TAO) Array.
Power Dissipation Index (PDI):
An aggregate measure of Atlantic hurricane activity, combining frequency, intensity, and duration of hurricanes in a single index