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Atmos 1020 Lecture Slides 4/1/2020
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
TOA Solar
Emitted IRClimate System
Something that modifies the input
Absorbed Solar
Feedbacks in the Climate System
What is a climate feedback? An internal process that causes the radiative forcing to change with temperature change
From Dufresne and Bony (2008) – Journal of Climate
Putting some numbers with the feedbacks…. (W/m2/K)
The BIG Feedback Wildcards:
Melting of Arctic Permafrost has the potential to quadruple CO2 concentrations. •Tipping point – once started, we can’t stop it…
Other tipping points: Antarctic and Greenland land ice.
Unknowns: Release of Methane Hydrates from the Ocean (happened in the distant past but likelihood is unknown)
Others…
Ice Shelves are extensions of continental glaciers that often extend far into the sea. These shelves tend to be stable over millennia and form a significant barrier to continental flows. Their loss would tend to accelerate continental mass loss resulting in accelerated sea level rise.
Breakup of Larsen B in 2002. It was thought to have have been stable for 10 millennia and then vanished in 3 weeks.
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
Feedbacks in the Earth system lead to oscillations on many timescales.
These processes are often realized as oscillations in the system
• Can be thought of in terms of a classic harmonic oscillator where a disturbance results in a restoring force that returns to that causes the system to move back towards equilibrium.
• Momentum built up in that movement back to equilibrium typically causes the system to overshoot.
• A continuous supply of energy keeps the system oscillating against dissipative forces.
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
The Madden Julian Oscillation (MJO) – A migratory disturbance that continuously propagates along the equator on a 30-60 day time scale.
https://upload.wikimedia.org/wikipedia/commons/4/42/Madden–Julian_oscillation_diagram.png
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
Outgoing IR Radiation Anomalies
Tim
e
The MJO is the primary source of intraseasonal variability in the tropics.
There are feedbacks to the middle latitudes also.
This feedback is due to location of latent heating in precipitation.
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
http://www.youtube.com/watch?v=QAPM02A8Atw
El Nino/La Nina refers to the interannual changes in SST and Sea Level over the Equatorial Pacific Ocean
What we see at the surface during an El Nino is a reflection of changes in the upper ocean heat content.
Heat and sea surface height anomalies propagate across the Pacific during the course of an El Nino.
Normal
Maturing El Nino
Developed El Nino
Sea temperature Red: 30°CBlue: 8°C
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
Atmospheric Response/Feedback to El Nino
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
• El Nino influences the seasonal weather around the planet. • For U.S. warm in the northwest and wet in the southeast are typical but change from event to event.
Weather Anomalies during El Nino
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
“The bi-monthly Multivariate El Niño/Southern Oscillation (ENSO) index (MEI.v2) is the time series of the leading combined Empirical Orthogonal Function (EOF) of five different variables (sea level pressure (SLP), sea surface temperature (SST), zonal and meridional components of the surface wind, and outgoing longwave radiation (OLR)) over the tropical Pacific basin (30°S-30°N and 100°E-70°W).”
https://www.esrl.noaa.gov/psd/enso/mei/
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
An animation of SST can be seen here:
http://www.youtube.com/watch?v=QAPM02A8Atw
Watch for the major El Nino events in 1982-3, 1997-8,
The North Atlantic Oscillation is an intra seasonal to annual oscillation in mass between the Bermuda high pressure zone and the Icelandic low pressure zone.
It influences the location and strength of winter storms from North America to Europe.
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
Recent NAO Indices
Source: Climate Prediction Center
Surface Pressure
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
Winter 2009-10 we had La Nina conditions but a positive NAO resulting in record low snowfall and warm temperatures.
Winter 2010-2011, the NAO was in the negative phase. This, coupled with La Nina, was likely the cause of the record cold and heavy snows in North America
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
Atlantic Multidecadal Oscillation is a long-term variation in SST. Implicated in hurricane frequency and intensity. Cause unknown.
NAO is an atmospheric phenomena and high frequency. AMO is oceanic and low frequency.
Atmos 1020 – Lecture 4The Natural Variability of the Earth-Atmosphere System
Pacific Decadal OscillationThe PDO is an oscillation in Midlatitude Pacific SST that seems to occur on decadal time scales. Cause is unknown but the PDO is correlated with other low frequency phenomena such as el Nino frequency and intensity.
Warm phase Cool Phase
Note changes that occur around 1980 in both time series…