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…