Atmospheric Energy Transports, Polar
Amplification and Midlatitude Climate
DARGAN M. W. FRIERSON
UNIVERSITY OF WASHINGTON, DEPARTMENT OF
ATMOSPHERIC SCIENCES
COLLABORATORS: YEN-TING HWANG (UW, SOON TO BE
SCRIPPS & NATIONAL TAIWAN UNIVERSITY),
JEN KAY (NCAR)
Can Polar Regions Affect Climate Elsewhere?
 Absolutely!!
 There’s much recent work on how climate changes in the
extratropics can affect far away locations
 As extreme examples, Arctic changes can affect
tropical rainfall and even the storm tracks over
the Southern Ocean
Can Sea Ice Affect Tropical Precipitation?
 Yes! Work by Chiang & Bitz demonstrated this
 Strong sensitivity of tropical rain bands to Arctic sea ice
increases alone
 Rain band shifts away from cooling
 Many subsequent studies have confirmed this idea
Drying
Moistening
Change in precipitation,
Last Glacial Maximum sea ice minus
current sea ice (Chiang and Bitz 2005)
NH cooling affects SH jet stream?
 Yes! Recent study shows an “interhemispheric
teleconnection”:

Poleward shift of SH jet stream in response to NH
extratropical cooling alone
Surface zonal wind change (contours) and control (shading) from cooling at 50 N
From Ceppi, Hwang, Liu, Frierson, and Hartmann 2013, JGR
Arctic Influence on Other Latitudes
 These are just a few examples in a growing body of
literature that takes high latitude influences on other
latitudes as a given…
 Mechanisms for these studies are based on
atmospheric energy transports

So let’s discuss energy transports…
Poleward Energy Transports
 Outside of the tropics, the atmosphere transports
much more heat than the ocean
Northward energy transport
Trenberth and Fasullo (2008)
Atmospheric Energy Transports
 Dry and latent energy transport both contribute to
the atmospheric poleward transport
Total transport
Latent energy transport
Dry static energy transport
When water vapor condenses, it releases latent heat
Movement of moisture is important for the energy budget
Source: Trenberth and Stepaniak (2003)
Dry and Moist Energy Divergence
Latent is smaller poleward of 60o N

 Heating Cooling the
the atmos atmos 
 Components of divergence of energy transport:
Heating from dry static energy transport dominates closer to
the North Pole
Source: Trenberth and Stepaniak (2003)
Eddy Moisture Fluxes
Water Vapor and Global Warming
 With global warming, the atmospheric moisture
content is increasing

7% increase per degree warming at constant relative humidity
 Increased atmospheric heat transport as a
mechanism for polar amplification?


More latent energy transported into the high latitudes, where
it condenses and releases heat
Shown to be partly significant for polar amplification in GCMs
with surface albedo feedback suppressed (e.g., Alexeev et al
2005, Graversen and Wang 2009)
Energy Transports and Arctic Amplification
 Does more energy transport lead to more Arctic
amplification in GCMs?
Arctic amplification
No! More polar amplification
is associated with less heat
transport into the Arctic
Atmospheric transport change
across 70 N
Results from CMIP3 simulations:
10 models using A1B scenario
10 models using A2 scenario
From Hwang, Frierson, and Kay 2011
Latent and Dry Static Energy Transports
 Decomposition into latent and dry static energy:
Latent always increases 
 Dry always decreases
Latent is similar among models
Dry static energy transport causes most of the variation
From Hwang, Frierson, and Kay 2011
Total Atmospheric Energy Transport
 Sum of latent transport and dry static energy
transport:
While some models increase, many decrease (i.e.,
transport less energy into the Arctic)
From Hwang, Frierson, and Kay 2011
Why the Anticorrelation?
 Transport is responding to temperature gradients
 Polar amplification causes weaker temperature gradients,
this causes less dry static energy transport into the Arctic
 More gradient = more transport (i.e., transport is diffusive)
 Let’s look at a couple of examples for illustrative
purposes…
Comparison of Extreme Cases
 CCCMA (T63) has less increase in flux into high
latitudes, MPI has more increase
These are slab ocean
2xCO2 experiments,
for illustrative purposes
Factor of two difference
in total atmospheric flux
in SH
Sea Ice and Cloud Induced Heating
More ice melts in CCCMA
Cloud-induced cooling
in MPI
Feedback terms calculated with approximate piecewise radiative perturbation (APRP)
method (Taylor et al 2007)
Heating from Sea Ice + Clouds
CCCMA has more net
heating in SH high
latitudes:
Energy transports
increase less
MPI has cooling in SH
b/w 45-65 degrees:
Energy transports
increase more
Our Argument
 We claim:
 Latent energy transport always increases (due to warming)
 Differences in energy fluxes are due to differences in heating
 Forcing by ice-albedo, clouds, aerosols, or ocean heat
uptake
 Take sea ice as an example:
 More sea ice melting => more absorbed SW at high latitudes
=> less flux into that region
 Can be modeled with a (moist) energy balance model
Moist Energy Balance Model
 Goal: predict the change in atmospheric energy
transport across 65o N

We also predict clear-sky radiation
 Assume diffusive transport of moist static energy
 Flux proportional to the gradient
 Diffusivity is assumed to be:
 Constant with latitude
 Not changing with climate change
 The same for every model
Polar Energy Transports with Global Warming
 Energy balance model is accurate at predicting
transports given cloud,
ice, ocean uptake/
transport changes
We don’t predict surface temperature
– need a characterization of lapse rate
feedback.
(work in progress with Sarah Kang)
See Hwang, Frierson & Kay 2011 for
details
Works in Lower Latitudes Too
 Can also predict transports at 40o N/S (below)
 Ice-albedo, aerosols, clouds & ocean uptake as heatings
 We’ve also used to study cross-equatorial energy
transports (e.g., Frierson and Hwang 2012)
Midlatitude transport
predictions:
Captures differences
among models, &
between slab and
coupled simulations
Hwang and Frierson (2010)
Implications for Polar Amplification
 Implies that polar amplification is determined
primarily by local processes

Moisture transports can cause some amplification, but doesn’t
explain model-to-model spread
 Other studies have shown that local feedbacks are
most important (e.g., Kay et al 2012, Pithan et al, in
prep)
Role of the Ocean?
 Ocean heat transport (calculated approximately
here) is fairly well-correlated with polar
amplification – could this drive stronger feedbacks?

Or is the ocean change driven by the amplification?
Change in ocean heat transport
Implications of the Diffusive Framework
 Implies that polar warming should spread to lower
latitudes

Warmer Arctic  warmer midlatitudes
 Models with more Arctic warming have anomalous
dry static energy transport southward – back
towards the midlatitudes
 Happens relatively independently to the storm track
amplitude/location change within model
Impact of Annular Mode Changes
 Our energy transport results were based on century-
long global warming though, was only explaining the
spread of models, etc

Energy transports are by no means the whole story…
 Annular modes are important: If the storm tracks
shift equatorward (negative phase AO), can
definitely have pronounced local cooling patterns

Can even happen coincident with quasi-diffusive energy
transport…
 Mechanisms for an equatorward shift?
What Determines Storm Track Location?
 Much science since CMIP3 on why storm tracks shift
poleward with global warming

Some have studied shifts with polar amplification though (e.g.,
Butler et al 2010)
 Two categories of mechanisms:
 Where eddies grow
 Where waves propagate
 Eddies grow where temperature gradients are large
& static stability is small
Changes in Eddy Growth/Baroclinicity
 Change in potential temperature in CMIP3 multi-
model mean global warming simulations:
Large decrease in lower tropospheric
temperature gradient in winter.
Also decrease in static stability though.
Very seasonal pattern though!
Frierson (2006)
Changes in Wave Propagation
 I’ve focused in the past on changes in critical line
dynamics (where waves break)

See Chen & Held (2007) for application to ozone depletion
 With deceleration of high latitude thermal winds, I’d
expect more wave breaking at higher latitudes

This would likely shift the circulation equatorwards (negative
phase AO)
 Baroclinicity and wave propagation are two zonally
symmetric mechanisms for an equatorward shift
response to sea ice loss...
Need for Intense Study/Simulations
 We should perform more studies with a range of
models to better understand connections between
rapid sea ice loss and midlatitude dynamics
 Will we see a similar burst of studies as with the
large poleward shift literature after AR4?

I hope so! I’d encourage an inclusion of energy budget
diagnostics in such studies
Conclusions
 Energy transport in CMIP simulations is quasi-
diffusive

Means this effect should cause a spreading of warming to
lower latitudes
 Several potential zonally symmetric mechanisms for
an equatorward shift of the storm track due to Arctic
sea ice loss

How robust though?