Factors influencing the atmospheric responses to Arctic sea ice reduction

- with focus on the Barents-Kara Sea region

Shu$ng Yang (shu$ng@dmi.dk) Ida Margrethe Ringgaard1,2, Jens Hesselbjerg Christensen1,2 and Eigil Kaas2

1Danish Meteorological Ins1tute, Denmark2 Niels Bohr Ins1tute, Copenhagen University, Denmark

PAMIP workshop, Totnes, UK, June 24-27, 2019

Photo: Steffen M. Olsen

Arctic sea ice influence: Eurasia cold surges link to Barents-Kara sea ice loss

Composite of SAT anomaly when the sea ice cover is lower by 0.5 standard deviations than normal in the Barents-Kara Seas

Low B-K SIAIn Nov.

Feb.Jan.

Dec. Feb.Jan.

Low B-K SIAIn Jan.

Overland et al, 2016: J. Clim.

Nov.Dec.

ECHAM5 AGCM: T42 L19

6 x 100 yr simulations

Same boundary forcing (SST/SIC) except for Barents and Kara Seas (see the sector), where the SIC In wintertime (Nov-Apr) set to

100%, 80%, 60%, 40%, 20%, 1%,

SSTs from year 2005-2006

1% of the NH

Courtesy: Semenov(Petoukhov and Semenov, 2010)

Atmospheric response to Arctic sea ice reduction: Model simulations

ECHAM5 results: winter response difference

Surface T (40% - 80%) 850 hPa Height (40% - 80%)

Atmospheric response to Sea Ice reduction: AGCM– Winters are colder and more cold winters in Europe

• EC-Earth – AGCM (IFS)– T159 L31

• Follow the experiment setup in Petoukhov and Semenov (2010)

– 6 x 50 yr simula_ons– Same boundary forcing

(SST/SIC) except for Barents and Kara Seas,

– where the SIC In winter_me (Nov-Apr) set to 100%, 80%, 60&, 40%, 20%, 1% of the climatology

– SSTs from a cold winter year 2005-2006

è Cold European winter experiments

Surface T change changes in Prob(T<-1.5σ)

changes in Prob(T>1.5σ)

Difference: 60% - 100%

T2M

(C)

DJF T2M in central Europe

Ice (%)

Atmospheric response to Sea Ice reduction: AOGCM

• AOGCM: EC-Earth3 ATM: T255 L91, Ocean: 1° x 1° L75• Nudging the sea ice concentration in Barents and Kara Seas

– Modify the non-solar hear flux received by the ocean (HF):

ΔHF = HF · ΔSIC · AWhere, ΔSIC = SICmodel − SICtarget

A – Empirical constant (A=5)• Experiment setup similar to the AGCM with 6 x 100 year simulations

– Free run to develop the climatological SIC– Five reduced SIC simulations with target reductions of 100%, 80&, 60%, 40%

and 20% of the climatological SIC only in Barents and Kara Seas in wintertime (Nov.-April)

– Everywhere else SST and SIC evolves freely following the model dynamics and thermaldynamics

Ringgaard et al, 2019, Clim. Dyn. in review

Atmospheric response to Sea Ice reduction: AOGCM

Mean T2M anomaly wrt 100% for CEU and central EU in PS2010

Mean T2M of the 5% coldest winter months in each grid cells for CEU, central EU in PS2010 and for area mean of CEU

Ringgaard et al, 2019, Clim. Dyn. in review

JF Mean MSLP Composite JF T2M for 5%-tile Coldest CEU

Difference: 60% - 100%JF Mean T2M

Is the atmospheric response robust? More AGCM ̶ Dependence of boundary condi_on

• EC-Earth – AGCM (IFS)• Same setup as the

cold European winter experiments but

• Using SSTs from a warm winter year 1989-1990

Changes in Prob(T<-1.5σ)Surface T changeDifference: 60% - 100%

changes in Prob(T>1.5σ)

Difference in the large scale circulation pattern: Z500

Cold case

100%

Warm case

100%

“background” flow Cold - Warm

Difference in Planetary waves (wavenumbe≤6)Cold case

60%-100%

Warm case

60%-100%

Nega_ve NAO palern

Difference in boundary conditions (SSTs):

The ‘Warm’ vs. ‘Cold’ case

The monthly mean SSTs in large area of North Atlantic are more than 1°C colder in year 1989-1990 than in 2005-2006.=> The Mixed Case: with SSTs from the ‘Cold’ case every-where but from the ‘warm’ case for N. Atlantic

SST 1989/90 – 2005/06 DJF

SST 1989/90 – 2005/06 MAM

SST 1989/90 – 2005/06 JJA

SST 1989/90 – 2005/06 SON

• EC-EARTH – atm• Same setup as the

cold/Warm European winter experiments, but

• forced with SSTs of the cold case everywhere except over North Atlantic where SSTs are set to be as in the warm case (the Mixedcase)

Difference: 60% - 100%Surface T change Changes in Prob(T<-1.5σ)

Changes in Prob(T<-1.5σ)

Is the atmospheric response robust?̶ Dependence of boundary condi_on

Summary

• Under certain condiZons, the changes in sea ice in the Barents-Kara Seas have significant impacts on NH circulaZon, resulZng in colder and more cold winters in Europe. The responses are nonlinear with the degree of sea ice loss;

• These responses are seen in both AGCM and AOGCM experiments, but the signals are weak in AOGCM;

• The atmospheric response to sea ice loss depends on the background large-scale circulaZon pa`erns that are maintained by the (global) SST condiZon. Ø This may explain some inconsistency seen in model studies

• The North AtlanZc SSTs have li`le impact on the responding pa`ern over Eurasia;Ø Where are the key regions of SSTs? What are the favorable circulaZon

pa`erns that interplay with ArcZc sea ice?