Arctic Change and Possible Influence on Midlatitude Climate and Weather. Judah Cohen (AER) and Xiangdong Zhang (UAF) co-chairs June 23, 2015

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1 Arctic Change and Possible Influence on Midlatitude Climate and Weather Judah Cohen (AER) and Xiangdong Zhang (UAF) co-chairs June 23, 2015

2 2

3 Outline! Over the past two decades the Arctic has been warming more than twice as fast as the rest of the globe and is referred to as Arctic Amplification (AA)! Concurrent with AA, extreme weather has been observed to be increasing.! There have been numerous theories linking AA to more frequent and extreme weather/climate events, though testing these theories is challenging due to large natural variability, short observational record and model shortcomings and conflicting results.! We have assembled the leading scientists studying this topic to move the science forward through meetings, coordinated studies and future publications.

4 Sea Ice Melt!"#$%&'()*"+,(

5 Sea Ice and Snow Cover Decline

6 Arctic Amplification (a) (b) DJF Area-Averaged Temperature Anomalies (c) -+./#(/0($12(3456(

7 !&'"#%!!!($%+!!&$ MAM!""#!""$! 0!""$!&$!"#$%&! %### %##$ %#!#!"#$% %&'$()* Trend = 0.23 C/10 yr (d)!!,$%+! 1! NH Mean SON Land Temperature Anomaly!""# SON!""$! #&$ %### %##$ = 0.28 C/10 %#!# yr Trend!"#$% %&'$()* Trend = 0.43 C/10 yr** # %!"'$%)!!"#$%&!!"'$%&!!!($ &!!!!$!!!!($23/45 )!!!"#$%&'%()*+(%#$(%,-#./011!"'$%)!!"#$%&!!"'$%&! %!!($%&!!!!$%!!!!($34056 )!!"#$%&'(&)*+,)&$%)&-.$/0122!"'$%)!!"#$%&!!"'$%)!!"#$%&! % % % 1990!""# 1995!""$ %### %##$!"#$% %&'$()* Time - [year] 2010 %#!# **p < 0.01!!*$%+! 2 1!"#$%&! (e)!!,$%+!!!($%+! 0!!*$%+!!!!"#!! #&$ % [ C]!&$ Trend = 0.35 C/10 yr**!!$"#)! #&$ % %!!($%+! #&$ 0#!!($ &!!!!$!!!!($23/45 )!!"!#$%&'%()*+(%#$(%,-#./011!!*$%+! NH Mean JJA Land Temperature Anomaly!""# 2% JJA!"'$%&!!!($%+!!&'"#)! Trend = 0.30 C/10 yr** # [ C] %### %##$ %#!#!"#$% %&'$()*Trend = 0.10 C/10 yr!"#$%&! (c)!!,$%+! 2 1 #&$ #&$!!*$%+! " $-# $-( $-. $-' $ $-' $-. $-( $-# " " $-# $-( $-. $-' $ $-' $-. $-( $-# " " $-# $-( $-. $-' $ $-' $-. $-( $-# "! "#$%&#'() %* #&$ % Trend = C/10 yr NH Mean MAM Land Temperature Anomaly! "#$%&#'() %* #&$ " $-# $-( $-. $-' $ $-' $-. $-( $-# "! "#$%&#'() %* 1!!&("#)! [ C]!&$ 0#!"#$%&'(&)*+,)&$%)&-.$/ (b)!!,$%+! Trend = C/10 yr [ C]!$#+,%-./#(01% %& 2*!$#+,%-./#(01% %& 2*!$#+,%-./#(01% %& 2*!$#+,%-./#(01% %& 2* 2% DJF! "#$%&#'() %* NH Mean DJF Land Temperature Anomaly (a)!"#$%&$%'()*$+,-.- /00.1 Northern Hemisphere Land Temperatures !"#$%&!!"'$%&!!!($%&!!!!$%!!!!($%)! [ C per 10 years] 1 ' " & 0-1 & '!"#$%&'$()* &+ -+./#(/0($12(3453(

8 Extreme Weather C7(D/,<(:/0(9$<(=,/>*=*0$%+#( -+./#(/0($12(3456( 8

9 Extreme Snowfall 9

10 Extreme Rainfall 10

11 Trends in Extremes K+&,>/L(M&#*>.)/(

12 Trend in Polar Cap Geopotential Height '0,$0+'=./,/($#9(.*"./,(./*".0'(*#(0./(N,>%>(0,+=+'=./,/(J#/"$%E/(NOA:/$P(=+1$,(E+,0/Q72((

13 PCH Oct-Mar

14 PCH Oct-Mar $ C( Sandy Early Nor easter Cold/snow Asia, Europe Blizzards in the US Major Stratospheric Warming Blizzard 2013 Blizzard New England Snow in the UK/ Arctic outbreak US Midwest-East Coast snowstorm Late season snow/ Arctic outbreaks US & Europe

15 Extreme Weather! Extreme weather is subjective and not well defined.! Extreme weather is predicted to increase under climate change and AA is not needed to explain an increase in extreme weather.! A challenge for the group is to identify which extremes may or may not be influenced by AA.! We are not simply focusing on extreme weather but rather AA and linkages to changes in the atmospheric circulation. However extreme weather is what the public is most concerned about.

16 Theories linking AA to Mid-latitude Weather! Changes to latitudinal temperature gradient! Changes to the Jet Stream/blocking/wave speed! Changes to atmospheric waves:!! Planetary waves (winter)!! Synoptic scale waves (summer)! Changes to troposphere-stratosphere coupling! Support of these theories are conditional and challenged by imperfect observations and models

17 O&R/#($#9(S'$&(3453(

18 V,$#>*'($#9(D$E,&'(345W( $,>%>;+'>*11$%+#(

19 X*".(K#+:(V+,>/9(-+19(K*"#$1(( 6( >1/8#'+*23%%?()-('6"()% Y( W( 5( 3( 9(#"+216% &('-*'710+2%% +,('%:"7('"1% ;2/'(1)(3%<*'1)"12%)2+=%/+,('% C(#10,(%.'/0/%D)/"6610+2%!"#$%&'())*'(%+,('%-$(%%.'/0/%123%4'(5*(2-%% /+63%1"'%+*-7'(18)% Z(!"#$ %%%&'$% %%%%%%()* % %+"' % % % %,-. % %/"0% -+./#(/0($12(344[(

20 \+:(K/$(!>/(V+,>/9(-+19(K*"#$1((

21 Surface temperature anomalies are inversely proportional to the speed of the wind.

22 Arctic Amplification Mid-latitude Weather OE/,1$#9(/0($12(345W(

23 Arctic Amplification - Jet Stream V,$#>*'(345Y(

24 Natural Variability! The role of natural variability on mid latitude weather is large and it is always a challenge to separate the signal from the noise.! There are many factors influencing mid-latitude weather and isolating one factor is difficult.! We know that the tropics and mid-latitudes influence the Arctic, therefore AA may be more of a response than a cause.! This is further complicated when studying extreme events which are infrequent, may be poorly observed and definitions are subjective and my be more societal based than metric based.

25 Mid-latitude Weather is Complicated L $%+(,+&$-!#,.,+$(,"/& /$(3%$#&'$%,$I,#,(5&!!,EH:;E=>&+>D9=H:&-BJ:C&!!6B>=;&+?@>:&!!'B>@=ED@&);8KABEC& 7#"I$#&+#,-$()&& +0$/7)& /0&-,12#$(,(31)& 4)$(0)%& -+./#(/0($12(3456(

26 Natural Variability in the Mid-latitudes Internal atmospheric variability is large (a) Latitude (a) Speed (ms 1 ) DJF Atlantic Jet Latitude Jet latitude: DJF Jet speed: DJF DJF Atlantic Jet Speed 20th Century Reanalysis jet latitude and speed! red line denote NCEP-NCAR Reanalysis! Woollings et al. (2014; QJRMS) Decadal variability of jet position and speed is large - Behavior over the past decade does not appear exceptional compared to the long-term variability CSU Elizabeth A. Barnes

27 Inverse AMV/NAO relationship in the 20CR reanalysis over Winter SLP Composite of DJFM SLP based on AMV polarity over (shading, anomalies significant at the 95% confidence level). Contours represent the NAM mode in surface. Adapted from Peings and Magnusdottir (2014)..]$( ^$##*>P(]/*#"'(

28 Tropical Forcing \//(/0($12(345W(

29 ! Increased tropical Pacific SST causes a southward shift of the jet stream, enhancing low troposphere baroclinicity and storm activity in US. HLG% M.M% Vertical cross section of zonally averaged (between longitude) u-wind (contours: climatology; shading: increased tropical Pacific SST)!"#$%&'%"()*%+,-.%

30 Challenges with Data and Models! Short time series in observations! M+9/1(9/_>*/#>*/'(! $#$1<'*'(

31 ( ( ( NR,*C&%+#(*'(-+#0,+E/,'*$1L( \/#"0.(+G(9$0$('/,*/'(Jd54;34(^/$,'7(*'('.+,0($#9(:/$0./,(*'(>.$+%>2( \$,"/(#$0&,$1(E$,*$C*1*0<(*#(0./('<'0/@(@$P/'(9/0/>%#"($('*"#$1(9*e>&102( 8./,/($,/(@$#<(G+,>*#"'(+G(0./('<'0/@(@$P*#"($R,*C&%+#(0+(f&'0(+#/(G+,>*#"($( >.$11/#"/2( OC'/,E$%+#$1(#/0:+,P(*#(0./(N,>%>(*'('=$,'/2( ( (

32 Same sea ice forcing different model response Internal atmospheric variability is large Fall Winter a b d e f Sea ice concentration (%) AMIP experiments with high and low sea-ice concentrations based on observed trends ( ) - same forcing different response! 100 years of Unified Model! 60 years of CAM! Screen, Deser et al. (2013; CDYN) perturbed sea ice minus control! (similar to ) hpa hpa geopotential height 80 o N 60 o N 40 response o N [SON] 80 o N 60 o N 40 o N 80 o N 60 o N 40 o N g CAM poleward jet shift h UM 80 o N 60 o N 40 o N 80 o N 60 o N 40 o N 80 o N 60 o N 40 o N j k l Geopotential height (10 m) no jet shift 80 o N 60 o N 40 o N 80 o N 60 o N 40 o N 80 o N 60 o N 40 o N i CSU Geopotential height (10 m) Minimum ensemble size Elizabeth A. Barnes Fig. 6 As Fig. 3, but for geopotential height (Z)

33 Working Group Members

34 Previous Workshops (not all listed)! g! \$,"/("$='(*#(+&,(&#9/,'0$#9*#"(( g! '.+,0(+C'/,E$%+#'( g! 8+=*>(*'(>+#0,+E/,'*$1(! G+,/>$'0'(! NR,*C&%+#(*'(>+#0,+E/,'*$1(! \*#P$"/'(:*11(C/(,/"*+#$1(!

35 ?1,F%L(-%:-'(1I% H/:(-+#'/#'&'( ( M+'0('0&9*/'(+#(NN;@*91$%0&9/(1*#P$"/'(G$E+,(/$,1<(( :*#0/,(1*#P$"/'(0.$0($,/(,/"*+#$1($#9(C$'/9(+#(( $@=1*_>$%+#(+G(/Q*'%#"(:/$0./,(=$R/,#'(1.%2)3"%4"-52( ( \*#P$"/'($,/($(>+@C*#$%+#(+G(*#0/,#$1(E$,*$C*1*0<k(0:+;:$<(@*9;1$%0&9/( 0/1/>+##/>%+#'k($#9(1+:/,;0,+=+'=./,*>(N,>%>(0/@=/,$0&,/($#+@$1*/'((((((( 677%-5"%13#)5$-.$% ( I$<(G+,:$,9L(!#E/'%"$0/(@&1%=1/(9<#$@*>(=,+>/''/'(+l/#(C&,*/9(*#(#+*'/m( H//9($(n,$#9(K>*/#>/(-.$11/#"/( Worth further investigation for potential of improving seasonal forecasts, especially with continued Arctic external forcing James Overland(

36 Proposed Tasks! '0&9*/'(G+,(*9/#%G<*#"(=.<'*>$1(=,+>/''/'(! -++,9*#$0/(:*0.(+0./,(N,>%>(",+&='(JKSN)-Xk(-1*-k(!NK-7! N('<#0./'*'A,/E*/:(=,+f/>0( ( ( ($2()/E*/:($,%>1/($#9A+,( ( ( (C2(U+&,#$1('=/>*$1(*''&/(J/$,1<(G$E+,*0/7 ((

37 Meetings! Bi-monthly teleconferences! I+,P'.+=(;8ai(

38 Contributions from WG Efforts! Better understanding of knowledge gaps! a/r/,(&'/(+g(0./(+c'/,e$%+#'(! Improved climate prediction

39 Summary! Over the past two decades the Arctic has undergone rapid and dramatic changes.! Strong warming and large variability in sea ice and snow cover could be influencing mid-latitude weather.! Many theories/studies argue/show that Arctic variability influences mid-latitude weather through wave interference and/or Jet Stream characteristics.! Skepticism remains high due to large natural variability, short observational record and inconclusive and ambiguous modeling studies.! The gathering of leading scientists to advance this complex but important challenge is timely.

40 Arctic Oscillation (AO)/Polar Vortex! Also known as the North Atlantic Oscillation.! Can be thought of as a metric of how much mixing of atmospheric masses is occurring in the atmosphere.! Positive AO/strong polar vortex little mixing with strong low pressure/cold air sitting over the pole and higher pressure/warmer air to the south.! Negative AO/weak polar vortex strong mixing causes warm air to rush the Pole and Arctic south spills equatorward

41 Melting sea and ice and increasing snow cover are contributing to a weakening of the polar vortex (and more extreme weather).!!warming Arctic!!Less sea ice!!more atmospheric moisture!!increasing snow cover!!decreasing Arctic Oscillation trend/weakening of the polar vortex -+./#(/0($12(3453C(

42 Arctic Amplification Mid-latitude Weather

43 Slower moving more persistent waves has resulted in greater frequency of heat waves in the era of Arctic Amplification (2000 to present)

44 Internal atmospheric variability is large Russian heat wave of 2010 DJF Atlantic Blocking Frequency NCEP B1D D2D M2D - 3 blocking identification methods - 4 seasons - 4 reanalyses - 3 different time periods - Decadal variability of blocking frequency is very large, like jet-stream variability (the two are dynamically linked) - Behavior over the past decade does not appear exceptional compared to the long-term variability Barnes et al. (2014); GRL CSU Elizabeth A. Barnes

45 Recent Trends in NH Circulation Resemble AO Variability Polar Night Jet Arctic Oscillation Mean Jet Anomalous Zonal Wind Thermally-Driven Jet EQ E. D. Mid-latitude Weather C. A. B. Eddy-Driven Jet NP Stratosphere Tropopause Temperature Gradient Surface Anomalous Pressure EQ L Mid-latitude Weather H NP Stratosphere Tropopause Anomalous Temperature Surface -+./#(/0($12(3456(

46 ! ARP drives warmer Arctic but cold Eurasian midlatitude, and extreme cold winter occurred when ARP went extremely negative /010%2311% H(/%NOOP%Q%G(7%NORO% 45"67%&'%"()*%+,-,%

47 Boston Annual Snow Fall %October 2014 Eurasian snow cover is highest since 1979 and so is Boston snowfall for winter 2014/15. 47