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M o n ic a I o n it a ( 1 , 2) , N o r el Ri mb u( 1 , 3)( 1 ) A l f r ed W e g e n e r I n s t i tu t e f o r P o l a r a n d M a r i ne R e s e ar c h , B r e m e rh a v e n, Ge r m a n y

(2 ) N a tiona l Meteorologic a l A dminis tra tion, Bu c ha rest, Roma nia( 3 ) U n i v e rs i t y o f B u c h ar e s t , F a c ul t y o f P h y s ic s , B u c h ar e s t , R o m a ni a

e-mail: Monica.Ionita@awi.de

Mu l ti d ec a d a l va r i a b il i ty o f s um m e r te m p e ra tu r eo v e r Ro m a n i a a n d is t r el a ti o n w i th

Atlantic Multidecadal Oscillation

stract

nvesti gate the mul tidecadal vari abi l i ty of summer temperaturer Romani a, as measured at 14 meteorol ogi cal stati ons, wi th

g t e r m o bs er va t i on al r e co r ds . I t i s s ho wn t h at i n te r de ca da l

ati ons of summer temperature are si gni fi cantl y correl ated wi th

At l a nt i c Mu l t id ec ad al Os ci l l at i on ( AMO) . Us in g a r e ce nt l y

l i shed l ong-term reconstructi on of dai l y ci rcul ati on patterns i n

North Atl anti c regi on, we show that i nterdecadal temperature

ati ons over Romani a are i nduced by AMO trough modul ati on of

f r e qu en cy o f t wo c i r cu l at i on p at t er n s, d ur i n g s um me r . T he se

u l ts h a ve i m pl i ca t i on s f or p r e di c ti n g t h e e vo lu t io n o f s um me r

perature over Romania on interdecadal time scales.

a

Monthl y mean temperature at 14 stati ons over Romani a, for themmer months (June, July and August).

An u pda te d ve rsi on ( 1 9 0 2 - 2 0 0 2 ) o f t he Ka pl an e t a l. ( 1 9 9 8 )

thl y reanal ysi s of gl obal SST anomal ies (wi th a resol uti on of 5).

AMO ti me seri es i ndex.p:/ / www.cdc.noaa.gov/ Timeseries/ AMO)

he frequency of dai l y ci rcul ati on patterns recentl y publ i shed byl ip e t a l . 2 0 0 7 . Th e d ai l y m ea n SLP da t as et u se d t o c om pu t e

d ai l y p at t er n s wa s t a ke n f r o m t h e d at a r e co ns tr u ct ed by An se ll. (20 06) wi thi n the European proj ect EMULATE.

p:// www.cru.uea.ac.uk/ cru/ projects/emulate/)

e1 . St at i ons coordi nat es

e Lat i tude Longi tude Al ti t ude ( m)i t a 4 7 0 9 2 4 3 1 3 6 6

Mar e 4 7 4 0 2 3 3 0 2 1 6ov 4 5 4 2 2 5 3 2 5 3 4

ur eti Fi lar et 4 4 2 5 2 6 0 6 8 2r asi 4 4 1 2 2 7 2 0 1 9

st ant a 4 4 1 3 2 8 3 8 1 3 4 7 1 0 2 7 3 8 1 0 2

a Sugatag 4 7 4 7 2 3 5 7 5 0 3an 4 6 5 8 2 6 5 5 2 1 6

4 5 4 8 2 4 0 9 4 4 3na 4 5 1 0 2 9 4 4 3

u Ji u 4 5 0 2 2 3 1 6 2 0 3soar a 4 5 4 6 2 1 1 5 8 6

u Sever i n 4 4 6 4 2 2 6 6 7 7

F i r st E O F o f JJ A t e m p er a t ur e

T h e t im e s e r ie s o f s u mm e r P C 1 ( b la c k l i ne ) a n d A M O i n d ex ( r e d l i n e )

R = 0.8

The co r r elatio n map between JJA P C1 and SST

The correlat ion coefficient s bet ween PC1 (red bar),

AM O index (black bar) and t he pat t ern frequency

T h e t i me s e ri e s o f P C 1 T T ( b la c k l i ne ) ,C l us t er 2 ( r ed l i ne ) a n d C l us t er 6 ( b lu e l i ne )

SLP pattern associated w ith multidecadal

v ariations in the frequency of cluster 2

SLP pattern associated with multidecadalv ariations in the frequency of cluster 6

E i ge n va l ue s d e ri v ed f r o m S S A o f t h e J J A P C 1

T h e t i m e s e r i es o f t h e n o r m a li z e d s um m e r P C 1 ( b l ac k l i ne )

an d th e fi rs t re c on s tru c ted c ompon e n t (re d l i ne )

wh i c h h as a pe ri od of ~6 0 ye ars an d i s bas e d on EOFs 1 an d 2

M E M s p e ct r u m o f t h e f i r s t r e c o ns t r u ct e dcomponent based on EOFs 1 and 2

M TM s pe ct r um o f J JA P C 1

Conclusions

1. The fi rst p ri nci pa l comp onent of summer t emp era t ure overR oma ni a p resent s a

st rong mul t i decad a l va ri a ti on.A cold p eri od b et ween 1902-1920, wa sfol l owed

b y a verywa rm p eri od b et ween 1925-1965. Si nce a round 1990, t he t i me series

shows t hei nd i cat i onof a newwa rmp eri od.

2 . T he se e xt r em e p ha se s a r e s t ro ng ly c or r el at ed w it h t h e p ha se s o f A MO i n de x.

Hi gh v al ue s o f P C1 o f s umme r t emp er at ur e o ve r Ro man ia ar e s tr on gl y

correl at ed wi t h a nomal ousl y hi gh SSTover t heent i re North At la nti c b asi n.

3. The correl at i oncoeffi ci ent s b etween PC1a nd AMO i nd exa nd t he frequency of

t he s um me r p at t er n s ( P hi l li p e t a l. , 2 00 7) s ho ws t ha t b ot h P C1 a nd A MO i n de x

a rest rongl y rel at ed wi t h t wop a t t erns,g i ven b y cl ust ers 2 a nd 6.

4 . O ne o f t h e m a in i mp or t an t a sp ec ts o f o ur s t ud y i s t ha t w e p r o ve d t h a t n ot o nl y

o n g lo ba l o r c on ti n en ta l s ca l e, b ut a ls o a t a r eg io na l s ca le , t he i n fl u en ce o f

AMO ha sa st rong i mpa ct, especia l l yd uri ng summer.

thods

d ata s ets were process ed in the s ame way. Firs t, the s ummerans ( JJ A) we re c al cu lat ed f ro m mo nt hl y me ans . Th en, t he

mme r a no ma li es wi t h r es pe ct t o t he me an a nd n or ma li ze d b y nd ar d d ev ia ti on , e st i ma te d f or t he p er io d 1 90 2- 20 02 , w er e

d uc ed. Sinc e our focus is the multidec ad al c ha ra cter of the d ataw e h av e a pp li ed a 2 1- ye ar r un ni ng me an t o t he s ta nd ar di ze d

e s eries for a ll d ata s ets .order to id entify the d ominant d ec ad al c omponents in the flow

e s eries we used Sing ular Spectrum Ana lysis . SSA is a novel a ndwerful tool for time series analysis that can identify intermittent

illation s pells in s hort, nois y time s eries. T he bas ic osc illationso which a time series decomposes are not functi ons of a

s cribed, harmonic form. I ns tea d, their s ha pes a re d eterminedm t he t i me s er ie s i t se lf . S SA h as b ee n s uc ce ss fu ll y a pp li ed t o

ny g eo ph ys ic al a nd c li ma to lo gi ca ll y t i me s er ie s t o s tu dy a nddict periodicactivities.