Deection of geomagnetic jerks using wavelet analysis Mioara, Alexa,ndrescu, x Dominique Gibert, 2 Ga,uthier Hulot,

Abstract. Wa,velet a,na,lysis is a.pI•lied to detect a.nd cha, ra.cte,'ize singula, r events, or singula, rities, or jerks, in the time series,,•a,de of the last centu,-y monthly mean values of the east component of the geomagnetic field fi'om Europea, n observa.tories. After choosing a, wel!-a,da,pted wavelet function, the analysis is first performed on synthetic series including a,n "inte,'na,l", or 'hnain'.', signal ma,de of smooth variation intervals epa.rated by singnla, r events with different "regula, rities", a white noise and an "externa.l " signa.1 ma,de of the sunt of a few ha, r,nonics of a, long-period va,ria.tion (11 yea,rs). The signa.tures of the,hain, noise, a.nd ha,rmonic signals a,re studied and compared, and the conditions in which the singular events ca,n be clea,rly isola, ted in the composite signa,1 a,re elucida,ted. The,t we a,lq•ly the n•ethod systema,tica.lly to the real geoma,gnetic series (monthly meaats of Y f,'om Eurolma. n ol>serva,t. ories) a,nd sl•ow that five a.nd only five re•a,,'ka,l•le vents a.re fo•nd i • 1901, 1913, 1925, 1969, and 1978. The cha,ra,cteristics of these singula,rities (i•t l•a,rticula,r, homogeneity of some derived functions of the waarelet tra.nsibrn • over a. la.rge ra,nge of timesca.les) demonstra.te tha.t these events ha.ve a. si•tgle source (of course, inte,'na.1). Also the events a, re more singula.r thaa • wa.s l•reviously S•l•l•osed (their "regula,rity " is closer to 1.5 tha,n to '2., indica.ting tlta.t noirinteger I•owers of ti•t•e should be used in representing the time series l•etween the jerks)