简介：Magneticreconnectionisthemostfundamentalenergy-transfermechanismintheuniversethatconvertsmagneticenergyintoheatandkineticenergyofchargedparticles.Forreconnectiontooccur,thefrozen-inconditionmustbreakdowninalocalizedregion,commonlycalledthe‘diffusionregion’.InEarth’smagnetosphere,iondiffusionregionshavealreadybeenobserved,whileelectrondiffusionregionshavenotbeendetectedduetotheirsmallscales(oftheorderofafewkm)(Paschmann,2008).Inthispaperwereport,forthefirsttime,insituobservationsofanactiveelectrondiffusionregionbythefourClusterspacecraftattheEarth’shighlatitudemagnetopause.Theelectrondiffusionregionischaracterizedbynongyrotropicelectrondistribution,strongfield-alignedcurrentscarriedbyelectronsandbi-directionalsuper-Alfvénicelectronjets.Alsoobservedweremultiplemicro-scalefluxropes,withascalesizeofabout5c/ωpe(12km,withc/ωpetheelectroninertiallength),thatarecrucialforelectronaccelerationintheguide-fieldreconnectionprocess(Drakeetal.,2006a).Thedatademonstratetheexistenceoftheelectrondiffusionregionincollisionlessguide-fieldreconnectionatthemagnetopause.