简介：Low-frequencychorusemissionshaverecentlyattractedmuchattentionduetothesuggestionthattheymayplayimportantrolesinthedynamicsoftheVanAllenBelts.However,themechanism(s)generatingtheselow-frequencychorusemissionshavenotbeenwellunderstood.Inthisletter,wereportaninterestingcaseinwhichbackgroundplasmadensityloweredthelowercutofffrequencyofchorusemissionsfromabove0.1fce(typicalordinarychorus)to0.02fce(extremelylow-frequencychorus).Thoseextremelylow-frequencychoruswaveswereobservedinaratherdenseplasma,wherethenumberdensityNewasfoundtobeseveraltimeslargerthanhasbeenassociatedwithobservationsofordinarychoruswaves.Forsuprathermalelectronswhosefreeenergyissuppliedbyanisotropictemperatures,lineargrowthrates(calculatedusingin-situplasmaparametersmeasuredbytheVanAllenProbes)showthatwhistlermodeinstabilitycanoccuratfrequenciesbelow0.1fcewhenthebackgroundplasmadensityNeincreases.EspeciallywhenNereaches90cm^-3ormore,thelowestunstablefrequencycanextendto0.02fceorevenless,whichisconsistentwithsatelliteobservations.Therefore,ourresultsdemonstratethatadensebackgroundplasmacouldplayanessentialroleintheexcitationofextremelylowfrequencychoruswavesbycontrollingthewavegrowthrates.

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简介：Whistler-modechoruswavesareregardedasanimportantaccelerationmechanismcontributingtotheformationofrelativisticandultra-relativisticelectronsintheJovianradiationbelts.QuantitativedeterminationofthechoruswavedrivenelectronscatteringeffectintheJovianmagnetosphererequiresdetailedinformationofbothambientmagneticfieldandplasmadensityandwavespectralproperty,whichhowevercannotbealwaysreadilyacquiredfromobservationsofexistedmissionstoJupiter.WethereforeperformacomprehensiveanalysisofthesensitivityofchorusinducedelectronscatteringratestoambientmagnetosphericandwaveparametersintheJovianradiationbeltstoelaboratetowhichextentthediffusioncoefficientsdependonanumberofkeyinputparameters.Itisfoundthatquasi-linearelectronscatteringratesbychoruscanbestronglyaffectedbytheambientmagneticfieldintensity,thewavelatitudinalcoverage,andthepeakfrequencyandbandwidthofthewavespectraldistributionintheJovianmagnetosphere,whiletheyonlyrelyslightlyonthebackgroundplasmadensityprofileandthepeakwavenormalangle,especiallywhenthewaveemissionsareconfinedatlowerlatitudes.Giventhechoruswaveamplitude,chorusinducedelectronscatteringratesstronglydependonJovianL-shelltoexhibitatendencyapproximatelyproportionaltoLJ3.OurcomprehensiveanalysisexplicitlydemonstratestheimportanceofreliableinformationofboththeambientmagnetosphericstateandwavedistributionpropertytounderstandingthedynamicelectronevolutionintheJovianradiationbeltsandthereforehasimplicationsforfuturemissionplanningtoexploretheextremeparticleradiationenvironmentofJupiteranditssatellites.