Our previous studies on low-frequency electromagnetic cyclotron waves(ECWs)with amplitudes larger than 0.1nT in the solar wind revealed that the left-handed(LH)polarized ECWs are the dominant waves,and these waves pre...Our previous studies on low-frequency electromagnetic cyclotron waves(ECWs)with amplitudes larger than 0.1nT in the solar wind revealed that the left-handed(LH)polarized ECWs are the dominant waves,and these waves preferentially occur in plasma conditions of high proton speed(V_(p)),high proton temperature(T_(p)),low proton density(N_(p)).In the present study,using magnetic field and plasma data from the Wind mission between 2005 and2015,we perform a survey of small-amplitude ECWs with amplitudes smaller than 0.1 nT.It is revealed for the first time that the small-amplitude right-handed(RH)polarized ECWs tend to frequently occur in plasmas characterized by low V_(p),low T_(p),low N_(p),although the small-amplitude LH ECWs still preferentially occur in plasma conditions similar to the LH ECWs with amplitudes larger than 0.1 nT.Further investigation shows that the occurrences of small-amplitude RH ECWs and long-lasting radial interplanetary magnetic field(lrIMF)share the similar preferential plasma conditions of low T_(p)and low N_(p).During lrIMF events,in particular,the occurrence rates of RH and LH ECWs are comparable,with the occurrence rate of small-amplitude RH ECWs slightly larger than that of small-amplitude LH ECWs.The generation mechanism of the small-amplitude ECWs is discussed.展开更多
According to Wind observations between 2005 and 2015,this paper investigates the dependences of the occurrence of low frequency electromagnetic cyclotron waves(ECWs)on the plasma parameters,the solar cycle,and the ori...According to Wind observations between 2005 and 2015,this paper investigates the dependences of the occurrence of low frequency electromagnetic cyclotron waves(ECWs)on the plasma parameters,the solar cycle,and the orientations of alpha-proton drift velocity(Vd)and the ambient magnetic field(B).The occurrence rates of ECWs with respect to six plasma parameters are calculated.Results show that the preferential conditions for generation of left-handed(LH)ECWs are higher proton temperature(Tp),higher proton velocity(Vp),lower proton density(Np),stronger proton temperature anisotropy(T⊥/T‖),higher normalized alpha-proton drift velocity(Vd/VA),and higher normalized alpha particle density(Nα/Np),where T⊥and T‖refer to proton temperatures perpendicular and parallel to B,and VAis the local Alfvén velocity.For right-handed(RH)ECWs,however,the dependences on these plasma parameters are not obvious.On the other hand,it is found that the occurrence rate of LH ECWs increases as the sunspot number decreases,and decreases as the sunspot number increases.Further investigation shows that the increased occurrence rate of LH ECWs is accompanied by an increase in the medians of Vp,Vd/VA,and Nα/Np.For RH ECWs,the occurrence rate appears to be nearly unrelated to the sunspot number,suggesting a negligible correlation with the solar cycle.In addition,a modified angle is introduced to include the factors of orientation of B(anti-sunward or sunward)and angle between Vdand B,simultaneously.It is found that the occurrence of LH ECWs has the strong preferential condition that Vdis anti-sunward,while a different situation arises for RH ECWs.These results are discussed in the context of the temperature-anisotropy-driven instabilities with the effect of alpha particles.展开更多
基金supported by NSFC under grant Nos.42174202,41874204,41974197,and 12103018supported partly by the Excellent Young Scientists Fund in Henan Province under grant No.222300420061。
文摘Our previous studies on low-frequency electromagnetic cyclotron waves(ECWs)with amplitudes larger than 0.1nT in the solar wind revealed that the left-handed(LH)polarized ECWs are the dominant waves,and these waves preferentially occur in plasma conditions of high proton speed(V_(p)),high proton temperature(T_(p)),low proton density(N_(p)).In the present study,using magnetic field and plasma data from the Wind mission between 2005 and2015,we perform a survey of small-amplitude ECWs with amplitudes smaller than 0.1 nT.It is revealed for the first time that the small-amplitude right-handed(RH)polarized ECWs tend to frequently occur in plasmas characterized by low V_(p),low T_(p),low N_(p),although the small-amplitude LH ECWs still preferentially occur in plasma conditions similar to the LH ECWs with amplitudes larger than 0.1 nT.Further investigation shows that the occurrences of small-amplitude RH ECWs and long-lasting radial interplanetary magnetic field(lrIMF)share the similar preferential plasma conditions of low T_(p)and low N_(p).During lrIMF events,in particular,the occurrence rates of RH and LH ECWs are comparable,with the occurrence rate of small-amplitude RH ECWs slightly larger than that of small-amplitude LH ECWs.The generation mechanism of the small-amplitude ECWs is discussed.
基金supported by NSFC under grant Nos.41874204,42174202,41974197,12103018supported partly by the Excellent Young Scientists Fund in Henan Province under grant No.222300420061。
文摘According to Wind observations between 2005 and 2015,this paper investigates the dependences of the occurrence of low frequency electromagnetic cyclotron waves(ECWs)on the plasma parameters,the solar cycle,and the orientations of alpha-proton drift velocity(Vd)and the ambient magnetic field(B).The occurrence rates of ECWs with respect to six plasma parameters are calculated.Results show that the preferential conditions for generation of left-handed(LH)ECWs are higher proton temperature(Tp),higher proton velocity(Vp),lower proton density(Np),stronger proton temperature anisotropy(T⊥/T‖),higher normalized alpha-proton drift velocity(Vd/VA),and higher normalized alpha particle density(Nα/Np),where T⊥and T‖refer to proton temperatures perpendicular and parallel to B,and VAis the local Alfvén velocity.For right-handed(RH)ECWs,however,the dependences on these plasma parameters are not obvious.On the other hand,it is found that the occurrence rate of LH ECWs increases as the sunspot number decreases,and decreases as the sunspot number increases.Further investigation shows that the increased occurrence rate of LH ECWs is accompanied by an increase in the medians of Vp,Vd/VA,and Nα/Np.For RH ECWs,the occurrence rate appears to be nearly unrelated to the sunspot number,suggesting a negligible correlation with the solar cycle.In addition,a modified angle is introduced to include the factors of orientation of B(anti-sunward or sunward)and angle between Vdand B,simultaneously.It is found that the occurrence of LH ECWs has the strong preferential condition that Vdis anti-sunward,while a different situation arises for RH ECWs.These results are discussed in the context of the temperature-anisotropy-driven instabilities with the effect of alpha particles.
