VLF波渗透电离层传播计算研究进展
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摘要
3~30 kHz的甚低频(Very-Low-ITcquency,VLF)电磁波对近地空间的高能粒子分布具有非常重要的作用.闪电和地面VLF通信台等VLF波主要辐射源产生的VLF波能够渗透进入电离层,并以哨声波模式继续传播至磁层与高能粒子发生相互作用.本文从VLF电磁波渗透电离层传播计算方法的发展、计算模型验证以及模型在电离层现象研究中的应用等方面对VLF波渗透进电离层之后的传播计算的研究进展进行综述,并对未来研究进行初步展望.
Very Low Frequency(VLF) electromagnetic wave(3~30kHz) mainly radiated by lightening and ground-based VLF transmitters,which plays a very important role on controlling the distribution of high energy particles in the magnetosphere.VLF radiation can penetrate into the ionosphere,and propagate in whistler mode in the ionosphere,and interact with high energy particles in the magnetosphere.In this paper,the development of the calculation model of VLF wave penetrating into the ionosphere,the validation of the model and the application of the model in the study of the ionospheric phenomena are reviewed,and a preliminary outlook for future work has also been made.
Very Low Frequency(VLF) electromagnetic wave(3~30kHz) mainly radiated by lightening and ground-based VLF transmitters,which plays a very important role on controlling the distribution of high energy particles in the magnetosphere.VLF radiation can penetrate into the ionosphere,and propagate in whistler mode in the ionosphere,and interact with high energy particles in the magnetosphere.In this paper,the development of the calculation model of VLF wave penetrating into the ionosphere,the validation of the model and the application of the model in the study of the ionospheric phenomena are reviewed,and a preliminary outlook for future work has also been made.
引文
[1]CHRISSAN D A,FRASER-SMITH A C.Seasonal variations of globally measured ELF/VLF radio noise[J].Radio Sci.,1996,31(5):1141-1152
[2]UMAN M A,HORNSTEIN J.The lightening discharge[J].Phys.Today,1989,42(5):75-76
[3]WATT T M.Obtaining local values of plasma scale height with the Alouette 1 topside sounder[J].J.Geophys.Res.,1967,72(15):3843-3853
[4]SWANSON E R,KUGEL C P.VLF timing:conventional and modern techniques including omega[J].Proc.IEEE,1972,60(5):540-551
[5]DAVIES K.Ionospheric Radio[M].London:The Institution of Electrical Engineering and Technology,1990
[6]STOREY L R O.An investigation of whistling atmospherics[J].Phil.Trans.Roy.Soc.A:Math.Phys.Eng.Sci.,1953,246(908):113-141
[7]HELLIWELL R A.Whistlers and Related Ionospheric Phenomena[M].California:Stanford University Press,1965
[8]XU Jisheng,MO Qixu.Transmission characteristics of low latitude whistlers through the lower ionosphere-full wave solution[J].Acta Geophys.Sin.,1989,32(3):256-261(徐继生,莫启绪.低纬哨声通过低电离层传播的透射特征—全波解[J].地球物理学报,1989,32(3):256-261)
[9]NAGANO I,MAMBO M,HUTATSUISHI G.Numerical calculation of electromagnetic waves in an anisotropic multilayered medium[J].Radio Sci.,1975,10(6):611-617
[10]HAYAKAWA M,TANAKA Y.On the propagation of lowlatitude whistlers[J].Rev.Geophys.,1978,16(1):111-123
[11]XU Jisheng,BAO Zongti,LIANG Baixian.A method of3-D ray tracing of whistler-mode waves using the IGRF model[J].Acta Geophys.Sin.,1985,28(5):443-451(徐继生,保宗悌,梁百先.国际地磁参考场中哨声模波的三维射线跟踪算法[J].地球物理学报,1985,28(5):443-451)
[12]XU Jisheng,TIAN Mao,MA Shuying,et al.Multistationed wide band direction finding measurements for whistlers at geomagnetic latitudes below 20°in China and some early results[J].Acta Geophys.Sin.,1989,32(2):125-134(徐继生,田茂,马淑英,等.磁纬20°以下地区哨声多台宽带定向观测及其初步结果[J].地球物理学报,1989,32(2):125-134)
[13]ONDOH T,KOTAKI M,MURAKAMI T,et al.Propagation characteristics of low-latitude whistlers[J].J.Geophys.Res.,1979,84(A5):2097-2104
[14]WU Xiangyang,BAO Zongti,NAGANO I,et al.Numerical simulation of the whistler penetration process through the lower ionosphere at very-low-latitude[J].Acta Geophys.Sin.,1996,39(5):588-600(吴向阳,保宗悌,长野勇,等.甚低纬哨声低电离层透射过程的数值模拟[J].地球物理学报,1996,39(5):588-600)
[15]KENNEL C F,PETSCHEK H E.Limit on stably trapped particle fluxes[J].J.Geophys.Res.,1966,71(1):1-28
[16]LYONS L R,THORNE R M,KENNEL C F.Pitch-angle diffusion of radiation belt electrons within the plasmasphere[J].J.Geophys.Res.,1972,77:3455-3474
[17]IMHOF W L,REAGAN J B,VOSS H D,et al.The modulated precipitation of radiation belt electrons by controlled signals from VLF transmitters[J].Geophys.Res.Lett,1983,10(8):615-618
[18]INAN U S,CARPENTER D L.Lightning-induced electron precipitation events observed at L~2.4 as phase and amplitude perturbations on subionospheric VLF signals[J].J.Geophys.Res.,1987,92(A4):3293-3303
[19]VAMPOLA A L.VLF transmission induced slot electron precipitation[J].Geophys.Res.Lett.,1977,4(12):569-572
[20]ABEL B,THORNE R M.Electron scattering loss in Earth's inner magnetosphere:2.Sensitivity to model parameters[J].J.Geophys.Res.,1998,103(A2):2397-2408
[21]BARR R,STUBBE P.ELF radiation from the Tromso"super heater"facility[J].Geophys.Res.Lett.,1991,18(6):1035-1038
[22]PLATINO M,INAN U S,BELL T F,et al.DEMETER observations of ELF waves injected with the HAARP HF transmitter[J].Geophys.Res.Lett.,2006,33(16):L16101
[23]WANG Feng,ZHAO Zhengyu,ZHANG Yuannong.Numerical modeling of ionospheric current artificial modulation at low latitude[J].Chin.J.Geophys.,2009,52(4):887-894(汪枫,赵正予,张援农.低纬地区电离层电流的人工调制数值模拟[J].地球物理学报,2009,52(4):887-894)
[24]INAN U S,CHANG H C,HELLIWELL R A.Electron precipitation zones around major ground-based VLF signal sources[J].J.Geophys.Res.,1984,89(A5):2891-2906
[25]ABEL B,THORNE R M.Electron scattering loss in Earth's inner magnetosphere:1.Dominant physical processes[J].J.Geophys.Res.,1998,103(A2):2385-2396
[26]BORTNIK J,INAN U S,BELL T F.L dependence of energetic electron precipitation driven by magnetospherically reflecting whistler waves[J].J.Geophys.Res.,2002,107(A8):SMP 1-1-SMP 1-13.DOI:10.1029/2001JA000303
[27]STARKS M J,QUINN R A,GINET G P,et al.Illumination of the plasmasphere by terrestrial very low frequency transmitters:model validation[J].J.Geophys.Res.,2008,113:A09320.DOI:10.1029/2008JA013112
[28]GOLDEN D I,SPASOJEVIC M,FOUST F R,et al.Role of the plasmapause in dictating the ground accessibility of ELF/VLF chorus[J].J.Geophys.Res.,2010,115:A11211.DOI:10.1029/2010JA015955
[29]CRARY J H.The Effect of the Earth-Ionosphere Waveguide on Whistlers[R].Stanford,California:Stanford Electron Laboratory,Stanford University,1961
[30]YAGITANI S,NAGANO I,MIYAMURA K,et al.Full wave calculation of ELF/VLF propagation from a dipole source located in the lower ionosphere[J].Radio Sci.,1994,29(1):39-54
[31]LEHTINEN N G,INAN U S.Radiation of ELF/VLF waves by harmonically varying currents into a stratified ionosphere with application to radiation by a modulated electrojet[J].J.Geophys.Res.,2008,113:A06301
[32]WAIT J R,CULLEN A L,FOCK V A,et al.Electromagnetic Waves in Stratified Media[M].Oxford:Pergamon Press,1970
[33]BUDDEN K G.The Propagation of Radio Waves:The Theory of Radio Waves of Low Power in the Ionosphere and Magnetosphere[M].Cambridge:Cambridge University Press,1985
[34]NYGREN T.A method of full wave analysis with improved stability[J].Planet.Space Sci.,1982,30(4):427-430
[35]CHO M,RYCROFT M J.Computer simulation of the electric field structure and optical emission from cloudtop to the ionosphere[J].J.Atmos.Sol.-Terr.Phys.,1998,60(7/8/9):871-888
[36]CUMMER S A.Modeling electromagnetic propagation in the Earth-ionosphere waveguide[J].IEEE Trans.Antenn.Propag.,2000,48(9):1420-1429
[37]HU W,CUMMER S A.An FDTD model for low and high altitude lightning-generated EM fields[J].IEEE Trans.Antenn.Propag.,2006,54(5):1513-1522
[38]SIMPSON J J,TAFLOVE A.Three-dimensional FDTD modeling of impulsive ELF propagation about the earthsphere[J].IEEE Trans.Antenn.Propag.,2004,52(2):443-451
[39]YANG Y,HU S M,CHEN R S.A combination of FDTD and least-squares support vector machines for analysis of microwave integrated circuits[J].Microw.Opt.Technol.Lett,2005,44(3):296-299
[40]LEHTINEN N G,INAN U S.Full-wave modeling of transionospheric propagation of VLF waves[J].Geophys.Res.Lett.,2009,36:L03104.DOI:10.1029/2008GL036535
[41]COHEN M B,LEHTINEN N G,INAN U S.Models of ionospheric VLF absorption of powerful ground based transmitters[J].Geophys.Res.Lett,2012,39:L24101.DOI:10.1029/2012GL054437
[42]NAGANO I,ROSEN P A,YAGITANI S,et al.Full wave analysis of the Australian Omega signal observed by the Akebono satellite[J].IEICE Trans.Commun.,1993,E76-B(12):1571-1578
[43]TAO X,BORTNIK J,FRIEDRICH M.Variance of transionospheric VLF wave power absorption[J].J.Geophys.Res.,2010,115:A07303.DOI:10.1029/2009JA015115
[44]FOUST F R,INAN U S,BELL T,et al.Quasi-electrostatic whistler mode wave excitation by linear scattering of EM whistler mode waves from magnetic fieldaligned density irregularities[J].J.Geophys.Res.,2010,115:A11310.DOI:10.1029/2010JA015850
[45]SHAO X,ELIASSON B,SHARMA A S,et al.Attenuation of whistler waves through conversion to lower hybrid waves in the low-altitude ionosphere[J].J.Geophys.Res.,2012,117:A04311.DOI:10.1029/2011JA017339
[46]BELL T F,INAN U S,PIDDYACHIY D,et al.Effects of plasma density irregularities on the pitch angle scattering of radiation belt electrons by signals from ground based VLF transmitters[J].Geophys.Res.Lett.,2008,35:L19103.DOI:10.1029/2008GL034834
[47]COHEN M B,INAN U S.Terrestrial VLF transmitter injection into the magnetosphere[J].J.Geophys.Res.,2012,117:A08310.DOI:10.1029/2012JA017992
[48]WANG Feng,ZHAO Zhengyu,CHANG Shanshan,et al.Radiation of ELF waves by ionospheric artificial modulation into a stratified ionosphere[J].Chin.J.Geophys.,2012,55(7):2167-2176(汪枫,赵正予,常珊珊,等.电离层人工调制在水平分层电离层中所激发的ELF波辐射[J].地球物理学报,2012,55(7):2167-2176)
[49]KUMAR A,KUMAR S,HAYAKAWA M,et al.Subionospheric VLF perturbations observed at low latitude associated with earthquake from Indonesia region[J].J.Atmos.Sol.-Terr.Phys.,2013,102(3):71-80
[50]PARROT M,INAN U S,LEHTINEN N G.V-shaped VLF streaks recorded on DEMETER above powerful thunderstorms[J].J.Geophys.Res.,2008,113:A10310.DOI:10.1029/2008JA013336
[51]SMITH R L.VLF observations of auroral beams as sources of a class of emissions[J].Nature,1969,224(5217):351-352
[52]JAMES H G.VLF saucers[J].J.Geophys.Res.,1976,81(4):501-514
[53]HAYAKAWA M,MOLCHANOV O A,ONDOH T,et al.Anomalies in the sub-ionospheric VLF signals for the 1995Hyogo-ken Nanbu earthquake[J].J.Phys.Earth,1996,44(4):413-418
[54]MOLCHANOV O A,HAYAKAWA M.Subionospheric VLF signal perturbations possibly related to earthquakes[J].J.Geophys.Res.,1998,103(A8):17489-17504
[55]ZHAO Shufan,ZHANG Xuemin,ZHAO Zhengyu,et al.The numerical simulation on ionospheric perturbations in electric field before large earthquakes[J].Ann.Geophys.,2014,32(12):1487-1493
[56]XU Wenyao.Effects of the ionization density distribution on non-ducted whistler wave propagation at middle and low latitudes[J].Acta Geophys.Sin.,1989,32(3):245-255(徐文耀.电离密度分布对中低纬非导管哨声波传播的影响[J].地球物理学报,1989,32(3):245-255)
[57]ZHAO Shufan,ZHANG Xuemin,ZHAO Zhengyu,et al.Temporal variations of electromagnetic responses in the ionosphere excited by the NWC communication station[J].Chin.J.Geophys.,2015,58(7):2263-2273(赵庶凡,张学民,赵正予,等.NWC通信台在电离层中激发电磁响应的时变特征[J].地球物理学报,2015,58(7):2263-2273)
[58]GRAF K L,LEHTINEN N G,SPASOJEVIC M,et al.Analysis of experimentally validated trans-ionospheric attenuation estimates of VLF signals[J].J.Geophys.Res.,2013,118(5):2708-2720
[2]UMAN M A,HORNSTEIN J.The lightening discharge[J].Phys.Today,1989,42(5):75-76
[3]WATT T M.Obtaining local values of plasma scale height with the Alouette 1 topside sounder[J].J.Geophys.Res.,1967,72(15):3843-3853
[4]SWANSON E R,KUGEL C P.VLF timing:conventional and modern techniques including omega[J].Proc.IEEE,1972,60(5):540-551
[5]DAVIES K.Ionospheric Radio[M].London:The Institution of Electrical Engineering and Technology,1990
[6]STOREY L R O.An investigation of whistling atmospherics[J].Phil.Trans.Roy.Soc.A:Math.Phys.Eng.Sci.,1953,246(908):113-141
[7]HELLIWELL R A.Whistlers and Related Ionospheric Phenomena[M].California:Stanford University Press,1965
[8]XU Jisheng,MO Qixu.Transmission characteristics of low latitude whistlers through the lower ionosphere-full wave solution[J].Acta Geophys.Sin.,1989,32(3):256-261(徐继生,莫启绪.低纬哨声通过低电离层传播的透射特征—全波解[J].地球物理学报,1989,32(3):256-261)
[9]NAGANO I,MAMBO M,HUTATSUISHI G.Numerical calculation of electromagnetic waves in an anisotropic multilayered medium[J].Radio Sci.,1975,10(6):611-617
[10]HAYAKAWA M,TANAKA Y.On the propagation of lowlatitude whistlers[J].Rev.Geophys.,1978,16(1):111-123
[11]XU Jisheng,BAO Zongti,LIANG Baixian.A method of3-D ray tracing of whistler-mode waves using the IGRF model[J].Acta Geophys.Sin.,1985,28(5):443-451(徐继生,保宗悌,梁百先.国际地磁参考场中哨声模波的三维射线跟踪算法[J].地球物理学报,1985,28(5):443-451)
[12]XU Jisheng,TIAN Mao,MA Shuying,et al.Multistationed wide band direction finding measurements for whistlers at geomagnetic latitudes below 20°in China and some early results[J].Acta Geophys.Sin.,1989,32(2):125-134(徐继生,田茂,马淑英,等.磁纬20°以下地区哨声多台宽带定向观测及其初步结果[J].地球物理学报,1989,32(2):125-134)
[13]ONDOH T,KOTAKI M,MURAKAMI T,et al.Propagation characteristics of low-latitude whistlers[J].J.Geophys.Res.,1979,84(A5):2097-2104
[14]WU Xiangyang,BAO Zongti,NAGANO I,et al.Numerical simulation of the whistler penetration process through the lower ionosphere at very-low-latitude[J].Acta Geophys.Sin.,1996,39(5):588-600(吴向阳,保宗悌,长野勇,等.甚低纬哨声低电离层透射过程的数值模拟[J].地球物理学报,1996,39(5):588-600)
[15]KENNEL C F,PETSCHEK H E.Limit on stably trapped particle fluxes[J].J.Geophys.Res.,1966,71(1):1-28
[16]LYONS L R,THORNE R M,KENNEL C F.Pitch-angle diffusion of radiation belt electrons within the plasmasphere[J].J.Geophys.Res.,1972,77:3455-3474
[17]IMHOF W L,REAGAN J B,VOSS H D,et al.The modulated precipitation of radiation belt electrons by controlled signals from VLF transmitters[J].Geophys.Res.Lett,1983,10(8):615-618
[18]INAN U S,CARPENTER D L.Lightning-induced electron precipitation events observed at L~2.4 as phase and amplitude perturbations on subionospheric VLF signals[J].J.Geophys.Res.,1987,92(A4):3293-3303
[19]VAMPOLA A L.VLF transmission induced slot electron precipitation[J].Geophys.Res.Lett.,1977,4(12):569-572
[20]ABEL B,THORNE R M.Electron scattering loss in Earth's inner magnetosphere:2.Sensitivity to model parameters[J].J.Geophys.Res.,1998,103(A2):2397-2408
[21]BARR R,STUBBE P.ELF radiation from the Tromso"super heater"facility[J].Geophys.Res.Lett.,1991,18(6):1035-1038
[22]PLATINO M,INAN U S,BELL T F,et al.DEMETER observations of ELF waves injected with the HAARP HF transmitter[J].Geophys.Res.Lett.,2006,33(16):L16101
[23]WANG Feng,ZHAO Zhengyu,ZHANG Yuannong.Numerical modeling of ionospheric current artificial modulation at low latitude[J].Chin.J.Geophys.,2009,52(4):887-894(汪枫,赵正予,张援农.低纬地区电离层电流的人工调制数值模拟[J].地球物理学报,2009,52(4):887-894)
[24]INAN U S,CHANG H C,HELLIWELL R A.Electron precipitation zones around major ground-based VLF signal sources[J].J.Geophys.Res.,1984,89(A5):2891-2906
[25]ABEL B,THORNE R M.Electron scattering loss in Earth's inner magnetosphere:1.Dominant physical processes[J].J.Geophys.Res.,1998,103(A2):2385-2396
[26]BORTNIK J,INAN U S,BELL T F.L dependence of energetic electron precipitation driven by magnetospherically reflecting whistler waves[J].J.Geophys.Res.,2002,107(A8):SMP 1-1-SMP 1-13.DOI:10.1029/2001JA000303
[27]STARKS M J,QUINN R A,GINET G P,et al.Illumination of the plasmasphere by terrestrial very low frequency transmitters:model validation[J].J.Geophys.Res.,2008,113:A09320.DOI:10.1029/2008JA013112
[28]GOLDEN D I,SPASOJEVIC M,FOUST F R,et al.Role of the plasmapause in dictating the ground accessibility of ELF/VLF chorus[J].J.Geophys.Res.,2010,115:A11211.DOI:10.1029/2010JA015955
[29]CRARY J H.The Effect of the Earth-Ionosphere Waveguide on Whistlers[R].Stanford,California:Stanford Electron Laboratory,Stanford University,1961
[30]YAGITANI S,NAGANO I,MIYAMURA K,et al.Full wave calculation of ELF/VLF propagation from a dipole source located in the lower ionosphere[J].Radio Sci.,1994,29(1):39-54
[31]LEHTINEN N G,INAN U S.Radiation of ELF/VLF waves by harmonically varying currents into a stratified ionosphere with application to radiation by a modulated electrojet[J].J.Geophys.Res.,2008,113:A06301
[32]WAIT J R,CULLEN A L,FOCK V A,et al.Electromagnetic Waves in Stratified Media[M].Oxford:Pergamon Press,1970
[33]BUDDEN K G.The Propagation of Radio Waves:The Theory of Radio Waves of Low Power in the Ionosphere and Magnetosphere[M].Cambridge:Cambridge University Press,1985
[34]NYGREN T.A method of full wave analysis with improved stability[J].Planet.Space Sci.,1982,30(4):427-430
[35]CHO M,RYCROFT M J.Computer simulation of the electric field structure and optical emission from cloudtop to the ionosphere[J].J.Atmos.Sol.-Terr.Phys.,1998,60(7/8/9):871-888
[36]CUMMER S A.Modeling electromagnetic propagation in the Earth-ionosphere waveguide[J].IEEE Trans.Antenn.Propag.,2000,48(9):1420-1429
[37]HU W,CUMMER S A.An FDTD model for low and high altitude lightning-generated EM fields[J].IEEE Trans.Antenn.Propag.,2006,54(5):1513-1522
[38]SIMPSON J J,TAFLOVE A.Three-dimensional FDTD modeling of impulsive ELF propagation about the earthsphere[J].IEEE Trans.Antenn.Propag.,2004,52(2):443-451
[39]YANG Y,HU S M,CHEN R S.A combination of FDTD and least-squares support vector machines for analysis of microwave integrated circuits[J].Microw.Opt.Technol.Lett,2005,44(3):296-299
[40]LEHTINEN N G,INAN U S.Full-wave modeling of transionospheric propagation of VLF waves[J].Geophys.Res.Lett.,2009,36:L03104.DOI:10.1029/2008GL036535
[41]COHEN M B,LEHTINEN N G,INAN U S.Models of ionospheric VLF absorption of powerful ground based transmitters[J].Geophys.Res.Lett,2012,39:L24101.DOI:10.1029/2012GL054437
[42]NAGANO I,ROSEN P A,YAGITANI S,et al.Full wave analysis of the Australian Omega signal observed by the Akebono satellite[J].IEICE Trans.Commun.,1993,E76-B(12):1571-1578
[43]TAO X,BORTNIK J,FRIEDRICH M.Variance of transionospheric VLF wave power absorption[J].J.Geophys.Res.,2010,115:A07303.DOI:10.1029/2009JA015115
[44]FOUST F R,INAN U S,BELL T,et al.Quasi-electrostatic whistler mode wave excitation by linear scattering of EM whistler mode waves from magnetic fieldaligned density irregularities[J].J.Geophys.Res.,2010,115:A11310.DOI:10.1029/2010JA015850
[45]SHAO X,ELIASSON B,SHARMA A S,et al.Attenuation of whistler waves through conversion to lower hybrid waves in the low-altitude ionosphere[J].J.Geophys.Res.,2012,117:A04311.DOI:10.1029/2011JA017339
[46]BELL T F,INAN U S,PIDDYACHIY D,et al.Effects of plasma density irregularities on the pitch angle scattering of radiation belt electrons by signals from ground based VLF transmitters[J].Geophys.Res.Lett.,2008,35:L19103.DOI:10.1029/2008GL034834
[47]COHEN M B,INAN U S.Terrestrial VLF transmitter injection into the magnetosphere[J].J.Geophys.Res.,2012,117:A08310.DOI:10.1029/2012JA017992
[48]WANG Feng,ZHAO Zhengyu,CHANG Shanshan,et al.Radiation of ELF waves by ionospheric artificial modulation into a stratified ionosphere[J].Chin.J.Geophys.,2012,55(7):2167-2176(汪枫,赵正予,常珊珊,等.电离层人工调制在水平分层电离层中所激发的ELF波辐射[J].地球物理学报,2012,55(7):2167-2176)
[49]KUMAR A,KUMAR S,HAYAKAWA M,et al.Subionospheric VLF perturbations observed at low latitude associated with earthquake from Indonesia region[J].J.Atmos.Sol.-Terr.Phys.,2013,102(3):71-80
[50]PARROT M,INAN U S,LEHTINEN N G.V-shaped VLF streaks recorded on DEMETER above powerful thunderstorms[J].J.Geophys.Res.,2008,113:A10310.DOI:10.1029/2008JA013336
[51]SMITH R L.VLF observations of auroral beams as sources of a class of emissions[J].Nature,1969,224(5217):351-352
[52]JAMES H G.VLF saucers[J].J.Geophys.Res.,1976,81(4):501-514
[53]HAYAKAWA M,MOLCHANOV O A,ONDOH T,et al.Anomalies in the sub-ionospheric VLF signals for the 1995Hyogo-ken Nanbu earthquake[J].J.Phys.Earth,1996,44(4):413-418
[54]MOLCHANOV O A,HAYAKAWA M.Subionospheric VLF signal perturbations possibly related to earthquakes[J].J.Geophys.Res.,1998,103(A8):17489-17504
[55]ZHAO Shufan,ZHANG Xuemin,ZHAO Zhengyu,et al.The numerical simulation on ionospheric perturbations in electric field before large earthquakes[J].Ann.Geophys.,2014,32(12):1487-1493
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