DEMETER卫星观测的LF/MF电场频谱特征初步研究
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摘要
利用法国DEMETER卫星观测的电场数据,研究了中国及邻区(0°—60°N,60°E—140°E),频段为10kHz—3MHz,时间段为2008年1月1日—2008年9月12日期间的平均功率谱密度特征.文中选择了Kp指数的日平均值小于或等于4的数据,获得LF频段(10—20kHz)和MF频段(20kHz—3MHz)以16天为周期的昼侧和夜侧的平均功率谱密度空间分布图,得到了以下初步结果.LF频段:①昼侧,不同频率的谱在对应时段上形态相似度不高,主要呈现纬度分带特征.夜侧,不同频率的谱在对应时段上形态相似度较高,主要差异在于谱的幅度,同一频率不同时段的谱分带特征不明显;②昼侧谱的幅度值跨度要比夜侧的小很多,前者一般为1—1.5个数量级,而后者一般在2个以上,甚至达到4个数量级;③在汶川地震前后,平均功率谱密度在成都—兰州一线存在明显的变化.MF频段:①昼侧,不同频率对应时段的谱形态没有明显的相似性,同一频率不同时段的谱形态可能具有较好、弱或不具有相似性,具有明显、弱或不具纬度分带特征.夜侧,某些频段对应时段的谱形态具有明显的相似性,同一频率不同时段或者分时期的不同时段的谱形态具有较好的相似性,不具有明显的纬度分带特征,具有弱分区或者弱经度分带特征;②昼侧和夜侧的谱幅度变化都不大,基本都在0.5个数量级之内;③在汶川地震前后没有发现明显的平均功率谱密度变化.
Characteristics of the average power spectrum density (APSD) are studied using the data of electric field observed by DEMETER satellite.The study area covers China and its adjacent regions (0°—60°N,60°E—140°E),and the time period ranges from January 1,2008,to September 12,2008.The observed data during the days with average Kp index smaller than or equal to 4 were selected for analysis.Spatial distributions of dayside and nightside APSD with 16-day period were mapped for LF (10—20 kHz) and MF (20 kHz—3 MHz).We obtained the following preliminary results.For LF:① Spatial distributions of dayside APSD in the same period and at different frequencies show poor similarity in pattern and are characterized by latitudinal zonation,while those of nightside APSD display good pattern similarity,with main difference only in amplitude and without clear zonation.② The range of amplitude variation of dayside APSD is much smaller than that of nightside APSD,the former being generally in 1—1.5 orders,while the latter varying beyond 2 orders and even up to 4 orders.③ The APSD near Chengdu--Lanzhou changes clearly before and after the 2008 Wenchuan earthquake.For MF:① Spatial distributions of dayside APSD in the same period and at different frequencies show no similarity,and the distributions in different periods and at the same frequency may have good,poor or no similarity and may show clear,poor or no zonation.While the distributions of nightside APSD in the same period and at some frequencies display very good pattern similarity.Good similarity can be seen in the nightside APSD patterns deduced from data in different periods and at the same frequency,but no latitudinal zonation or only weak longitudinal zonation can be found.② Amplitude variations of both dayside and nightside APSD are not significant,being generally less than 0.5 orders.③ The APSD near Chengdu--Lanzhou did not show clear changes before and after the 2008 Wenchuan earthquake.
Characteristics of the average power spectrum density (APSD) are studied using the data of electric field observed by DEMETER satellite.The study area covers China and its adjacent regions (0°—60°N,60°E—140°E),and the time period ranges from January 1,2008,to September 12,2008.The observed data during the days with average Kp index smaller than or equal to 4 were selected for analysis.Spatial distributions of dayside and nightside APSD with 16-day period were mapped for LF (10—20 kHz) and MF (20 kHz—3 MHz).We obtained the following preliminary results.For LF:① Spatial distributions of dayside APSD in the same period and at different frequencies show poor similarity in pattern and are characterized by latitudinal zonation,while those of nightside APSD display good pattern similarity,with main difference only in amplitude and without clear zonation.② The range of amplitude variation of dayside APSD is much smaller than that of nightside APSD,the former being generally in 1—1.5 orders,while the latter varying beyond 2 orders and even up to 4 orders.③ The APSD near Chengdu--Lanzhou changes clearly before and after the 2008 Wenchuan earthquake.For MF:① Spatial distributions of dayside APSD in the same period and at different frequencies show no similarity,and the distributions in different periods and at the same frequency may have good,poor or no similarity and may show clear,poor or no zonation.While the distributions of nightside APSD in the same period and at some frequencies display very good pattern similarity.Good similarity can be seen in the nightside APSD patterns deduced from data in different periods and at the same frequency,but no latitudinal zonation or only weak longitudinal zonation can be found.② Amplitude variations of both dayside and nightside APSD are not significant,being generally less than 0.5 orders.③ The APSD near Chengdu--Lanzhou did not show clear changes before and after the 2008 Wenchuan earthquake.
引文
何宇飞,杨冬梅,陈化然,钱家栋,朱荣,Parrot M.2009.DEMETER卫星探测到可能与汶川地震有关的地面VLF发射站信号的信噪比变化[J].中国科学:D辑,39(4):403--412.
朱荣,杨冬梅,荆凤,杨俊英,欧阳新艳.2008.DEMETER卫星观测到的云南普洱地震前的电离层扰动[J].地震学报,30(1):76--81.
Chmyrev V M,Isaev N V,Bilichenko S V,Stanev G.1989.Observation by space-borne detectors of electric fields andhydromagnetic waves in the ionosphere over an earthquake center[J].Phys Earth Planet Inter,57(1-2):110--114.
Hayakawa M,Molchanov O A,Ondoh T,Kawai E.1996.Precursory signature of the Kobe Earthquake on VLFsubion-ospheric signals[J].J At mos Electr,16(3):247--257.
Henderson T R,Sonwalker V S,Helli well R A,Inan US,Fraser-Smith A C.1993.Asearch for ELF/VLF emissionsinduced by earthquake as observedin theionosphere by the DE-2satellite[J].J Geophys Res,98(A6):9503--9514.
Larkina VI,Migulin V V,Molchanov O A,Galperin Iu I.1985.Earthquake effects in the ionosphere according to I N-TERCOSMOS-19and AUREOL-3satellite data[C]∥Results of the ARCAD-3Project and of the Recent Pro-grammes in Magnetospheric and Ionospheric Physics.Toulouse:Cepadues-Editions:685--699.
Molchanov O A,Hayakawa M,Afonin V V,Akentieva O A,Mareev E A,Trakhtengerts V Yu.2002.Possible influ-ence of seismicity by gravity waves onionospheric equatorial anomalyfromdata of IK-24satellite2.Equatorial anom-aly and small-scaleionospheric turbulence[C]∥Hayakawa M,Molchanov O Aeds.Seismo Electromagnetics:Litho-sphere-At mosphere-Ionosphere Coupling.Tokyo:TERRAPUB:287--296.
Parrot M.1995.Statistical study of ELF/VLF emissions recorded by a lowaltitude satellite during seismic events[J].JGeophys Res,99(A12):23339--23347.
Parrot M,Mogilevsky M.1989.VLFemission associated with earthquakes and observedin theionosphere and magneto-sphere[J].Phys Earth Planet Inter,57(1-2):86--99.
Parrot M,Lefeuvre F.1985.Correlation between GEOS VLFemissions and earthquakes[J].Ann Geophys,3(6):737--747.
Rodger C J,Dowden R L,Thomson N R.1996.Asearch for ELF/VLF activity associated with earthquakes using ISISsatellite data[J].J Geophys Res,101(A6):13369--13378.
Serebryakova O N,Bilichenko V M,Chmyrev V M,Parrot M,Rauch J L,Lefeuvre F,Pokhotelov O A.1992.Electro-magnetic ELF radiation fromearthquake region as observed by low-altitude satellites[J].Geophys Res Lett,19(2):91--94.
朱荣,杨冬梅,荆凤,杨俊英,欧阳新艳.2008.DEMETER卫星观测到的云南普洱地震前的电离层扰动[J].地震学报,30(1):76--81.
Chmyrev V M,Isaev N V,Bilichenko S V,Stanev G.1989.Observation by space-borne detectors of electric fields andhydromagnetic waves in the ionosphere over an earthquake center[J].Phys Earth Planet Inter,57(1-2):110--114.
Hayakawa M,Molchanov O A,Ondoh T,Kawai E.1996.Precursory signature of the Kobe Earthquake on VLFsubion-ospheric signals[J].J At mos Electr,16(3):247--257.
Henderson T R,Sonwalker V S,Helli well R A,Inan US,Fraser-Smith A C.1993.Asearch for ELF/VLF emissionsinduced by earthquake as observedin theionosphere by the DE-2satellite[J].J Geophys Res,98(A6):9503--9514.
Larkina VI,Migulin V V,Molchanov O A,Galperin Iu I.1985.Earthquake effects in the ionosphere according to I N-TERCOSMOS-19and AUREOL-3satellite data[C]∥Results of the ARCAD-3Project and of the Recent Pro-grammes in Magnetospheric and Ionospheric Physics.Toulouse:Cepadues-Editions:685--699.
Molchanov O A,Hayakawa M,Afonin V V,Akentieva O A,Mareev E A,Trakhtengerts V Yu.2002.Possible influ-ence of seismicity by gravity waves onionospheric equatorial anomalyfromdata of IK-24satellite2.Equatorial anom-aly and small-scaleionospheric turbulence[C]∥Hayakawa M,Molchanov O Aeds.Seismo Electromagnetics:Litho-sphere-At mosphere-Ionosphere Coupling.Tokyo:TERRAPUB:287--296.
Parrot M.1995.Statistical study of ELF/VLF emissions recorded by a lowaltitude satellite during seismic events[J].JGeophys Res,99(A12):23339--23347.
Parrot M,Mogilevsky M.1989.VLFemission associated with earthquakes and observedin theionosphere and magneto-sphere[J].Phys Earth Planet Inter,57(1-2):86--99.
Parrot M,Lefeuvre F.1985.Correlation between GEOS VLFemissions and earthquakes[J].Ann Geophys,3(6):737--747.
Rodger C J,Dowden R L,Thomson N R.1996.Asearch for ELF/VLF activity associated with earthquakes using ISISsatellite data[J].J Geophys Res,101(A6):13369--13378.
Serebryakova O N,Bilichenko V M,Chmyrev V M,Parrot M,Rauch J L,Lefeuvre F,Pokhotelov O A.1992.Electro-magnetic ELF radiation fromearthquake region as observed by low-altitude satellites[J].Geophys Res Lett,19(2):91--94.
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