The Responses Of Ionosphere To Seismic Activity And Solar Wind Disturbance

In this report, observational study on seismic-ionosphere coupling processes are made mainly based on DEMETER spacecraft observations, with emphasis on background char-acter and establishing model of ionosphere, ionosphere anomalies induced by earthquqke as well as the responsing process of magnetospheric-ionosphere system to interplanetary shocks.1. The background characteristics and the observational model of the ionosphere(1) The background characteristics of global ionosphereStudying the plasma and VLF electric field power spectra at the DEMETER satellite alititude ionosphere we found that there are some intresting phenomena occurred in addi-tion to the conventional aomalies such as day and night differences, annual, semi-annual, season, equtatial anomaly and so on.①the deviation of palsma from the macro electroneutrality? The total ionos density is much less than that of the electron at nightside ionosphere, which deviating from the palsma macro electroneutrality, so it could be inferred that there should be a considerable number of other types positive ionos or radical ionos generated in nightside ionosphere, and the generation mechanism needs further study.②The effect of Solar radiation on the different parameters is differentialIonospheric plasma originated from the solar ultraviolet and X-ray radiation dissoci-ating upper atmosphere, so the plasma density increases with solar radiation enhancement. The solar activity is in the decreasing phase from 2006 to 2008 with the weakening solar radiation, as a result, electron and O+ density reduce correspondingly, however, H+ and He+ density is observed decreasing with the Solar radiation increasing, showing different mechanisms of generating these particles. Moreover, Seasonal effect is also a manifestation of this, electron and O+ density is significantly higher in the summer hemisphere than in the winter hemisphere, but there is no clear different of H+ and He+ density between summer and winter hemisphere.Solar activity on the temperature of ions and electrons are also not the same, there is no significant change of electron temperature in inter-annual or between seasons, but obvious changes are observed of inter-annual or seasonal ions temperatures, showing the solar activity influence on the ion temperature is greater than the impact on the electronic temperature. There exists little effect of solar activity on electric field power spectrum in EM or HISS frequency band, no significant change is observed in 2006-2008, also no clear change occurs between summer and winter hemisphere.(2) The preliminary establishment of ionosphere observational model at satellite alti-tudeMainly using the DEMETER satellite plasma and VLF electric field power spectrum data, we have studied the temporal and spatial variation of corresponding ionosphere parameters, starting from analyzing of the global ionospheric distribution for each month, summed up the normal observation model of ionosphere which could be used to extract the earthquake ionospheric anomalies, and the corresponding statistical error is analyzed finally.The results show that there exists little different between months in geomagnetic winter or summer season for almost parameters, this allows us to establish ionospheric observation model based on the whole seasonal data. Moreover, we can establish electron density or temperature model using only two months data in the same geomagnetic season for its relatively high time resolution. The analyzing of model error showing that the statistical error of electron parameters is smallest, its relative error is less than 10%. The statistical error of ion parameter models is relatively large at several local area; The error of Electric field power spectrum model is very small in addition to the North American continental region where the spectrum intensity is very strong.2.The characteristics of the ionosphere anomalous induced by earthquake(1)The statistical studyAiming at the global 299 earthquakes with Ms>5, we have studied the disturbances of plasma and VLF electric field power spectra occurred in ionosphere before and after the seismics, the mainly conclusions are as follows:0 Plasma parameterstime-space region:①Paying attention to ionosphere character in the three days time interval before and after the EQs, we found that the anomalies mainly occur in 40 hours before and after EQs;②The occurrence frequency of electron (ionos) density anomalous is far greater than that of the temperature comparing, density anomales account for more than 80% of the total abnormal;③By comparing the electron with ionos anomalous, it is found the electron anomalous is far more than that of the ions, electron abnormal account for 78%; ④The positive density anomalies of electron (ionos) are main (comparing to the negative ones), which occupy 64%, and the occurrence frequency of positive and negative temperature anomalies are comparable.VLF electric field power spectra①time-frequercy region:By comparing the ionosphere disturbances occurring around the earthquakes and random events in the time-space region, it is found that the electric field power spectra around EQs is much weaker than that around random events in 50-300 Hz band, and there is no clear difference between the two in other band.②time-space region:Aiming at 50-300 Hz frequency band in time-space region, we found that ionosphere disturbances mainly appear in the 400 km range of distance from epicenter, and the positive and negative anomalous are both observed.③space-space region:Aiming at 50-300 Hz frequency band in space-space region, it is found that the disturbances in north hemisphere shift northerly, and south hemi-sphere disturbances shift southerly; The phenomenon of disturbances shifting westward is observed in both hemispheres in geomagnetic winter season. positive disturbances are the main ones observed around the epicenter of sea EQs and negative disturbances are the main around the epicenter of land EQs.(2) The ionosphere disturbances induced by several typical earthquakes Aiming at YuShu, WenChuan and YuTian three earthquakes occurred in our county, we have analyzed the ionosphere disturbance characteristecs of plasma and electric field just before these EQs, respectively. The main results are:electeric field and plasma anomalouses are both observed before EQs, SNR of VLF electric field power spectra decrease in a DEMETER revisited period before YuShu earth-quake; The ionos anomalies are also observed several times before EQs, the plasma density anomalouses are major ones among all the plasma disturbance observed, and only one temperature anomalous is observed before the three EQs, this is consistent with the sta-tistical results; The time interval of three days before EQs is the frequent period of plasma anomalies occurrence. There is the very good correspondence between the anomalies of H+ density and seismic activity, and H+ density disturbancees is not affected clearly by geomagnetic activities. The characteristics of O+ density responsing to the geomagnetic activities are significant.The nagative and positive anomalies are mainly induced seismic and geomagnetic activities respectively by checking the time serial character in a typical region.3. The response of the magnetosphere-ionosphere system to the solar wind disturbanceIn terms of the interplanetary shock event occured on November 7,2004, observational study on the response of magnetosphere-ionosphere system to it are made mainly based on TC-1 and DEMETER spacecraft observations, especially the response of the magnetotail plasma sheet (PS) and the low-mid latitude ionosphere.(1) The convection oscillations enhancement in the magnetotail plssma sheetWhen the shock interacts with the magnetosphere, the magnetic field impulsively increases 1～2 min after the geomagnetic field sudden impulse (SI) judged from the Sym-H index change, and the magnetic field line is stretched. On the other hand, all of the ion density, the ion temperature, and the velocity of ion flow in the plasma sheet increase. Interestingly, quasi-periodical oscillations of the ion flow are suddenly enhanced, and the plasma flow is basically perpendicular to the local magnetic field. The responses of the magnetic field and the plasma are nearly simultaneous. The responses in the plasma sheet are probably caused by the lateral compression due to the dynamic pressure enhancement downstream the shock when the shock propagates antisunward in the magnetosheath. As far as we know, the quasi-periodical convection oscillations enhancement directly induced by shocks have never been reported in previous studies.(2) The two-phase response of low-mid latitude ionosphereIt is a very complicated process for low-mid latitude ionosphere responding to the in-terplanetary shock. Firstly, the enhancements of electric field power spectrum and plasma velocity disturbances are observed at nightside ionosphere simultaneously to the shock compressing the magnetopause, so the reason of the disturbance is regarded as the direct interaction between shock and magnetosphere-ionosphere system. After 3 min of the shock acting on the magnetopause, the stronger electric field and plasma disturbances are ob-served again by DEMETER satellite companied with plasma wave occurring, these second disturbances is observed 110s after the magnetotail disturbance observed by TC-1. The disturbances propagate along with magnetic field which could be judged from the dis-turbing plasma flowing almost along the magnetic field observed by DEMETER satellite. As we know,1-2 minutes are needed for near-Earth magnetotail disturbance propagating into the ionosphere, so the second disturbances in the ionosphere 3 minutes after the shock compressing the magnetopause is propagated from magnetotail as the form of magnetichy-drodynamic wave. As far as we know, this is the first observation of the two-phase response of ionosphere to the interplanetary shock.