| The propagation, evolution and e?ect on the geospace environment of in-terplanetary disturbances is always the frontier and hot issue of space weather.The interplanetary shocks and structures with southward magnetic ?eld are twoof the major interplanetary disturbances. Based on the observations, relevantmodels and simulations, we focus on studying the e?ect of these two interplan-etary disturbances on the geospace environment, especially the geosynchronousmagnetic ?eld and geomagnetic ?eld. Moreover, a comprehensive study of geo-magnetic storm, the Earth's cusp and polar cap potential drop is also presentedin this doctoral dissertation.1. E?ects of Interplanetary Shocks on Geospace EnvironmentThe interplanetary shock interacts with the Earth's magnetosphere, causingsudden changes of geosynchronous magnetic ?eld and geomagnetic ?eld. Themagnitude of the geosynchronous magnetic ?eld responses depends on the localtime, peaking near the noon and reducing to the nightside; however, the rela-tive magnitude of the response depends only weakly on the local time. Thesefeatures are similar to those obtained from the statistical study of the responsesto solar wind dynamic pressure pulses. Unexpectedly, negative responses weresometimes observed on the nightside of the magnetosphere, which were usuallyassociated with southward interplanetary magnetic ?eld (IMF). The responseof dayside geosynchronous magnetic ?eld, the magnitude of geomagnetic sud-den impulse, and the interplanetary shock correlate linearly to each other. Bysummarizing the related empirical formulas, we developed an inversion modelto obtain the interplanetary shock characteristics and geosynchronous magnetic?eld responses just from the observation of geomagnetic sudden impulses. Itsvalidity was also veri?ed. This inversion model would help to study the historicinterplanetary shocks without solar wind observations, and could be regarded asa spare detection of space weather when the direct observations at L1 point andgeosynchronous orbit were unavailable. 2. Integrated Study of Geomagnetic Storms Caused by Interplan-etary Structures with Southward Magnetic FieldThe interplanetary structures with southward magnetic -eld are the ma-jor origins of geomagnetic storms. There exists good linear correlation betweenthe storm intensity and the solar wind reconnection E--eld, EK-L. We iden-ti-ed speci-c interplanetary conditions for the occurrence of superstorms withSY MH≤-300 nT as follows: IMF BZ < -27 nT lasts for at least～1 hour;solar wind dynamic pressure, Pd >～12 nPa; EK-L >～30 mV/m. The 360-panoramic views of geosynchronous BZ signature for storms with di-erent inten-sities were -rst obtained and found to be signi-cantly di-erent from each other.For moderate storms (-100 < SY MH≤-50 nT), the distribution of geosyn-chronous magnetic BZ versus the local time was very similar to a bell-shapedGaussian distribution, with a peak pre-noon. While for superstorms, the distri-bution even reversed. Further analysis, we found that the mid-day magnetopausewas located earthward of the geosynchronous orbit during superstorms.The storm-time magnetospheric energetics was studied. We con-rmed thecrucial role of the total energy input in controlling the magnitude of a magneticstorm. Their correlation coe-cient was as high as 0.90. The input e-ciency ofenergy transfers from the solar wind into the magnetosphere is positively cor-related with the storm intensity, and peaks in the main phase. The relativeimportance of the ring current injection and high-latitude ionospheric dissipa-tion was clari-ed. The ratio of them (ξ) increases linearly as the storm intensityincreases. For moderate storms, the high-latitude ionospheric dissipation is dom-inant, whereas for big storms (SYMH≤～-200 nT), the ring current injectionbecomes dominant gradually. Comparing to the recovery phase and whole stormperiod,ξis much greater in the main phase. The storm-time magnetosphericenergy budget was also quanti-ed. The coupling e-ciency decays exponentiallyas the storm intensity increases. The energy entered the magnetosphere does nothave to be released in full during a intense storm, which could be stored in themagnetosphere and serves as an additional energy source for next a moderatestorm. From statistical study, we obtained the dawn-dusk asymmetry of horizontalcomponent of disturbed geomagnetic ffeld, together with its evolving characteris-tics during the development of magnetic storms. With some reliable assumptions,we ffrst quantitatively studied the contribution of partial ring current to the Dstindex and its evolving characteristics. During the main phase, the contributionof partial ring current is predominant, and gradually increases until the Dst in-dex reaches its minimum. During the recovery phase, the contribution of partialring current decreases rapidly and even could be neglected in the later recoveryphase. Further analysis shows that the corresponding contributions of partialring current decreases gradually as the storm intensity increases.We also simulated the responses of the magnetosphere-ionosphere system tothe extreme solar storm during"Carrington Event". The dayside magnetopauseand bow shock are compressed to 4.3 and 6.0 RE, and their ffanks are also stronglycompressed. During that storm, the region-1 ffeld-aligned current increases byabout 60 times, and the cross polar potential drop increases by about 80 times;the reconnection voltage is about 5 to 6 times bigger than a common storm. Alarger amount of the solar wind energy enters the magnetosphere, resulting insevere space weather phenomena.3. Integrated Study of Earth's Cusp and Polar Cap Potential DropBased on the T96 model, we obtained the topology of the Earth's cusp anddeffned some parameters to describe its conffguration. We further studied theinffuences of the solar wind dynamic pressure, the IMF and storm intensity onthe cusp's conffguration. By comparing to some former observational results, thecusp obtained from T96 model was still good on the whole.We proposed a quasi-steady nonlinear circuit model for the solar wind-magnetosphere-ionosphere coupling to study the observed saturation of polarcap potential drop. Our model could match the observations very well. Theasymptotic saturation level increases with decreasing the internal resistance ofthe dynamo region, increasing the length of dayside reconnection line, increasingthe ratio of nightside to dayside reconnection potentials, and increasing the ratioof nightside to dayside internal resistances.
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