Study On The Interplanetary-Flux-Rope's Structures And Analysis To The Shock-Transit-Time Forecasting Method

In this dissertation, attentions are paid to the observational study on In-terplanetary Flux Ropes (IFRs) after review of the solar-terrestrial physics andthe associated concepts for space weather forecasting. A new Minimum Residue(MR) method is proposed for the axial orientation inferring of the IFRs. Twomagnetic cloud (MC) events with the field-aligned residual ?ows are identifiedand the inertial e?ects due to the plasma inside the magnetic clouds are alsohighlighted in this dissertation. Additionally, theories about the blast-wave-propagation from a point source in a moving, steady-state, medium with variabledensity are applied to the Shock Arrival Time (SAT) forecasting with the ShockPropagation Model (SPM). A statistical analysis on the forecasting capability ispresented in this dissertation. Ways of further development of the original SPMare discussed and we highlight the potential value of the non-similarity-theory-based SPM in application to the SAT forecasting.There are many 2 D models that can be used to describe the structure ofthe IFRs, such as the force-free model, the non-force-free model, and the inertialmodel. For each model, one or multiple field line invariants exist. We introducea new definition of the quantity, residue, based on all field line invariants of aspecified ?ux rope model to measure the de?ection between the assumed axisand the true ?ux rope axis. Then, a new MR method is proposed to infer theaxial orientation of IFR with the observational data from a single spacecraft.For an arbitrarily assumed ?ux rope axis, the natural coordinate system can beconstructed, then a magnetic ?ux function, A, and each invariant of the specified?ux rope model can also be concurrently calculated under this coordinate system.The direction corresponding to the minimum residue is expected to be the realaxial orientation. In previous study, the residue was first defined with A and asingle invariant Pt of a static equilibrium ?ux rope model. Here, the new MRmethod is tested with simulated magnetic cloud (MC) data sets constructed fromthe analytical model outputs of two di?erent ?ux rope models with"trend noise" added. It shows that the new MR method is applicable in real case analysis andthe inferring results are acceptable for cases with small closest approach distanceand proper noise level. Compared with results from traditional methods, accu-racy of the inferred axial orientation is improved by the new method. The newMR method is also applied to a typical in-situ event observed by WIND space-craft. The comparison of the inferring results from di?erent models indicate thatapplication of a more accurate ?ux rope model is useful for inferring techniques.Two MC events observed by WIND spacecraft are identified that there aregood examples of field-aligned residual ?ow inside those MC structures. Forboth events, the co-moving frames are determined through the deHo?man-Teller(HT) analysis and the axial orientations are inferred by the newly developedminimal residue (MR) method. The nature coordinate system for both eventsare constructed with velocity of the HT frame and the inferred MC axis, the fieldand ?ow remaining in the HT frame are analyzed at this coordinate system. As aresult, we find that the residual ?ows in the co-moving HT frame of the two MCevents are almost anti-parallel to the helical magnetic field. We speculate thatthe field-aligned residual ?ows are large scale coherent hydrodynamic vortices co-moving with the MCs at the supersonic speed near 1 AU. Data analyses show thatthe event in slow ambient solar wind is expanding at 1 AU and another one in fastsolar wind does not show apparent expansion. Proton behaviors for both eventsare quasi-isothermal. Accelerated HT analysis shows that both events have nosuitable HT frame with constant accelerations, which suggests that both eventsmay be moving at the constant speed near 1 AU under the assumptions of theHT analysis. For both events, the ratio of the dynamic pressure to the magneticpressure is larger than that of the thermal pressure to magnetic pressure, whichsuggests that the dynamic e?ects due to the plasma ?ows remaining in the co-moving HT frame are more important than the thermal e?ects in the study ofMC evolution and propagation.Methods to improve the predictions of SAT of the original SPM are inves-tigated in the last portion of this dissertation. According to the classical blastwave theory adopted in the SPM, the shock propagating speed is determinedby the total energy of the original explosion together with the background solar wind speed. Noting that there exists an intrinsic limit to the transit times com-puted by the SPM predictions for a specified ambient solar wind, we present astatistical analysis on the forecasting capability of the SPM using this intrinsicproperty. Two facts about SPM are found: (1) the error in shock energy estima-tion is not the only cause of the prediction errors and we should not expect thatthe accuracy of SPM to be improved drastically by an exact shock energy in-put; (2) there are systematic di?erences in prediction results both for the strongshocks propagating into a slow ambient solar wind and for the weak shocks intoa fast medium. Statistical analyses indicate the physical details of shock prop-agation and thus clearly point out directions of the future improvement of theSPM. A simple modification is presented here, which shows that there is roomfor improvement of SPM and thus that the original SPM is worthy of furtherdevelopment.