Statistical Analysis And Simulation Study On Interplanetary Disturbances And Their Geoeffectiveness

Solar transient activities, such as solar ?ares, coronal mass ejections (CMEs),radio bursts, and fast solar wind from coronal hole are important drivers of spaceweather as they can induce interplanetary disturbances and trigger geomagneticstorms. They play important roles in leading to adverse solar-terrestrial environ-ment. In this paper, based on numerical simulation and statistical analysis, thecorrelations between the solar transients, interplanetary disturbances and corre-sponding geomagnetic disturbances together with the related prediction methodsare investigated.Three kinds of interplanetary structures:"pure"corotating interaction re-gions (CIR), interaction of CIR with interplanetary coronal mass ejection (ICME),and"pure"ICME caused by transient events, are identified for the first time byusing the Hakamada-Akasofu-Fry (HAF) model. We investigated CIRs'recur-rent geomagnetic activity and the relations among CIRs, shocks and geomagneticstorms in the heliosphere (< 1AU) during solar cycle 23 (1996～2005). The mainresults are: (1) There are 157"pure"CIRs in the 23rd solar cycle and most ofCIRs occur in the declining phase. (2) CCKCCR is calculated to represent thelevel of recurrent geomagnetic disturbances. The maximum CCKCCR appearsduring the descending phase near solar minimum so that recurrent geomagneticactivity is dominant during this period. The relation between the latitude ofcoronal hole and CCKCCR shows that CIRs play important roles in recurrentgeomagnetic activity. (3) 41% of CIRs are associated with interplanetary shocksat 1AU and most of shocks are forward shocks. This is probably the reason whyWind and ACE near the ecliptic plane are expected to see more forward shocks'propagating antisunward, westward, and equatorward than reverse shocks'prop-agating sunward, eastward, and poleward if both types of shocks form near oneAU. (4) CIR-related shock is not a necessary condition for generating a mag-netic storm, only 44% CIR-related storms were related to CIR-related shocks,but most CIR-related shocks are related to storms. (5) The Dst index that cor- responds to CIR-related storms has a better linear relationship with IMF Bz,Ey, and the coupling function (ε) when the Dst indices are higher than -100 nT.(6) The geoe?ectiveness of CIRs appears clearly to have seasonal e?ects due tothe changing relative orientation of the Earth and the Sun. The overall geomag-netic disturbance levels are higher at autumn equinox for antisunward directionof interplanetary magnetic field( IMF) and spring equinox for sunward direc-tion. These statistical results will be useful for the long-term prediction in thegeoe?ectiveness of CIRs.A practical database method for predicting the interplanetary shock arrivaltime at L1 point is presented. A shock transit time database based on HAFv.1(version 1 of the Hakamada-Akasofu-Fry model) is established. The databaseorganized on a multidimensional grid of source location, initial coronal shockspeed, and the year of occurrence of the hypothetical solar event. The arrivaltime at L1 for any given solar event occurring in the 23rd solar cycle can bepredicted by looking up in the grid of the database according to source location,the initial coronal shock speed, and the year of occurrence in cycle 23. Theprediction test of the 130 observed solar events during the period from February1997 to August 2002 shows that its success rate could be practically equivalentto those by the shock time of arrival (STOA) model, the interplanetary shockpropagation model (ISPM), and the HAFv.2 model. In particular, this method'sperformance for a set of events in other cycles is as good as that of the STOAand ISPM models. This gives us confidence in its application to other cycles.From the viewpoint of long-term periodicity for solar activity, it is expected thatthe database method can be applicable to the next solar cycle 24. However, thedatabase method also has its shortcomings. We do not take into account of theshort-time variations of coronal magnetic field, which will make the large-scalestructure of the heliospheric current sheet and background solar wind somewhatdeviate from the real situations. And these factors would induce some errors forprediction of the database method. Moreover, for simplicity, the phase of othersolar cycle does not well correspond to the one of cycle 23 for the applicationto other cycles. This will be considered in the future work. The present workprovides us a new method to predict the shock arrival time rapidly. Two shock propagation models are established to predict the arrival timeof interplanetary shocks at 1AU. One interplanetary shock propagation modelis built up based on 1D-HD equations by using Roe scheme. Another is a 1D-MHD shock propagation model by using the space-time conservation elementand solution element (CE/SE) method. Applying these models to solar eruptiveevents during the 23rd solar cycle to evaluate the forecasting skill, it is found thatour models could be practically equivalent to the other models in forecasting theshock arrival time. These results might demonstrate a potential capability of ourmodels in terms of real-time forecasting. Although these models are simple 1Dnumerical models, but they can predict the shock arrival time rapidly. Moreover,they were expected to forecast"no shock"by improving them in the future work.