Statistical Analysis On The Solar-Terrestrial Transients And Comprehensive Research On The Related Prediction Methods

It is well known that various kinds of solar transient activities such as solar flares, radio bursts, and coronal mass ejections (CMEs) are responsible for strong interplanetary (IP) disturbances and corresponding nonrecurrent geomagnetic disturbances. They are the main aspects of space weather as being extremely geoeffective. In this paper, a large number of data set in the solar-terrestrial observations are collected. The correlations between the solar transients, interplanetary disturbances and corresponding geomagnetic disturbances together with the related prediction methods are investigated based on this data set. A comprehensive study is carried out on whether/when the solar wind storm would reach the Earth and its related geomagnetic storm intensity.A data set of 347 solar flare-type II radio burst events during Feb. 1997-Aug. 2002 is collected. The influences of the observational characteristics of solar eruptions and the heliospheric current sheet (HCS) on the associated IP disturbance's arrival at Earth are investigated. The following results could be found. (1) The most probable source location for the Earth-encountered shocks is [E10°,W30°] in solar longitude. (2) There exists an east-west asymmetry in the distribution of the geoeffects of the IP shocks along the associated flare's longitude. Most severe geomagnetic storms (Dst min≤-100 nT) are usually caused by flare-associated shocks originating from western hemisphere or middle regions near central meridian. And for the shocks associated with strong flares greater than M5.0, their geoeffects have more evident east-west asymmetry. The most probable location for those strong flares associated with more large geomagnetic storms is W20°in longitude. (3) The shock arrival probability decreases with the increment of the angular distance from the associated flare source to the Sun-Earth line. (4) The shape and location of the HCS have great influence on the shock's arrival at Earth; On one hand, the weak shocks with the associated flares located near the HCS would have a lower probably of reaching the Earth although the maximum of the event numbers is near the HCS; On the other hand, the shocks whose associated flares are located on the same side of the HCS as the Earth (called as"same side events") would have a greater chance of reaching the Earth than those opposite side shocks.Based on the eruptive source locations of CMEs and the solar magnetic field observations at the source surface, a Current sheet Magnetic Coordinate (CMC) system is established in order to quantitatively depict the relative locations between the CME source, the HCS and the Earth. The distribution characteristics of 100 Earth-encountered CME–ICME events during 1997.01–2002.11 and their geoeffects are analyzed under this CMC system. The statistical results are as follows. The sources of CMEs are mainly centralized near the heliospheric current sheet (HCS). Among these Earth-encountered CMEs, more than three quarters have their solar sources located on the same side of the HCS as the Earth. The opposite-side CMEs have relatively rare probability to reach the Earth. The HCS might have the"impeding"effect on the trans-propagation of CMEs. The great geomagnetic storms are mainly caused by the same-side CMEs. The percentage of the same-side events increases with the increment of the geomagnetic storm intensity, while that opposite-side percentage decreases. The extremely large geomagnetic storms with Dst<-200nT are 100% correlated to the same-side CMEs. A new Shock Propagation Model (called SPM) is given for predicting the arrival time of interplanetary shocks at Earth. The inputs of this model includes the begin time of the solar eruption, the duration time of the X-ray flare, the initial shock speed, the angular width, and background solar wind speed. The outputs can give the predicted transit time of the shock to any point in interplanetary space. As the input parameters are all observational characteristics near the Sun, the outputs given time could be 1~3 days earlier than the shock's real arrival time at the Earth. Applying this model to 165 solar events, we found that our model could be practically equivalent to the prevalent models of STOA, ISPM and HAFv.2 in forecasting the shock arrival time. The absolute error in the transit time of our model is not larger than those of the other three models for the same sample events. Also, the prediction test shows that the relative error of our model is≤10% for 27.88% of all events,≤30% for 71.52%, and≤50% for 85.46%, which is comparable to the relative errors of the other models. These results might demonstrate a potential capability of this SPM model in terms of real-time forecasting.In context of this CMC coordinate system, new methods to predict the CME's arrival time and corresponding geomagnetic storm intensity are proposed after considering the contribution of the relative locations between the CME source, the HCS and the Earth.