Xinhua Zhao

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (5)12.69 Total impact

  • Source
    Xinhua Zhao, Xueshang Feng, Chin-Chun Wu
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    ABSTRACT: 1] We study the source locations of 130 solar flare-type II radio burst events with the associated interplanetary shocks observed by L1 spacecraft (type A events) and 217 flare-type II events without such shocks observed at L1 (type B events) during February 1997–August 2002. In particular, we investigate the relative positions between the flare sources, the heliospheric current sheet (HCS), and the Earth. We found the following results: (1) Solar flares are usually distributed within [S30°, N30°] in heliographic latitude and [S30°, N30°] Â [E10°, W30°] is the predominant source region on the solar disk that includes the majority of geoeffective solar flares. (2) The shocks with the associated flares located near the HCS would have a lower probably of reaching the Earth. For the Earth-encountered shocks, their initial speeds are distinctly higher when their associated flares are located near the HCS. (3) The angular distance from the flare source to the Earth (defined as Y below) also contributes to the probability of the associated shock being observed at the Earth. The shock arrival probability decreases with the increment of Y and the mean initial shock speed increases with Y for those Earth-encountered shocks. (4) The so-called ''same-opposite side effect'' of the HCS is confirmed to exist. That is, the shocks whose associated flares are located on the same side of the HCS as the Earth (called as ''same side events'') have a greater chance of reaching the Earth than those shocks with their associated flares on the opposite side (''opposite side events''). Here for the first time, a comprehensive sample of solar transient events of both arriving and nonarriving ones (at Earth) is used to testify to the same-opposite side effect. These results would be valuable in understanding the solar-terrestrial relations, and helpful for space weather prediction.
    Journal of Geophysical Research 01/2007; 112. · 3.17 Impact Factor
  • Source
    Xueshang Feng, Xinhua Zhao
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    ABSTRACT: Solar transient activities such as solar flares, disappearing filaments, and coronal mass ejections (CMEs) are solar manifestations of interplanetary (IP) disturbances. Forecasting the arrival time at the near Earth space of the associated interplanetary shocks following these solar disturbances is an important aspect in space weather forecasting because the shock arrival usually marks the geomagnetic storm sudden commencement (SSC) when the IMF Bz component is appropriately southward and/or the solar wind dynamic pressure behind the shock is sufficiently large. Combining the analytical study for the propagation of the blast wave from a point source in a moving, steady-state, medium with variable density (wei, 1982; wei and dryer 1991) with the energy estimation method in the ISPM model (smith and dryer 1990, 1995), we present a new shock propagation model (called SPM below) for predicting the arrival time of interplanetary shocks at Earth. The duration of the X-ray flare, the initial shock speed and the total energy of the transient event are used for predicting the arrival of the associated shocks in our model. Especially, the background speed, i.e., the convection effect of the solar wind is considered in this model. Applying this model to 165 solar events during the periods of January 1979 to October 1989 and February 1997 to August 2002, 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 in 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 our model in terms of real-time forecasting.
    Solar Physics 01/2006; 238(1):167-186. · 3.26 Impact Factor
  • Source
    Xueshang Feng, Xinhua Zhao
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    ABSTRACT: Using 100 CME–ICME events during 1997.01–2002.11, based on the eruptive source locations of CMEs and solar magnetic field observations at the photosphere, a current sheet magnetic coordinate (CMC) system is established in order to statistically study the characteristics of the CME–ICME events and the corresponding geomagnetic storm intensity. The transit times of CMEs from the Sun to the Earth are also investigated, by taking into account of the angle between the CME eruption normal (defined as the vector from the Sun center to the CME eruption source) and the Sun-Earth line. Our preliminary conclusions are: 1. The distribution of the CME sources in our CMC system is obviously different from that in the ordinary heliographic coordinate system. The sources of CMEs are mainly centralized near the heliospheric current sheet (HCS), and the number of events decreases with the increment of the angular distance from the CME source to the HCS on the solar surface; 2. A large portion of the total events belong to the same–side events (referring to the CME source located on the same side of the HCS as the Earth), while only a small portion belong to the opposite–side events (the CME source located on the opposite side of the HCS as the Earth). 3. The intense geomagnetic storms are usually induced by the same–side events, while the opposite side events are commonly associated with relatively weak geomagnetic storms; 4. The angle between the CME normal and the Sun–Earth line is used to estimate the transit time of the CME in order to reflect the influence of propagation characteristic of the CME along the Sun–Earth direction. With our new prediction method in context of the CMC coordinate, the averaged absolute error for these 100 events is 10.33 hours and the resulting relative error is not larger than 30% for 91% of all the events.
    Astrophysics and Space Science 01/2006; 305(1):37-47. · 2.06 Impact Factor
  • Source
    Xinhua Zhao, Xueshang Feng, Chin-Chun Wu
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    ABSTRACT: 1] Solar flares and metric type II radio bursts are one kind of preliminary manifestations of solar disturbances and they are fundamental for predicting the arrival of associated interplanetary (IP) shocks at Earth. We statistically studied 347 solar flare type II radio burst events during 1997.2–2002.8 and found (1) only 37.5% of them were followed by the IP shocks at L1 (in other words, at Earth), the others without such IP shocks account for 62.5%; (2) the IP shocks associated with intense flares have large probability to arrive at Earth; (3) the IP shocks associated with central flares are more likely to arrive at Earth than those associated with the limb flares, and the most probable location for flares associated with IP shocks at Earth is W20°; and (4) there exists a east-west asymmetry in the distribution of geoeffectiveness of flare-associated IP shocks along the flare longitude. Most severe geomagnetic storms (Dst min À100 nT) are usually caused by flare-associated shocks originating from western hemisphere or middle regions near central meridian, and the most probable location for strong flares associated with more intense geomagnetic storms is W20° as well. These results could provide some criteria to estimate whether the associated shock would arrive at Earth and corresponding geomagnetic storm intensity.
    Journal of Geophysical Research 01/2006; 111. · 3.17 Impact Factor
  • Xinhua Zhao, Xueshang Feng
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    ABSTRACT: Using 80 CME-ICME events during 1997.1–2002.9, based on the eruptive source locations of CMEs and solar magnetic field observation at the photosphere, a current sheet magnetic coordinate (CMC) system is established in order to study the propagation of CME and its geoeffectiveness. In context of this coordinate system, the effect of the eruptive source location and the form of heliospheric current sheet (HCS) at the eruptive time of CME on the geomagnetic storm intensity caused by CME and the CME’s transit time at the Earth is investigated in detail. Our preliminary conclusions are: 1) The geomagnetic disturbances caused by CMEs tend to have the so-called “same side-opposite side effect”, i.e. CMEs erupt from the same side of the HCS as the earth would be more likely to arrive at the earth and the geomagnetic disturbances associated with them tend to be of larger magnitude, while CMEs erupting from the opposite side would arrive at the earth with less probability and the corresponding geomagnetic disturbance magnitudes would be relatively weaker. 2) The angular separation between the earth and the HCS affect the corresponding disturbance intensity. That is, when our earth is located near the HCS, adverse space weather events occur most probably. 3) The erupting location of the CME and its nearby form of HCS will also affect its arrival time at the earth. According to these conclusions, in this context of CMC coordinate we arrive at new prediction method for estimating the geomagnetic storm intensity (Dst min) caused by CMEs and their transit times. The application of the empirical model for 80 CME-ICME events shows that the relative error of Dst is within 30% for 59% events with Dst min≤−50 nT, while the averaged absolute error of transit time is lower than 10 h for all events. Keywordscoronal mass ejections-current sheet magnetic coordinate system-geomagnetic storm intensity-transit time-prediction method
    Science in China Series E Technological Sciences 48(6):648-668. · 1.02 Impact Factor

Publication Stats

25 Citations
12.69 Total Impact Points

Institutions

  • 2006
    • Chinese Academy of Sciences
      • Center for Space Science and Applied Research
      Peping, Beijing, China