Session 2: Solar, Planetary and Space Physics

Title: Spatio-temporal analysis techniques for detailed investigations of space storm dynamics
Author(s): D. Vassiliadis, I. A. Daglis, A. J. Klimas, and C. R. Clauer (Poster)

  We present several spatio-temporal analysis techniques, which integrate mid-latitude ground magnetogram data and are useful in identifying key features in the ring current response. In this way we can quantify
a) the intensity and spatial extent of inner magnetosphere convection,
b) the intensity of the geomagnetic response to interplanetary pressure pulses,
c) the penetration of the substorm current wedge to lower latitudes and
d) the effect of particle injections on the ring current.
  The first technique creates a spatio-temporal storm "portrait" based on the axial component of the ground magnetic field H(UT;LT) [Clauer and McPherron, 1974]. Displaying the field data in UT-LT coordinates allows comparison of the activity in the inner magnetosphere. In addition to visual identification of the above features, we introduce a second technique that uses principal component analysis (PCA) of the storm portrait. PCA peaks correspond, in order of decreasing eigenvalue, to symmetric ring current, asymmetric ring current and substorm current wedge, and injections into the ring current, typically during substorms. Identification of the major PCA peaks with large-scale current systems is confirmed by correlation with and timing relative to geomagnetic indices (Dst, AL, etc). The intensity and direction of ring current injections is estimated by a bandpass filter technique for individual magnetograms. Examples using the storms of June 4, 1991, and September 26, 1998, are given. In these cases the asymmetric ring current can have a geomagnetic effect as strong as the azimuthally symmetric part meaning the majority of plasma sheet particles convecting deep into the inner magnetosphere are quickly (~2-3 hours) lost at the dayside magnetopause. On the other hand, the estimate for particle injections compared to slow convection reaches up to 30% in terms of the average geomagnetic field amplitude. Thus, individual substorms can have a significant influence on the storm-time ring current composition and dynamics.