Browsing by Subject "Geomagnetic storm"
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Item Open Access Association of ionospheric storms and substorms of global electron content with proxy AE index(Pergamon Press, 2015) Yenen, S. D.; Gulyaeva, T. L.; Arikan, F.; Arıkan, OrhanStorm time modeling of Global Electron Content (GEC) calculated from GIM-TEC for 1999-2013 is associated with new proxy of Auroral Electrojet variability expressed as a smoothed and normalized Auroral Electrojet index (AEsn). The variability in GEC is captured by the computation of DGEC which is obtained by taking the hourly ratio of instant GEC to median of GEC values at the same hour of 7 preceding days. The storm onset is determined by a joint analysis of variations in IMF-B magnitude, its derivative (dB/dt) and direction of IMF-Bz together with sudden increase in AE exceeding 900 nT. The start of the pre-storm period is chosen to be 7 h prior to the storm onset time and the storm recovery period ends 41 h after the storm onset. The hourly AEsn is related to DGEC during the storm period through a polynomial whose coefficients are estimated in the linear least squares sense. Estimated coefficients are examined and grouped with respect to different kinds of auroral storms. Examples of modeling methodology are provided using four different kinds of intense storms and substorms, namely, Positive Arctic, Positive Antarctic, Negative Arctic and Negative Antarctic that occurred between 1999 and 2013. The estimated coefficients for storm periods are compared with those of non-storm periods. It is observed that the positive correlation between the increase of AE and GEC can be a promising precursor of space weather variability.Item Open Access Investigation of total electron content variability due to seismic and geomagnetic disturbances in the ionosphere(Wiley-Blackwell Publishing, 2010-10-20) Karatay S.; Arikan, F.; Arıkan, OrhanVariations in solar, geomagnetic, and seismic activity can cause deviations in the ionospheric plasma that can be detected as disturbances in both natural and man-made signals. Total electron content (TEC) is an efficient means for investigating the structure of the ionosphere by making use of GPS receivers. In this study, TEC data obtained for eight GPS stations are compared with each other using the cross-correlation coefficient (CC), symmetric Kullback-Leibler distance (KLD), and L2 norm (L2N) for quiet days of the ionosphere, during severe geomagnetic storms and strong earthquakes. It is observed that only KLD and L2N can differentiate the seismic activity from the geomagnetic disturbance and quiet ionosphere if the stations are in a radius of 340 km. When TEC for each station is compared with an average quiet day TEC for all periods using CC, KLD, and L2N, it is observed that, again, only KLD and L2N can distinguish the approaching seismicity for stations that are within 150 km radius to the epicenter. When the TEC of consecutive days for each station and for all periods are compared, it is observed that CC, KLD, and L2N methods are all successful in distinguishing the geomagnetic disturbances. Using sliding-window statistical analysis, moving averages of daily TEC with estimated variance bounds are also obtained for all stations and for all days of interest. When these bounds are compared with each other for all periods, it is observed that CC, KLD, and L2N are successful tools for detecting ionospheric disturbances.