Average properties of geomagnetic storms in 1932–2009

Abstract

[1] We investigate the average properties of geomagnetic storms using the global and local Dxt indices at four Dst stations in 1932Dst stations in -2009. Imposing the condition of complete data availability during storms, our study includes 1268/362/134/59 storms with Dxt minimum less than À50/À100/À150/À200 nT, respectively. The global Dxt minima were, on an average, À94/À156/À216/À275 nT, while deepest storm-time local Dxt minima were À137/À214/À285/À350 nT. Accordingly, the local Dxt minima are typically 25-30% stronger than the global Dxt minima. The distribution of largest storm-time disturbances is strongly peaked at 18 local time (LT), challenging local midnight as the dominant ion source. Relative timing of local minima verifies that stations at earlier LT hour observe their minimum a couple of hours after the deepest minimum, in agreement with westward drift of ions. Storm-time maximum asymmetries were found to increase with storm intensity level from about 70 nT to 150 nT for À50 to À200 nT storms. However, strong storms are relatively more symmetric than weak storms when compared to the typical level of local disturbance. During individual storms the asymmetry can be more than 200 nT. The rate of evolution of storm-time asymmetry is found to be roughly twice as fast for large storms. We emphasize that the unique database of local Dxt indices proves to be very useful in studying the average spatial distribution and temporal evolution of storms.

Short-term variability of the Sun-Earth system: an overview of progress made during the CAWSES-II period

“…One of the common indicators of the strength of geomagnetic storms is the Dst index (expressed in nT), which is computed as the horizontal component of Earth's magnetic field measured at several equatorial stations (now, a SYM-H index is available which is essentially a 1-min resolution Dst index). Yakovchouk et al (2012) reported significant difference between the local and global peak storm intensities: the local storm minima were found to be 25% to 30% stronger than the global minima. Here, we consider only global peak intensities.…”

“…They found that roughly half of the storms that were caused by CME/sheaths were due to CMEs and half due to sheath fields. Yakovchouk et al (2012) found that 10% of major storms are caused by CIRs. Echer et al (2008a) determined that 13% of the cycle 23 storms were caused by CIRs.…”

Annual fractions of high‐speed streams from principal component analysis of local geomagnetic activity

“…This is rather surprising since it is obvious that there is more information included in a large set of local geomagnetic indices than in one single global index (normally a weighted average of several local indices). Recently, local indices have been used to study, e.g., the spatial properties of the ring current, which is often very asymmetric in local time [Yakovchouk et al, 2012;Newell and Gjerloev, 2012].…”

Occurrence rate of extreme magnetic storms

“…One of the main problems of solar‐terrestrial physics and space weather is the study and prediction of magnetic storms including extreme ones (see, e.g., recent papers and reviews by Echer et al [], Alves et al [], Podladchikova and Petrukovich [], Yakovchouk et al [], Yermolaev et al [], and references therein). A useful technique for solving these types of problems is the calculation of frequency (occurrence rate) distributions of events based on observations in the form d N = F ( x )d x , where d N is the number of events recorded with the parameter x of interest between x and x +d x , and F ( x ) is a frequency distributions (see, e.g., recent reviews and papers by Koons [], Tsubouchi and Omura [], Crosby [], Gorobets and Messerotti [], Riley [], Love [], and references therein).…”