10 research outputs found
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The variation of geomagnetic storm duration with intensity
Variability in the near-Earth solar wind conditions can adversely affect a number of ground- and space-based technologies. Such space-weather impacts on ground infrastructure are expected to increase primarily with geomagnetic storm intensity, but also storm duration, through time-integrated effects. Forecasting storm duration is also necessary for scheduling the resumption of safe operating of affected infrastructure. It is therefore important to understand the degree to which storm intensity and duration are correlated. The long-running, global geomagnetic disturbance index, aa , has recently been recalibrated to account for the geographic distribution of the component stations. We use this aaH index to analyse the relationship between geomagnetic storm intensity and storm duration over the past 150 years, further adding to our understanding of the climatology of geomagnetic activity. Defining storms using a peak-above-threshold approach, we find that more intense storms have longer durations, as expected, though the relationship is nonlinear. The distribution of durations for a given intensity is found to be approximately log-normal. On this basis, we provide a method to probabilistically predict storm duration given peak intensity, and test this against the aaH dataset. By considering the average profile of storms with a superposed-epoch analysis, we show that activity becomes less recurrent on the 27-day timescale with increasing intensity. This change in the dominant physical driver, and hence average profile, of geomagnetic activity with increasing threshold is likely the reason for the nonlinear behaviour of storm duration
Comprehensive Analysis of the Geoeffective Solar Event of 21 June 2015: Effects on the Magnetosphere, Plasmasphere, and Ionosphere Systems
International audienc
Distribution of Interstellar Hydrogen Atoms in the Heliosphere and Backscattered Solar Lyman-α
We review the modern concepts of penetration of interstellar atoms of hydrogen into the heliosphere up to 1 AU. Before entering into the heliosphere the atoms penetrate through the region of the solar wind (SW) interaction with the local interstellar medium (LISM). In the interaction region the atoms can exchange charge with both solar wind and interstellar protons disturbed in the SW/LISM interaction region. Charge exchange results in a disturbance of the pristine interstellar atom flow in the interaction region, and, therefore, the parameters of interstellar gas inside the heliosphere are different from their interstellar values. This makes it more difficult to determine local interstellar parameters from measurements of the interstellar atoms inside the heliosphere, but, on the other side, opens possibilities to study the SW/LISM interaction region remotely. This paper overviews the main physical phenomena and modern models of the SW/LISM interaction and presents a state-of-art 3D kinetic model of the interstellar hydrogen gas inside the heliosphere. The distributions of the gas parameters are compared with the distributions obtained in the context of the classical hot model. Quantitative and qualitative differences are discussed. The state-of-art model is employed to calculate spectra of the backscattered Lyman- α radiation as they would be measured at 1 AU and the zero, first and second moments of the spectra. It is shown that the SW/LISM interaction imprints in the spatial and velocity distribution of the interstellar atoms are revealed in the intensities, line-shifts, and line-widths of the distribution functions. A qualitative comparison of the model results with SOHO/SWAN data are presented