Studying auroral activity using the SME index at the magnetic storm main phase during CIR and ICME events

In this paper, we examine the relationship of the SME index with magnetic storm characteristics and interplanetary medium parameters during the main phase of magnetic storms caused by CIR and ICME events. Over the period 1990–2017, 107 magnetic storms driven by (64) CIR and (43) ICME events have been selected. In contrast to AE and Kp, a stronger correlation is shown to exist between the average SME index (SMEaver) and interplanetary medium parameters during the magnetic storm main phase. Close correlation coefficients between SMEaver and the SW electric field (southward IMF Bz) have been obtained for CIR and ICME events. SMEaver has been found to increase with the rate of magnetic storm development and |Dstmin|. For CIR and ICME events, no difference has been revealed between SMEaver and |Dstmin| in linear regression equations.

Studying auroral activity using the SME index at the magnetic storm main phase during CIR and ICME events

. In this paper, we examine the relationship of the SME index with magnetic storm characteristics and interplanetary medium parameters during the main phase of magnetic storms caused by CIR and ICME events. Over the period 1990–2017, 107 magnetic storms driven by (64) CIR and (43) ICME events have been selected. In contrast to AE and Kp, a stronger correlation is shown to exist between the average SME index (SMEaver) and interplanetary medium parameters during the magnetic storm main phase. Close correlation coefficients between SMEaver and the SW electric field (southward IMF Bz) have been obtained for CIR and ICME events. SMEaver has been found to increase with the rate of magnetic storm development and |Dstmin|. For CIR and ICME events, no difference has been revealed between SMEaver and |Dstmin| in linear regression equations.

New Horizons Detection of the Local Galactic Lyman-α Background

Since 2007 the Alice spectrograph on the New Horizons (NH) spacecraft has been used to periodically observe the Lyman-α (Lyα) emissions of the interplanetary medium (IPM), which mostly result from resonant scattering of solar Lyα emissions by interstellar hydrogen atoms passing through the solar system. Three observations of IPM Lyα along a single great circle were made during the NH cruise to Pluto, and these have been supplemented by observations along six great circles (spread over the sky at 30° intervals), acquired one month before and one day after the NH flyby of Pluto, and on a further five occasions since then, out to just over 47 au from the Sun. These data indicate a distant Lyα background of 43 ± 3 Rayleigh brightness (equivalent to 56 ± 4 nW m−2 sr−1), which is present in all directions (i.e., not only in the upstream direction, as previously reported). This result is found independently by: (1) the falloff with distance from the Sun of the IPM Lyα brightness observed by NH–Alice in several directions on the sky, and (2) the residual between the observed brightness and a model brightness accounting for the resonantly scattered solar Lyα component alone. The repeated observations show that this distant Lyα background is constant and uniform over the sky, and represents the local Galactic Lyα background. The observations show no strong correlation with the cloud structure of the local IPM. The observed brightness constrains the absorption coefficient of interstellar dust at Lyα to 0.2 ± 0.01 kpc−1.

Learning about comets from the study of mass distributions and fluxes of meteoroid streams

Meteor physics can provide new clues about the size, structure, and density of cometary disintegration products, establishing a bridge between different research fields. From meteor magnitude data we have estimated the mass distribution of meteoroids from different cometary streams by using the relation between the luminosity and the mass obtained by Verniani (1973). These mass distributions are in the range observed for dust particles released from comets 1P/Halley and 81P/Wild 2 as measured from spacecraft. From the derived mass distributions, we have integrated the incoming mass for the most significant meteor showers. By comparing the mass of the collected Interplanetary Dust Particles (IDPs) with that derived for cometary meteoroids a gap of several orders of magnitude is encountered. The largest examples of fluffy particles are clusters of IDPs no larger than 100 µm in size (or 5×10–7 g in mass) while the largest cometary meteoroids are centimeter-sized objects. Such gaps can be explained by the fragmentation in the atmosphere of the original cometary particles. As an application of the mass distribution computations we describe the significance of the disruption of fragile comets in close approaches to Earth as a more efficient (and probably more frequent) way to deliver volatiles than direct impacts. We finally apply our model to quantify the flux of meteoroids from different meteoroid streams, and to describe the main physical processes contributing to the progressive decay of cometary meteoroids in the interplanetary medium.

Dynamics of energetic spectrum of solar-diurnal variations of cosmic rays in 19-24 solar activity cycles

The anisotropic angular distribution of cosmic rays (CR) in the interplanetary medium manifests itself on Earth as periodic diurnal intensity variations. Ground-based detectors of CRs have different energy sensitivity to the primary CR radiation and, therefore, the amplitude and phase recorded by them are also different. This fact makes it possible to study the energy spectrum of the variations when using a sufficient number of detectors. In this work, the results of the investigation of the energy spectrum of solar-diurnal variations of CRs obtained by a network of neutron monitors and muon telescopes are presented. The network allows measuring CRs with median energies from units to hundreds of GeV. The expected values of the amplitude and phase of the daily CR variations at the selected ground-based stations for different types of the energy spectrum are shown. The calculated data are compared with experimental data for 19-24 solar activity cycles.

On the Origin of High–Frequency Magnetic Fluctuations in the Interplanetary Medium: A Brownian–like Approach

Low–frequency fluctuations in the interplanetary medium have been extensively investigated and described in the framework of turbulence, and the observed universal scaling behavior represents a clear signature of the underlying energy cascade. On the contrary, the interpretation of observations of plasma fluctuations at high frequencies, where wave–wave coupling, collisionless dissipation, and anomalous plasma heating play a key role, still represents a challenge for theoretical modeling. In this paper the high frequency fluctuations occurring in the interplanetary space are described through a Brownian–like approach, where the plasma dynamics at small scales is described through a stochastic process. It is shown that a simple model based on this framework is able to successfully reproduce the main features of the spectrum of the observed magnetic fluctuations. Moreover, the Fluctuation-Dissipation Relation, derived by our model, leads to a power law between dissipation rate and temperature, which is compatible with the occurrence of Landau damping, interpreted thus as the main mechanism of dissipation in the solar wind plasma.

Relating 27-day Averages of Solar, Interplanetary Medium Parameters and Geomagnetic Activity Proxies in Solar Cycle 24

Correlations between solar, interplanetary medium parameters and geomagnetic activity proxies in 27-day averages (a Bartels’ rotation) were analysed for the 2009-2016 time interval. In this analysis, two new proxies were considered: 1) B ZS GSM, calculated as the daily percentage of the IMF southward component along the GSM Z-axis and then averaged every 27 days; 2) four magnetospheric indices (T-indices), calculated from the local North-South (X) contributions of the magnetosphere's cross-tail (TAIL), the symmetric ring current (SRC), the partial ring current (PRC) and the Birkeland current (FAC), derived from Tsyganenko and Sitnov 2005 (TS05) semi-empirical magnetospheric model. Our results suggest that, among the parameters tested in this study, solar facular areas, interplanetary magnetic field intensity and new proxies derived from TS05 model could be taken into account in an empirical model, with a 27-day resolution, to explain geomagnetic activity felt on the Earth's surface in terms of solar surface features and the IMF condition. We further retrieve a clear annual oscillation in series of 27-day-mean values of toward/away asymmetries of geomagnetic activity indices, which can be interpreted in the light of Russell-McPherron hypothesis for the semiannual variation of geomagnetic activity.