Multifractal structure and intermittence in the AE index time series

The conventional approach to magnetospheric dynamics has not provided until now a satisfactory description of the singular behaviour of magnetospheric substorms. In this paper we present a multifractal analysis of AE time series, based on singularity analysis, a new tool to investigate signal dynamics features. The existence of a multifractal structure of the AE index with respect to time dilation has been investigated. The resulting multifractal behaviour of the signal can be interpreted as the signature of an underlying intermittence phenomenon. The derived singularity spectrum is well in agreement with the one of a two-scale Cantor model (P-model), a pure multiplicative model. The presence of intermittence in AE might indicate the occurrence of turbulence in magnetospheric dissipation processes

On Geometrical Invariants of the Magnetic Field Gradient Tensor in Turbulent Space Plasmas: Scale Variability in the Inertial Range

In a recent paper, Consolini et al. investigated the statistics of geometrical invariants of the coarse-grained gradient tensor of plasma velocity for a case study of space plasma turbulence. They showed how, at spatial scales near the proton inertial length, there is evidence for the occurrence of dissipation structures along the Vieillefosse's tail. Here, we extend the previous analysis to the statistics of the geometrical invariants of the magnetic field coarse-grained gradient tensor, computed using magnetic field measurements by the ESA-Cluster mission in the solar wind region. In detail, we investigate the evolution of the joint probability distribution functions of the magnetic geometrical invariants at different scales in the inertial range of turbulent solar wind. The results show a clear dependence of the joint statistics of geometrical invariants on the distance from the proton inertial length scale in the inertial range, which seems to be compatible with a variation of the dimensionality of the fluctuation field from two dimensions to three dimensions at the smallest scales. Evidence of an increasing role of the ingoing spiral saddle and current-associated dissipation structures is found at the smallest investigated scales, where dissipation can occur

Global Diagnostics of Ionospheric Absorption During X-Ray Solar Flares Based on 8- to 20-MHz Noise Measured by Over-the-Horizon Radars

An analysis of noise attenuation during 80 solar flares between 2013 and 2017 was carried out at frequencies 8–20 MHz using 34 Super Dual Auroral Radar Network radars and the EKB ISTP SB RAS radar. The attenuation was determined on the basis of noise measurements performed by the radars during the intervals between transmitting periods. The location of the primary contributing ground sources of noise was found by consideration of the propagation paths of radar backscatter from the ground. The elevation angle for the ground echoes was determined through a new empirical model. It was used to determine the paths of the noise and the location of its source. The method was particularly well suited for daytime situations, which had to be limited for the most part to only two crossings through the D region. Knowing the radio path was used to determine an equivalent vertical propagation attenuation factor. The change in the noise during solar flares was correlated with solar radiation lines measured by GOES/XRS, GOES/EUVS, SDO/AIA, SDO/EVE, SOHO/SEM, and PROBA2/LYRA instruments. Radiation in the 1 to 8 Å and near 100 Å are shown to be primarily responsible for the increase in the radionoise absorption, and by inference, for an increase in the D and E region density. The data are also shown to be consistent with a radar frequency dependence having a power law with an exponent of −1.6. This study shows that a new data set can be made available to study D and E regions

The CAESAR project for the ASI space weather infrastructure

This paper presents the project Comprehensive spAce wEather Studies for the ASPIS prototype Realization (CAESAR), which aims to tackle the relevant aspects of Space Weather (SWE) science and develop a prototype of the scientific data centre for Space Weather of the Italian Space Agency (ASI) called ASPIS (ASI SPace Weather InfraStructure). To this end, CAESAR involves the majority of the SWE Italian community, bringing together 10 Italian institutions as partners, and a total of 92 researchers. The CAESAR approach encompasses the whole chain of phenomena from the Sun to Earth up to planetary environments in a multidisciplinary, comprehensive, and unprecedented way. Detailed and integrated studies are being performed on a number of well-observed “target SWE events”, which exhibit noticeable SWE characteristics from several SWE perspectives. CAESAR investigations synergistically exploit a great variety of different products (datasets, codes, models), both long-standing and novel, that will be made available in the ASPIS prototype: this will consist of a relational database (DB), an interface, and a wiki-like documentation structure. The DB will be accessed through both a Web graphical interface and the ASPIS.py module, i.e., a library of functions in Python, which will be available for download and installation. The ASPIS prototype will unify multiple SWE resources through a flexible and adaptable architecture, and will integrate currently available international SWE assets to foster scientific studies and advance forecasting capabilities

Coordinated cluster and ground-based instrument observations of transient changes in the magnetopause boundary layer during an interval of predominantly northward in the magnetopause boundary layer during an interval of predominantly northward IMF: relation to the reconnection pulses and FTE signatures

We study a series of transient entries into the low-latitude boundary layer (LLBL) of all four Cluster craft during an outbound pass through the midafternoon magnetopause ([XGSM, YGSM, ZGSM] ≈ [2, 7, 9] RE). The events take place during an interval of northward IMF, as seen in data from the ACE satelliteand lagged by a propagation delay of 75 min that is well defined by two separate studies: (1) of the magnetospheric variations prior to the northward turning (Lockwood et al., 2001, this issue) and (2) of the field clock angle seen by Cluster after it had emerged into the magnetosheath (Opgenoorth et al., 2001, thisissue). With an additional lag of 16.5 min, the transient LLBL events correlate well with swings of the IMF clock angle (in GSM) to near 90°. Most of this additional lag is explained by ground-based observations, which reveal signatures of transient reconnection in the pre-noon sector that then take 10-15min to propagate eastward to 15 MLT, where they are observed by Cluster. The eastward phase speed of these signatures agrees very well with the motion deduced by cross-correlation of the signatures seen on the four Cluster craft.The evidence that these events are reconnection pulses includes: transienterosion of the noon 630 nm (cusp/cleft) aurora to lower latitudes; transient and travelling enhancements of the flow into the polar cap, imaged by the AMIE technique; and poleward-moving events moving into the polar cap, seen by the EISCAT Svalbard Radar (ESR). A pass of the DMSP-F15 satellite reveals that the open field lines near noon have been opened for some time: the more recently opened field lines were found nearer dusk where the flow transient and the poleward-moving event intersected the satellite pass. The events at Clusterhave ion and electron characteristics predicted and observed by Lockwood and Hapgood (1998) for a Flux Transfer Events (FTE), with allowance for magnetospheric ion reflection off Alfvénic disturbances in the magnetopause reconnection layer. Like FTEs, the events are about 1RE in their direction of motion and show a rise in the magnetic field strength but, unlike FTEs, in general they show no pressure excess in their core and hence no characteristic bipolar signature in the boundary-normal component. However, most of the events were3 observed where the magnetic field was southward, i.e. on the edge of the interior magnetic cusp, or when the field was parallel to the magnetic equatorial plane. Only when the satellite begins to emerge into the exterior boundary (where the field was northward), do the events start to show a pressure excess in their core and the consequent bipolar signature. We identify the events as the first observations of flux transfer events at middle altitudes