No abstract

Jupiter is a complex and at the same time very powerful radio source in the decameter wavelength range. The emission is anisotropic, intrinsically variable at millisecond to hour timescales, and also modulated by various external processes at much longer periods, ranging from ∼10 h to months or years (including Jovian day and year, solar activity and solar wind variations, and for groundbased observations, terrestrial day and year). As a consequence, long-term observations and their statistical study have proved to be necessary for disentangling and understanding the observed phenomena. We have built a database from the available 26 yr of systematic, daily observations conducted at the Nançay Decameter Array and recorded in digital format. This database contains all observed Jovian decametric emissions, classified with respect to the time-frequency morphology, their dominant circular polarization, and maximum frequency. We present the results of the first statistical analysis of this database. We confirm the earlier classification of Jovian decameter emissions in Io-A, -A , -B, -C, -D and non-Io-A, -B, -C types, but we also introduce new emission types (Io-A and Io-B ) and precise and characterize the non-Io-D type. We determine the contours of all emission types in the CML−Φ Io plane (Central Meridian Longitude in Jupiter's System III coordinates versus Io Phase), provide representative examples of their typical time-frequency patterns, and the distribution of emission's maximum frequency as a function of Λ Io (Io's Longitude). Finally, we present a statistical analysis of the distributions of the occurrence rate, duration, intensity and polarization for each emission type. non-Io-DAM appears to be related to small-scale, possibly bursty auroral structures.

[1] Corotating interaction regions (CIRs) are structures formed when high-speed solar wind streams overtake slow solar wind streams as they propagate outward. These structures produce regions of enhanced density and magnetic field strength in the solar wind near the ecliptic plane. In this paper, the geoeffectiveness of CIRs, as measured by the geomagnetic Dst index, is assessed during the solar wind observational period . A catalogue of CIRs is constructed by consulting high-speed plasma streams (HSPS) lists present in the literature and by analyzing solar wind parameters for each HSPS event. The geoeffectiveness of CIRs is analyzed by determining the number of intense (Dst À100 nT), moderate (À100 < Dst À50 nT), or weak (À50 < Dst À30 nT) magnetic storms that followed each CIR event. Statistical distributions of CIR parameters (maximum solar wind speed, maximum convection electric field, southward magnetic field peak) and geoeffectiveness (Dst peak) are obtained. Correlation analyses of Dst index with various solar wind parameters are presented. A comparison with the geoeffectiveness of other interplanetary structures such as shocks, magnetic clouds, and sector boundaries is performed. Our results show that 33% of CIRs are followed by moderate/intense magnetic activity (Dst < À50 nT), i.e., approximately one third of the CIR events observed near Earth are geoeffective.

Energy coupling between the solar wind and the Earth's magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how ultralow frequency (ULF) wave activity during the passage of Alfvénic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on 22 September 2014, which coincides with the corotating interaction region preceding a high-speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground-and space-based observational data and global magnetohydrodynamic simulations and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L-shells. Magnetohydrodynamic simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfvén modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by phase space density calculations for this global recovery period.