Identifying ionospheric shadowing signatures of ringlets and plateaus in Saturn's C Ring

<p>During the Grand Finale of the Cassini mission, the southern hemisphere of Saturn was shadowed by its rings and the substructures within, whose more intense shadows can be mapped to specific ionospheric altitudes. We successfully connect small-scale variations (dips) in the ionospheric H<sub>2</sub><sup>+</sup> density below 2500 km, measured by the Ion and Neutral Mass Spectrometer (INMS) during orbits 288 and 292, to the shadows of individual ringlets and plateaus in the C Ring. From the H<sub>2</sub><sup>+</sup> density signatures we estimate lower limits of the associated ringlet or plateau opacities. These will be compared with results obtained from stellar occultations. Potential implications/constraints on the ionospheric dynamics will be discussed. The ringlet and plateau shadows are not associated with obvious dips in the electron density.</p>

Contribution to the Research of the Effects of Etna Volcano Activity on the Features of the Ionospheric Total Electron Content Behaviour

This research represents a contribution to the theory on the coupling of the volcanic activity and the ionospheric dynamics, represented by total electron content (TEC) patterns and their behaviour. The ionospheric response to the activity of the Etna volcano has been analysed using global navigation satellite system (GNSS)-derived TEC values, employing data from International GNSS Service (IGS) reference station near the volcano and on two distant IGS locations. Volcanic activity has been modelled using volcanic radiative power (VRP) data obtained by the Middle InfraRed Observation of Volcanic Activity (MIROVA) system. The estimated minimal night TEC values have been averaged over defined index days of the VRP increase. During the analysed period of 19 years, the volcano activity was categorised according to pre-defined criteria. The influence of current space weather and short-term solar activity on TEC near the volcano was systematically minimised. The results showed mean/median TEC increases of approximately +3 standard deviations from the overall mean values, with peak values placed approximately 5 days before the VRP increase and followed by general TEC depletion around the time of the actual volcanic activity increase. Additionally, TEC oscillation pattern was found over the volcano site with a half-period of 6.25 days. The main interpretation of results indicates that the volcanic activity has modified the ionospheric dynamics within the nearby ionospheric region before the actual VRP increase, and that the residual impact in the volcano’s surrounding area refers to terrestrial endogenous processes and air–earth currents. Those changes can be detected during criteria predefined in the research: during quiet space weather conditions, observing night-time TEC values and within the limits of low short-term solar influence.

Ionospheric shadowing signatures of ringlets and plateaus in Saturn's C Ring

<p>During the Grand Finale of the Cassini mission, the southern hemisphere of Saturn was shadowed by its rings and the substructures within, whose more intense shadows can be mapped to specific ionospheric altitudes. We successfully connect small-scale variations (dips) in the ionospheric H<sub>2</sub><sup>+</sup> density below 2500 km, measured by the Ion and Neutral Mass Spectrometer (INMS) during orbits 288 and 292, to the shadows of individual ringlets and plateaus in the C Ring. From the H<sub>2</sub><sup>+</sup> density signatures we estimate lower limits of the associated ringlet or plateau opacities. These will be compared with results obtained from stellar occultations and potential implications/constraints on the ionospheric dynamics will be discussed. The ringlet and plateau shadows are not associated with obvious dips in the electron density.</p>

Ionospheric dynamic and coupling processes during geomagnetic storms

<p>Geomagnetic storms cause the largest disturbances in the ionosphere-thermosphere system. We use measurements with satellites and ground based radars to study storm-induced variations in ionospheric plasma drift, ion density, and ion composition at low latitudes. It is found that the storm-time change of ion drift velocity in the equatorial ionosphere can reach 200-300 m/s, the change of ion density can be one or two orders of magnitude, and the change of ion composition can be 50-80%. These extremely large changes in the ionosphere can last for several hours or even a few days during the main and recovery phases of magnetic storms. The longitudinal, latitudinal and hemispheric differences of storm-time ionospheric disturbances are analyzed from measurements of multiple satellites or radar chain. Very long, continuous penetration of interplanetary electric fields to the equatorial ionosphere for 6 or even 14 hours are observed, and the time when disturbance dynamo electric fields become dominant is identified. The interplay of penetration, shielding, and disturbance dynamo electric fields in the storm-time ionosphere will be addressed. Mechanisms responsible for storm-time ionospheric dynamics will be discussed.</p>

Hemispheric Asymmetry in the Mars Summer Ionosphere at Various Solar Forcing Conditions

<p>The MAVEN satellite has now made two Martian-years of ionosphere-thermosphere (I-T) observations enabling limited studies of seasonal changes in the upper atmosphere. Before examining the ionospheric dynamics associated with space weather, we wish to understand the climatological conditions of the system.  For example, previous studies have revealed the morning electron temperature overshoot as well as a close dependence between electron temperatures and neutral densities in the equatorial regions. In this presentation, we will examine differences in the northern and southern dayside ionosphere during the summer season of each hemisphere. The differences between these two cases will be contrasted with the seasonal dependence at the equator. Differences between the equatorial and polar regions are expected due to (A) differences in neutral scale heights, (B) differences in the solar zenith angle, and (C) the equilibration of I-T coupling due to differences in solar illumination.</p><p>In this work, we present a statistical analysis of MAVEN measurements comparing the north and south summer I-T. We find that when controlling for neutral pressure and latitude, the north and south plasma densities and temperatures are nearly identical below the demagnetization altitude (higher neutral pressures). Above the demagnetization altitude (lower neutral pressures), the southern hemisphere electron densities are higher than those in the northern hemisphere by ~100%. A significantly lower electron temperature is also observed in the south at these lower pressures. Given that the difference in solar EUV (and corresponding neutral heating) is ~20% between the two summer seasons, we postulate that the significantly lower plasma densities (above the demagnetization altitude) in the northern summer are due in part to an increase in ionospheric loss. This loss may be associated with the acceleration of ionospheric particles by the draped magnetic fields at an altitude where ions are not demagnetized. Furthermore, the loss may be diminished in the southern hemisphere where crustal magnetic fields increase the standoff distance to the solar wind magnetic field.</p>

Ground-based measurements of ionospheric dynamics

Different methods are used to research and monitor the ionospheric dynamics using ground measurements: Digisonde Drift Measurements (DDM) and Continuous Doppler Sounding (CDS). For the first time, we present comparison between both methods on specific examples. Both methods provide information about the vertical drift velocity component. The DDM provides more information about the drift velocity vector and detected reflection points. However, the method is limited by the relatively low time resolution. In contrast, the strength of CDS is its high time resolution. The discussed methods can be used for real-time monitoring of medium scale travelling ionospheric disturbances. We conclude that it is advantageous to use both methods simultaneously if possible. The CDS is then applied for the disturbance detection and analysis, and the DDM is applied for the reflection height control.