Space physics and solar-terrestrial relationships
Solar variability and its effects on circumterrestrial space
Variation in solar irradiance and effects on Earth's atmosphere
The Sun exhibits a variation in the radiation emitted during the activity cycle, related to the presence of active regions on its surface. This variation is very small when observed over the entire electromagnetic spectrum but is most significant in the ultraviolet region and influences ozone production processes in the Earth's stratosphere. We studied these relationships by analyzing time series of solar irradiance observations made aboard artificial satellites (SOLSTICE experiment) using some spectral techniques to highlight correlations between irradiance variations in the UV spectrum and defining an equivalent of the color index used in astronomy, defined for the FUV (Far UltaViolet) and MUV (Medium UltraViolet) bands, and another widely used index that is the variation of the intensity ratio in the minima and wings of the MgII spectral line, comparing them with stratospheric ozone densities.
Solar flares forecasting
In collaboration with colleagues from Georgia State University, the Jet Propulsion Laboratory (JPL), the European Space Agency and the University of Tor Vergata, we developed the pipeline to analyze full-disk solar images observed with the MOTH II telescope, which operated at the Amundsen Antarctic Station for two different observing campaigns (2016-2017 and 2017-2018). This telescope works using magneto-optical filters (MOFs) in two different wavelength bands.
The Tor Vergata Synoptic Solar Telescope (TSST) is a compact, robotic multichannel instrument designed to conform to the main objectives described in the SPRING project, developed under the European Union-funded H2020-SOLARNET program and focuses on a preliminary design study of a synoptic solar observing facility. The TSST currently consists of two full-disk Sun observing instruments, an H-alpha telescope and a telescope based on a magneto-optical potassium filter (MOF) (KI D1) operating at 769.9 nm. The TSST is designed to be later upgraded with a second MOF channel.
Interaction of coronal mass ejections with the Earth and the circumterrestrial environment
Coronal mass ejections (CMEs) are the most energetic events occurring on the Sun and release huge amounts of plasma into interplanetary space at very high velocities. A CME that encounters the Earth on its path can interact with the Earth's magnetosphere, becoming an important source of risk, especially for space and terrestrial technological infrastructures. For this reason, the need to properly understand the mechanisms of formation, launch and propagation of CMEs from the Sun has become a key task in current space weather science. Our group, together with the Solar Physics group at Tor Vergata University, is collaborating on implementing numerical models of increasing complexity, from simplified dynamical models to more elaborate fluid dynamics simulations, to provide such predictive information.
Plasmasphere monitoring
The plasmasphere is a torus-like region of cold plasma (energy of the order of 1 eV) that encircles the Earth and extends from 1000 km up to 4-6 Earth radii (R⊕). Although the cold plasma is not a direct threat to human activity in space, its interaction with more energetic particle populations, such as ring currents and radiation belts, can determine space weather conditions. It is, therefore, essential to continuously monitor the state of the plasmasphere for nowcasting and forecasting purposes.
A technique to remotely sense the equatorial plasma mass density in the near-Earth space is based on spectral analysis of Ultra Low Frequency (ULF) magnetic signals recorded by magnetometer arrays on the ground. The technique uses data collected by pairs of magnetometers slightly separated in latitude and approximately aligned along the same magnetic meridian. A latitudinally extended network can monitor the radial dependence of the equatorial plasma mass density along with the longitudinal sector identified by the array. The procedure can be operative on a near real-time basis. EMMA, the European quasi-Meridional Magnetometer Array, is a prototype of this monitoring system established in 2012 in the PLASMON FP7 European project framework. It currently consists of 27 stations and is suitable for determining plasma mass densities for an extended range of L values (1.6-6.2R⊕). 1-sec data are collected and automatically processed every 15 min with an automated procedure to infer the equatorial plasma mass densities.
Solar wind-magnetosphere interaction
The solar wind variability reflects the variability of the solar atmosphere and manifests itself through the solar cycle by different geoeffective structures.
During the declining phase of the solar cycle and near the minimum, high speed streams originate from stable coronal holes. Due to the Sun rotation, they interact periodically (~27 days) with the Earth’smagnetosphere producing a recurrent geomagnetic activity. Near the solar maximum, geomagnetic perturbations are mostly driven by transient structures related to coronal mass ejections.
The interaction of the solar wind structures with the Earth’s magnetosphere produces both global and local geomagnetic field perturbations which occur at different time scales.
ULF waves
Ultra Low Frequency (ULF) fluctuations of the geomagnetic field lines characterize the geomagnetic activity in the frequency range ~1 mHz - 5 Hz. They are observed both in the magnetosphere and on the ground. ULF waves at lower frequencies (1.7-6.7 mHz, Pc5 pulsations on the ground) are believed to be driven by the Kelvin Helmholtz instability along the flanks of the magnetopause and/or by solar wind pressure variations associated to high speed streams. These waves are involved in the acceleration of magnetospheric electrons in the radiation belts.
The main source for ULF waves in the mid-frequency range (10–100 mHz, Pc3 pulsations) is supposed to be represented by upstream waves. They are generated in the Earth's foreshock region by a wave-particle interaction between already existing waves and solar wind protons reflected off the bow shock along the interplanetary magnetic field lines.
ULF higher frequency waves (0.1-5 Hz, magnetospheric EMIC waves, Pc1-2 pulsations on the ground) are generated near the plasmapause by unstable distributions of ring current ions and near the magnetopause by solar wind pressure pulse driven instability. Electromagnetic ion-cyclotron (EMIC) waves are responsible for relativistic electron precipitations at high latitude.
Development of sensors for the characterization of space plasmas
Effects on the polar atmosphere
The MAgnetosphere Ionosphere and Geomagnetic Induced Currents (MA.I.GIC.) model.
Magnetosphere-Ionosphere-Lithosphere (M.I.L.C.) coupling model.
