Abstracts

1) Studio in-situ dell'evoluzione radiale della cascata turbolenta nell'eliosfera interna tramite vari indicatori

L. Sorriso-Valvo

Studio delle proprietà spettrali, di intermittenza, e formazione di strutture coerenti. Leggi di scala per il trasferimento di energia turbolenta in varie versioni: MHD incomprimibile, MHD comprimibile, Hall-MHD, e inclusione di anisotropia. Determinazione dell'evoluzione radiale del flusso di energia turbolenta globale e locale, e possibile relazione con processi cinetici per stabilire quali siano i meccanismi di dissipazione a varie distanze dal sole e nell'evoluzione della turbolenza. Misure necessarie: campi e plasma.

2) Magnetic reconnection, intermittency and particle acceleration in the turbulent solar wind

S. Servidio, A. Greco, F. Valentini F. Pecora, O. Pezzi, S. Perri, G. Nigro, F. Catapano, L. Sorriso-Valvo, P. Veltri

Systematic analysis of numerical simulations of plasma turbulence reveals the presence of a large number of magnetic islands and X-type neutral points, where magnetic reconnection locally occurs. These reconnecting regions appear as coherent structures, intermittent in space, and represent a crucial component of turbulence. In this picture, turbulence can be envisioned as a sea of flux tubes, different in size and energy, merging in a complex network, where reconnection is a very active process that leads to turbulent heating and particle acceleration. In the past decade, the above picture has become widely accepted for both the solar wind at 1 A.U. and for the Earth's magnetosheath. This description has been supported by simulations and data analysis of the turbulent wind, where new statistical analysis techniques have been adopted. This strong link between reconnection, particle acceleration and turbulent heating can now be inspected in the vicinity of the Sun, thanks to the Solar Orbiter mission. This study might shed new lights on the heating process of the solar corona and, in general, on the understanding of turbulence in other stellar winds.

3) Studio della riconnessione nel vento solare

M.F. Marcucci

Solo negli ultimi dieci anni si è stati in grado di evidenziare tramite osservazioni in situ eventi di riconnessione nel vento solare (e.g. Golsling et al. 2012, Phan et al. 2010). Questo processo può avere un ruolo rilevante nei principali meccanismi fisici che determinano l’evoluzione del vento solare e la generazione e il trasporto di particelle energetiche. Per quanto è a mia conoscenza, lo studio statistico più esteso sulla riconnessione del vento solare è quello di Phan et. al 2010. In tale studio sono state utilizzate le misure fatte a bordo dei satelliti WIND ed ACE. Più specificatamente, e per quanto riguarda WIND, ci si è basati sulle misure di campo magnetico ed i momenti, calcolati a bordo, con una risoluzione temporale di 3 s. Sempre nel suddetto studio si è mostrato come esista una condizione di soppressione della riconnessione legata al plasma beta e all’angolo di shear a cavallo dello strato di corrente (Swisdak et al. 2010). Ciò suggerisce che la riconnessione, specialmente a basso shear, sia favorita nelle regioni a basso beta, come per esempio negli strati di corrente sul fronte delle ICME e nelle regioni più vicine al Sole. Penso sia dunque importante utilizzare le misure di plasma e campo magnetico di Solar Orbiter per fare un approfondito studio statistico del verificarsi della riconnessione durante la fase di crociera e fino alla distanza minima dal Sole, in relazione alle diverse strutture del vento solare e, a seconda dei casi, in sinergia con le osservazioni da remoto.

4) The nature and origin of quasi-periodic solar wind density fluctuations.

S. Di Matteo and U. Villante

An important open question of solar wind (SW) research is to evaluate the fraction of small-scale structures in the interplanetary medium and understand if they are signatures of coronal aspects or features that develop within the SW during propagation. Among the mesoscale structures (with timescales of tens of minutes to several hours), the periodic density structures (PDS), related to the release processes of coronal plasma by magnetic reconnection, have been already successfully used to study the source of some SW parcels. An example is the recent identification of PDS in the inner heliosphere at 0.3, 0.4, and 0.6 AU using in situ measurements from the Helios1 and Helios2 probes (Di Matteo et al., 2019). In addition, studies of coronagraph images have shown that plasma parcels are released from the top of helmet streamers on timescales of many hours down to many minutes, sometimes in a periodic manner with ≈90 minutes being a characteristic timescale. In this regard, the measurements from the Solar Wind Analyzer (SWA) onboard Solar Orbiter (the ion and electron bulk properties as well as SW ion composition), and the METIS coronagraph would provide a new insight on these processes. The work could be also supported by scientists from NASA-GSFC, interested in a possible collaboration.

5) Assessing the physical conditions of the heliospheric environment via observations of comets with Solar Orbiter

Giuseppe Nisticò, Valery M. Nakariakov, Karl Battams, Volker Bothmer, Gaetano Zimbardo

Observations of comets with space instruments allow a better understanding of the local environment where the comets are travelling (Schrijver et al. 2013, Jones et al. 2018). Cometary tails are observed to be highly dynamic, exhibiting disconnections, wave-like motion, and responding to the solar wind flows and the passage of coronal mass ejections (Vourlidas et al. 2007, DeForest et al. 2015, Nisticò et al. 2018). Furthermore, there is a special class of comets, defined as “sungrazers”, that plunge into the Sun’s atmosphere. Few exceptional cases of comets have been observed crossing the entire corona and detected with EUV telescopes at distances less than 1 solar radius from the photosphere (e.g. Comet Lovejoy, Downs et al. 2012). The Solar Orbiter mission is highly suitable for the study of comets and the assessment of their coupling with the heliospheric environment. The remote-sensing instruments, e.g. the EUI telescope, the METIS coronagraph, and the heliospheric imager SoloHI, can provide observations at high temporal resolution, covering distances from some AU to about one solar radius, while the in-situ instruments, e.g. the Solar Wind Analyser, may measure the properties of cometary tails crossed by Solar Orbiter on its journey around the Sun.

6) Swarm and Solar Orbiter: bridging scientific disciplines

F. Catapano, E. Qamili, R. D’ Amicis, L.Trenchi, J. Bouffard, A. Stromme

Swarm is ESA's first constellation mission for Earth Observation. The main scientific goal of the mission is to study the different contributions (external and internal) to the terrestrial magnetic field. This include the study of the current system flowing in the magnetosphere and ionosphere. The solar radiation varies over multiple temporal scales and modulates the evolution of the ionosphere. The dependence of the ionosphere on the solar activity is a key and fundamental issue in ionospheric physics. The synergy between Swarm and Solar Orbiter would provide essential information to understand the variations in the ionosphere and its physical processes. For example measurements such as the one of the interplanetary magnetic field, obtained from the MAG instrument on board Solar Orbiter, can be used as input for modelling the external contributions to the terrestrial magnetic field. Also, the SWA instrument could provide useful information on the solar wind conditions, supporting the investigations of the ionosphere-magnetosphere coupling driven by solar activity. Is this a good chance to bridge scientific disciplines?

7) Linking fluid and kinetic scales turbulence

R. Bruno, R. D’Amicis, R. De Marco, D. Telloni, R. Marino, L. Sorriso-Valvo

One of the most important results in space plasma turbulence would be that of linking fluid and kinetic scales to understand how energy is reversed towards the dissipation range. Future observations from in-situ instruments onboard Solar Orbiter and in particular from SWA will be used to study this problem. We will focus on the range of frequencies across the transition between fluid and kinetic scales aiming to a full characterization of both magnetic and plasma fluctuations with particular emphasis on kinetic features of the proton VDF.

8) Evolution of Alfvénicity in the inner heliosphere

R. D’Amicis, R. Bruno, R. De Marco, M. Velli, D. Telloni, L. Matteini

Solar wind fluctuations, especially within the main portion of fast streams, are characterized by large amplitude fluctuations showing an Alfvénic nature. Although fast wind is usually more Alfvénic than slow wind, recent results have shown that the slow solar wind can also sometimes display a high degree of Alfvénicity, with velocity and magnetic field fluctuations as large as those found in the fast wind, even at 1 AU where one would expect a degradation of the Alfvénic correlation due to the solar wind expansion. With the proposed study, we intend to investigate why Alfvénic fluctuations are destroyed during the solar wind evolution in the non-Alfvénic slow solar wind, or on the contrary, why they persist at 1 AU in the Alfvénic slow solar wind.

9) Investigating the origin of the Alfvénic slow solar wind with Solar Orbiter and Parker Solar Probe observations

R. D’Amicis, M. Velli, O. Panasenco

One of the objectives of the Solar Orbiter is to study the origin of the solar wind and to understand the physics which connects the plasma at the solar surface. Observations from SWA, in synergy with observations with other in-situ instruments on board Solar Orbiter and Parker Solar Probe, can be used to this purpose to study and characterize different types of slow solar wind. A series of field-aligned solar wind models will be used to associate different streams with their source regions. Moreover, this study will focus on photospheric and low corona magnetic field configurations enabling the origin of regular slow wind and peculiar slow solar wind streams hosting Alfvénic turbulence.