1,721,126 research outputs found
Dynamics of the solar photosphere: THEMIS observations
No full textWe present the results of 2D narrow- and broad-band photometry of quiet granulation field as observed at the center of the Sun by the THEMIS telescope in IPM mode. The broad-band spectral images have been used to derive geometrical and statistical properties of the pattern produced by convective flows rising from deep layers of the Sun. The narrow-band spectral observations, in the C I 538.0 nm, Fe I 537.9 nm, and Fe I 557.6 nm photospheric lines, have been used to calculate velocity and intensity maps at different heights in the solar atmosphere. The auto-correlation functions of the velocity fields at different heights suggest that, near the solar surface, the dynamics resemble the behavior of a complex out-of-equilibrium system, characterized by a dynamical heterogeneity. Conversely, in the middle photosphere, where only one characteristic time exists, the dynamical heterogeneity disappears. Moreover, the characteristic scales, derived from photospheric velocity maps by means of wavelet and information entropy analysis', show a dependence of their properties on the formation height of photospheric lines and an enlargement of the velocity features with height
Dynamics of the Overshooting Photospheric Region from THEMIS-IPM Observations
No full textHere, we present the results of our investigation on quiet photospheric fields. We study the features of intensity and velocity solar fields as derived from observations of photospheric lines, obtained at the French-Italian THEMIS telescope (Observatorio del Teide, Tenerife) using the Italian Panoramic Monochromator (IPM). In detail, the vertical dynamics is investigated using monochromatic observations at three spectral lines (C I 538.0, Fe I 537.9, and Fe I 557.6), as representative of three atmospheric heights in the overshooting photosphere. Moreover, granulation properties and horizontal flows are also studied using broad band images
The spectrum of kink-like oscillations of solar photospheric magnetic elements
Full text linkRecently, the availability of new high spatial and temporal resolution observations of the solar photosphere has allowed for the study of the oscillations in small magnetic elements. Small magnetic elements have been found to host a rich variety of oscillations detectable as intensity, longitudinal, or transverse velocity fluctuations that have been interpreted as magneto-hydrodynamic (MHD) waves. Small magnetic elements, at or below the current spatial resolution achieved by modern solar telescopes, are thought to play a relevant role in the energy budget of the upper layers of the Sun's atmosphere, as they are found to cover a significant fraction of the solar photosphere. Unfortunately, the limited temporal length and/or cadence of the data sets or the presence of seeing-induced effects have prevented accurate estimates of the power spectra of kink-like oscillations in small magnetic elements so far. Motivated by this, we studied kink-like oscillations in small magnetic elements, by exploiting very long duration and high cadence data acquired with the Solar Optical Telescope on board the Hinode satellite. In this paper, we present the results of a statistical study of the power spectral density of kink-like oscillations. We found that small magnetic elements exhibit a large number of spectral features in the range 1-12 mHz. Most of these spectral features are not shared among magnetic elements rather they represent a unique signature of each magnetic element itself
Evolution of velocity granulation fields (based on THEMIS-IPM observations)
No full textThe overshooting into the stable photosphere of convective flows, coming from the deeper layers of the solar structure, produces a granulation pattern. that evolves on short time scales and that is well correlated in intensity and velocity. In this work we present the first results of the analysis of observations obtained at the THEMIS telescope with the IPM (Italian Panoramic Monochromator). In particular we investigate the time lag of velocity spatial pattern at different heights and how this lag evolves with time
Magnetic network dynamics in photosphere
No full textIn order to investigate the interaction between the photospheric velocity field and emerging magnetic elements, observations with high spectral and temporal resolution and with a spatial scale of about 100 km on the solar surface are necessary. The convective advection of magnetic elements produces the magnetic network which is a key component of solar irradiance and of the energy transport toward the solar upper atmosphere. Furthermore, the magnetic network structures are suspected to be the roots of solar wind emanating from localized regions along boundaries of magnetic network cells. We present the results of the preliminary analysis of observations carried out with the panoramic monochromator IBIS, installed at the Dunn Solar Telescope, Sacramento Peak (NM), in the spectral lines Ca II 854.2 nm, Fe I 709.0 nm, and Fe II 722.4 nm
Fractal time statistics of AE-index burst waiting times: evidence of metastability
No full textRecent observations and analyses evidenced that the magnetotail, as well as the magnetospheric dynamics are characterised by a scale-free behaviour and intermittence.
These results, along with numerical simulations on cellular automata, suggest that the observed scale-invariance may
be due to forced and/or self-organised criticality (FSOC), meaning that the magnetotail operates near a marginally stable
state (Chang, 1999). On the other hand, it was underlined that a complex magnetic field topology in the geotail regions may play a relevant role in the impulsive energy relaxation (Consolini and Chang, 2001).Published419-4233.9. Fisica della magnetosfera, ionosfera e meteorologia spazialeJCR Journalope
Lagrangian evolution of field gradient tensor invariants in magneto-hydrodynamic theory
Full text linkDynamics of the solar granulation
No full textTemporal series of quiet region images near the center of the Sun are analysed. The images, monochromatic and in white light, have been acquired at the French-Italian solar telescope THEMIS (Tenerife, Canarie, Spain) by the Italian panoramic monochromator IPM. Solar granules evolution and the physical properties of the penetration convective photospheric region are discussed analysing velocity and intensity fields at the center of spectral lines. The observed lines are: C 5380, Fe 5379 and Fe 5576, which represent respectively the low, medium and high solar photosphere
Magnetic energy balance in the quiet sun on supergranular spatial and temporal scales
Full text linkSmall-scale magnetic fields are ubiquitous in the quiet solar photosphere and may store and transfer huge amounts of energy to the upper atmospheric layers. For this reason, it is fundamental to constrain the energetics of the quiet Sun. By taking advantage of a 24 hr long magnetogram time series acquired by the Hinode mission without interruption, we computed, for the first time, the average rate of change of magnetic energy density on supergranular spatial and temporal scales. We found that the regions where this quantity is positive correspond with the longest magnetic field decorrelation times, with the latter being consistent with the timescales of magnetic energy density variation. This suggests that, on average, the energy provided by photospheric electric and magnetic fields and current density is effective in sustaining the magnetic fields in the network
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