P. Mein

Vertical structure of sunspots from THEMIS observations

We have analysed two-dimensional spectro-polarimetric data taken with the MSDP observing mode of THEMIS in the Na I D1 line to investigate the height variation of the magnetic eld in sunspot umbrae. From the Zeeman-induced circular polarization measured at individual MSDP channels within the line prole, maps of the longitudinal magnetic eld have been computed. A method based on Response Functions has been developed to estimate the depth in the atmosphere at which the Zeeman measurements are originated, thus providing the line-of-sight eld at dierent altitudes in the photosphere. The magnetogram corresponding to the deepest level has served as a boundary condition to perform the potential eld extrapolation into the corona. We have found that the spatial distribution of vertical eld gradient contours predicted from extrapolation is in qualitatively good agreement with that inferred from observations. Quantitatively, however, the longitudinal eld gradients obtained with both methods dier about one order of magnitude, being larger for observations. The origin of this discrepancy has been discussed with respect to possible observation biases, as well as to idealizations used for eld extrapolation. This is a crucial problem to be addressed in future work, and may have important implications for the physics of how the magnetic eld evolves through sunspots and how the flux is distributed in the corona.

Investigation of temperature and velocity fluctuations through the solar photosphere with the Na I D lines

In this work we explore the diagnostic properties of the Na I D resonance lines by calculating the response functions of their line proles to temperature and velocity perturbations in the atmosphere. We propose a method to transform spectral line intensity fluctuations measured at several wavelengths into temperature and velocity disturbances at dierent height levels. Results from tests done with several theoretical models of perturbations are discussed. Perturbations that vary as linear functions of depth are eciently reproduced. The method also provides good estimations for exponential models. As an example we present an application to solar granulation data obtained with Multichannel Subtractive Double Pass (MSDP) spectroscopy.

High resolution solar magnetometry with the spectrograph of the Pic du Midi Turret Dome

We present arguments which show that in all likelihood mesogranulation is not a true scale of solar convection but the combination of the effects of both highly energetic granules, which give birth to strong positive divergences (SPDs) among which we find exploders, and averaging effects of data processing. The important role played by SPDs in horizontal velocity fields appears in the spectra of these fields where the scale

High spatial resolution capabilities of Doppler measurements with the Pic du Midi MSDP spectrograph

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Sub arcsec evolution of solar magnetic fields

4 Mm is most energetic; we illustrate the effect of averaging with a one-dimensional toy model which shows how two independent non-moving (but evolving) structures can be transformed into a single moving structure when time and space resolution are degraded. The role of SPDs in the formation of the photospheric network is shown by computing the advection of floating corks by the granular flow. The coincidence of the network bright points distribution and that of the corks is remarkable. We conclude with the possibility that supergranulation is not a proper scale of convection but the result of a large-scale instability of the granular flow, which manifests itself through a correlation of the flows generated by SPDs.We present the flrst results obtained with a new Ferroelectric Liquid Crystal (FLC) polarimeter operating with the spectrograph of the Pic du Midi Turret Dome, since September 2003. We observed the solar granulation around active region NOAA 0459 with the Multichannel Subtractive Double Pass (MSDP) operating mode and analysed the circular polarization of the Na D1 589.6 nm spectral line in terms of longitudinal magnetic flelds in a 2D fleld of view (16 x 142 arc sec). Image quality was fairly good and limited to 0.4 arc sec due to the pixel sampling. This observation reveals the presence of magnetic concentrations of several hundred Gauss which are mainly located in the intergranular lanes. Data analysis performed at two difierent optical depths (line core and line wings) also suggests that magnetic lines are curved and diverge with increasing altitude.

Results from high resolution solar images and spectra obtained at the Pic du Midi Observatory (1986–1990)

We analyse observations in the NaD1 line (λ 5896 A) obtained with the MSDP spectrograph of the Turret Dome of the Pic du Midi Observatory. Individual images reveal high spatial resolution and the data reduction shows the high capabilities of the spectrograph to get doppler measurements up to the limit of the resolution of the refractor (0. �� 3). Dopplershifts are obtained in the middle and high photosphere. The smallest granules 0. �� 4 show upward motions in the middle photosphere.

Temporal height properties of the exploding granules

Context: .The evolution of the concentrated magnetic field in flux tubes is one challenge of the nowadays Solar physics which requires time sequence with high spatial resolution. Aims: .Our objective is to follow the properties of the magnetic concentrations during their life, in intensity (continuum and line core), magnetic field and Doppler velocity. Methods: .We have observed solar region NOAA 0644 on 2004 July 15 at Pic du Midi observatory with the Multichannel Subtractive Double Pass (MSDP) operating mode and analysed the circular polarization of the Na D1 589.6 nm spectral line in terms of longitudinal magnetic field in 2D field of view (5.6 arcsec× 80 arcsec), during 41 mn at two altitudes 327 km and 170 km in the photosphere. Results: .Our data analysis reveals that all the concentrated magnetic features are associated with downward motions and the magnetic field remains very stable during the 41 mn. At different height 327 and 170 km, a clear depth effect is visible on Doppler velocity but not in the magnetic field strength.

Dynamics of the solar granulation.

Abstract We present an overview of our recent results about solar granulation and mesogranulation, obtained with Pic du Midi observations. These results were obtained during 1986–1990 using image and spectrographic analysis of high spatial resolution data. The study of the solar granulation, with 2 Dim. “Multichannel Subtractive Double Pass” (M.S.D.P.) spectra, shows a clear change of the dynamical regime at 3″ ( ⋍ 2200 km ) of the photospheric velocity field when oscillatory components are filtered out. A three hour movie obtained on film at Pic du Midi Observatory and analyzed at the Lockheed Research Laboratory and the National Solar Observatory (Sacramento Peak) was used to calculate the horizontal flow pattern. The mean lifetime of the diverging areas related to mesogranulation is estimated at 3 hours; these diverging areas are swept by the supergranulation flow towards the supergranule boundary with a mean speed of 0.4 km/s.