Radiative transfer modeling of the Hanle effect in convective atmospheres

AbstractThis paper summarizes the results of a recent investigation on the Hanle effect in atomic and molecular lines, which indicates that there is a vast amount of “hidden” magnetic energy and (unsigned) magnetic flux in the internetwork regions of the quiet solar photosphere. This hidden magnetic energy, localized in the (intergranular) downflowing plasma of the solar photosphere, is carried mainly by tangled fields at sub-resolution scales with strengths between the equipartition field values and ∼1 kG, and is more than sufficient to compensate the radiative energy losses of the solar outer atmosphere.

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Spectropolarimetric diagnostics of unresolved magnetic fields in the quiet solar photosphere

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313002330 ◽

2012 ◽

Vol 8 (S294) ◽

pp. 107-118 ◽

Cited By ~ 3

Author(s):

Nataliya G. Shchukina ◽

Javier Trujillo Bueno

Keyword(s):

Magnetic Field ◽

Magnetic Energy ◽

Zeeman Effect ◽

Three Dimensional ◽

Solar Photosphere ◽

Magnetic Energy Density ◽

Hanle Effect ◽

Molecular Lines ◽

Surface Convection ◽

Ubiquitous Presence

AbstractA few years before the Hinode space telescope was launched, an investigation based on the Hanle effect in atomic and molecular lines indicated that the bulk of the quiet solar photosphere is significantly magnetized, due to the ubiquitous presence of an unresolved magnetic field with an average strength 〈B〉, ≈ 130 G. It was pointed out also that this “hidden” field must be much stronger in the intergranular regions of solar surface convection than in the granular regions, and it was suggested that this unresolved magnetic field could perhaps provide the clue for understanding how the outer solar atmosphere is energized. In fact, the ensuing magnetic energy density is so significant that the energy flux estimated using the typical value of 1 km/s for the convective velocity (thinking in rising magnetic loops) or the Alfvén speed (thinking in Alfvén waves generated by magnetic reconnection) turns out to be substantially larger than that required to balance the chromospheric energy losses. Here we present a brief review of the research that led to such conclusions, with emphasis on a new three-dimensional radiative transfer investigation aimed at determining the magnetization of the quiet Sun photosphere from the Hanle effect in the Sr I 4607 Å line and the Zeeman effect in Fe I lines.

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Microwave temperature and pressure measurements with the Odin satellite: I. Observational method

Canadian Journal of Physics ◽

10.1139/p01-158 ◽

2002 ◽

Vol 80 (4) ◽

pp. 443-454 ◽

Cited By ~ 6

Author(s):

J R Pardo ◽

M Ridal ◽

D Murtagh ◽

J Cernicharo

Keyword(s):

Radiative Transfer ◽

Outer Space ◽

Atmospheric Temperature ◽

Upper Atmosphere ◽

Operational Mode ◽

Altitude Range ◽

Molecular Lines ◽

Temperature And Pressure ◽

Radiative Transfer Modeling ◽

Temperature Vertical Profile

The Odin satellite is equipped with millimetre and sub-millimetre receivers for observations of several molecular lines in the middle and upper atmosphere of our planet (~25100 km, the particular altitude range depending on the species) for studies in dynamics, chemistry, and energy transfer in these regions. The same receivers are also used to observe molecules in outer space, this being the astrophysical share of the project. Among the atmospheric lines that can be observed, we find two corresponding to molecular oxygen (118.75 GHz and 487.25 GHz). These lines can be used for retrievals of the atmospheric temperature vertical profile. In this paper, we describe the radiative-transfer modeling for O2 in the middle and upper atmosphere that we will use as a basis for the retrieval algorithms. Two different observation modes have been planned for Odin, the three-channel operational mode and a high-resolution mode. The first one will determine the temperature and pressure on an operational basis using the oxygen line at 118.75 GHz, while the latter can be used for measurements of both O2 lines, during a small fraction of the total available time for aeronomy, aimed at checking the particular details of the radiative transfer near O2 lines at very high altitudes (>70 km). The Odin temperature measurements are expected to cover the altitude range ~3090 km. PACS Nos.: 07.57Mj, 94.10Dy, 95.75Rs

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The second solar spectrum and the hidden magnetism

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309030464 ◽

2008 ◽

Vol 4 (S259) ◽

pp. 211-222

Author(s):

Jan O. Stenflo

Keyword(s):

Magnetic Flux ◽

Spatial Resolution ◽

Zeeman Effect ◽

Solar Spectrum ◽

Coherent Scattering ◽

Small Scale ◽

Solar Photosphere ◽

Resolution Limit ◽

New Paradigm ◽

Hanle Effect

AbstractApplications of the Hanle effect have revealed the existence of vast amounts of “hidden“ magnetic flux in the solar photosphere, which remains invisible to the Zeeman effect due to cancellations inside each spatial resolution element of the opposite-polarity contributions from this small-scale, tangled field. The Hanle effect is a coherency phenomenon that represents the magnetic modification of the linearly polarized spectrum of the Sun that is formed by coherent scattering processes. This so-called “Second Solar Spectrum” is as richly structured as the ordinary intensity spectrum, but the spectral structures look completely different and have different physical origins. One of the new diagnostic uses of this novel spectrum is to explore the magnetic field in previously inaccessible parameter domains. The earlier view that most of the magnetic flux in the photosphere is in the form of intermittent kG flux tubes with tiny filling factors has thereby been shattered. The whole photospheric volume instead appears to be seething with intermediately strong fields, of order 100G, of significance for the overall energy balance of the solar atmosphere. According to the new paradigm the field behaves like a fractal with a high degree of self-similarity between the different scales. The magnetic structuring is expected to continue down to the 10m scale, 4 orders of magnitude below the current spatial resolution limit.

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