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61.
J. O. Stenflo 《Solar physics》1988,114(1):1-19
A search for linear polarization due to the transverse Zeeman effect in quiet regions near the heliographic north pole has been carried out. The aim is to determine new constraints on the properties of the hidden or turbulent magnetic flux of the Sun. As more than 90% of the total flux seen in magnetograms has its source in kG fluxtubes with an average filling factor of less than 1%, the term hidden magnetic flux refers to the field in the remaining 99% of the photospheric volume, which remains undetected in ordinary magnetograms (at available levels of spatial resolution and sensitivity).Simultaneous recordings of the Stokes I, Q, and V profiles of the Fei 5250.22 and 5247.06 Å lines with 5 × 5 sec of arc spatial resolution have been made with the NSO McMath solar telescope. The analysis shows how the observed Stokes Q amplitudes, as well as the Q/V ratio in combination with the 5250/5247 Stokes V line ratio, provide constraints on the field strength and the angular distribution of the field vectors of the hidden magnetic flux. The field has to be tangled with opposite polarities mixed on a subarcsec scale, and the field vectors have to have large inclinations with respect to the vertical direction, with an angular distribution not far from being isotropic in the photosphere. Constraints on the strength of this tangled or turbulent magnetic field have been obtained by previous methods, which are reconsidered in view of their dependence on the assumed angular distribution. An upper limit of 100 G comes from determinations of magnetic line broadening, a lower limit of 10 G from observed Hanle-effect depolarization.In our observations the linear polarization has been recorded with a precision of 10-4 with good spectral resolution. Further improvements are impeded by the lack of telescopes with large photon collecting areas and small instrumental polarization. 相似文献
62.
J. O. Stenflo 《Solar physics》1975,42(1):79-105
Analysis of magnetograph recordings made simultaneously in different spectral lines have shown that the quiet-region network and active-region plages with average field strengths less than about 100 G are made up by the same type of elementary structures, each having the same physical properties. Magnetograph data are used together with continuum, line profile, and EUV data to derive a model of these subarcsec, spatially unresolved elementary structures. The field strength at the center of each basic element is about 2 kG. The temperature enhancement starts at a height of about 180 km (above the level 0 = 1 in HSRA), and increases rapidly with height. The brightness structures are coarser than the magnetic-field structures.The magnetic field cannot be contained by either gas pressure or dynamic pressure. The magnetic pressure must be balanced by the constricting force of strong electric currents along the magnetic filaments (pinch effect). A mechanism is proposed for the amplification of the field, involving vortex motions around the downdrafts in the network and plages. Efficient heating by hydromagnetic waves builds up an excess gas pressure inside the twisted fluxropes. The excess pressure is released by the ejection of spicules, which have to move out along the helically shaped field lines and thereby will acquire a spinning motion.The continuum emission in the fluxropes, which are located in the intergranular lanes, washes out the contrast between cell interiors and cell boundaries and creates an abnormal granulation pattern. When more and more magnetic flux is brought into a given area, the interaction between the fluxropes and the granulation starts to change the physical structure of the fluxropes. This begins at an average field B
obs 100 G, with a gradual transition to pores and sunspots as b
obs is increased. 相似文献
63.
L. Stenflo 《Planetary and Space Science》1973,21(3):391-397
The coupled equations for the resonant nonlinear interaction between three waves in cold magnetized plasmas are derived and written in a comparatively simple and symmetric form. The deficiencies of previous papers are pointed out and the possibility of explosive interactions in the solar corona is suggested. 相似文献
64.
Henrik Lundstedt Anders Johannesson Göran Scharmer Jan Olof Stenflo Ulf Kusoffsky Birgitta Larsson 《Solar physics》1991,132(2):233-245
A high-resolution videomagnetograph that records the images of opposite circular polarization simultaneously has been constructed for the Swedish vacuum solar telescope at La Palma. Magnetograms are obtained by off-line integration of bursts consisting of typically 50 frames of 20 ms exposures, with bad frames rejected, and the frame-to-frame image motion of the remaining frames compensated for by cross-correlation techniques. The short exposures combined with frame selection and elimination of image motion optimizes the resolution and thereby also the S/N, allowing good magnetograms to be obtained with an effective exposure time of less than 1 s at an image scale of 0.1 pixel–1. The advantages and limitations of the system are discussed and compared with other techniques of making filter magnetograms are discussed. 相似文献
65.
K. Stucki S.K. Solanki I. Rüedi J.O. Stenflo A. Brković U. Schühle K. Wilhelm M.C.E. Huber 《Astrophysics and Space Science》1998,264(1-4):53-61
We present a preliminary analysis of spectral lines obtained with the SUMER instrument (Solar Ultraviolet Measurements of
Emitted Radiation) onboard the Solar and Heliospheric Observatory (SOHO), as observed during three observing campaigns. From
the 70 observed spectral lines, we selected 12, representing 9 ions or atoms, in order to analyse line intensities, shifts
and widths in polar coronal holes as well as in the normal quiet Sun.
We find that coronal lines show a distinct blueshift in coronal holes relative to the quiet Sun at equal heliospheric angle,
while there is no evidence for such a shift for lines formed at temperatures below 105K. The widths of lines formed at temperatures above 3 – 104K are slightly increased inside the coronal hole, but unaffected for lower temperatures. Intensity measurements clearly show
the center-to-limb variation, as well as an intensity diminution inside the coronal hole for lines formed above approximately
105K.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
66.
Jan Olof Stenflo 《Solar physics》1969,8(2):260-263
The polarization of a normal Zeeman triplet is discussed for the case in which the lifetime of the excited state of the atom is comparable to or shorter than the period of Larmor precession. 相似文献