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The day/night cycle at a single observatory prevents definitive observations of many aspects of solar activity, convection, and oscillations with timescales near 1 day. Solutions to this problem include multi-site networks, spacecraft observatories, and observations from high-latitude sites during their summer season. We report here on our experience in using Alaska as a high-latitude site for observations of solar oscillations. 相似文献
2.
We define for observational study two subsets of all polar zone filaments, which we call polemost filaments and polar filament bands. The behavior of the mean latitude of both the polemost filaments and the polar filament bands is examined and compared with the evolution of the polar magnetic field over an activity cycle as recently distilled by Howard and LaBonte (1981) from the past 13 years of Mt. Wilson full-disk magnetograms. The magnetic data reveal that the polar magnetic fields are built up and maintained by the episodic arrival of discrete f-polarity regions that originate in active region latitudes and subsequently drift to the poles. After leaving the active-region latitudes, these unipolar f-polarity regions do not spread equatorward even though there is less net flux equatorward; this indicates that the f-polarity regions are carried poleward by a meridional flow, rather than by diffusion. The polar zone filaments are an independent tracer which confirms both the episodic polar field formation and the meridional flow. We find:
- The mean latitude of the polemost filaments tracks the boundary of the polar field cap and undergoes an equatorward dip during each arrival of additional polar field.
- Polar filament bands track the boundary latitudes of the unipolar regions, drifting poleward with the regions at about 10 m s-1.
- The Mt. Wilson magnetic data, combined with a simple model calculation, show that the filament drift expected from diffusion alone would be slower than observed, and in some cases would be equatorward rather than poleward.
- The observation that filaments drift poleward along with the magnetic regions shows that fields of both polarities are carried by the meridional flow, as would be expected, rather than only the f-polarity flux which dominates the strength. This leads to the prediction that in the mid-latitudes during intervals between the passage of f-polarity regions, both polarities are present in nearly equal amounts. This prediction is confirmed by the magnetic data.
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Barry LaBonte 《Solar physics》2004,221(2):191-207
The scattering of light over the field of view of a solar spectropolarimeter affects all Stokes parameters. The magnetic field
vector inferred from the Stokes spectra then has systematic error. The reason is that scattering affects polarized radiation
as well as unpolarized. Accurate correction of the Stokes spectra from the Imaging Vector Magnetograph (IVM) of the Mees Solar
Observatory illustrates the problem and the solutions. 相似文献
4.
Measurements of the brightness of the clear daytime sky at Haleakala, Maui are presented for the interval 1955 through 2002. The observations are made near the direction of the Sun, where forward scattering off aerosols dominates the sky brightness. The Haleakala summit at 3054 m is normally above the inversion layer. The Haleakala sky is dark; the observed brightness per airmass has a median of 10 millionths of the solar disk and a mode of 5 millionths, with Rayleigh scattering contributing 1 millionth. There is no demonstrable long-term trend in the data. 相似文献
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Solar Physics - It is well known that flares cause changes in the azimuthal direction of chromospheric magnetic field lines (e.g. Zirin, 1983). It is less well known that flares also cause changes... 相似文献
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We present observations of high frequency, intermediate degree, Ca-K line solar intensity oscillations. We compare the peak
frequencies determined from these 1991.4 observations with the peak frequencies from 1987.9 South Pole observations (Duvallet al., 1991) in that portion of the spatio-temporal diagram where the two datasets overlap (degrees between 30 and 150 and frequencies
between 4 and 6.6 mHz). We find that temporal changes are detectable in the high frequency spectrum and are particularly large
near 5.4 mHz. The m-averaged high frequency peaks decreased in frequency in 1991.4 compared to the peak frequencies measured
in 1987.9. The magnitude of the frequency shift is of the order of 10 μHz near 5.4 mHz, increases with degree, and decreases to near zero both above and below 5.4 mHz. It is unlikely that these temporal
changes in the high frequency spectrum are due to a change in the height of the subphotospheric acoustic source layer. A physical
mechanism for these frequency shifts has not yet been identified. 相似文献
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D. L. Mickey R. C. Canfield B. J. LaBonte K. D. Leka M. F. Waterson H. M. Weber 《Solar physics》1996,168(2):229-250
We describe an instrument we have built and installed at Mees Solar Observatory on Haleakala, Maui, to measure polarization in narrow-band solar images. Observations in Zeemansensitive photospheric lines have been made for nearly all solar active regions since the instrument began operations in 1992. The magnetograph includes a 28-cm aperture telescope, a polarization modulator, a tunable Fabry-Pérot filter, CCD cameras and control electronics. Stokes spectra of a photospheric line are obtained with 7 pm spectral resolution, 1 arc sec spatial resolution over a field 4.7 arc min square, and polarimetric precision of 0.1%. A complete vector magnetogram observation can be made every eight minutes. The flexibility of the instrument encourages diverse observations: besides active region magnetograms we have made, for example, composite vector magnetograms of the full solar disk, and H polarization movies of flaring regions. 相似文献
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The Imaging Vector Magnetograph (`IVM') at Mees Solar Observatory, Haleakal, Maui, Hawai`i, is designed to measure the magnetic field vector over an entire solar active region on the Sun. The first step in that process is to correct the raw data for all known systematic effects introduced by the instrument and Earth's atmosphere. We define a functional model of the atmosphere/instrument system and measure the corrections for the degradation introduced by each component of the model. We demonstrate the feasibility of this method and assess the accuracy of the IVM spectra with a direct comparison of the resulting Stokes spectra to a well-described spectropolarimeter. 相似文献
9.
Mean line bisector positions were found for the neutral iron line at 5250.2 using disk-integrated sunlight. After correction for the apparent time variation of the instrumental profile, it was found that the mean bisector position was constant during the period from May 1982 to February 1983.The correlation between the total magnetic flux as measured at Mount Wilson and the line asymmetry results of Livingston is not high. In particular, the magnetic flux dropped in 1982, suggesting a large line asymmetry that was not observed. However, the correlation between the 30-day average of the mean magnetic field and Livingston's results is quite high (-0.95), suggesting that the asymmetry of the disk-integrated line profile is related to the old plage regions rather than to the active regions.Now at the Institute for Astronomy, University of Hawaii, Honolulu, HI 96822, U.S.A. 相似文献
10.
Barry J. LaBonte 《Solar physics》1982,113(1-2):285-288
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