[Show abstract][Hide abstract] ABSTRACT: The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector magnetic fields on the Sun through precise spectropolarimetry of solar spectral lines with a spatial
resolution of 0.2 – 0.3arcsec. Aphotometric accuracy of 10−3 is achieved and, after the polarization calibration, any artificial polarization from crosstalk among Stokes parameters is
required to be suppressed below the level of the statistical noise over the SOT’s field of view. This goal was achieved by
the highly optimized design of the SOT as a polarimeter, extensive analyses and testing of optical elements, and an end-to-end
calibration test of the entire system. In this paper we review both the approach adopted to realize the high-precision polarimeter
of the SOT and its final polarization characteristics.
[Show abstract][Hide abstract] ABSTRACT: The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope
being designed for high spatial, spectral and temporal resolution, as
well as IR and low-scattered light observations. The overall limit of
performance of the telescope is strongly influenced by the qualities of
the site at which it is located. Six sites were tested with a seeing
monitor and a sky brightness instrument for 1.5 to 2 years. The sites
were Big Bear (California), Haleakala (Hawaii), La Palma (Canary
Islands, Spain), Panguitch Lake (Utah), Sacramento Peak (New Mexico),
and San Pedro Martir (Baja California, Mexico). In this paper we will
describe the methods and results of the site survey, which chose
Haleakala as the location of the ATST.
No preview · Article · Jul 2006 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The site survey for the Advanced Technology Solar Telescope concluded recently after more than two years of data gathering and analysis. Six locations, including lake, island and continental sites, were thoroughly probed for image quality and sky brightness. The present paper describes the analysis methodology employed to determine the height stratification of the atmospheric turbulence. This information is crucial because day-time seeing is often very different between the actual telescope aperture (~30 m) and the ground. Two independent inversion codes have been developed to analyze simultaneously data from a scintillometer array and a solar differential image monitor. We show here the results of applying them to a sample subset of data from May 2003, which was used for testing. Both codes retrieve a similar seeing stratification through the height range of interest. A quantitative comparison between our analysis procedure and actual in situ measurements confirms the validity of the inversions. The sample data presented in this paper reveal a qualitatively different behavior for the lake sites (dominated by high-altitude seeing) and the rest (dominated by near-ground turbulence). Comment: To appear in the Publications of the Astronomical Society of the Pacific (PASP). Note: Figures are low resolution versions due to file size limitations
Full-text · Article · Aug 2005 · Publications of the Astronomical Society of the Pacific
[Show abstract][Hide abstract] ABSTRACT: Co-ordinated observations of the Sun and inner heliosphere using a large number of space- and ground-based instruments were carried out in August–September 1996, August 1998 and August–September 1999 as the first, second and third Whole Sun Months. These observations provided unprecedented cover of the Sun and inner heliosphere at solar minimum (1996) and during the rising phase of the new solar cycle (1998, 1999). In this paper we review the observations made during the three Whole Sun Months and consider the changes in the large-scale structure of the heliosphere seen over the four years.
No preview · Article · Nov 2000 · Journal of Atmospheric and Solar-Terrestrial Physics
[Show abstract][Hide abstract] ABSTRACT: Observations of interplanetary scintillation (IPS) made using the EISCAT facility provide accurate measurements of solar wind velocity between 15 and 120 solar radii. In this paper we present observations of the solar wind at low latitudes made between 1994 and 1997. Of 178 observations of the solar wind at low heliographic latitudes, 112 showed evidence of flow velocities significantly faster than the normal slow wind across a portion of the ray-path. In all cases, these enhanced flow speeds were clearly associated with coronal holes extending towards or across the heliographic equator. Fast flow from very close to the heliographic equator is clearly associated with equator-crossing coronal holes in all cases, suggesting that discrete streams of fast wind observed at low latitudes originate exclusively in coronal holes.
No preview · Article · Sep 2000 · Advances in Space Research
[Show abstract][Hide abstract] ABSTRACT: Observations of interplanetary scintillation (IPS) made using the EISCAT facility provide accurate measurements of solar wind velocity between 15 and 120 solar radii (R). In this paper we present observations of the solar wind at low latitudes made between 1991 and 1998, with particular emphasis on flow from trans-equatorial coronal holes.
[Show abstract][Hide abstract] ABSTRACT: The Whole Sun Month campaign (August 10 to September 8, 1996) brought together a wide range of space-based and ground-based observations of the Sun and the interplanetary medium during solar minimum. The wealth of data collected provides a unique opportunity for testing coronal models. We develop a three-dimensional magnetohydrodynamic (MHD) model of the solar corona (from 1 to 30 solar radii) applicable to the WSM time period, using measurements of the photospheric magnetic field as boundary conditions for the calculation. We compare results from the computation with daily and synoptic white-light and emission images obtained from ground-based observations and the SOHO spacecraft and with solar wind measurements from the Ulysses and WIND spacecraft. The results from the MHD computation show good overall agreement with coronal and interplanetary structures, including the position and shape of the streamer belt, coronal hole boundaries, and the heliospheric current sheet. From the model, we can infer the source locations of solar wind properties measured in interplanetary space. We find that the slow solar wind typically maps back to near the coronal hole boundary, while the fast solar wind maps to regions deeper within the coronal holes. Quantitative disagreements between the MHD model and observations for individual features observed during Whole Sun Month give insights into possible improvements to the model.
[Show abstract][Hide abstract] ABSTRACT: Two-site observations of interplanetary scintillation using the EISCAT facility can provide measurements of solar wind velocity at any point in the heliosphere between 15 and 120 solar radii (R). In this paper we discuss a series of observations made as part of the Whole Sun Month campaign (August 10 to September 8 1996) and compare the results with coronal data and in-situ measurements made during the campaign. The results of the comparison revealed extremely good agreement between solar wind speeds measured by IPS at 16-73 R and in situ measurements at 213 R and beyond, both in the general morphology of the solar wind and in the absolute velocities observed. These results confirm that structures in the solar wind, originating in the corona, preserve their form out to 910 R or more. Observations of fast solar wind were always associated with coronal holes and slow wind with the bright corona. Velocities intermediate between normal fast and slow flow speeds are associated with interaction regions between fast and slow flow and are also found above the boundaries of coronal holes.
[Show abstract][Hide abstract] ABSTRACT: In this report, we summarize measurements made by the plasma experiment on the Ulysses spacecraft during the period designated as ``Whole Sun Month'' (WSM, August 10 to September 8, 1996). This interval coincided with the return of solar wind variability at Ulysses. Ulysses was located at ~28°N heliographic latitude, at a heliocentric distance of 4.25 AU, and on the opposite side of the Sun from Earth. In particular, we explore the evolution of the solar wind between the Sun and Ulysses for several rotations surrounding WSM. Specifically, we map Ulysses measurements back toward the Sun by applying a two-dimensional inverse MHD algorithm. This approach is compared with the commonly used constant speed (or ballistic) approximation. We find that the MHD mapping technique produces substantially better results when compared with solar observations. Both the Ulysses MHD-mapped results and the solar observations are consistent with a picture of a modestly tilted streamer belt (
[Show abstract][Hide abstract] ABSTRACT: A large number of synoptic maps from a variety of instruments are used to show the general morphology of the Sun at the time of the First Whole Sun Month Campaign. The campaign was conducted from August 10 to September 8, 1996. The synoptic maps cover the period from Carrington rotation 1912/253° to Carrington rotation 1913/45°. The synoptic maps encompass both on-disk data and limb data from several heights in the solar atmosphere. The maps are used to illustrate which wavelengths and data sets show particular features, such as active regions and coronal holes. Of particular interest is the equatorial coronal hole known as the ``elephant's trunk,'' which is clearly evident in the synoptic maps of on-disk data. The elephant's trunk is similar in appearance to the Skylab-era, ``Boot of Italy,'' equatorial coronal hole. The general appearance of the limb maps is explained as well. The limb maps also show evidence for equatorial coronal holes.
No preview · Article · May 1999 · Journal of Geophysical Research Atmospheres
[Show abstract][Hide abstract] ABSTRACT: We compare coronal data from three different coronagraphs operating during the flight of SPARTAN 201-5 on Nov 1-3, 1998. The SPARTAN 201/White Light Coronagraph provides reliable data from 1.5--4.0 solar radii, bridging a gap in the radial coverage between the Mark 3 Coronagraph (which has reliable data from 1.16--1.8 solar radii) and the SOHO/LASCO C2 (2.5--6 solar radii). We will compare the radial brightness profiles of different coronal features as seen by the three different instruments, comparing the apparent structures in total white-light and polarized brightness.
[Show abstract][Hide abstract] ABSTRACT: This paper presents first observations of dynamics of the white-light solar corona detected during the few minutes of totality
of a solar eclipse. Perturbations of a polar plume associated with an embedded `jet' structure observed simultaneously at
195Åwith the EUV Imaging Telescope (EIT) aboard the SOHO spacecraft lead to estimates of the electron density fluctuations
accompanying the jet: ±15%. The morphological behavior of the jet, its apparent upward propagation speed of ≈200kms−1, and the inferred density perturbations suggest that the jet is led by a weak, outward-propagating shock resulting from the
injection of material at high velocity at the base of the corona. Smaller perturbations of the white-light corona are apparent
at many other locations, sustaining hope that propagating Alfvén waves may be measurable in the solar corona. Density perturbations
associated with the jet follow from empirical electron density models of the polar inter-plume and plume regions, as derived
from the ground-based eclipse measurements of coronal polarization brightness. These models indicate polar plume densities
4–6times that of the interplume low corona.
[Show abstract][Hide abstract] ABSTRACT: Co-rotating interaction regions (CIRs) between fast and slow streams of plasma are a prominent feature of the solar wind. Measurements of interplanetary scintillation (IPS) using the three widely separated antennas of the EISCAT facility have been used to detect the compression regions at the leading edges of interaction regions and to determine the location and velocity of the structure. Observations show that interaction regions have developed as close to the Sun as 25?30 solar radii, a result supported by theoretical modelling which shows that the conditions needed for CIRs to develop exist inside 30 solar radii.
Full-text · Article · Feb 1998 · Annales Geophysicae
[Show abstract][Hide abstract] ABSTRACT: The solar wind streams observed from the Solar and Heliospheric Observatory (SOHO) and Ulysses, WIND spacecraft during the whole solar month are discussed. These solar wind streams, with speeds in excess of 500 km/s, were detected from 10 August to 8 September 1996. The data covering Carrington rotations 1912 and 1913 are presented. The magnetic field azimuthal angle observations at 1 AU from WIND show that all the streams are associated with outward fields near the sun. The stream structure near 320 deg was associated with the central meridian passage of a coronal hole. The Fe XIV ground based observations show a region of low intensity in the zero to 170 deg longitude. The question of whether the streams arise from equatorial features or represent flows coming from higher latitude features is not solved.
[Show abstract][Hide abstract] ABSTRACT: We compare the calibrated polarized brightness (pB) from the Spartan 201 White Light Coro-nagraph (WLC) to corresponding data from the Mauna Loa Solar Observatory (MLSO) Mark III (Mk3) and IV (Mk4) K-Coronameters and the Solar and Heliospheric Observatory's Large An-gle and Spectrometric Coronagraph (SOHO/LASCO) C2 coronagraph. The WLC bridges an important gap in the radial coverage of polarized brightness (pB) between the Mk4 and C2. The combined data set gives continuous coverage of polarized brightness from 1.1 – 6 R for all azimuthal angles. We find that during the 1995 Spartan 201 flight WLC and the Mk3 pB values agree to a factor of 1.2 or better. During the 1998 Spartan 201 flight the correspondence between WLC and the Mk4 varied from day to day, agreeing to a factor of 1.7 or better for R ∼ < 2R on the best day. WLC and LASCO/C2 agreed to a factor of 1.2 or better.