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We analyze Sun-as-a-star observations spanning over solar cycles 22 – 24 from the ground-based network BiSON and solar cycles 23 – 24 collected by the space-based VIRGO and GOLF instruments on board the SoHO satellite. Using simultaneous observations from all three instruments, our analysis suggests that the structural and magnetic changes responsible for modifying the frequencies remained comparable between cycle 23 and cycle 24 but differ from cycle 22. Thus we infer that the magnetic layer of the Sun has become thinner since the beginning of cycle 23 and continues during the current cycle.
Using continuous observations for 22 years from ground-based network GONG and space-borne instruments MDI onboard SoHO and HMI onboard SDO, we report both global and local properties of the convection zone and their variations with time.
Solar five-minute oscillations of intermediate-degree ℓ were observed both before and after a very strong white-light flare. Intensity images of the full Sun taken on two sides of the Fe I λ 5576 spectral line were recorded on film, digitized with 8″ spatial resolution, and then converted into Doppler velocities. The data were projected onto both equatorial and polar sectoral modes and Fourier transformed in time. Comparing the resulting power spectra, we find a substantial increase in power in the p5 ridge of the equatorial modes on the day after the flare; such an increase may be a consequence of the solar flare. When data from all the ridges are considered, there is an average increase in power of only a few percent the day after the flare. This overall increase is probably not significant due to uncertainties from effects of the beating of unresolved modes.
Full disk observations of the 5-min solar oscillations have been obtained with a lithium niobate Fabry-Perot filter. The equatorial solar rotation rate as a function of depth has been inferred from the sectoral modes of oscillation using the Backus-Gilbert optimal averaging inversion method. The results show a rotation rate that slowly decreases over the depths of 15 to 56 Mm below the photosphere. The results are in agreement with the previous Duvall-Harvey observations.
The equatorial rotation rate has been inferred as a function of depth through the outer 16 Mm of the Sun from observations of high-degree five-minute oscillations. An optimal averaging inversion procedure due to Backus & Gilbert (1970) has been applied to frequency splittings measured from power spectra obtained using Doppler data spanning three and five consecutive days. The resulting rotation curves have proven to be much more stable than the curves obtained from data sets of single days. The results imply that the solar rotation rate increases with depth by 0.023 μHz reaching a maximum at about 2 Mm below the surface, then decreases by 0.037 μHz down to 16 Mm.
Since the early 1990s, politicians, policymakers, the media and academics have increasingly focused on religion, noting the significant increase in the number of cases involving religion. As a result, law and religion has become a specific area of study. The work of Professor Norman Doe at Cardiff University has served as a catalyst for this change, especially through the creation of the LLM in Canon Law in 1991 (the first degree of its type since the time of the Reformation) and the Centre for Law and Religion in 1998 (the first of its kind in the UK). Published to mark the twenty-fifth anniversary of the LLM in Canon Law and to pay tribute to Professor Doe's achievements so far, this volume reflects upon the interdisciplinary development of law and religion.
Helioseismology from a single ground-based observatory is severely compromised by the diurnal rising and setting of the Sun. This causes sidelobes to appear in the helioseismic power spectrum at multiples of ± 11.57 μHz from each solar line, contaminating the spectrum and rendering mode identification and frequency measurement extremely difficult. The difficulty can be overcome in three ways — observing from a fully sunlit orbit in space, observing from the Polar regions, or observing with a network of stations placed around the Earth. This paper discusses the networks that are either currently in operation or being planned. These include the Global Oscillation Network Group (GONG) project, the Birmingham network, the IRIS network of the University of Nice, and the SCLERA network of the University of Arizona. The scientific objectives and instrumentation of these networks are briefly described. Theoretical predictions for network performance are compared with actual results. The problem of merging simultaneous data from multiple instruments is discussed, as well as the relationship of the networks with the helioseismology experiments on the SOHO space mission.
Two-dimensional power spectra of solar five-minute oscillations display prominent ridge structures in (k, ω) space, where k is the horizontal wavenumber and ω is the temporal frequency. The positions of these ridges in k and ω can be used to probe temperature and velocity structures in the subphotosphere. We have been carrying out a continuing program of observations of five-minute oscillations with the diode array instrument on the vacuum tower telescope at Sacramento Peak Observatory (SPO). We have sought to establish whether power spectra taken on separate days show shifts in ridge locations; these may arise from different velocity and temperature patterns having been brought into our sampling region by solar rotation. Power spectra have been obtained for six days of observations of Doppler velocities using the Mg I λ5173 and Fe I λ5434 spectral lines. Each data set covers 8 to 11 hr in time and samples a region 256″ × 1024″ in spatial extent, with a spatial resolution of 2″ and temporal sampling of 65 s. We have detected shifts in ridge locations between certain data sets which are statistically significant. The character of these displacements when analyzed in terms of eastward and westward propagating waves implies that changes have occurred in both temperature and horizontal velocity fields underlying our observing window. We estimate the magnitude of the velocity changes to be on the order of 100 m s -1; we may be detecting the effects of large-scale convection akin to giant cells.