The Influence of Magnetic Field on Oscillations in the Solar Chromosphere

Two sequences of solar images obtained by the Transition Region and Coronal Explorer in three UV passbands are studied using wavelet and Fourier analysis and compared to the photospheric magnetic flux measured by the Michelson Doppler Interferometer on the Solar Heliospheric Observatory to study wave behavior in differing magnetic environments. Wavelet periods show deviations from the theoretical cutoff value and are interpreted in terms of inclined fields. The variation of wave speeds indicates that a transition from dominant fast-magnetoacoustic waves to slow modes is observed when moving from network into plages and umbrae. This implies preferential transmission of slow modes into the upper atmosphere, where they may lead to heating or be detected in coronal loops and plumes.

Making hay while the sun shines? Socio-economic change, cereal production and climatic deterioration in Early Medieval Ireland

The Early Medieval period in Ireland (c. A.D. 400–1150) has been the subject of much archaeological and historical study. The recent application of various forms of archaeological sciences, as well as palaeoenvironmental studies, to the archaeological record have, however, added fresh impetus to this study area. It seems increasingly evident that significant changes to economy and society occurred during this period and were not recorded in detail in the contemporary documentary sources. This paper will attempt to outline those changes and to assess whether, or to what extent, they were influenced by climate change.

Determining the Sun's influence on Lateglacial and Holocene climates: a focus on climate response to centennial-scale solar forcing at 2800 cal. BP

The influence of solar variability on the climate of the Lateglacial and Holocene periods has been the subject of increasing discussion during the last decade. In the Mid-Holocene, several studies have identified cold/wet events that occur at ca 2800 cal. BP and a link with a reduction in solar activity, inferred from the C-14 record, has been postulated. We present results from a multi-proxy study of peat humification, plant macrofossils and testate amoebae from a raised bog at Glen West, northwest Ireland, that indicate that dry bog surface conditions were experienced in the north of Ireland at the time of the solar anomaly starting at 2800 cal. BP. With the aid of C-14 wiggle-matching and tephrochronology, an abrupt shift to wetter conditions is dated to ca 2700 cal. BP, coinciding with a C-14 maximum but clearly post-dating the 2800 cal. BP event identified elsewhere in Europe. We explore the significance of this apparent lag in the Irish record, considering the possible role of the ocean in generating spatial and temporal complexities in the climate patterns of the North Atlantic region. We conclude that these complexities are likely to give rise to time-transgressive climate responses around the North Atlantic that will only be recognised by more critical chronological approaches.

Trends in reported sun bed use, sunburn, and sun care knowledge and attitudes in a UK region: results of a survey of the Northern Ireland population

Background Sunburn and sun bed use increase risk of malignant melanoma, the incidence of which continues to rise.

A nocturnal mammal, the greater mouse-eared bat, calibrates a magnetic compass by the sun

Recent evidence suggests that bats can detect the geomagnetic field, but the way in which this is used by them for navigation to a home roost remains unresolved. The geomagnetic field may be used by animals both to indicate direction and to locate position. In birds, directional information appears to be derived from an interaction of the magnetic field with either the sun or the stars, with some evidence suggesting that sunset/sunrise provides the primary directional reference by which a magnetic compass is calibrated daily. We demonstrate that homing greater mouse-eared bats (Myotis myotis) calibrate a magnetic compass with sunset cues by testing their homing response after exposure to an altered magnetic field at and after sunset. Magnetic manipulation at sunset resulted in a counterclockwise shift in orientation compared with controls, consistent with sunset calibration of the magnetic field, whereas magnetic manipulation after sunset resulted in no change in orientation. Unlike in birds, however, the pattern of polarization was not necessary for the calibration. For animals that occupy ecological niches where the sunset is rarely observed, this is a surprising finding. Yet it may indicate the primacy of the sun as an absolute geographical reference not only for birds but also within other vertebrate taxa.

Small-scale Hα jets in the solar chromosphere

Aims. High temporal and spatial resolution observations from the Rapid Oscillations in the Solar Atmosphere (ROSA) multiwavelength imager on the Dunn Solar Telescope are used to study the velocities of small-scale Hα jets in an emerging solar active region.
Methods. The dataset comprises simultaneous imaging in the Hα core, Ca ii K, and G band, together with photospheric line-of-sight magnetograms. Time-distance techniques are employed to determine projected plane-of-sky velocities.
Results. The Hα images are highly dynamic in nature, with estimated jet velocities as high as 45 km s-1. These jets are one-directional, with their origin seemingly linked to underlying Ca ii K brightenings and G-band magnetic bright points.
Conclusions. It is suggested that the siphon flow model of cool coronal loops is suitable for interpreting our observations. The jets are associated with small-scale explosive events, and may provide a mass outflow from the photosphere to the corona.

Transverse Oscillations in Chromospheric Mottles

A number of recent investigations have revealed that transverse waves are ubiquitous in the solar chromosphere. The vast majority of these have been reported in limb spicules and active region fibrils. We investigate long-lived, quiet-Sun, on-disk features such as chromospheric mottles (jet-like features located at the boundaries of supergranular cells) and their transverse motions. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope. The data set is comprised of simultaneous imaging in the Ha core, Ca II K, and G band of an on-disk quiet-Sun region. Time-distance techniques are used to study the characteristics of the transverse oscillations. We detect over 40 transverse oscillations in both bright and dark mottles, with periods ranging from 70 to 280 s, with the most frequent occurrence at ~165 s. The velocity amplitudes and transverse displacements exhibit characteristics similar to limb spicules. Neighboring mottles oscillating in-phase are also observed. The transverse oscillations of individual mottles are interpreted in terms of magnetohydrodynamic kink waves. Their estimated periods and damping times are consistent with phase mixing and resonant mode conversion.

A study of velocity fields in the transition region of ε Eri (K2 V)

Analyses of the widths and shifts of optically thin emission lines in the ultraviolet spectrum of the active dwarf e Eri (K2 V) are presented. The spectra were obtained using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer. The linewidths are used to find the non-thermal energy density and its variation with temperature from the chromosphere to the upper transition region. The energy fluxes that could be carried by Alfvén and acoustic waves are investigated, to test their possible roles in coronal heating. Acoustic waves do not appear to be a viable means of coronal heating. There is, in principle, ample flux in Alfvén waves, but detailed calculations of wave propagation are required before definite conclusions can be drawn concerning their viability. The high sensitivity and spectral resolution of the above instruments have allowed two-component Gaussian fits to be made to the profiles of the stronger transition region lines. The broad and narrow components that result share some similarities with those observed in the Sun, but in e Eri the broad component is redshifted relative to the narrow component and contributes more to the total line flux. The possible origins of the two components and the energy fluxes implied are discussed. On balance our results support the conclusion of Wood, Linsky & Ayres, that the narrow component is related to Alfvén waves reaching to the corona, but the origin of the broad component is not clear.

Trends in skin cancer knowledge, sun protection practices and behaviours in the Northern Ireland population

Background: Sun exposure increases risk of skin cancer, especially melanoma, incidence of which continues to rise. Reported skin cancer knowledge and trends in sun care behaviours are documented in a UK region where there has been 20 years of sun-related health promotion campaigns. Methods: In 2000, 2004 and 2008, a 'care in the sun' module was included in the Northern Ireland (NI) Omnibus survey. Randomly selected subjects were asked to complete a sun-related questionnaire and proportions of respondents analysed by demographic and socio-economic factors, with differences tested using z-tests and the chi-squared test. Results: Around 3623 persons responded. Skin cancer knowledge was high (97). Sun avoidance decreased with time and was lowest among younger age groups and males. Sunscreen use was high (70), unchanged over 8 years, and more likely among younger age groups, females, those in paid employment, and those with tertiary level education. Use of sunscreen with minimum Sun Protection Factor (SPF) 15 (a campaign message) increased from 45 to 70 (P

The influence of the magnetic field on running penumbral waves in the solar chromosphere

We use images of high spatial and temporal resolution, obtained using both ground- and space-based instrumentation, to investigate the role magnetic field inclination angles play in the propagation characteristics of running penumbral waves in the solar chromosphere. Analysis of a near-circular sunspot, close to the center of the solar disk, reveals a smooth rise in oscillatory period as a function of distance from the umbral barycenter. However, in one directional quadrant, corresponding to the north direction, a pronounced kink in the period-distance diagram is found. Utilizing a combination of the inversion of magnetic Stokes vectors and force-free field extrapolations, we attribute this behavior to the cut-off frequency imposed by the magnetic field geometry in this location. A rapid, localized inclination of the magnetic field lines in the north direction results in a faster increase in the dominant periodicity due to an accelerated reduction in the cut-off frequency. For the first time, we reveal how the spatial distribution of dominant wave periods, obtained with one of the highest resolution solar instruments currently available, directly reflects the magnetic geometry of the underlying sunspot, thus opening up a wealth of possibilities in future magnetohydrodynamic seismology studies. In addition, the intrinsic relationships we find between the underlying magnetic field geometries connecting the photosphere to the chromosphere, and the characteristics of running penumbral waves observed in the upper chromosphere, directly supports the interpretation that running penumbral wave phenomena are the chromospheric signature of upwardly propagating magneto-acoustic waves generated in the photosphere.