Observed Patterns Of Variability Research Articles

Short timescale variability in large-amplitude internal waves on the western Portuguese shelf

Timescales in the ocean can range from the transient turbulence to the long-term climate scales. Quantifying its changes involves establishing meaningful background states, but that can be challenging if an extensive array of wave phenomena is masking the ocean's variability. Internal Waves (IWs) are a fundamental part of these wave phenomena, which are now widely acknowledged as major contributors in ocean dynamics. In this study we use satellite imagery from Synthetic Aperture Radars (SAR) and moored temperature records to assess the variability scales and magnitudes of coastal IW systems propagating onshore off the western Portuguese shelf. The data shows significant variability in timescales of just a few days, and hence within the waves' typical propagation lifespan. A regional ocean circulation model is used together with linear theory to assess how mesoscale variability is contributing to the observed variability patterns observed in the IWs in the SAR and in situ data. According to linear theory, the IW variability is mostly owing to variable mesoscale currents, which off the Portuguese coast typically result from geostrophic flows, eddies and upwelling dynamics. IW variability owing to changes in stratification is found to amount to about half of that in background flows, but their effect can go unnoticed within the largest contributions from mesoscale currents. One extreme event is highlighted in which IWs from consecutive tidal cycles could possibly decouple from (i.e. not traceable back to) their originating tides in just a few days and hence within their typical lifespans.

Sexual dimorphism and variability of craniomandibular morphology in the Japanese giant flying squirrel, Petaurista leucogenys (Rodentia: Sciuridae)

We examined sexual dimorphism and variability of craniomandibular morphology in the Japanese giant flying squirrel (Petaurista leucogenys) using different statistical analyses. Among 31 measurements using 33 adult skulls (19 males and 14 females), females showed slightly larger mean size for all traits. Univariate analysis revealed that females were significantly larger than males for the greatest length of skull, zygomatic breadth, and mandibular length. Discriminant functions indicated well distinctiveness between the sexes. Moreover, six additional mandibular measurements were taken for estimating the mechanical advantage of the primary masticatory muscles, of which females showed significantly larger incisor resistance arm and moment arms of the superficial masseter (most ventral fibers) and the anterior deep masseter than males. These traits could increase the surface area for the attachment of masticatory muscles and thus have a role in biting mechanism. These suggest that larger females have relatively greater absolute bite force, which may contribute to obtain more access for greater ecological resources. Additionally, the coefficients of variation did not differ significantly between the sexes. Patterns of variability tended to differ in the cranial dimensions based on longitudinal and transverse axes, but not obviously in the major subdivisions of the skull. The observed variability patterns suggest the existence of developmental factors and higher integration to maintain functional relationship related to their lifestyle. Finally, we identified craniomandibular dimorphism in P. leucogenys as a size related phenomenon mostly associated with resource benefits, despite similarities in variability caused by morphological constraint.

Probing an X-Ray Flare Pattern in Mrk 421 Induced by Multiple Stationary Shocks: A Solution to the Bulk Lorentz Factor Crisis

Abstract The common observations of multiple radio VLBI stationary knots in high-frequency-peaked BL Lacs (HBLs) can be interpreted as multiple recollimation shocks accelerating particles along jets. This approach can resolve the so-called “bulk Lorentz factor crisis” of sources with a high Lorentz factor deduced from maximum γ–γ opacity and fast variability and apparently inconsistent slow/stationary radio knots. It also suggests that a unique pattern of the nonthermal emission variability should appear after each strong flare. Taking advantage of the 13 yr of observation of the HBL Mrk 421 by the X-ray Telescope on the Neil Gehrels Swift Observatory (Swift-XRT), we probe for such an intrinsic variability pattern. Its significance is then statistically estimated via comparisons with numerous similar simulated light curves. A suggested variability pattern is identified, consistent with a main flare emission zone located in the most upstream 15.3 GHz radio knot at 0.38 mas from the core. Subsequent flux excesses in the light curve are consistent with a perturbation crossing all of the downstream radio knots with a constant apparent speed of 45c. The significance of the observed variability pattern not arising from stochastic processes is found above three standard deviations, opening a promising path for further investigations in other blazars and with other energy bands. In addition to highlighting the role of stationary radio knots as high-energy particle accelerators in jets, the developed method allows estimates of the apparent speed and size of a jet perturbation without the need to directly observe any motion in jets.

Patterns and drivers of spatio-temporal variability of suspended sediment in the Waikato lakes, New Zealand

ABSTRACTQuantifying and interpreting variability in ecological systems allows us to better understand the driving forces that determine ecosystems functioning. We utilised earth observation-based remote sensing to determine total suspended sediment (TSS) concentrations for 109 lakes over 16 years. The coefficient of variation (CV) was used to quantify variability of TSS at three temporal scales (monthly, annual and long-term) and at the horizontal spatial scale. CV values varied between 0.14 and 1.09. Drivers of observed variability patterns were explored using five lake morphological and catchment characteristics. Lake area was the most important variable to predict variability of TSS. De-vegetated lakes displayed significantly higher TSS concentrations than vegetated lakes; however, aquatic vegetation was found to moderate only spatial variability of TSS. As spatio-temporal variability can be assumed to drive key ecosystem functions, determining characteristic variability patterns for various attributes should be a prerequisite when setting management goals and developing monitoring regimes.

Ocean Modeling on a Mesh With Resolution Following the Local Rossby Radius

AbstractWe discuss the performance of the Finite Element Ocean Model (FESOM) on locally eddy‐resolving global unstructured meshes. In particular, the utility of the mesh design approach whereby mesh horizontal resolution is varied as half the Rossby radius in most of the model domain is explored. Model simulations on such a mesh (FESOM‐XR) are compared with FESOM simulations on a smaller‐size mesh, where refinement depends only on the pattern of observed variability (FESOM‐HR). We also compare FESOM results to a simulation of the ocean model of the Max Planck Institute for Meteorology (MPIOM) on a tripolar regular grid with refinement toward the poles, which uses a number of degrees of freedom similar to FESOM‐XR. The mesh design strategy, which relies on the Rossby radius and/or the observed variability pattern, tends to coarsen the resolution in tropical and partly subtropical latitudes compared to the regular MPIOM grid. Excessive variations of mesh resolution are found to affect the performance in other nearby areas, presumably through dissipation that increases if resolution is coarsened. The largest improvement shown by FESOM‐XR is a reduction of the surface temperature bias in the so‐called North‐West corner of the North Atlantic Ocean where horizontal resolution was increased dramatically. However, other biases in FESOM‐XR remain largely unchanged compared to FESOM‐HR. We conclude that resolving the Rossby radius alone (with two points per Rossby radius) is insufficient, and that careful use of a priori information on eddy dynamics is required to exploit the full potential of ocean models on unstructured meshes.

NSV 1907 - A new eclipsing, nova-like cataclysmic variable

NSV 1907, formerly listed as an irregular variable in variability catalogues, was classified as an Algol-type eclipsing binary in the Catalina Surveys Periodic Variable Star Catalogue. We have identified NSV 1907 as an ultraviolet (UV) bright source using measurements from the GALEX space telescope and detected obvious out-of-eclipse variability in archival photometric data from the Catalina Sky Survey, which instigated a closer examination of the object. A spectrum and extensive multicolour photometric observations were acquired, from which we deduce that NSV 1907 is a deeply eclipsing, nova-like cataclysmic variable. Apart from the orbital variations (deep eclipses with a period of P ≈ 6.63 hours), changes in mean brightness and irregular short-term variability (flickering) were observed. The presence of a secondary minimum at phase φ ≈ 0.5 was established, which indicates a significant contribution of the companion star to the optical flux of the system. We find possible evidence for sinusoidal variations with a period of P ≈ 4.2 d, which we interpret as the nodal precession period of the accretion disc. No outbursts or VY Scl-like drops in brightness were detected either by the CSS or during our photometric monitoring. Because of its spectral characteristics and the observed variability pattern, we propose NSV 1907 as a new moderately bright long-period SW Sextantis star. Further photometric and spectroscopic observations are encouraged.

A search for photometric variability in magnetic chemically peculiar stars using ASAS-3 data

The (magnetic) chemically peculiar (CP) stars of the upper main sequence are well-suited laboratories for investigating the influence of magnetic fields on the stellar surface because they produce abundance inhomogeneities (spots), which results in photometric variability that is explained in terms of the oblique rotator model. CP stars exhibiting this phenomenon are normally classified as alpha2 Canum Venaticorum (ACV) variables. It is important to increase the sample of known rotational periods among CP stars by discovering new ACV variables. The ASAS-3 data were cross-correlated with the Catalogue of Ap, HgMn, and Am stars in order to analyse the light curves of bona fide CP and related stars. The light curves were downloaded and cleaned of outliers and data points with a flag indicating bad quality. Promising candidates showing a larger scatter than observed for constant stars in the corresponding magnitude range were searched for periodic signals using a standard Fourier technique. In total, we found 323 variables, from which 246 are reported here for the first time, and 77 were probably wrongly classified before. The observed variability pattern of most stars is in accordance with an ACV classification. For some cases, it is difficult to distinguish between the light curves of double-waved ACVs and the variability induced by orbital motion (ellipsoidal variables/eclipsing variables), especially for objects exhibiting very small amplitudes and/or significant scatter in their light curves. Thus, some eclipsing or rotating ellipsoidal variables might be present. However, we are confident that the given periods are the correct ones. There seems to be a possible weak correlation between the rotational period and colour, in the sense that cooler magnetic CP stars rotate more slowly. However, this correlation seems to disappear when correcting for the interstellar reddening.

Evolutionary Trends of the Transposase-Encoding Open Reading Frames A and B (orfA and orfB) of the Mycobacterial IS6110 Insertion Sequence.

BackgroundThe IS6110 insertion sequence, a member of the IS3 family of insertion sequences, was found to be specific to the Mycobacterium tuberculosis complex (MTBC). Although IS6110 has been extensively characterized as a transposable genetic marker, the evolutionary history of its own transposase-encoding sequence has not, to the best of our knowledge, been investigated.Methodology/Principal FindingsHere we explored the evolution of the IS6110 sequence by analysing the genetic variability and the selective forces acting on its transposase-encoding open reading frames (ORFs) A and B (orfA and orfB). For this purpose, we used a strain collection consisting of smooth tubercle bacilli (STB), an early branching lineage of the MTBC, and present-day M. tuberculosis strains representing the full breadth of genetic diversity in Tunisia. In each ORF, we found a major haplotype that dominated over a flat distribution of rare descendent haplotypes, consisting mainly of single- and double-nucleotide variant singletons. The predominant haplotypes consisted of both ancestral and present-day strains, suggesting that IS6110 acquisition predated the emergence of the MTBC. There was no evidence of recombination and both ORFs were subjected to strict purifying selection, as demonstrated by their dN/dS ratios (0.29 and 0.51, respectively), as well as their significantly negative Tajima’s D statistics. Strikingly, the purifying selection acting on orfA proved much more stringent, suggesting its critical role in regulating the transpositional process. Maximum likelihood analyses further excluded any possibility of positive selection acting on single amino acid residues.Conclusions/SignificanceTaken together our data fit with an evolutionary scenario according to which the observed variability pattern of the IS6110 transposase-encoding ORFs is generated mainly through random point mutations that accrued on a functionally optimal IS6110 copy, whose acquisition predated the emergence of the MTBC complex. Background selection acting against deleterious mutations led to an excess of low-frequency variants.

INVESTIGATING BROADBAND VARIABILITY OF THE TeV BLAZAR 1ES 1959+650

We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift UVOT, X-ray observations by the Swift X-ray Telescope (XRT), high-energy gamma-ray observations with the Fermi Large Area Telescope (LAT) and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 17 April 2012 and 1 June 2012 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected-emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected-emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected emission model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV.

Time-dependent modelling of PKS 2155-304 in a low state

We apply both leptonic and leptohadronic emission scenarios for modelling the multiwavelength photon spectra and the observed variability in the optical, X-ray, and TeV gamma-ray energy bands of blazar PKS 2155-304 while being in a low state between 25 August and 6 September 2008. We consider three emission models, i.e. a one-component synchrotron self-Compton model (1-SSC), a one-zone proton synchrotron model (LHs), and a two-component SSC model (2-SSC). Only in the first scenario can the emission from the optical up to TeV gamma-rays be attributed to a single particle population from one emission region. Using a time-dependent numerical code that solves the kinetic equations for each particle species, we derived, in all cases, acceptable fits to the time-averaged SED. By imposing variations to one (or more) model parameters according to observed variability pattern in one (or more) frequencies we calculated the respective light curves and compared them with the observations. We show that the 1-SSC model cannot account for the anticorrelation observed between the X-rays and VHE gamma-rays, although it can explain the time-averaged SED. The anticorrelation can be more naturally explained by the two-component emission models. Both of them reproduce satisfactorily the optical, X-ray, and TeV variability but at the cost of additional free parameters, which from four in the 2-SSC model increase to six in the LHs model. Although the results of our time-resolved analysis do not favour one of the aforementioned models, they suggest that a two-component scenario is more adequate for the emission of PKS 2155-304 in the low state of 2008, which agrees with a recent independent analysis. This suggests that the quiescent blazar radiation might result from a superposition of the radiation from different components, while a flare might still be the result of a single component.

LONG-TERM PROFILE VARIABILITY IN ACTIVE GALACTIC NUCLEUS WITH DOUBLE-PEAKED BALMER EMISSION LINES

An increasing number of Active Galactic Nuclei (AGNs) exhibit broad, double-peaked Balmer emission lines,which represent some of the best evidence for the existence of relatively large-scale accretion disks in AGNs. A set of 20 double-peaked emitters have been monitored for nearly a decade in order to observe long-term variations in the profiles of the double-peaked Balmer lines. Variations generally occur on timescales of years, and are attributed to physical changes in the accretion disk. Here we characterize the variability of a subset of seven double-peaked emitters in a model independent way. We find that variability is caused primarily by the presence of one or more discrete "lumps" of excess emission; over a timescale of a year (and sometimes less) these lumps change in amplitude and shape, but the projected velocity of these lumps changes over much longer timescales (several years). We also find that all of the objects exhibit red peaks that are stronger than the blue peak at some epochs and/or blueshifts in the overall profile, contrary to the expectations for a simple, circular accretion disk model, thus emphasizing the need for asymmetries in the accretion disk. Comparisons with two simple models, an elliptical accretion disk and a circular disk with a spiral arm, are unable to reproduce all aspects of the observed variability, although both account for some of the observed behaviors. Three of the seven objects have robust estimates of the black hole masses. For these objects the observed variability timescale is consistent with the expected precession timescale for a spiral arm, but incompatible with that of an elliptical accretion disk. We suggest that with the simple modification of allowing the spiral arm to be fragmented, many of the observed variability patterns could be reproduced.

Evidence for interaction between speech rhythm and gesture.

Temporal patterns in speech occur on multiple timescales. Speech gestures generally occur on a fast timescale; previous work has found evidence for a c‐center effect in complex syllable onsets (e.g. /spa/), whereby initiations of tongue blade and lip movements associated with /s/ and /p/ are equally displaced in opposite directions from initiation of tongue body movement associated with the vowel [C. Browman and L. Goldstein, Phonetica 45, 140–155 (1988)]. Speech rhythms occupy a slower timescale; in metronome‐driven phrase repetition tasks, rhythmic timing is more variable for higher‐order target ratios of intervals between stressed syllables and phrases [F. Cummins and R. Port, J. Phonetics 26, 145–171 (1998)]. An experiment was conducted to investigate how these gestural and rhythmic patterns interact. Gestural kinematics were recorded using electromagnetic articulometry during a repetition task with the phrase “take on a spa.” Significantly greater variance in relative timing of tongue and lower lip movements associated with /s/ and /p/ was observed with the more difficult (less harmonic) target rhythms. Within‐gesture effector synergies between jaw and tongue differed systematically across rhythmic conditions. These results demonstrate a substantial interaction between rhythmic and gestural systems. Observed variability patterns are simulated with a dynamical model of phase‐coupled oscillators.

Variability of the Fe K line relativistic component in a sample of Seyfert 1 galaxies

AbstractWe present the analysis of X‐ray spectral variability made on a sample of 7 Seyfert 1 bright galaxies, using XMM‐Newton data. From the “XMM‐Newton Science Archive” we selected those bright Seyfert 1 showing one or more prominent flares in their 2–10 keV light curves. For each of them we extracted spectra in 3 different time intervals: before, during and after the flare. We fitted them with a simple power law and then shifted a narrow emission and absorption line template across the 2.5–10 keV data, in order to investigate the presence of line‐like features with a confidence level greater than 99%. Some highly significant features were detected in 3 out of 7 sources studied. In particular, the 3 sources, namely PG 1211+143, NGC 4051 and NGC 3783, showed the presence of a variable emission feature in the 4.5–5.8 keV band, characterized by an increase of its intensity after the flare peak. Because of the observed variability pattern, this feature seems to be ascribable to a reverbered redshifted relativistic component of the Fe K line. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synchrotron outbursts in Galactic and extragalactic jets, any difference?

AbstractWe discuss differences and similarities between jets powered by super-massive black holes in quasars and by stellar-mass black holes in microquasars. The comparison is based on multi-wavelength radio-to-infrared observations of the two active galactic nuclei 3C 273 and 3C 279, as well as the two galactic binaries GRS 1915+105 and Cyg X-3. The physical properties of the jet are derived by fitting the parameters of a shock-in-jet model simultaneously to all available observations. We show that the variable jet emission of galactic sources is, at least during some epochs, very similar to that of extragalactic jets. As for quasars, their observed variability pattern can be well reproduced by the emission of a series of self-similar shock waves propagating down the jet and producing synchrotron outbursts. This suggests that the physical properties of relativistic jets is independent of the mass of the black hole.

Evidence for a connection between photospheric and wind structure in HD 64760

We report on the results of an extended optical spectroscopic monitoring campaign on the early-type B supergiant HD 64760 (B0.5 Ib). The study is based on high-resolution echelle spectra obtained with the Landessternwarte Heidelberg's Heros instrument at ESO La Silla. Ninety-nine spectra were collected over 103 nights between January 19 and May 1, 1996. The Halpha line shows a characteristic profile with a central photo-spheric absorption superimposed by symmetrically blue- and red-shifted wind-emission humps. The time-averaged line profile is well described by a differentially rotating and expanding radiation-driven wind: the redistribution of the wind emission flux into a double peak profile is interpreted in terms of the resonance zone effect in rotating winds as first described by Petrenz & Puls (1996). Detailed time-series analyses of the line profile variations across the Halpha profile reveal for the first time in an optical data set of HD 64760 a periodic 2.4-day modulation of the inner and outer flanks of the Halpha emission humps. The stronger modulations of the inner flanks of the emission humps at photospheric velocities are due to complex width variations of the underlying photospheric Halpha profile. The weaker variations of the outer flanks are in phase and reflect variations at the base of the stellar wind. The detected 2.4-day modulation period together with a second period of 1.2 days (in the red emission hump only) is in excellent agreement with the outer-wind modulation periods as reported by Fullerton et al. (1997) from intensive IUE UV time-series observations in 1993 and 1995. The 2.4-day period is further detected in the photospheric He I lambda4026 line as prograde traveling (pseudo-)absorption and emission features. The observed variability pattern is indicative for low-order non-radial pulsations in the photosphere of HD 64760. The non-radial pulsations are identified as the source of persistent, regularly spaced stellar surface structure which is maintained throughout the photosphere - wind transition zone (this work) out into the UV regime of the terminal velocity outflow.

Propagation and mechanism of decadal upper‐ocean variability in the North Pacific

Two types of anomaly pathways associated with decadal thermocline variability in the North Pacific Ocean are identified on constant density surfaces (isopycnals): one westward and the other southwestward around the subtropical gyre. A theory, based on two buroclinic planetary wave modes in the thermocline, is proposed to account for the observed variability pattern. The variability along the westward wave path is ascribed to the non‐Doppler‐shift 1st mode and seems to be forced mainly by wind stress forcing; the anomaly along the southwestward subduction path is associated with the advective nature of the 2nd mode and could be excited mainly by surface buoyancy anomalies. This study may provide a dynamically unified, three‐dimensional picture of decadal thermocline variability in the North Pacific Ocean.

Variability of the central region in active galactic nuclei

We review implications of the observed optical and X-ray variability (periodicities and light-curves), relevant for the understanding of physical conditions in the deep interiors of active galactic nuclei. We discuss in detail kinematical, hydrodynamical, thermal and radiative transfer effects which may be responsible for observed variability patterns. We put emphasis on theoretical options which can predict basic accretion parameters, such as the mass of the central black hole, the accretion rate and the inclination angle, in terms of observable quantities. Closed analytical results are given whenever available.

Interassemblage variability and levallois styles: The case of the northern african middle palaeolithic

The potential of a particular category of artifacts, Levallois flakes, with regard to the explanation of Middle Palaeolithic lithic variability is examined in this paper. After an assessment of the way in which Levallois reductions operate in different site contexts, 45 Levallois flake samples representing different taxonomic groups in the Northern African Middle Palaeolithic are treated in an attribute analysis. In attempts to explain the observed variability pattern, which is largely concordant with the traditionally recognized assemblage groups, environmental, chronological, and stylistic factors must be taken into account. Two important points emerge. First, diachronic changes are evident in various aspects of Levallois flake samples. Second, the apparent equation between Levallois style groups and traditional taxonomy may indicate that the latter at least partly represents culturally different groups.

FOREST FLOOR VARIABILITY AND FACTOR ANALYSIS: A CASE STUDY

A case study is presented to illustrate how factor analysis can be used to quantify probable causes of physical and chemical forest-floor variability. Twenty forest-floor variables were examined for a 30 × 30-m sampling plot located within a mature, naturally regenerated conifer stand. "Slough" (the degree of accumulation of decayed stumps, logs, branches, etc.), litter (hardwood- vs. softwood-type in terms of base-status) and insolation (degree of canopy closure) factors appeared to underlie the observed variability pattern. Factor identification was facilitated by the following variable association pattern: (i) total C with total Fe, Al, N, P, K; (ii) total C with LFH-mass and thickness; (iii) water-extractable P with 2 N potassium-chloride-extractable NH4-H; (iv) total and 1 N ammonium-acetate-extractable Ca with pH; and (v) ground cover vegetation density with forest floor moisture content and thickness. Key words: Forest floor, lateral variability, factor analysis

Distribution model of human ovulatory cycles

It is shown in this analysis that the distribution of human ovulatory cycles can be described based upon one simple assumption. This assumption is that the random variable underlying ovulation is the follicle development rate. Previous attempts to describe variability in ovulation cycles have assumed that the measured time interval was the random variable. The assumption that the random variable is the rate rather than the time, leads mathematically to the observed skew towards longer ovulatory cycles. The resultant distribution model is shown to agree with observed variability patterns for the preovulatory phase, the postovulatory phase and overall menstrual cycle.