Dominant Time Scales Research Articles

Relationship between summer rainfall anomalies and sub-seasonal oscillation intensity in the ChangJiang Valley in China

Sub-seasonal variability of summer (May–October) rainfall over the ChangJiang Valley exhibits two dominant timescales, one with a quasi-biweekly (QBW) period (10–20 days) and the other with an intraseasonal oscillation (ISO) period (20–60 days). A significant positive correlation (at a 99% confidence level) was found between the summer precipitation anomaly and the intensity of the QBW and ISO modes in the region. By examining the composite structure and evolution characteristics, we note that the QBW mode is characterized by a northwest–southeast oriented wave train pattern, moving southeastward. The perturbations associated with the ISO mode propagate northwestward in strong ISO years but southeastward in weak ISO years. A marked feature is the phase leading of low-level moisture to convection in both the QBW and ISO mode. When the summer rainfall is strong in the ChangJiang Valley, large-scale atmospheric conditions in the strong QBW/ISO activity region are characterized by deeper moist layer, convectively more unstable stratification and greater ascending motion. Such mean conditions favor the growth of the QBW and ISO perturbations. Thus, a significant positive correlation between the summer precipitation and the strength of sub-seasonal variability arises from the large-scale control of the summer mean flow to perturbations.

NONLINEAR DYNAMICS OF MAGNETOHYDRODYNAMIC ROSSBY WAVES AND THE CYCLIC NATURE OF SOLAR MAGNETIC ACTIVITY

The solar dynamo is known to be associated with several periodicities, with the nearly 11/22 yr cycle being the most pronounced one. Even though these quasiperiodic variations of solar activity have been attributed to the underlying dynamo action in the Sun's interior, a fundamental theoretical description of these cycles is still elusive. Here, we present a new possible direction in understanding the Sun's cycles based on resonant nonlinear interactions among magnetohydrodynamic (MHD) Rossby waves. The WKB theory for dispersive waves is applied to magnetohydrodynamic shallow-water equations describing the dynamics of the solar tachocline, and the reduced dynamics of a resonant triad composed of MHD Rossby waves embedded in constant toroidal magnetic field is analyzed. In the conservative case, the wave amplitudes evolve periodically in time, with periods on the order of the dominant solar activity timescale (~11 yr). In addition, the presence of linear forcings representative of either convection or instabilities of meridionally varying background states appears to be crucial in balancing dissipation and thus sustaining the periodic oscillations of wave amplitudes associated with resonant triad interactions. Examination of the linear theory of MHD Rossby waves embedded in a latitudinally varying mean flow demonstrates that MHD Rossby waves propagate toward the equator in a waveguide from –35° to 35° in latitude, showing a remarkable resemblance to the structure of the butterfly diagram of the solar activity. Therefore, we argue that resonant nonlinear magnetohydrodynamic Rossby wave interactions might significantly contribute to the observed cycles of magnetic solar activity.

The Oslo temperature series 1837-2012: homogeneity testing and temperature analysis

A 175 years long homogenized composite record of monthly mean temperatures is presented for Oslo, the capital of Norway. The early raw data have been digitised and quality controlled, and monthly means have been calculated. Some early original observations carried out in a Wild screen (1877–1936) were found to be spuriously high because of inappropriate sheltering from sunlight. These spurious temperatures were not used in the composite record, but alternative temperatures measured (1837–1933) by thermometers placed outside windows at the Astronomical Observatory were used instead. No inhomogeneity was detected in the latter series after adding an instrument correction of +0.3 °C, but the start year of the correction remains uncertain. The more recent part of the composite record used the long-term series (1937 to present) from Blindern in Oslo, the premises of The Norwegian Meteorological Institute. Two small inhomogeneities were detected in the Blindern series, possibly caused by a weak urban heat island effect or growing/cutting of trees. The study revealed that the annual mean temperature has increased by 1.5 °C in the period 1838–2012. The most pronounced increase in annual temperature occurred during the last 50 years, and in the early 20th century that ended with a local maximum in the 1930s. The temperature has increased significantly in all seasons; however, the temperature increase in summer was less than a half of that in winter and spring, which were the seasons with largest increase. In addition the monthly mean temperature of the coldest month in each year has increased two times faster than the warmest one. The most significant temperature variations were associated to ∼ 5-year time scales in its early part, but since 1930 and up to present, the dominant time scales were 10–20 years.

Zonal movement of the Mascarene High in austral summer

Temporal variations in the Mascarene High (MH), defined by the sea level pressure (SLP) maximum within the region of [40°–120°E, 50°–10°S] in austral summer (November–January), were investigated using atmospheric reanalysis datasets. The MH longitudinal position has a dominant timescale at about 6 years, which appears to be independent of the MH intensity variation. The MH longitudinal movement is caused by a combination of SLP variations in the eastern South Indian Ocean (ESIO) and in the western South Indian Ocean (WSIO), as follows. (1) Pressure variations in the ESIO region are confined to the lower atmosphere up to the mid-troposphere, and are associated with the El Nino-Southern Oscillation events. (2) Pressure variations in the WSIO region, characterized by a quasi-barotropic structure throughout the troposphere, are related to the meridional movement of storm track. Sea surface temperature anomalies associated with the longitudinal movement of the MH show a southwest–northeast dipole structure, but this is shifted 10° westward in longitude compared with that associated with the MH intensity.

Delayed feedback and detection of weak periodic signals in a stochastic Hodgkin–Huxley neuron

We study the effect of the delayed feedback loop on the weak periodic signal detection performance of a stochastic Hodgkin–Huxley neuron. We consider an electrical autapse characterized by its coupling strength and delay time. The stochastic Hodgkin–Huxley neuron exhibits subthreshold oscillations, and thus has an intrinsic time scale with the subthreshold oscillations. Therefore, we investigate the interplay of the subthreshold oscillations, coupling strength and delay time on the weak periodic signal detection. Results indicate that the delayed feedback either enhances or suppresses the weak signal detection depending on its parameters, when compared to that without the feedback. The delayed feedback augments the weak periodic signal detection for the optimal values of the intrinsic noise and the coupling strength when the delay time is close to the integer multiples of the period of the intrinsic oscillations, due to the multiple resonance among the weak signal, the intrinsic oscillations, and the delayed feedback.We analyze the interspike interval histograms and show that the delayed feedback enhances or suppresses the weak periodic signal detection by increasing or decreasing the phase locking (synchronization) between the spiking and the weak periodic signal. We also show that an optimal phase locking is obtained when the delay time is close to the period of the intrinsic oscillations, leading a single dominant time scale in the spike trains.

Using wavelet transforms to estimate surface temperature trends and dominant periodicities in Iran based on gridded reanalysis data

In this paper, the discrete wavelet transform (DWT), the Mann–Kendall (MK) trend test, and the sequential Mann–Kendall test are applied to temperature series at different time scales in order to detect the long-term trends (1956–2010) in synoptic-scale surface temperatures in Iran, as well as the dominant time scales affecting these temperature time series. The relevant data was extracted from a gridded data file of the region (44°E to 63.5°E, 25°N to 40°N) and divided into 12 regular zones (of dimensions 5×5°), each of which was analyzed as an individual unit. The results of this research show that at the monthly, seasonal and annual time scales, the trends in temperature were significant and positive in all of the study zones. In addition, the 2-month and 4-month components were dominant at the monthly time scale, the 48-month component dominant at the seasonal time scale, and the 8-year and 16-year components dominant at the annual time scale. Also, the temperature trends in the northern, and especially central, regions of the study zones increased from west to east, and these increasing trends in temperature were most prominent for the spring and summer seasons. The methodology applied here is generally applicable and quite useful for studying both trends and the dominant time scales affecting climatic data series and could find significant applications in related fields.

The use of δ13C values of leporid teeth as indicators of past vegetation

δ13C records from vertebrate teeth offer an opportunity to gain insight into changes in past vegetation. Increasingly, teeth from small mammals are used for such purposes, but because their teeth grow rapidly, seasonal changes in vegetation are potentially a large source of variability in their carbon isotope composition, complicating interpretations of isotope data. To investigate the influence of seasonality on the stable isotope composition of fossil teeth, we constructed a Monte-Carlo-based model to simulate the effects of changes in the seasonal pattern of diet in leporid lagomorphs (rabbits and hares) on the distribution of δ13C values in random populations of leporid teeth from the Edwards Plateau in central Texas. Changes in mean-state, seasonal vegetation range, and relative season length manifest themselves in predictable ways through changes in the median, standard deviation, and skewness of simulated tooth δ13C populations, provided sufficient numbers of teeth are analyzed. This Monte Carlo model was applied to the interpretation of a 20,000year record of leporid tooth δ13C values from Hall's Cave on the Edwards Plateau in central Texas. Populations of teeth from different climate intervals (e.g., the late Glacial, Younger Dryas, and the Holocene) display changes in tooth δ13C distributions that may reflect changes in seasonal vegetation. The inferred changes in seasonality of vegetation based upon our modeling are consistent with hypothesized climatic changes. These results indicate that small mammal teeth can potentially provide unique insights into climate and vegetation on seasonal and longer timescales that complement other approaches, but should be interpreted with a careful consideration of local conditions, taxon ecology and physiology, and the dominant timescales of isotope variability in a rigorous statistical framework.

Variability of the Deep-Water Overflow in the Luzon Strait*

Abstract The Luzon Strait, with its deepest sills at the Bashi Channel and Luzon Trough, is the only deep connection between the Pacific Ocean and the South China Sea (SCS). To investigate the deep-water overflow through the Luzon Strait, 3.5 yr of continuous mooring observations have been conducted in the deep Bashi Channel and Luzon Trough. For the first time these observations enable us to assess the detailed variability of the deep-water overflow from the Pacific to the SCS. On average, the along-stream velocity of the overflow is at its maximum at about 120 m above the ocean bottom, reaching 19.9 ± 6.5 and 23.0 ± 11.8 cm s−1 at the central Bashi Channel and Luzon Trough, respectively. The velocity measurements can be translated to a mean volume transport for the deep-water overflow of 0.83 ± 0.46 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) at the Bashi Channel and 0.88 ± 0.77 Sv at the Luzon Trough. Significant intraseasonal and seasonal variations are identified, with their dominant time scales ranging between 20 and 60 days and around 100 days. The intraseasonal variation is season dependent, with its maximum strength taking place in March–May. Deep-water eddies are believed to play a role in this intraseasonal variation. On the seasonal time scale, the deep-water overflow intensifies in late fall (October–December) and weakens in spring (March–May), corresponding well with the seasonal variation of the density difference between the Pacific and SCS, for which enhanced mixing in the deep SCS is possibly responsible.

Quasi-Decadal Variation in Intensity of the Western Part of the Winter Subarctic SST Front in the Western North Pacific: The Influence of Kuroshio Extension Path State

Abstract Variations of the subarctic front (SAF), which is extracted as a strong sea surface temperature (SST) gradient in the longitudinal band of 146°–152°E, were investigated over 30 winters (January–March) from 1982 to 2011, using high-spatial-resolution satellite-derived SST dataset and hydrographic observations. The SAF had little meridional movement in this longitudinal band, lying between 40° and 41°N throughout the analysis period. The SAF intensity had a dominant quasi-decadal time scale (about 8 yr); its intensity in the strong phase was up to about 50% higher than in the weak phase. The SAF intensity strongly reflected upper-ocean conditions in the Kuroshio–Oyashio Confluence (KOC) region just south of the SAF. In the strong SAF phase, large positive anomalies in both temperature and salinity were found in the KOC region, not only at the sea surface but also below 300 m, and the water properties in the KOC region were those of the Kuroshio water. The warm, salty water in the KOC region was supplied by mesoscale eddies, which detached northward from the Kuroshio Extension during the unstable state of the Kuroshio Extension path.

Low-frequency variability and zonal contrast in Sahel rainfall and Atlantic sea surface temperature teleconnections during the last century

This study systematically examines teleconnections between Atlantic sea surface temperature (SST) and the west–east distribution of Sahel rainfall throughout the twentieth century, taking nonstationarity into account. Sahel rainfall variability of six selected rain gauges displays three dominant time scales: multi-decadal (>20 years), quasi-decadal (8–18 years) and interannual (2–8 years). Regarding their patterns of low-frequency scales, three coherent Sahelian subregions can be identified: the Atlantic Coast (Dakar), western–central Sahel (Nioro and Mopti) and eastern Sahel (Niamey, Maradi, Maine-Soroa). Cross-analyses combining spectral and multivariate analyses of 20 station-based data and West-African gridded rainfall data statistically confirm dissimilarities between the western and eastern Sahel. Western and eastern Sahel rainfall data are correlated with SSTs from different regions of the Atlantic Ocean, especially in the North and tropical South Atlantic. As determined by wavelet coherence and phase, in-phase relationship with North Atlantic SSTs only occurs in wet periods and at the multi- and quasi-decadal scales. This teleconnection depends on the time period and the time scale, displaying a NW–SE pattern, which suggests nonuniform modulations of meridional displacements of the Intertropical Convergence Zone (ITCZ). Tropical South Atlantic SST variability is often related to opposite patterns between the Gulf of Guinean Coast (in phase) and Sahel region (out of phase). Theoretical and Applied Climatology Theoretical and Applied Climatology Look Inside

The large-scale spatio-temporal variability of precipitation over Sweden observed from the weather radar network

Abstract. Using measurements from the national network of 12 weather radar stations for the 11-year period 2000–2010, we investigate the large-scale spatio-temporal variability of precipitation over Sweden. These statistics provide useful information to evaluate regional climate models as well as for hydrology and energy applications. A strict quality control is applied to filter out noise and artifacts from the radar data. We focus on investigating four distinct aspects: the diurnal cycle of precipitation and its seasonality, the dominant timescale (diurnal versus seasonal) of variability, precipitation response to different wind directions, and the correlation of precipitation events with the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). When classified based on their intensity, moderate- to high-intensity events (precipitation > 0.34 mm/3 h) peak distinctly during late afternoon over the majority of radar stations in summer and during late night or early morning in winter. Precipitation variability is highest over the southwestern parts of Sweden. It is shown that the high-intensity events (precipitation > 1.7 mm/3 h) are positively correlated with NAO and AO (esp. over northern Sweden), while the low intensity events are negatively correlated (esp. over southeastern parts). It is further observed that southeasterly winds often lead to intense precipitation events over central and northern Sweden, while southwesterly winds contribute most to the total accumulated precipitation for all radar stations. Apart from its operational applications, the present study demonstrates the potential of the weather radar data set for studying climatic features of precipitation over Sweden.

Detecting transient signals in geodetic time series using sparse estimation techniques

AbstractWe present a new method for automatically detecting transient deformation signals from geodetic time series. We cast the detection problem as a least squares procedure where the design matrix corresponds to a highly overcomplete, nonorthogonal dictionary of displacement functions in time that resemble transient signals of various timescales. The addition of a sparsity‐inducing regularization term to the cost function limits the total number of dictionary elements needed to reconstruct the signal. Sparsity‐inducing regularization enhances interpretability of the resultant time‐dependent model by localizing the dominant timescales and onset times of the transient signals. Transient detection can then be performed using convex optimization software where detection sensitivity is dependent on the strength of the applied sparsity‐inducing regularization. To assess uncertainties associated with estimation of the dictionary coefficients, we compare solutions with those found through a Bayesian inference approach to sample the full model space for each dictionary element. In addition to providing uncertainty bounds on the coefficients and confirming the optimization results, Bayesian sampling reveals trade‐offs between dictionary elements that have nearly equal probability in modeling a transient signal. Thus, we can rigorously assess the probabilities of the occurrence of transient signals and their characteristic temporal evolution. The detection algorithm is applied on several synthetic time series and real observed GPS time series for the Cascadia region. For the latter data set, we incorporate a spatial weighting scheme that self‐adjusts to the local network density and filters for spatially coherent signals. The weighting allows for the automatic detection of repeating slow slip events.

Relationship between summer rainfall anomalies and sub-seasonal oscillations in South China

Sub-seasonal variability of summer (May–October) rainfall over South China exhibits two dominant timescales, one with a quasi-biweekly (QBW) period (10–20 days) and the other with an intraseasonal oscillation (ISO) period (20–60 days). A significant positive correlation (at a 99 % confidence level) was found between the summer precipitation anomalies and the intensity of the QBW and ISO modes. By examining the composite structure and evolution characteristics, we note that the QBW and ISO modes are characterized by a northwest-southeast oriented wave train pattern with a pronounced baroclinic vertical structure, moving northwestward. A marked feature is the phase leading of low-level moisture relative to convection. For the QBW mode, such a phase leading feature appears in both the strong and weak composites. However, for the ISO mode, this feature is only clearly seen in the strong composite. The high positive correlation between the summer precipitation and the sub-seasonal variability suggests that the summer mean state may exert a large-scale control on the sub-seasonal modes. It is found that when South China is anomalously wet, large-scale atmospheric conditions in the key QBW/ISO activity region are characterized by deeper moist layer, more convectively unstable stratification, and greater ascending motion. Such environmental conditions favor the growth of the QBW and ISO perturbations.

Spectral Analysis of Turbulent Aerosol Fluxes by Fourier Transform, Wavelet Analysis, and Multiresolution Decomposition

Aerosol number fluxes are spectrally analyzed using fast Fourier transform analysis, wavelet analysis and multiresolution decomposition. All three methods yield similar spectral features in general, although a detailed evaluation of the cospectra shows some differences, e.g. due to different resolutions in the time and frequency domains. Wavelet analysis yields aerosol flux estimates with a high time resolution that can be used to assess the flux variability. Multiresolution decomposition has been applied successfully to evaluate cospectra of the aerosol number flux, the buoyancy flux and the momentum flux of three 1-day datasets from diverse environments. For all scalars and all environments, the dimensionless frequency (f) of the cospectral peak was found between \(f = 0.1\) and 0.2. In addition, the cospectral gap time scale of the aerosol number flux was found between 100 and 1,000 s. Thus, in this study several spectral features such as the dominant time scale and the cospectral gap time scale of aerosol number fluxes are similar to buoyancy fluxes. However, the shape of aerosol number flux cospectra often deviates from buoyancy and momentum flux cospectra, especially at very small and at very large time scales.

Multiple temporal scale relationships of bankfull discharge with streamflow and sediment transport in the Yellow River in China

This paper presents a study on the characteristics of multiple time scales of bankfull discharge and its delayed response to changes of flow conditions using continuous wavelet analysis for data from selected hydrological stations in the Yellow River basin. Results showed that bankfull discharge series had one or two dominant time scales. For example, the Huayuankou station in the lower reach of the Yellow River had two dominant time scales of 19–20 years and 5–6 years. The dominant time scales of the bankfull discharge series were generally consistent with the dominant time scales of water discharge and sediment concentration series, indicating that the channel morphology inherits the characteristics of the hydrological system in terms of multiple time scales. In addition, the wavelet coefficients of the bankfull discharge series had a phase difference in relation to those of the sediment concentration series, with a delay time that varied from 3 to 16 years at different sites. This delay time or relaxation time is a result of the delayed response of bankfull discharge to flow conditions, which was significant for channel adjustments in response to changes of flow conditions. The findings of the multiple time scales and the delayed response are of importance for further study of channel morphology of fluvial systems.

Temporal geochemical variations in lavas from Kīlauea's Pu‘u ‘Ō‘ō eruption (1983–2010): Cyclic variations from melting of source heterogeneities

Geochemical time series analysis of lavas from Kīlauea's ongoing Pu‘u ‘Ō‘ō eruption chronicle mantle and crustal processes during a single, prolonged (1983 to present) magmatic event, which has shown nearly two‐fold variation in lava effusion rates. Here we present an update of our ongoing monitoring of the geochemical variations of Pu‘u ‘Ō‘ō lavas for the entire eruption through 2010. Oxygen isotope measurements on Pu‘u ‘Ō‘ō lavas show a remarkable range (δ18O values of 4.6–5.6‰), which are interpreted to reflect moderate levels of oxygen isotope exchange with or crustal contamination by hydrothermally altered Kīlauea lavas, probably in the shallow reservoir under the Pu‘u ‘Ō‘ō vent. This process has not measurably affected ratios of radiogenic isotope or incompatible trace elements, which are thought to vary due to mantle‐derived changes in the composition of the parental magma delivered to the volcano. High‐precision Pb and Sr isotopic measurements were performed on lavas erupted at ∼6 month intervals since 1983 to provide insights about melting dynamics and the compositional structure of the Hawaiian plume. The new results show systematic variations of Pb and Sr isotope ratios that continued the long‐term compositional trend for Kīlauea until ∼1990. Afterward, Pb isotope ratios show two cycles with ∼10 year periods, whereas the Sr isotope ratios continued to increase until ∼2003 and then shifted toward slightly less radiogenic values. The short‐term periodicity of Pb isotope ratios may reflect melt extraction from mantle with a fine‐scale pattern of repeating source heterogeneities or strands, which are about 1–3 km in diameter. Over the last 30 years, Pu‘u ‘Ō‘ō lavas show 15% and 25% of the known isotopic variation for Kīlauea and Mauna Kea, respectively. This observation illustrates that the dominant time scale of mantle‐derived compositional variation for Hawaiian lavas is years to decades.

Stochastically-forced multidecadal variability in the North Atlantic: a model study

Observations show a multidecadal signal in the North Atlantic ocean, but the underlying mechanism and cause of its timescale remain unknown. Previous studies have suggested that it may be driven by the North Atlantic Oscillation (NAO), which is the dominant pattern of winter atmospheric variability. To further address this issue, the global ocean general circulation model, Nucleus for European Modelling of the Ocean (NEMO), is driven using a 2,000 years long white noise forcing associated with the NAO. Focusing on key ocean circulation patterns, we show that the Atlantic Meridional Overturning Circulation (AMOC) and Sub-polar gyre (SPG) strength both have enhanced power at low frequencies but no dominant timescale, and thus provide no evidence for a oscillatory ocean-only mode of variability. Instead, both indices respond linearly to the NAO forcing, but with different response times. The variability of the AMOC at 30°N is strongly enhanced on timescales longer than 90 years, while that of the SPG strength starts increasing at 15 years. The different response characteristics are confirmed by constructing simple statistical models that show AMOC and SPG variability can be related to the NAO variability of the previous 53 and 10 winters, respectively. Alternatively, the AMOC and the SPG strength can be reconstructed with Auto-regressive (AR) models of order seven and five, respectively. Both statistical models reconstruct interannual and multidecadal AMOC variability well, while on the other hand, the AR(5) reconstruction of the SPG strength only captures multidecadal variability. Using these methods to reconstruct ocean variables can be useful for prediction and model intercomparision.

The Role of SST Structure in Convectively Coupled Kelvin–Rossby Waves and Its Implications for MJO Formation

Abstract The dynamics of the Madden–Julian oscillation (MJO) are investigated using an aqua-planet general circulation model (GCM) and a simple one-and-a-half-layer model with a first-baroclinic mode and a planetary boundary layer. The aqua-planet GCM with zonally symmetric SST conditions simulates tropical intraseasonal disturbances with a dominant time scale of about 20 days, which is much faster than that of the observed MJO, although the GCM with realistic surface boundary conditions is shown to reproduce the observed MJO reasonably well. The SST with a broader meridional structure slows down the propagation speed. Several experiments done with various zonally symmetric surface boundary conditions showed that the meridional structure of the SST in fact is a control factor for the propagation characteristics of the MJO. With a simple theoretical model for the MJO, it is shown that the instability of the moist coupled Kelvin–Rossby waves depends on the SST structure, which determines the lower-level moisture field. The SST with a narrow meridional structure prefers to enhance only the fast eastward Kelvin wave, while the broader SST provides enough off-equatorial moisture for the growth of the Rossby component, which couples strongly with the Kelvin component and slows down the eastward modes. The SST influences the coupled Kelvin–Rossby waves through changes in the moist static stability of the free atmosphere and the frictional moisture convergence in the planetary boundary layer. The present results suggest that the essential dynamics of the MJO are rooted in a convectively coupled Kelvin–Rossby wave packet with frictional moisture convergence.

Assessment of rhythmic entrainment at multiple timescales in dyslexia: Evidence for disruption to syllable timing

Developmental dyslexia is associated with rhythmic difficulties, including impaired perception of beat patterns in music and prosodic stress patterns in speech. Spoken prosodic rhythm is cued by slow (<10 Hz) fluctuations in speech signal amplitude. Impaired neural oscillatory tracking of these slow amplitude modulation (AM) patterns is one plausible source of impaired rhythm tracking in dyslexia. Here, we characterise the temporal profile of the dyslexic rhythm deficit by examining rhythmic entrainment at multiple speech timescales. Adult dyslexic participants completed two experiments aimed at testing the perception and production of speech rhythm. In the perception task, participants tapped along to the beat of 4 metrically-regular nursery rhyme sentences. In the production task, participants produced the same 4 sentences in time to a metronome beat. Rhythmic entrainment was assessed using both traditional rhythmic indices and a novel AM-based measure, which utilised 3 dominant AM timescales in the speech signal each associated with a different phonological grain-sized unit (0.9–2.5 Hz, prosodic stress; 2.5–12 Hz, syllables; 12–40 Hz, phonemes). The AM-based measure revealed atypical rhythmic entrainment by dyslexic participants to syllable patterns in speech, in perception and production. In the perception task, both groups showed equally strong phase-locking to Syllable AM patterns, but dyslexic responses were entrained to a significantly earlier oscillatory phase angle than controls. In the production task, dyslexic utterances showed shorter syllable intervals, and differences in Syllable:Phoneme AM cross-frequency synchronisation. Our data support the view that rhythmic entrainment at slow (∼5 Hz, Syllable) rates is atypical in dyslexia, suggesting that neural mechanisms for syllable perception and production may also be atypical. These syllable timing deficits could contribute to the atypical development of phonological representations for spoken words, the central cognitive characteristic of developmental dyslexia across languages.This article is part of a Special Issue entitled <Music: A window into the hearing brain>.

Cointegration and the Empirical Mode Decomposition for the Analysis of Diagnostic Data

The use of cointegration has been proposed recently as a potentially powerful means of removing confounding influences from structural health monitoring (SHM) data. On the other hand the Empirical Mode Decomposition method is a recent multi-scale decomposition technique with the ability to decompose a signal into meaningful signal components. In this paper the EMD method will be used to highlight the dominant time-scales that have been affected by varying environmental and operational conditions and the time-scales that are related to damage. Then cointegration will be used to remove the nonstationary effects not associated with damage at the time-scales of interest in the data. The final step of the damage detection approach proposed, will be the use of two different amplitude-frequency separation methods, the Hilbert Transform and the more recent Teager Kaiser energy operator approach in order to compare the merits of both, concerning the estimation of the instantaneous characteristics of the signals.