Large Amplitude Variations Research Articles

Denoising of natural images using FREBAS transformation

AbstractIf two algorithms of Fresnel transformation are used with suitable parameters, the expansion of images modeled after multiresolution analysis (FREBAS transformation) is possible. This paper proposes a denoising technique of natural images using FREBAS transformation. Constrained least square filter applying in FREBAS transformed space removes noise superimposed on signals very well, however, that noise with specific patterns might remain on the images when processing images have small SN ratio. In this paper we focus our attention on this noise that exhibits isolationism in FREBAS transformed space and propose a new denoising technique that introduces non‐linear noise processing in FREBAS transformed space. It was shown that the noises with specific patterns were favorably removed in simulation experiment. In addition, we applied the proposed technique to natural images which contain noise to and compare the method with other denoising techniques from the viewpoint of SNR improvement, image degradation, remained noises. As a result, the proposed technique could remove noise while controlling image degradation and also obtain significant improvements in the SNR on average. In particular, we confirmed that the proposed technique had excellent denoising performance for images with large variations in amplitude. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(3): 1–11, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20675

The Interplanetary Causes of the Anormalous SSC Events

磁暴急始(SSC)是强烈太阳风动压或行星际激波与磁层相互作用的结果.通常SSC事件的上升时间在4～10 min,我们把上升时间超过15 min的SSC事件称为异常SSC事件.本文利用地磁SYM-H指数鉴别出了5个有地磁观测历史以来发生的上升时间大于15 min的异常SSC事件,并利用Wind,ACE,IMP 8,Goes,Geotail多点卫星太阳风观测数据和地磁观测数据,分析了异常SSC事件的行星际原因.结果表明,异常SSC事件通常都是强烈行星际扰动引起的,5个异常SSC事件有4个对应于行星际激波,有3个对应于多步太阳风动压跃变,有1个对应于行星际电场大幅度变化;由行星际激波产生的异常SSC事件,其上升时间依赖于行星际激波的方向,方向相对于日地连线越偏,上升时间越长;异常SSC事件上升时间与行星际磁场方向关系不明显.

A climatology of tides and gravity wave variance in the MLT above Rothera, Antarctica obtained by MF radar

A cumulative total of over 5 years of data from an MF radar situated at Rothera (67°S, 68°W) on the Antarctic Peninsula have been used to derive climatologies of periodic motions in the wind field in the mesosphere and lower thermosphere with periods less than or equal to 1 day. Strong tidal motions are observed at 24, 12 and 8 h and monthly mean climatologies are presented between 74 and 94 km altitude for comparison with the HWM-93 horizontal wind model. The 24 h tide shows a strong seasonal dependence in both the zonal and meridional components with a summertime maximum and wintertime minimum over all altitudes. The monthly mean maximum amplitude is 12(±2) ms −1 at 94 km in January and the minimum is <1 ms −1 around 86 km in early winter. The 12 h wave shows large short-term amplitude variability with a peak in amplitude around late autumn. It reaches a minimum at high altitudes in winter and below ∼80 km during summer, characteristic of a mixture of migrating and non-migrating modes. The phase of the 12 h wave is relatively constant throughout winter with a minimum mean vertical wavelength of ∼75 km around equinox. The 8 h wave is predominantly a summertime high altitude phenomenon. It is seen most strongly in the winds above 85 km and reaches monthly mean amplitudes of 6(±2) ms −1 in the zonal winds at 94 km altitude. Finally, a seasonal climatology of gravity wave variances is generated by calculating the daily mean variance in the raw winds after subtracting the fitted tidal components. This index shows a strong seasonal and height dependence in both components with a wintertime peak of ∼2000 m 2s −2 in the zonal component at the highest altitudes. This peak occurs when the stratospheric zonal jets are strongest and therefore the filtering of upward-propagating waves in the stratosphere should be greatest; implying that either a significant part of this wintertime wave activity is generated from a region above the peak stratospheric wind or that there is a strong annual variability in the source or propagation of the gravity wave activity at Rothera.

The dependence of quasar variability on black hole mass

In order to investigate the dependence of quasar variability on fundamental physical parameters like black hole mass, we have matched quasars from the Quasar Equatorial Survey Team, Phase 1 (QUEST1) variability survey with broad-lined objects from the Sloan Digital Sky Survey. The matched sample contains ≈100 quasars, and the Sloan spectra are used to estimate black hole masses and bolometric luminosities. Variability amplitudes are measured from the QUEST1 light curves. We find that black hole mass correlates with several measures of the variability amplitude at the 99 per cent significance level or better. The correlation does not appear to be caused by obvious selection effects inherent to flux-limited quasar samples, host galaxy contamination or other well-known correlations between quasar variability and luminosity/redshift. We evaluate variability as a function of rest-frame time lag using structure functions and find further support for the variability–black hole mass correlation. The correlation is strongest for time lags of the order of a few months up to the QUEST1 maximum temporal resolution of ≈2 yr, and may provide important clues for understanding the long-standing problem of the origin of quasar optical variability. We discuss whether our result is a manifestation of a relation between characteristic variability time-scale and black hole mass, where the variability time-scale is typical for accretion disc thermal time-scales, but find little support for this. Our favoured explanation is that more massive black holes have larger variability amplitudes, and we highlight the need for larger samples with more complete temporal sampling to test the robustness of this result.

Further Evidence for Variable Synchrotron Emission in XTE J1118+480 in Outburst

We present simultaneous multicolor infrared and optical photometry of the black hole X-ray transient XTE J1118+480 during its short 2005 January outburst, supported by simultaneous X-ray observations. The variability is dominated by short timescales, ~10 s, although a weak superhump also appears to be present in the optical. The optical rapid variations, at least, are well correlated with those in X-rays. Infrared JHK_s photometry, as in the previous outburst, exhibits especially large-amplitude variability. The spectral energy distribution (SED) of the variable infrared component can be fitted with a power law of slope α = -0.78 ± 0.07, where F_ν ∝ ν_α. There is no compelling evidence for evolution in the slope over five nights, during which time the source brightness decayed along almost the same track as seen in variations within the nights. We conclude that both short-term variability and longer timescale fading are dominated by a single component of constant spectral shape. We cannot fit the SED of the IR variability with a credible thermal component, either optically thick or thin. This IR SED is, however, approximately consistent with optically thin synchrotron emission from a jet. These observations therefore provide indirect evidence to support jet-dominated models for XTE J1118+480 and also provide a direct measurement of the slope of the optically thin emission, which is impossible, based on the average spectral energy distribution alone.

The variable X-ray light curve of GRB 050713A: the case of refreshed shocks

We present a detailed study of the spectral and temporal properties of the X-ray and optical emission of GRB050713a up to 0.5 day after the main GRB event. The X-ray light curve exhibits large amplitude variations with several rebrightenings superposed on the underlying three-segment broken powerlaw that is often seen in Swift GRBs. Our time-resolved spectral analysis supports the interpretation of a long-lived central engine, with rebrightenings consistent with energy injection in refreshed shocks as slower shells generated in the central engine prompt phase catch up with the afterglow shock at later times. Our sparsely-sampled light curve of the optical afterglow can be fitted with a single power law without large flares. The optical decay index appears flatter than the X-ray one, especially at later times.

Near-IR variability properties of a selected sample of AGB stars

We present the results of a near-infrared monitoring programme of a selected sample of stars, initially suspected to be Mira variables and OH/IR stars, covering more than a decade of observations. The objects monitored cover the typical range of IRAS colours shown by O-rich stars on the Asymptotic Giant Branch and show a surprisingly large diversity of variability properties. 16 objects are confirmed as large-amplitude variables. Periods between 360 and 1800 days and typical amplitudes from 1 to 2 magnitudes could be determined for nine of them. In three light curves we find a systematic decrease of the mean brightness, two light curves show pronounced asymmetry. One source, IRAS 07222-2005, shows infrared colours typical of Mira variables but pulsates with a much longer period (approx. 1200 days) than a normal Mira. Two objects are ither close to (IRAS 03293+6010) or probably in (IRAS 18299-1705) the post-AGB phase. In IRAS 16029-3041 we found a systematic increase of the H-K colour of approximately 1 magnitude, which we interpret as evidence of a recent episode of enhanced mass loss. IRAS 18576+0341, a heavily obscured Luminous Blue Variable was also monitored. The star showed a continued decrease of brightness over a period of 7 years (1995 - 2002).

Optical Monitoring of BL Lacertae Object OJ 287: A 40 Day Period?

We present the results of our optical monitoring of the BL Lacertae object OJ 287 during the first half of 2005. The source did not show large-amplitude variations during this period and was in a relatively quiescent state. A possible period of 40 days was derived from its light curves in three BATC wavebands. A bluer-when-brighter chromatism was discovered, which is different from the extremely stable color during the outburst in 1994--96. The different color behaviors imply different variation mechanisms in the two states. We then re-visited the optical data on OJ 287 from the OJ-94 project and found as well a probable period of 40 days in its optical variability during the late-1994 outburst. The results suggest that two components contribute to the variability of OJ 287 during its outburst state. The first component is the normal {\sl blazar} variation. This component has an amplitude similar to that of the quiescent state and also may share a similar periodicity. The second component can be taken as a `low-frequency modulation' to the first component. It may be induced by the interaction of the assumed binary black holes in the center of this object. The 40-day period may be related to the helical structure of the magnetic field at the base of the jet, or to the orbital motion close to the central primary black hole.

SU‐FF‐J‐04: A Computerized Method for Peak and Valley Detection in Respiratory Waveforms Without Flow Measurement

Purpose: To develop a computerized method for reliable peak (end inspiration) and valley (end expiration) detection in respiratory waveforms for gated radiotherapy and 4D CT. Method and Materials: A computerized method for peak (end inspiration) and valley (end expiration) detection in respiratory waveforms without flow measurement is described. The respiratory period T was estimated by applying a Fast Fourier Transform. The intercepts of the respiratory waveform with a moving average curve were determined with an averaging width of 2T. Peaks and valleys were defined respectively as the maximum and minimum between pairs of interwoven intercepts. While this method worked well the majority of the time, both automatic corrections and manual user interventions were employed to correct errors and adjust the results. Results: The method was implemented in MATLAB on a PC with a 3.0 GHz Pentium IV CPU and 2.0 GB RAM. On average, the respiratory waveform was 575.3 s long and contained a total of 307 peaks and valleys. For each patient, 99% of all peaks and valleys were correctly located by the automatic algorithm in 2.8 s. Only three (1%) points required manual user adjustment. A user spent 66.8 s for reviewing, and manually adding or deleting points. For nine of the 20 patients, all peaks and valleys were automatically detected. The high efficiency of the automatic algorithm is clear. Conclusion: The results demonstrated that this method was reliable and efficient for peak detection in respirator waveforms with noise and large variations in baseline level, amplitude and period.

A deepXMM-Newtonobservation of the ultraluminous X-ray source Holmberg II X-1: the case against a 1000-M⊙black hole

We present results from a 112-ks long look by XMM-Newton at the ultraluminous X-ray source (ULX) Holmberg II X-1 (Ho II X-1), long thought to be the one of best candidates for the missing class of intermediate-mass black holes (IMBHs). Our data comprises the first high-quality XMM-Newton/RGS (reflection grating spectrometer) spectrum of an ULX, and an XMM-Newton/EPIC (European Photo Imaging Camera) spectrum with unprecedented signal-to-noise ratio. A detailed timing analysis shows that any variability on time-scales of minutes to hours is very weak (less than a few per cent fractional rms), though larger amplitude variations on much shorter time-scales could be hidden by photon counting statistics. This result suggests that if Ho II X-1 harbours an IMBH, then we are observing this source in a highly unusual and atypical state when compared with the known variability behaviour of other accreting systems of large mass. Moreover, unlike galactic X-ray binaries, our spectral analysis indicates the possible presence of an optically thick low-temperature corona. Taken together our timing and spectral analysis suggests that the compact companion is most likely a high-luminosity analogue of black hole binary systems similar to GRS 1915+105, the galactic microquasar, harbouring a compact object of mass no greater than 100 M⊙.

Draping or overriding: The effect of horizontal stress gradients on internal layer architecture in ice sheets

Internal isochronic layers in ice sheets sensed by radar show two characteristic relationships to the basal topography: Either they override it, with layers above the crests of rises lying essentially flat, or they drape over it, with the layers following rises and falls in basal topography. A mechanical theory is presented which shows that overriding is the expected behavior when topographic wavelengths are comparable with or less than the ice thickness, while draping occurs at longer wavelengths. This is shown with analytical perturbation solutions for Newtonian fluids, numerical perturbation solutions for nonlinear fluids, and finite element solutions for nonlinear fluids and large-amplitude variations. Bed variation from topography and changes in the basal boundary condition are considered, for fixed bed and sliding beds, as well as three-dimensional flows and thermomechanically coupled flows. In all cases, the dominant effect on draping/overriding is the wavelength of the topography or variation in basal boundary conditions. Results of these full mechanical system calculations are compared with those from the shallow ice approximation and the longitudinal stress approximation. Some calculations are carried out for zero accumulation, where the age of the ice and therefore isochrone geometry is not defined. It is shown that there is a close relationship between isochrones and streamlines, and that they behave similarly when bed wavelength divided by the ice thickness is small compared with the ratio of ice velocity and accumulation rate, which is a useful approximation. Numerical comparisons of isochrones and streamlines show them to be virtually coincident.

보현산천문대 단주기변광성 탐사(SPVS)연구

We have been performing a wide-field photometric monitoring program, named SPVS (Short-Period Variability Survey), at the Bohyunsan Optical Astronomy Observatory (BOAO). The observation system consists of a small refracting telescope (D = 155 mm, f = 1050 mm) and a <TEX>$2k{\times}3k$</TEX> CCD Camera. The field of view is <TEX>$1.0^{\circ}{\times}1.5^{\circ}$</TEX>. Detection limit is about V = 13 for short-period small amplitude variables such as <TEX>${\delta}$</TEX> Scuti-type pulsating stars, and about V = 15 for long-period large amplitude variables such as eclipsing binaries and RR Lyrae stars. The instrument is designed to be remote-controlled through internet. The primary purpose of this project is to search for variable objects in bright Galactic open clusters. We present results of test observations conducted towards NGC 7092.

Flares in Long and Short Gamma-Ray Bursts: A Common Origin in a Hyperaccreting Accretion Disk

Early-time X-ray observations of GRBs with the Swift satellite have revealed a more complicated phenomenology than was known before. In particular, the presence of flaring activity on a wide range of time scales probably requires late-time energy production within the GRB engine. Since the flaring activity is observed in both long and short GRBs, its origin must be within what is in common for the two likely progenitors of the two classes of bursts: a hyperaccreting accretion disk around a black hole of a few solar masses. Here, we show that some of the observational properties of the flares, such as the duration-time scale correlation, and the duration-peak luminosity anticorrelation displayed by most flares within a given burst, are qualitatively consistent with viscous disk evolution, provided that the disk at large radii either fragments or otherwise suffers large amplitude variability. We discuss the physical conditions in the outer parts of the disk, and conclude that gravitational instability, possibly followed by fragmentation, is the most likely candidate for this variability.

Galactic Centre stellar winds and Sgr A* accretion

We present a detailed discussion of our new 3D numerical models for the accretion of stellar winds on to Sgr A*. In our most sophisticated models, we put stellar wind sources on realistic orbits around Sgr A*, we include recently discovered ‘slow’ winds (vw∼ 300 km s−1), and we account for optically thin radiative cooling. We test our approach by first modelling only one-phase ‘fast’ stellar winds (vw∼ 1000 km s−1). For stellar wind sources fixed in space, the accretion rate is of the order of , fluctuates by ≲10 per cent, and is in good agreement with previous models. In contrast, decreases by an order of magnitude for wind sources following circular orbits, and fluctuates by ∼50 per cent. Then we allow a fraction of stars to produce slow winds. Much of these winds cool radiatively after being shocked, forming cold clumps and filaments immersed into the X-ray-emitting gas. We investigate two orbital configurations for the stars in this scenario, an isotropic distribution and two rotating discs with perpendicular orientation. The morphology of cold gas is quite sensitive to the orbital distribution of the stars. In both cases, however, most of the accreted gas is hot, producing a quasi-steady ‘floor’ in the accretion rate, of the order of ∼3 × 10−6 M⊙ yr−1, consistent with the values deduced from Chandra observations. The cold gas accretes in intermittent, short but powerful accretion episodes, which may give rise to large-amplitude variability in the luminosity of Sgr A* on time-scales of tens to hundreds of years. The circularization radii for the flows are about 103 and 104 Schwarzschild radii, for the one- and two-phase wind simulations, respectively, never forming the quasi-spherical accretion flows suggested in some previous work. Our work suggests that, averaged over time-scales of hundreds to thousands of years, the radiative and mechanical luminosity of Sgr A* may be substantially higher than it is in its current state. Further improvements of the wind accretion modelling of Sgr A* will rely on improved observational constraints for the wind velocities, mass-loss rates and stellar orbits.

X-ray variability of NGC 3227 and 5506 and the nature of active galactic nucleus 'states'

We use X-ray monitoring data obtained over a broad range of time-scales to measure the broad-band power spectral density functions (PSDs) of two Seyfert galaxies: the broadline Seyfert 1 NGC 3227 and the Seyfert 2 NGC 5506, which has recently been identified as an obscured narrow-line Seyfert 1 (NLS 1). Using a Monte Carlo fitting technique, we demonstrate that both PSDs are reminiscent of the PSD of black hole X-ray binaries (BHXRBs) in the high/soft state, and specifically rule out a low/hard-state PSD shape in NGC 3227. This result demonstrates that, at least where variability is concerned, broad-line Seyferts with hard X-ray spectra (photon index � ∼ 1.6) are not simply the analogues of the low/hard state in BHXRBs, and the dichotomy of NLS 1 and broad-line Seyferts cannot be simply interpreted in terms of the two states. We show that the PSD normalization in NGC 3227 is strongly energy-dependent, with larger variability amplitudes at lower energies, unlike NGC 5506 which shows little energy dependence of variability. We demonstrate that this difference is caused by spectral pivoting of the continuum in NGC 3227 at high energies, which is probably also related to the large amplitude of variability seen in the 2‐10 keV band in this active galactic nucleus (AGN). Using the new PSD data and new results in the literature, we replot the PSD break time-scale versus mass plot for all AGNs with PSD breaks measured so far, and demonstrate that higher accretion rate AGNs appear to have relatively shorter break time-scales for their black hole mass than lower accretion rate AGNs. Ke yw ords: methods: statistical ‐ galaxies: active ‐ galaxies: individual: NGC 3227 ‐ galaxies: individual: NGC 5506 ‐ galaxies: Seyfert ‐ X-rays: galaxies.

Ionospheric effects on GPS positioning

Ionospheric scintillation results from a single frequency global positioning system (GPS) receiver have been presented in this paper. Ionospheric scintillation is rapid variation in the amplitude and phase of radio signals caused by irregularities in the ionosphere. Ionosphere contains large amplitude variations over spatial scales from few cm to 100s of km. It is observed that VHF–UHF communications as well as automated navigation and precision positioning via GPS are affected by scintillations. Scintillations do not have major effects on mid latitude regions, but low latitude scintillations are the greatest cause of GPS position errors. In the present work, we study the effect of ionospheric scintillations on GPS signal at low latitude station, Chiang Rai, Thailand. The data were analyzed from January 2001 to December 2001. Results show that scintillation has a significant problem at this latitude and position error increases during active scintillation condition, which causes loss of lock on several satellites.

An X‐Ray Variable Millisecond Pulsar in the Globular Cluster 47 Tucanae: Closing the Link to Low‐Mass X‐Ray Binaries

We report the discovery of peculiar X-ray spectral variability in the binary radio millisecond pulsar PSR J0024--7204W in the globular cluster 47 Tucanae. The observed emission consists of a dominant non-thermal component, which is eclipsed for a portion of the orbit, and a thermal component, which appears to be persistent. We propose that the non-thermal X-rays originate in a relativistic intrabinary shock, formed due to interaction between the relativistic particle wind from the pulsar and matter from the main-sequence companion star, while the thermal photons are from the heated magnetic polar caps of the millisecond pulsar. At optical wavelengths, the emission exhibits large-amplitude variations at the orbital period, which can be attributed to heating of one side of the tidally-locked secondary star by the pulsar wind. The observed X-ray and optical properties of PSR J0024--7204W are remarkably similar to those of the low mass X-ray binary and X-ray millisecond pulsar SAX J1808.4--3658 in quiescence. This supports the conjecture that the non-thermal X-ray emission and optical modulations seen in the SAX J1808.4--3658 system in a quiescent state are due to interaction between the wind from a reactivated rotation-powered pulsar and matter from the companion star. The striking similarities between the two systems provide support for the long-sought connection between millisecond radio pulsars and accreting neutron star systems.

Optical continuum properties of the NLS1 galaxy Mrk 335 in 1995-2004

We present results of UBVRI photometry of Mrk 335 in 1995-2004. This object has a large amplitude of variability, reaching about 1.1, 0.9, 0.7 mag in the U, B, V and 0.3 mag in the Rc, Ic bands, respectively. This photomerical behaviour as well as the spectral energy distribution in the optical part of the spectrum is typical of Seyfert 1 galaxies. The structure function (SF) analysis of Mrk 335 has shown that the variability of Mrk 335 can be caused by stochastic superposition of independent flares in a wide interval of durations, the longest of which has a duration of about several hundred days. The slope of the power-law portion of the SF b ∼ 0.6-0.7 for the time scale from several days to several hundreds of days. It is close to the estimates for disk instability models. The estimate of the extension of the instability zone in an accretion disk (about 300Rs) is also evidence that the instability in an accretion disk is able to explain the long-term optical variability. A cross-correlation function (CCF) shows some evidence that the delay of fluxes in the V,R, I bands relative to the U band can be of some days, and there is a tendency for lags lo be systematically higher for the R, I bands than for B, V.

Performance Analysis of AC-Coupled Burst-Mode Receiver for Fiber-Optic Burst Switching Networks

A generalized theoretical analysis of an AC-coupled fiber-optic burst-mode receiver is presented. This receiver is designed to operate in optical burst-switching networks using DC-balanced data coding such as 8B10B. Analytic expressions for the recovery time are derived as a function of the system dynamic range, power penalty, and data coding format. The theoretical calculations are verified with a detailed simulation. It is shown that locking time of the order of nanoseconds can be achieved with commercially available AC-coupled receivers. The burst-mode receiver can adapt to large (>10 dB) amplitude variations in 30 ns with a power penalty of 2 dB at 12.5 Gb/s. An overall optimization of the transmitter-receiver link-setup time is performed for an optical burst-switching network based on tunable laser transmitters. The dark interval during laser tuning (/spl sim/50 ns) is shown to have a beneficial impact on the receiver's response time, effectively reducing its locking time to a few nanoseconds, thus resulting in an overall link setup time of about 50 ns, limited by the laser's tuning time.

Physics and Dynamics of Density-Compensated Temperature and Salinity Anomalies. Part I: Theory

AbstractSubducted temperature anomalies have been invoked as a possible way for midlatitudes to alter the climate variability of equatorial regions through the so-called thermocline bridge, both in the Pacific and Atlantic Oceans. To have a significant impact on the equatorial heat balance, however, temperature anomalies must reach the equatorial regions sufficiently undamped. In the oceans, the amplitude of propagating temperature (and salinity) anomalies can be altered both by diabatic (nonconservative) and adiabatic (conservative) effects. The importance of adiabatic alterations depends on whether the anomalies are controlled by wave dynamics or by passive advection associated with density compensation. Waves being relatively well understood, this paper seeks to understand the amplitude variations of density-compensated temperature and salinity anomalies caused by adiabatic effects, for which no general methodology is available. The main assumption is that these can be computed independent of amplitude variations caused by diabatic effects. Because density compensation requires the equality T′/S′ = βS/α to hold along mean trajectories, the ratio T′/S′ may potentially undergo large amplitude variations if the ratio βS/α does, where α and βS are the thermal expansion and haline contraction coefficients, respectively. In the oceans, the ratio βS/α may decrease by an order-1 factor between the extratropical and tropical latitudes, but such large variations are in general associated with diapycnal rather than isopycnal motion and hence are likely to be superimposed in practice with diabatically induced variations. To understand the individual variations of T′ and S′ along the mean streamlines, two distinct theories are constructed that respectively use density/salinity and density/spiciness as prognostic variables. If the coupling between the prognostic variables is neglected, as is usually done, both theories predict at leading order that temperature (salinity) anomalies should be systematically and significantly attenuated (conserved or amplified), on average, when propagating from extratropical to tropical latitudes. Along particular trajectories following isopycnals, however, both attenuation and amplification appear to be locally possible. Assuming that the density/spiciness formulation is the most accurate, which is supported by a theoretical assessment of higher-order effects, the present results provide an amplification mechanism for subducted salinity anomalies propagating equatorward, by which the latter could potentially affect decadal equatorial climate variability through their slow modulation of the equatorial mixed layer, perhaps more easily than their attenuated temperature counterparts. This could be by affecting, for instance, barrier layers by which salinity is known to strongly affect local heat fluxes and heat content.