Short-period Variations Research Articles

On the Temperature Correction of the Aquatrak Acoustic Tide Gauge

Temperature corrections for the Aquatrak acoustic tide gauge are derived. These account for variable temperature (and hence sound velocity) along the sounding tube, thermal expansion of the calibration tube, and the thermal response of the transducer/controller combination. When averaged over long periods (e.g., seasonal), the corrections are typically several millimeters in magnitude, with short-period (e.g., diurnal) variations as large as several centimeters. The correction associated with thermal expansion of the calibration tube is of the same order as the correction for variable sound velocity, which is already applied at some Aquatrak installations. The corrections derived here relate to the situation in which an initial adjustment has been made by the manufacturer (making the calibration tube a fixed known length under factory conditions), and a subsequent calibration is performed to define a single zero offset for the instrument.

The seasonal behavior of water ice clouds in the Tharsis and Valles Marineris regions of Mars: Mars Orbiter Camera Observations

The Mars Global Surveyor Mars Orbiter Camera was used to obtain global maps of the martian surface with equatorial resolution of 7.5 km/pixel in two wavelength ranges: blue (400–450 nm) and red (575–625 nm). The maps used were acquired between March 15, 1999 ( L s =110°) and July 31, 2001 ( L s =205°), corresponding to approximately one and a quarter martian years. Using the global maps, cloud area (in km 2) has been measured daily for water ice clouds topographically corresponding to Olympus Mons, Ascraeus Mons, Pavonis Mons, Arsia Mons, Alba Patera, the western Valles Marineris canyon system, and for other small surface features in the region. Seasonal trends in cloud activity have been established for the three Tharsis volcanoes, Olympus Mons, and Alba Patera. Olympus, Ascraeus, and Pavonis Mons show cloud activity from about L s =0°–220° with a peak in cloud area near L s =100°. One of our most interesting observational results is that Alba Patera shows a double peaked feature in the cloud area with peaks at L s =60° and 140° and a minimum near L s =100°. Arsia Mons shows nearly continuous cloud activity. The altitudes of several of these clouds have been determined from the locations of the visual cloud tops, and optical depths were measured for a number of them using the DISORT code of Stamnes et al. (1988, Appl. Opt. 27, 2502–2509). Several aspects of the observations (e.g., cloud heights, effects of increased dust on cloud activity) are similar to simulations in Richardson et al. (2002, J. Geophys. Res. 107, 5064). A search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours; unambiguous evidence for other periodicities was not found.

Morphological evidence of Holocene coseismic deformation in the Taormina region (NE Sicily)

In southern Italy, strongly uplifted coastal regions are located along the footwall of the main seismogenic fault segments which affect the Tyrrhenian side of southern Calabria and the Ionian coast of eastern Sicily. This morphotectonic picture is generally associated with high-level historical seismicity. An anomaly is represented by the Ionian coast of NE Sicily that, located on the footwall of the offshore Taormina Fault, is affected by very low to absent historical seismicity. A detailed levelling survey of dated Holocene marine notches has been carried out along the coast of Taormina and Capo S. Alessio, at the southern termination of the Taormina Fault, where a converging set of Late Quaternary strandlines marks the tip of this offshore structure. The Holocene marine marks, represented by three main notch levels separated by lithophaga bands dated at 5 ka and post-3.2 ka, are severely tilted towards the onshore and show a clear divergence from the southern tip of the Taormina Fault towards the north. Taking into account the slow rate of sea-level rise characterising the Central Mediterranean during the last 5 ka (0.3–1.0 mm/year), the vertical distribution of the Holocene strandlines can be interpreted as the result of short-period variations in the rate of tectonic uplifting. The notches and their related bio-morphological bands developed at low-rate of uplifting and have been displaced by three major seismic events in the past 5 ka, the strongest of which ( M∼7) occurred at about 3.2 ka. This confirms the temporary seismic gap for the Taormina Fault and strongly suggests that the seismogenic potential of this sector of Sicily needs to be re-evaluated.

Time-series analysis of remote-sensed chlorophyll and environmental factors in the Santa Monica–San Pedro Basin off Southern California

The time-series of remote-sensed surface chlorophyll concentration measured by SeaWiFS radiometer from September 1997 to December 2001 and the relevant hydrological and meteorological factors (remote-sensed sea surface temperature, atmospheric precipitation, air temperature and wind stress) in Santa Monica Bay and adjacent waters off southern California were analyzed using wavelet and cross-correlation statistical methods. All parameters exhibited evident seasonal patterns of variation. Wavelet analysis revealed salient long-term variations most evident in air temperature during El Niño 1997–1998 and in wind stress during La Niña 1998–1999. Short-period (<100 days) variations of remote-sensed chlorophyll biomass were mostly typical to spring seasons. Chlorophyll biomass was significantly correlated with air temperature and wind stress: an increase of chlorophyll biomass followed with 5–6-day time lag an increase of wind stress accompanied by a simultaneous decrease of air temperature. The mechanism of these variations was an intensification of phytoplankton growth resulting from the mixing of water column by wind stress and entrainment of nutrients into the euphotic layer.

Diurnal Variations in the Rate of Gas Exchange between Lake Baikal and the Atmosphere

The diurnal course of gas exchange between Lake Baikal and the atmosphere during the summer warming up is calculated using the data of continuous 102-hour observations in August 2000 and the published materials of individual diurnal measurements of the dissolved gases concentrations made in different years. The diurnal course of the rate of gas exchange in both the coastal and open parts of the lake is found to be due to the fact that slow gas-exchange processes fail to compensate fast changes in the partial pressures of gases dissolved in the upper water layer. The changes are associated with the diurnal dynamics of the hydrometeorological conditions and the intensity of the production–destruction processes. It is found that under light winds, the contribution of biological factors to the formation of short-period variations in the CO2 and O2 fluxes through the lake water surface makes about 80% and that of abiotic factors, 20%. Considerable aperiodic changes in the diurnal course of hydrometeorological conditions are found to essentially distort the normal diurnal course of the gas-exchange processes.

Sea-Level Trend at the Korean Coast

Based on the tide gauge data from the Permanent Service for Mean Sea Level (PSMSL) collected at 23 locations in the Korean coast, the long-term sea-level trend was computed using a simple linear regression fit over the recorded length of the monthly mean sea-level data. The computed sea-level trend was also corrected for the vertical land movement due to post glacial rebound(PGR) using the ICE-4G(VM2) model output^12). It was found that the PGR-corrected sea-level trend near Korea was 2.310 ± 2.220 mm/yr, which is higher than the global average at 1.0~20.mm/yr, as assessed by the Intergovernmental Panel on Climate Change(IPCC)^1). The regional distribution of the long-term sea-level trend near Korea revealed that the South Sea had the largest sea-level rise followed by the West Sea and East Sea, respectively, supporting the result of the previous study by Seo et al.^7) However, due to the relatively short record period and large spatial variability, the sea-level trend from the tide gauge data for the Korea coast could be biased with a steric sea-level rise by global warming during the 20th century.

Insights from Pulsating Nova Envelopes

AbstractBased on a linear and non-linear study of radial pulsations in the envelopes of classical novae (Schenker, 1999), I discuss the results both from the point of view of pulsation theory as well as their consequences for current nova models. Starting from initially static envelope structures at various stages during the decline of a nova outburst, strong ‘running-wave’ instabilities have been found that rapidly grow into shocks. Improved analytical concepts give a new direction to the interpretation of such highly non-adiabatic radial pulsations. For direct observational confirmation, a search for short period variability in the UV and soft X-ray is suggested during the very late decline phase. Speculative consequences for mass-loss scenarios in novae due to these instabilities will need some more work in the future.

CCD Photometry of Variable Stars in the Galactic Open Cluster NGC 7419

AbstractWe present results of a CCD variability search in the field of the young open cluster NGC 7419. This cluster contains a large number of Be stars and almost all of them turned out to be variable. They show mostly irregular variations on different time-scales with ranges up to 0.4 mag in the IC band. The most interesting result is the discovery of short-period variability in some of the Be stars.

Low-frequency variability and binarity of theδScuti star XX Pyx

We analyse 147 h of single-site CCD time series photometry of the multiperiodic low-amplitude δ Scuti star XX Pyx with the aim of investigating variability at low frequencies. Part of the data were obtained in the context of the 1998 multisite campaign on XX Pyx, the results of which were described by Handler et al. We find that periodic low-frequency variations are present in the XX Pyx light curves, and we detect two frequencies at fA=0.8695 cycle d−1 and fB=1.7352 cycle d−1, respectively, with amplitudes of 4.5 and 5.4 mmag. The low-frequency variability is intrinsic to XX Pyx, and cannot be attributed to instrumental or atmospheric effects. The near 2:1 ratio of the frequencies leads us to suggest that XX Pyx is a δ Scuti star in a binary system, with a possible binary period of 27.6 h. This is strongly supported by the detection of radial velocity variations from the re-analysis of echelle spectra obtained by Handler et al. However, in the absence of a spectroscopic period, alternative explanations of the photometric variability involving pulsation are also possible; the variations occur close to possible combination frequencies of the short-period (δ Scuti) variations, but high Q values of 0.57 and 0.28 d suggest that the variations are not a result of normal (p-)modes. They could possibly be due to g-modes excited to observable amplitudes as a result of resonance effects. Surface features (spots) are unlikely to be the cause of the variations. We searched for combination frequencies ( fi−fj), f being the normal δ Scuti frequencies detected by Handler et al., but failed to detect any.

Short-Period Light Variation of an Eclipsing Binary System: RZ Cassiopeiae

The eclipsing binary system RZ Cas is known to exhibit variation in its light curves at the primary minimum, usually showing a partial-eclipse–type curve but sometimes indicating a flat minimum, which is evidence for a total eclipse. We observed RZ Cas not only during the primary eclipse, but also during the out-of-eclipse phase, and we have found a short-period light variation with a frequency of 62.20 cycles day-1 (period of 23.15 minutes), whose maximum amplitude is 0.02 mag. This short-period variation can modulate the shape of the light curve at the primary minimum effectively. The brightness-color relationship of the short-period variation suggests a δ Scuti type oscillation.

Entropy, entropy rate, and pattern classification as tools to typify complexity in short heart period variability series.

An integrated approach to the complexity analysis of short heart period variability series (approximately 300 cardiac beats) is proposed and applied to healthy subjects during the sympathetic activation induced by head-up tilt and during the driving action produced by controlled respiration (10, 15, and 20 breaths/min, CR10, CR15, and CR20 respectively). The approach relies on: 1) the calculation of Shannon entropy (SE) of the distribution of patterns lasting three beats; 2) the calculation of a regularity index based on an entropy rate (i.e., the conditional entropy); 3) the classification of frequent deterministic patterns (FDPs) lasting three beats. A redundancy reduction criterion is proposed to group FDPs in four categories according to the number and type or of heart period changes: a) no variation (0V); b) one variation (1V); and c) two like variations (2LV); 4) two unlike variations (2UV). We found that: 1) the SE decreased during tilt due to the increased percentage of missing patterns; 2) the regularity index increased during tilt and CR10 as patterns followed each other according to a more repetitive scheme; and 3) during CR10, SE and regularity index were not redundant as the regularity index significantly decreased while SE remained unchanged. Concerning pattern analysis we found that: a) at rest mainly three classes (0V, 1V, and 2LV) were detected; b) 0V patterns were more likely during tilt; c) 1V and 2LV patterns were more frequent during CR10; and d) 2UV patterns were more likely during CR20. The proposed approach based on quantification of complexity allows a full characterization of heart period dynamics and the identification of experimental conditions known to differently perturb cardiovascular regulation.

The Mu radar study of nonlinear advective accelerations in the lower and middle atmosphere

A multi-beam method was used to calculate zonal, sx. and meridional, sy, nonlinear advective accelerations from the MU radar observations with the antenna beam pointing in 9 directions. The results of simultaneous measurements of sx and sy in the tropostratosphere (altitudes 2 -- 18 km) and in the mesosphere (65 -- 80 km) in April 1999 are presented. Short-period variations of sx and sy may show regions of increased generation of atmospheric gravity waves. The wave generation increases with the increase in the mean wind and have maxima at the altitudes, where the maxima of tropospheric and mesospheric jets are located. The dependence of sx and sy on the mean wind is weaker in the mesosphere than in the tropo-stratosphere.

Short-period variations of ionospheric drifts at Collm an their connection with the dynamics of the lower and middle atmosphere

Studies of the intensity of horizontal drift velocity perturbations with periods 0.7 – 3 hours at the altitudes 80 – 110 km are made from the data of regular low-frequency D1 ionospheric reflection observations at Collm, Germany (52° N, 15° E) in 1983 – 1999. Seasonal changes of variances of short-period perturbations of zonal velocity reveal the main maximum in summer and a smaller maximum in winter near the altitude 80 km and the two maxim at equinoxes near and above 100 km. Perturbation variances had the minima in 1985 -- 1987 and in 1996 -- 1998. Numerical modeling shows that IGW's generated in the strato-mesospheric jet stream may have substantial amplitudes at altitudes near and above 100 km and may modify seasonal variations of tropospheric IGWs.

Short-period variations in the proper motions of sunspots from SOHO (MDI) observations

Short-period (1–60 min) variations in the coordinates of the centers of gravity of isolated sunspots are analyzed. The sunspot coordinated were determined using two sets of observational data—magnetograms and intensities—obtained by SOHO (MDI) on December 6, 1998, from 01:00 to 21:57 UT with temporal resolution 60 s and spatial resolution 0.6″/pixel. A slow drift in the sunspot coordinates was removed using a low-frequency filter with a 61-min integration window. The guiding errors (RMS∼0.014″) were determined by analyzing correlated motions in pairs of sunspots, and were removed from the time series before determining the sunspot proper motions. Based on the calculated power spectra for the sunspot proper motions, two period intervals containing appreciable power were identified. One coincides with the well-known 5-min acoustic solar oscillations. The concentration of power in this interval is greater for the coordinate variations derived the magnetograms than those derived from the intensities; the harmonic amplitude for some peaks reaches ∼±30 km. The other spectral interval corresponds to periods exceeding 30 min. Overall, the rms short-period variations in the sunspot proper motions are 9.9±2.2 and 16.7±7.6 km (0.014″±0.003″ and 0.024″±0.010″) for the magnetogram and intensity data, respectively.

Stochastic Modeling of Short Term Variations of Sea Level in Eastern Canada

Hourly sea level records from three stations in eastern Canada (Québec-Lauzon, Harrington-Harbour and Halifax) are analyzed both in frequency domain from 1970 to 1979 and in time domain during 1973. At the three stations, the deterministic model explains 90 to 96% of the total variability of sea level. The semidiurnal and diurnal tides contribute largely to its variations. The residual series, less than 10% of the initial variations of sea level, contain irregular values including extreme values of seiches and storm surges. Such random variations are analyzed and modeled following the method described by Box and Jenkins (1976). The long period variations (2 to 30 days) can be attributed to meteorological forcing (atmospheric pressure and winds). The short period variations (some hours to one day) can be attributed to longitudinal seiches, semidiurnal and diurnal atmospheric tides, and inertial oscillations. The water discharge from the St. Lawrence River contributes 29% of the monthly residual sea level at Qué

The total-field geomagnetic coast effect: The CICADA97 line from deep Tasman Sea to inland New South Wales

In the CICADA97 experiment a line of simultaneously recording stationary vector magnetometers was deployed from inland NSW, across the east Australian coast, and into the Tasman Sea. The purpose of the experiment was to investigate the effect of electrical conductivity structure near a coastline on natural timevariations in Earth’s magnetic field. Aeromagnetic surveys regularly take place in such coastal areas, and removal of time variations of the magnetic field is a prime task of data reduction. CICADA97 data show that long-period variations of the total field are systematically enhanced near the NSW coast, while spatial patterns of short-period variations (such as pulsations) may be strongly influenced by electrical conductivity structures on a smaller scale, such as bays and inlets.

On structure and temporal variation of the bifurcation current off the Kii Peninsula

The Kii Bifurcation Current is often found along the southwest coast of the Kii Peninsula, and its frequency of occurrence reaches about 70% in the period from 1988 to 1996 (Takeuchi et al., 1998a). In order to clarify the structure and short-period variability of the Kii Bifurcation Current, detailed observations were made four times on board the R/V Seisui-maru of Mie University on October 29–31, 1996, on June 24–26, 1997, October 14–16, 1997, and December 3–4, 1997. The measured horizontal structure of the Kii Bifurcation Current indicates that the eastern portion of the Current (eastward flow near Cape Shionomisaki) consists of a part of the current zone of the Kuroshio. It is shown that the current structure, including the Kii Bifurcation Current in the vicinity of Cape Shionomisaki, is stable when the Kuroshio is flowing in a stationary straight path, but that the current structure is considerably changed when small-scale eddies pass by the cape. Such short-period variation can be monitored by using the daily variation of the sea level difference between Kushimoto and Uragami. In particular, in the case of October 29–31, 1996, when an eminent small-scale eddy passed by Cape Shionomisaki, and when the Kuroshio axis tentatively moved southwards about 50 km apart from the coast, the Kii Bifurcation Current seems to have disappeared.

Short-period Variations of 28 CMa during 1998/9

AbstractThe Be star 28 CMa was one of the first periodic Be stars to be discovered and shows very large line profile variations with a period of 1.37 d. Recently, it has been shown that the line profile and light variations can be modeled by a patch of gas suspended above the photosphere. We present echelle observations of the Hβ and Hϒ line and several helium and metal absorption lines. We show that the radial velocity variations of these lines are unchanged since they were first observed two decades ago. We also examined several emission lines of Fe II and show that they do not partake of the periodic variation. We attribute the periodic variations of the lines formed close to the photosphere to a co-rotating cloud, whereas the Fe II emission lines are formed in the circumstellar disk outside the co-rotating radius.

Interpretation of the short period variations in geomagnetic anomalies of Shaanxi region

A temporary profile from Shiquan in the southern part of Shaanxi Province to Ningxian in Gansu Province for observation of geomagnetic short period variations was set up. The characteristics of geomagnetic short period variations in the profile region was analyzed through geomagnetic transfer functions at measurement sites (Fan, et al, 1998). According to the theory of multi-scale analysis of wavelet transform, the components affected by regional origin in the region is extracted in this paper. The components of regional origin is used as original data in the inversion study for investigation of 2-D conductivity structure corresponding to the regional origin. The inversion method (Zhdanov, Traynin, 1997) which is based on the minimum of the total energy of the residual field between observational electro-magnetic field and the calculated theoretical field of conductivity model and the conception of migrated residual field is introduced into our inversion of the data of magneto-variation sounding. The result of the inversion gives the underground conductivity structure in depth range of 100 km beneath the profile, and shows that a high conductivity area is located under Wugong and Qianling. The main characteristics of the inversion method is briefly discussed, that is, it can reflect the depth and the distribution of anomalous conductivity area comparatively well, and large number of parameters of inversion model is allowed to be used in the inversion.

Some new relationships between temperature variations and sunspot cycles—2. Short-period variations

It is shown analytically that if f 0 represents the frequency of the 11-year sunspot cycle or that of the 22-year sunspot cycle or that of the 35- to 40-year sunspot cycle or that of the seasonal cycle, then large heat/temperature oscillations should exist in the surface–atmosphere system (SAS) at frequencies 1 3 f 0 , 2 3 f 0 , 1 1 3 f 0 and 2 f 0. Also if f 0 represents the frequency of the seasonal cycle alone, then large heat/temperature oscillations should exist in the SAS not only at the frequencies listed above but also at the additional frequencies 1 2 3 f 0 and 1 2 f 0 . Actual existence of heat/temperature oscillations in the SAS at the frequencies given above has been amply verified by means of past temperature records. Furthermore, we illustratively show that both the 11-year sunspot cycle and corresponding heat/temperature oscillations in the SAS at a period of 11 years maintain approximately stable phase relationships with each other as long as each of the latter oscillations steadily keeps to one amplitude–modulation state. The phase relationship may change if the heat/temperature oscillation involved switches into a different amplitude–modulation state. One of the spin-offs of the analysis reported herein is a realisation that the quasi-biennial oscillation is apparently composed of individual components at periods 1 1 2 , 2 and 3 years.