Tidal Parameters Research Articles

Observations of high‐latitude lower thermospheric winds from Thule Air Base and Søndre Strømfjord, Greenland

Lower thermospheric winds have been determined from Fabry‐Perot interferometer (FPI) measurements of the Doppler shift of the 5577‐Å O(1S) emission over Thule Air Base (76.5°N, 69.0°W) and Søndre Strømfjord (67.0°N, 50.9°W), Greenland. These winds normally correspond to the altitude of the peak of the airglow O(1S) emission layer, near 97 km. The altitude ambiguity due to auroral contamination has been reduced by eliminating data when the intensity of the emission increases significantly. Contamination by airglow emission of 5577‐Å O(1S) originating from higher altitudes has been investigated by an FPI simulation code. The simulation results indicate that this latter emission may contribute an anomalous diurnal oscillation to ground‐based 5577‐Å O(1S) FPI measurements of lower thermospheric wind. The agreement of diurnal phases between that deduced from the green‐line measurements and that determined from simultaneous red‐line observation supports this conclusion. The same simulation applied to observations from Søndre Strømfjord shows that the upper layer contamination is much weaker and is not serious. Significant day‐to‐day variation is evident in the lower thermospheric wind field. Average neutral winds are calculated, and a harmonic analysis is carried out to examine the major low‐frequency wind components. The seasonal variations of these wind components are compared with radar data and model predictions. The observations are generally in good agreement with model results. The comparison between FPI and radar results also shows reasonable agreement. The semidiurnal amplitudes observed with the Søndre Strømfjord radar during the Lower Thermospheric Coupling Study (LTCS‐I) and LTCS‐2 periods are always greater than the climatological values obtained from averaging FPI and Chatanika radar observations. This result shows the variability that can be expected when comparing “instantaneous” estimates of tidal parameters with climatological results.

Perinatal lung function measurements and prediction of respiratory problems in infancy

The aim of this study was to determine which lung function test employed in the perinatal period gave the results most significantly associated with respiratory problems in infancy. The ratio of the proportion of time to reach peak tidal expiratory flow to total expiratory time , thoracic gas volume (TGV) and airway resistance (from which specific conductance was calculated) measurements were examined from 85 infants born at or near term. The infants were followed until at least one year of age and described as symptomatic if they wheezed for at least 24 hours. Twenty-three infants were symptomatic in the first year. The symptomatic group, compared to the asymptomatic, had a higher median FRC (p < 0.01) and (p < 0.001); their median was lower (p < 0.001). It was possible to obtain results from only 61 infants; the median did not differ significantly between symptomatic and asymptomatic infants. Logistic regression analysis demonstrated a high and FRC, but not a low , independently related to positive symptom status. A high was the most sensitive (83%) predictor of subsequent respiratory problems, but all the tests examined had low positive predictive values. Keywords: lung function tests, tidal breathing parameters

Two years of continuous measurements of tidal and nontidal variations of gravity in Boulder, Colorado

We report here on the results of an analysis of 2 years of data from NOAA's superconducting gravimeter located at the Table Mountain Gravity Observatory in Boulder, Colorado. Observed tidal parameters, corrected for ocean loading effects, are compared with theoretical tidal parameters predicted for a non‐hydrostatic inelastic Earth model and demonstrate excellent agreement. Tidal residuals, corrected for polar motion and a linear instrument drift are highly correlated with gravity changes measured by two absolute gravimeters over the same time period. The admittance to local pressure is found to be −0.356 µGal/mbar. However, this admittance factor is found to be seasonally and frequency dependent. Correlations between rainfall events and gravity changes are observed. Attempts to model these gravity changes as exponential functions of time were unsuccessful.

Assessment of prematurely born children at follow-up using a tidal breathing parameter

Prematurely born children frequently have respiratory problems at follow-up. A non-invasive and easily performed lung function test would greatly facilitate their evaluation and appropriate treatment. We have, therefore, assessed whether the shape of the tidal breathing expiratory flow curve would give useful information in such a population. One hundred and twenty traces were randomly selected from plethysmographic measurements of thoracic gas volume and airway resistance made during a follow-up study of a prematurely born population. The children had a median gestational age of 29 (range 23-35, interquartile range 27-31) weeks and postnatal age at the time of measurement of 11 (range 6-24, interquartile range 7-13) months. From the flow and volume signals, the mean time to reach peak tidal expiratory flow as a proportion of the total expiratory time was determined for each child. The median differed significantly between children who, in the neonatal period, had or had not required mechanical ventilation and had or had not had an increased inspired oxygen requirement (p < 0.01), and who were or were not symptomatic at follow-up (p < 0.001). Logistic regression analysis demonstrated that a low ratio was independently associated with symptom status. These results suggest that assessment of a tidal breathing parameter during follow-up of prematurely born children may be useful. As can be measured without sedation, relatively quickly and with simple equipment, potentially large study populations could be investigated, and this technique should now be evaluated in a non-sedated group of young prematurely born children. Keywords: prematurity, lung function measurement, tidal breathing parameters

The use of testate amoebae in studies of sea-level change: a case study from the Taf Estuary, south Wales, UK

Micropalaeontological techniques play an important role in high-resolution studies of sea-level change. Salt-marsh foraminifera are among the most valuable groups of sea-level indicators as their distribution shows a narrow vertical zonation which can be accurately related to former sea level. This paper focuses on testate amoebae (‘thecamoebians’), a closely related group of protozoans which have also been widely reported in salt marshes, but only in low numbers and diversities and only in the size fraction used in foraminiferal analyses (&lt;63 μm). A new preparation technique is described which is based on the analysis of the &lt;63,um fraction using high power light microscopy. This technique is applied to surface sediment samples from a salt marsh in the Taf estuary in south Wales. The results show that small testate amoebae (&lt;63 μm) are much more abundant and diverse in salt-marsh sediments than the larger testate amoebae (&gt;63 μm). Species diversity increases from 2 (&gt;63 prm) to 36 (&lt;63 μm) and the maximum abundance is 65 600 individuals per cm3. The assemblages display a distinct spatial zonation across the marsh surface which appears to be closely related to elevation and to tidal parameters. The surface distribution of the testate amoebae is compared with the distribution of foraminifera and diatoms at the same site. The implications of using &lt;63-μm testate amoebae as a tool for sea-level reconstruction are discussed.

Short‐period fluctuations of the diurnal tide observed with low‐latitude MF and meteor radars during CADRE: Evidence for gravity wave/tidal interactions

MF and meteor radar data from four equatorial and subtropical sites (Hawaii, Christmas Island, Jakarta, and Adelaide) are used to examine diurnal tide amplitude and phase variability at mesosphere and lower thermosphere altitudes. All sites exhibit significant seasonal variability, with the largest amplitude fluctuations occurring at Hawaii and Adelaide. Shorter‐term variability is found to occur primarily on timescales of ∼5 to 30 days. Amplitude and phase fluctuations are well correlated among different sites on occasion, but in general, the amplitude and phase coherences are low and suggest significant local influences on the tidal structures. The temporal behavior of height variations of the diurnal tide amplitude and phase is also examined. Cross correlations and cross spectra of these tidal parameters, especially between the amplitude and phase, are examined closely. The tendency for phase maxima to lead amplitude maxima is consistent with tidal modulation of gravity wave propagation and momentum fluxes, with a corresponding feedback by the gravity wave momentum flux divergences on the observed tidal structures. These results substantially extend previous more limited studies of gravity wave/tidal interactions and provide a statistical basis for the possible importance of this interaction and its influences on the diurnal tidal structure.

Continuous record of the gravity changes at Mt. Vesuvius

High precision relative and absolute gravity measurements are periodically carried out at Mt. Vesuvius (Southern Italy) to monitor the changes in the gravity field caused by the internal dynamics of the volcano. Moreover, a recording gravity station is also operating at the Osservatorio Vesuviano (Old Building) aimed at measuring in continuous mode the time variations of the gravity and the tidal parameters, possibly due to changes in the physical state of the volcano. The analysis carried out on an hourly data set spanning the 1994-1996 time interval and a comparison of the results with those previously obtained, exhibit a change in the tidal parameters which occurred between 1991 and 1994. A gravity decrease of about 60 µGal was observed during the same time interval in the same area. Consistent with relative and absolute gravity observations, no significant variations have been detected since 1994 in the tidal parameters and gravity residuals.

Experiments with a lunar atmospheric tidal model

A lunar tidal model similar to that of Forbes [1982] is used to investigate the effects of changes in background zonal winds on the structure of the lunar tide in the upper atmosphere. It is found that changes in the winds have a greater effect than changes in the background temperature profile with latitude. Observed changes in the structure of the lunar tide from year to year at Saskatoon may be explained by introducing stratospheric warmings into the model. The addition of an associated mesospheric cooling gives an even better fit to the observed phase data. It is also seen that northern hemisphere warmings are predicted to give considerable amplitude changes in southern hemisphere lunar tides. It is expected that much of the difficulty in measuring lunar tides in the upper atmosphere is due to changes in the tidal parameters at these levels brought about by variations in the underlying atmosphere.

Monitored arterial and end-tidal carbon dioxide during in-flight mechanical ventilation

Introduction: Mechanical ventilation with monitored arterial carbon dioxide tension is necessary for optimum pulmonary support and hemodynamic stability. Ongoing monitoring is necessary to ensure adequate ventilation parameters. The prospective study purpose was to (1) compare mechanical ventilation to historic manual ventilation, (2) evaluate the effectiveness of institutional tidal volume parameters, (3) determine the effect of institutional tidal volume manipulation on end-tidal carbon dioxide tension, and (4) explore the relationship between in-flight end-tidal carbon dioxide tension and arterial carbon dioxide tension. Methods: Randomized groups were mechanically ventilated (tidal volume = 12 cc/kg, rate = 14/min) with a target arterial carbon dioxide tension between 30 and 35 torr. Group I was monitored with in-line end-tidal carbon dioxide tension, and group II was monitored with arterial carbon dioxide tension by means of inflight arterial blood gas. Results: Arterial carbon dioxide tension varied less with monitored mechanical than with manual ventilation ( p = 0.001). The gradient between arterial and end-tidal carbon dioxide tension was 5.3 ± 4.4 (mean ± standard deviation [SD]). End-tidal and arterial carbon dioxide tension positively correlated ( r = 0.76, p = 0.001), yet end-tidal carbon dioxide tension accounted for only 58% variation of arterial carbon dioxide tension ( r 2 = 0.58). Conclusion: Mechanical ventilation is more precise but inconsistent in achieving a target arterial carbon dioxide tension with current ventilation parameters. End-tidal carbon dioxide tension is a reasonable estimate of, but cannot exclusively replace, arterial carbon dioxide tension in critically ill patients.

Tidal breathing parameters in the first week of life and subsequent cough and wheeze.

Assessment of tidal breathing parameters may be a useful method of predicting respiratory problems in early childhood. Low values of TPTEF/TE (the ratio of the proportion of time to reach peak tidal expiratory flow to total expiratory time) outside the neonatal period have been significantly related to respiratory tract illness with wheezing in boys in the first year of life. TPTEF/TE measurements in the perinatal period were evaluated in nonsedated infants and the predictive value of this early measurement for subsequent respiratory morbidity during infancy was assessed. Flow during tidal breathing was measured while the infant slept quietly in a plethysmograph using a Fleisch pneumotachograph inserted into an infant face mask. Recruitment continued until traces from 60 infants with 10 consecutive flow curves without artefacts were obtained. In addition, plethysmographic measurements of airway resistance (Raw) and thoracic gas volume (TGV) were measured and specific conductance (sGaw) calculated. Parents recorded their infant's cough and wheeze during the first 12 months of life. Sixty five measurements were made in 60 infants with a mean age of two days and gestational age of 40 weeks. Two observers separately calculated TPTEF/TE ratios on 25 traces randomly selected from the pool of 60. The mean difference between the two observers was -0.004 (limits of agreement 0.048 to -0.056). Thirteen infants became symptomatic (wheeze, with or without cough); their median TPTEF/TE ratio (0.349) was significantly lower than the rest of the cohort (median 0.412) and they also had significantly higher Raw and lower sGaw. The positive predictive value of a low TPTEF/TE ratio, however, was only 41%. These results suggest that the use of this test in the prediction of future respiratory disease in an individual is limited.

Patterns of tidal flow asymmetry on shoreface-connected ridge topography off Spiekeroog Island, German Bight

Asymmetry in spring-neap, flood-ebb, and acceleration-deceleration near-bottom tidal current parameters is assessed on the basis of fair-weather measurements at nineteen locations off Spiekeroog Island, German Bight. The study is aimed at a better understanding of flow-substrate interactions and, by implication, the development of shoreface-conneeted ridges which occur in 8–18 m water depth off the East Frisian coast. The ridges are spaced 1–1.5 km apart, have a relief of 3–5 m, widths of 1–2 km, and flank steepnesses of < 1‡. Flood-current peak-velocity asymmetry on each ridge was found to increase from the trough across the crest towards the seaward flank at both spring and neap tide. Tidal excursion was flood asymmetric at spring tide, but the asymmetry diminished with offshore distance. Flood and ebb accelerating currents had higher mean velocities than the decelerating counterparts at spring tide. The mean velocity of decelerating currents tended to be flood-asymmetric at neap tide. Asymmetry was also noted between flood and ebb current directions, on the one hand, and between spring tide and neap tide cross-ridge flow angle (0–44‡) of these currents, on the other. The observed asymmetries in tidal flow parameters are considered critical to ridge growth and maintenance, and most probably result from a combination of overtides as well as geometric and inertial effects due to the ridge topography.

Determination of ocean tidal parameters from the long-period analysis of the orbit of Starlette

The orbit of Starlette has been determined over a two-year period utilizing satellite laser range data. A novel long-period analysis technique has been used to find the long-term evolution of the orbit due to ocean tides. Ocean tidal parameters have been determined by fitting the changes in the inclination, eccentricity and right ascension of the ascending node by a least-squares method. A simultaneous solution for the ocean tidal parameters has also been found whilst constraining the values to those of the Schwiderski ocean tide model. The results are compared with those for global ocean tide models.

Neutral dynamics of the high latitude E region from EISCAT measurements: a new approach

We have analysed the EISCAT data from two long campaigns, in October 1992 and in January 1993, in order to derive the three components (N-S, E-W, vertical) of the neutral wind in the E region. The winds are derived using the simultaneously measured ion-neutral collision frequency. We calculate the tidal parameters of the measured winds and compare them with models. In addition the CP2 experiment allows us to determine the vertical wind in two independent ways. During the disturbed day of the October campaign we derived a very large vertical wind. Such large values are not reproduced in any model. In this article we discuss the validity of our results.

Investigation of the interaction between variations in atmospheric thermal tides and anomalous ozone concentration

This paper discusses the variations of atmospheric semi-diurnal tidal parameters caused by global ozone anomalies of the Antarctic “ozone hole” type and to establish some regularities of their evolution. The analysis of preliminary data showed that the anomalous decrease of ozone concentration in October at high latitudes of the Southern hemisphere results in a simultaneous abrupt drop of the semi-diurnal tidal amplitude values at high latitudes of the lower thermosphere in the Northern hemisphere. Inasmuch as such an abrupt decrease of amplitude values in the lower thermosphere in October is observed from experimental data since 1953 the authors have set up the hypothesis that the Antarctic “ozone hole” had appeared at least not later than this time period.

Venus' Free Obliquity

The predicted orientation of Venus' rotation axis relative to its orbit can be uniquely determined given knowledge of its J2 gravity coefficient and polar moment of inertia C if its free obliquity is fully damped. This assumption seems warranted given the dominant damping mechanism: turbulent fluid friction at a core mantle boundary (CMB). This skin friction results from differential obliquity of mantle and core spin axes, and the associated damping rate could be as short as 1/10 6 year. However, the observed pole orientation indicates a free obliquity amplitude ϵ ≃ 2.1° compared with a nominal forced amplitude of 0.5°. There are two plausible explanations. The most likely is that the observed obliquity is a tidally evolved end state in which core friction, modulated by CMB ellipticity and core obliquity amplitude, counterbalances solid and atmospheric tidal torques. This concept is similar to the explanation for the retrograde spin to as an end state in which solid and atmospheric thermal tidal torques balance at the present spin rate because of the ω-1 dependence of the axial thermal torque. Large core ellipticity e c ≡ (C c - 1 2 (A c + B c ))/C c (C c ≥ B c ≥ A c are core moments of inertia) can substantially increase fluid friction damping time if e c is significantly larger than the whole body ellipticity e o = J 2 MR 2/ C ≃ 1.3 × 10 -5 by reducing the relative obliquity of core and mantle spin vectors. Note that the hydrostatic contribution to oblateness ∼1.7 × 10 -7 is presently negligible. Weaker effects such as solid and thermal tides can then compete with core friction and for plausible models, their sum tends to increase free obliquity. The obliquity balance is controlled by the nonlinear (and nearly quadratic) dependence of the CMB turbulent "skin friction" torque on obliquity. I find that a steady state is achieved for e c ≃ 29 e o ≃ 4 × 10 -4. If the CMB topography is dynamically supported, then the necessary bottom density anomaly is constrained to the bottom ∼10% of the mantle. An alternative model is that the obliquity results from resonant excitation due to small amplitude (≤0.002°), prograde oscillations in Venus' orbit, one of which happens nearly to match Venus' precession rate σ. This mechanism can account for the obliquity even if the iron core has solidified, but also requires a tectonically quiescent planet ( d| J 2/ dt| < 10 -15 year -1). This model has been explored numerically for a wide range of initial conditions, tidal parameters, temporal J 2 variations, and chaotic wander of the driving frequencies for the orbit. Only four frequencies, in or near the predicted band for σ, have a significant effect and also have a narrow range of effectiveness. I estimate the polar moment to be in the range 0.0341 ≤ ( C/ MR 2) ≤ 0.331 and hence the precession rate σ to be in the range 44.1 ≤ σ ≤ 45.8″ year -1 based on construction of a suite of density profiles in which mantle composition and core size have theoretically limited variations. Comparing resonance widths to the σ uncertainty, I find that the resonance hypothesis has about a 30% chance of being correct. Core ellipticity also has a profound effect on tidal evolution of Venus obliquity. The ratio of turbulent core and solid tidal friction scales like ω -4, implying that core friction "turns on" only as the spin ω approaches its end state. I also find that the semiannual atmospheric tide can have a dramatic effect on evolution, allowing for inversion of spin orientation from prograde to retrograde if the initial obliquity is sufficiently large (≥45°). Potential measurements which have a bearing on these models including precession rate, tidal Love number k 2, and semidiurnal variation in atmospheric pressure at Venus' surface. Perhaps the most useful parameter is k 2, which is detectable from orbit, requires only a modest improvement in the tracking accuracy and spacecraft stability over that provided by Magellan, and is an excellent proxy for core fluidity and if fluid, core size and composition.

A critical assessment of uncalibrated respiratory inductance plethysmography (Respitrace®) for the measurement of tidal breathing parameters in newborns and infants

We have compared results obtained with an uncalibrated respiratory inductance plethysmograph (RIP) with those of a face mask and pneumotachograph (PNT) for the computerized measurement of the time to reach peak tidal expiratory flow as a ratio of total expiratory time (tPTEF:tE). Simultaneous measurements were made in 32 healthy neonates aged 0-3 weeks, 35 healthy infants aged 5-82 weeks, and 28 infants aged 15-94 weeks with physician diagnosed recurrent wheeze. The group mean (+/- SD) values of tPTEF:TE determined using a PNT were 0.455 (+/- 0.129), 0.263 (+/- 0.077), and 0.232 (+/- 0.089) for the neonates, healthy infants and infants with recurrent wheeze respectively. RIP gave mean (+/- SD) values that were 0.055 (+/- 0.044) and 0.025 (+/- 0.104) lower than the PNT in healthy neonates and infants with recurrent wheeze respectively; RIP values were 0.002 (+/- 0.073) higher in the healthy infants over 4 weeks of age than measurements by PNT. Although the difference between the two measurements was not related to the thoracoabdominal phase angle, as measured from Lissajous figures, examination of the RIP ribcage and abdominal signals revealed that many healthy subjects, while appearing clinically in phase, had ribcage and abdominal signals that differed markedly from each other in terms of convexity/concavity during early expiration. This may explain the lack of agreement between the two methods. We conclude that uncalibrated RIP should be used with caution for the determination of tPTEF:tE, even in subjects whose ribcage and abdomen appear to move synchronously. The measurement of tPTEF:tE did not differentiate between the healthy infants and infants with recurrent wheezing.

The wind regime of the mesosphere and lower thermosphere during the DYANA campaign—II. Semi-diurnal tide

Co-ordinated ground-based radar measurements carried out during the 15 January–15 March 1990 DYANA campaign at 14 different geographical sites have provided a good opportunity to investigate the characteristics of semi-diurnal tidal variations in the mesosphere/lower thermosphere over a wide spectrum of space/time scales. It is pointed out that significant differences of monthly mean tidal parameters observed at the various sites may be explained by latitudinal and longitudinal effects. Well-defined 2–3-week oscillations of the tidal parameters are found to be typical of all observational sites. Their estimated space scales do not contradict the hypothesis about a possible coupling between these oscillations and the low wave-number processes in the stratosphere. Tidal parameter oscillations with 2–5-day periods may be explained to be effects of the nonstationary processes with longitudinal wave numbers S > 3.

Analysis of tidal breathing parameters in infancy: how variable is TPTEF:TE?

During recent years there has been increasing interest in the measurement of tidal breathing parameters, such as the time to reach peak tidal expiratory flow as a proportion of total expiratory time (TPTEF:TE), and their application to population-based studies of the determinants of early respiratory morbidity. However, little is known about factors influencing the within and between-subject variability of these parameters. This study examines the influence of sedation on TPTEF:TE, estimates the optimal number of breaths and breath epochs required to measure TPTEF:TE, and assesses short-term repeatability of this parameter during the first year of life, taking account of age-related differences. Measurements were made in 266 healthy infants and young children (1 d to 19 mo old). Mean (SD) TPTEF:TE fell from 0.49 (0.11) in the first 2 wk of life to 0.34 (0.09) by 5 to 8 wk, remaining similar thereafter. Sedation with triclofos sodium (75 mg/kg) had no significant effect on TPTEF:TE, which was 0.33 (0.10) in 23 unsedated 6-wk-old infants and 0.32 (0.08) in 49 sedated infants of similar age and weight (95% CI for the difference: -0.05, 0.04). At least 10 breaths in each of two separate epochs from each infant were required to provide a representative estimate of TPTEF:TE. The mean (SD) difference between repeat measurements made 5 to 108 min apart was 0.02 (0.08) in 34 infants younger than 6 wk of age (95% limits of agreement: -0.15, 0.18) and -0.01 (0.04) (95% limits of agreement -0.09, 0.08) in 30 infants 6 wk and older.(ABSTRACT TRUNCATED AT 250 WORDS)

Global tidal parameters

Global tidal parameters are shown to have recently increased in accuracy, after more than twenty years of LLR and a decade of superconducting gravimetry, whereas the numerical values for the Earth have not changed substantially. Numerical values of Love numbers for terrestrial planets and the moon are also given for degrees higher than four as load numbers are basically linear combinations of Love numbers, at least for spherical non-rotation approximations. Numerical values for planetary moons, as far as they are known, have also been included in the paper. The static and dynamic behaviour of long-period and pole tide is discussed. Inner solid and outer fluid core effects are critically reviewed, also in view of a century of terrestrial tide observations of the classical type. The separation of long-period tides from secular effects (on a rotating Earth) such as Jn (n<5), is considered.

A new data bank for tidal gravity measurements (DB 92)

Tidal gravity parameters are now available in 352 permanent or temporary stations all over the world. Previous tentative interpretations of these data were made on the basis of a data bank created in 1980–1982 which contained all available results without any discrimination which could have appeared as arbitrary. These interpretations were criticized on the basis of the different qualities of instruments (null instruments or not), data, calibration and necessary corrections for ocean-continent interactions. As we agree that a careful re-examination of the basic data is needed before any geophysical discussion, we have built this new data bank which contains only those 211 stations where rigid control of every step in the observations, calibrations and reduction could be made either because the original data are stored in the World Data Center C, or because the published results give enough information to permit checks and revisions. As a result, the scattering in the tidal parameters is reduced by a factor of 2 with respect to the previous data while the mean values of the amplitude factors of the two main waves ( O 1 diurnal; M 2 semi-diurnal) calculated continent by continent, agree with the best available earth model. It is expected that this new data bank will be used for renewed discussions of the results.