Changes In Rotation Rate Research Articles

DIFFERENTIAL ROTATION RATE OF X-RAY BRIGHT POINTS AND SOURCE REGION OF THEIR MAGNETIC FIELDS

The differential rotation rate of the solar corona has statistically been estimated from the motion of X-ray bright points (XBPs) that were observed with the Yohkoh soft X-ray telescope and the source region of magnetic fields is discussed from the evaluated rotation rate. The rotation rate of a pair of XBPs in a given latitude band is calculated from the position of an XBP in an X-ray image and that of an arbitrary-chosen XBP in a different X-ray image obtained with a time lag Δt. We have made the histogram of rotation rate from such samples in each latitude band for many X-ray images, and it shows a symmetric distribution that is well fitted by a Voigt function, not a Gaussian function, with a background. The modal rates at various longitudes in a given latitude band become the same value when a height is adopted as a characteristic height of XBPs, and we define the modal value against latitude as the differential rotation rate of XBPs in the present study. The differential rotation rate shows a similar trend as that of photospheric magnetic fields evaluated from the local correlation technique. We find that the differential rotation rate changes with a parameter Δt that is associated with the lifetime of XBPs, and that it becomes smaller in height for shorter Δt with the lower end that approaches to the rotation rate determined from the photospheric Doppler measurements. This trend suggests that magnetic fields associated with XBPs with a short lifetime are rooted just below the surface of the Sun at the top of the convection zone, and that they have a different origin from active regions.

Inner core rotation from event-pair analysis

The last decade has witnessed an animated debate on whether the inner core rotation is a fact or an artifact. Here we examine the temporal change of inner core waves using a technique that compares differential travel times at the same station but between two events. The method does not require precise knowledge of earthquake locations and earth models. The pairing of the events creates a large data set for the application of statistical tools. Using measurements from 87 events in the South Sandwich Islands recorded at College, Alaska station, we conclude the temporal change is robust. The estimates of the temporal change range from about 0.07 to 0.10 s/decade over the past 50 yr. If we used only pairs with small inter-event distances, which reduce the influence of mantle heterogeneity, the rates range from 0.084 to 0.098 s/decade, nearly identical to the rate inferred by Zhang et al. [Zhang, J., Song, X.D., Li, Y.C., Richards, P.G., Sun, X.L., Waldhauser, F., Inner core differential motion confirmed by earthquake waveform doublets, Science 309 (5739) (2005) 1357–1360.] from waveform doublets. The rate of the DF change seems to change with time, which may be explained by lateral variation of the inner core structure or the change in rotation rate on decadal time scale.

The dynamical evolution of uniformly rotating asteroids subject to YORP

A detailed derivation is given of the effect of solar radiation on the rotational dynamics of asteroids, commonly called the YORP effect. The current derivation goes beyond previous discussions published in the literature and provides a comprehensive secular dynamical analysis of the effect of solar radiation torques acting on a uniformly rotating body, and the evolution of its rotation state over time. Our predicted model has the global radiation properties of the asteroid as explicit parameters, and hence can be specified independent of these parameters. The resulting secular equations for the rotation rate and rotation pole are characterized by three parameters of the body's shape and explicitly includes the effect of thermal inertia on the evolution of these rotation state parameters. With this detailed model, in conjunction with estimated asteroid shapes and poles, we compute the expected YORP torques and dynamic response of several asteroids and the change in rotation rate for specific shapes as a function of obliquity. Finally, we define a convenient dimensionless parameter that is only a function of the body geometry and that can be used to characterize the effects of YORP.

Reanalysis of ancient eclipse, astronomic and geodetic data: A possible route to resolving the enigma of global sea-level rise

Predictions of the Earth's response to the ice age appear to simultaneously reconcile a set of astronomical, geodetic and ancient eclipse observations related to changes in rotation, thus ruling out ice melting as a major contributor to 20th century sea-level rise. We demonstrate that the reconciliation disappears when an improved theory of rotational stability is applied. Furthermore, our reanalysis of longer satellite records renders previous estimates of the secular change in rotation rate suspect. The updated ice-age predictions and observations permit an anomalous 20th century ice flux of ∼1 mm/yr equivalent sea-level rise. Thus, the full suite of Earth rotation observations are consistent with a connection between climatic warming and recent melting of ice reservoirs.

The effect of bearing properties on the eigenvalues of a rotordynamic system

Natural frequencies and associated modal damping ratios are important in the diagnosis of rotating machinery problems. This work examines how the modal properties of a rotating shaft/disk system are affected by changes in rotation rate, lubricant viscosity, and bearing clearance. The system under analysis is a uniform, elastic, rotating shaft with a single, rigid disk concentrically mounted to the shaft away from mid-span. The shaft is supported by short-length, plain journal bearings. Standard lubrication theory is used to generate the stiffness and damping matrices for the bearings. The clearance and lubricant viscosity are independently adjustable at each bearing. A Ritz series expansion is used to generate the mass, stiffness, and gyroscopic matrices describing the shaft and disk. The combined action of the bearings and shaft/disk system is represented by stationary and rotational inertia, stiffness, and internal and external damping. A nonsymmetric generalized eigenvalue problem solver is used to calculate system eigenvalues from the system matrices over the speed range of interest. The behavior of the system is quantified in terms of dependence of the real and imaginary parts of system eigenvalues on the rotation rate. The real part of the eigenvalue is proportional to the modal damping ratio, and the imaginary part is the natural frequency. The analysis results include plots of natural frequency and damping ratio versus mode for varying bearing clearance and viscosity.

Numerical general circulation experiments of sensitivity to Earth rotation rate

The ECHAM4 general circulation model was tested for its skill in reproducing the sensitivity of the general circulation to the rotation rate of the Earth. The experiments have been designed to investigate the be- havior of the model under conditions that are not typical of the parametric regime under which the model has been developed. The model was set at spectral T30 res- olution, has 19 vertical levels and it includes a rather complete set of physical parametrizations, seasonal and diurnal cycles, and a mixed layer ocean. The other pa- rameters have been prescribed at present climate values to offer a good comparison with the simulation of the present climate (24 h rotation rates). In particular, the present land-sea mass distribution and mountain ranges have been used. The dynamical response to rotation rate changes was investigated by performing sensitivity ex- periments at fixed rotation rates, from 18 to 360 h, each integrated for 20 years. The latitudinal extent and the strength of the Hadley Cell increased as the rotation rate was decreased, as expected from idealized models and theory. The tropospheric jets underwent a similar evo- lution, moving poleward and modifying their intensity, as the rotation rate was decreased. The winter stationary waves have been found to be very sensitive to the rota- tion rate, turning into longer and longer wavelength quickly as the rotation slowed. The model has been also used to investigate the stability of the general circulation to the variations of the rotation rate. The model was run with a rotation period of 240 h and a direct Hadley Circulation equator to pole was observed. The rotation rate was subsequently increased until baroclinic insta- bilities at midlatitudes appeared. The experiment demonstrated how ECHAM4 handles the unstable character of the eddy-free circulation typical of slow rotations and the transition to turbulent, eddy rich, re- gimes. The overall results indicate that rotation rate changes need to be taken into account when designing paleoclimatic simulations. The good agreement between the results of the simulations and the bounds provided by the dynamical theories of the general circulation en- hances our confidence in the capability of the model to represent the general circulation in different situations from the present climate.

Enhancement of the electrochemical oxidation of formic acid. Effects of anion adsorption and variation of rotation rate

Results are presented from a study on the electrochemical oxidation of formic acid. Perturbing a HCOOH+HClO 4 solution by causing a small amount of any one of several different anions to be present dramatically changes observed nonlinear behavior in an apparently unique manner. Quantitative changes are also observed. In current-control experiments, the presence of fluoroborate ions causes a substantial increase in the value of the applied current density for which low valued stationary potentials remain stable. In potential-control experiments, the current density substantially increases at relevant potential values. Although most properties possessed by the fluoroborate anion exist among the other anions studied, the presence of any one of these other ions in solution yields inferior current–potential characteristics. Results from current-control experiments show that changes in rotation rates have no effect on the observed behavior regardless of anion composition or whether the limiting state is stationary or oscillating.

Vela-size glitch rates in youthful pulsars

have been observed from pulsars aged 10±10 yr, 80 per cent of them come from the youthful pulsars, aged 10±10 yr. For pulsars older than 10 yr, the glitch activity is found to be proportional to the logarithm of the spin-down rate, nC . Based on this relationship, we identify six other pulsars that are most likely to yield frequent large glitches. Since these pulsars are of comparable ages to the Vela pulsar, real-time glitch detection on them and studies of their subsequent recovery would play a vital role in improving understanding of the neutron star interior and the pulsar glitch mechanisms. Key words: methods: statistical ± stars: neutron ± pulsars: general. 1 I N T R O D U C T I O N In addition to a predictable general slow-down in their rotation rate (n ), some pulsars exhibit timing irregularities in the form of glitches or timing noise. A glitch is a spectacular step change in rotation rate, usually accompanied by a change in spin-down rate ( _ n ). While large glitches have a well-defined signature, Dn;D _ n † ˆ 1;2†; microglitches exhibit all possible signatures (Cordes, Downs & Krause-Polstorff 1988). Some of these microglitches have been explained as mere timing noise (e.g. Cordes & Helfand 1980), which is a fairly continuous erratic behaviour in phase, frequency or frequency derivative. In this paper, we have restricted the term glitch to jumps characterized by fractional changes in rotation rate, Dn=n $ 10. It is known that glitches are not due to sudden changes in the external electromagnetic torques on the neutron star, and glitch models are therefore built on changes in the structure of the neutron star or in the distribution and transfer of angular momentum in the neutron star (Alpar 1995). There has been no lack of theories to explain pulsar glitch trigger mechanisms and subsequent postglitch behaviour, as well as timing noise [see D'Alessandro (1996) for a recent review]. Here, our focus is on the `large-glitch' rates of youthful (10± 10 yr) pulsars. In Section 2, we present the glitch magnitudes of all those observed to date. The glitch activity of those pulsars with repeated glitches is used in Section 3 to establish a relationship with observable pulsar parameters. Based on the relationship, we identify pulsars that would make the best targets for frequent observations to detect very large glitches soon after they happen. 2 G L I T C H S I Z E D I S T R I B U T I O N Table 1 shows that 71 glitches have so far been reported in 30 pulsars, representing about 4 per cent of the total pulsar population. About two-thirds of these glitches occur in youthful pulsars, which constitute fewer than half of these 30. The fractional changes in spin-down rate have been measured only in about two-thirds of the reported glitches. The distribution of these jump sizes as a function of age is shown in Fig. 1. Smaller values of Dn /n and D _ n= _ n are seen to be more common in pulsars older than 10 yr. The `Vela-size' jumps Dn=n , 1026† represent about two-fifths of the total glitches in Table 1, the youthful pulsars contributing over 80 per cent of them. None has been reported thus far on very young , 10 yr† pulsars. For all the pulsars for which ages have been determined (unpublished catalogue of Taylor et al. 1995), we also find that nearly 70 per cent of the youthful pulsars have glitched (Fig. 2a). The average number of glitches per pulsar is also highest for this age group (Fig. 2b). No glitch has been observed in radio pulsars older than 10 yr and, out of five pulsars younger than 10 yr, only one (the Crab pulsar) has glitched. The surprisingly low level of glitch activity in these very young pulsars has been attributed to their higher internal temperatures which reduce the importance of pinning, resulting in a relatively smooth transfer of angular momentum to their crusts (McKenna & Lyne 1990). Owing to long inter-observation gaps, fractional changes in spin-down rate are poorly measured, with errors in excess of 200 per cent in some cases (e.g. McKenna & Lyne 1990; Shemar & Lyne 1996). This makes DnC/nC poorly suited to a statistical analysis of glitch behaviour. High-precision values of DnC/nC have

Solar internal rotation rate and the latitudinal variation of the tachocline

A new set of accurately measured frequencies of solar oscillations are used to infer the rotation rate inside the Sun, as a function of radial distance as well as latitude. We have adopted a regularized least squares technique with iterative refinement for both 1.5D inversion using the splitting coefficients and 2D inversion using individual m splittings. The inferred rotation rate agrees well with earlier estimates showing a shear layer just below the surface and another one around the base of the convection zone. The tachocline or the transition layer where the rotation rate changes from differential rotation in the convection zone to almost latitudinally independent rotation rate in the radiative interior is studied in detail. No compelling evidence for any latitudinal variation in position and width of tachocline is found though it appears that the tachocline probably shifts to slightly larger radial distance at higher latitudes and possibly becomes thicker also. However, these variations are within the estimated errors and more accurate data would be needed to make a definitive statement about latitudinal variations.

Seismology of the base of the solar convection zone

The base of the solar convection zone is a region of transition not just for the temperature gradient, but also for the internal rotation of the Sun. The discontinuity in the derivatives of the sound speed at the base of the overshoot layer below the solar convection zone (CZ) introduces a characteristic oscillatory component in the frequencies of solar p modes as a function of the radial order n. The amplitude of this signal can be calibrated using a sequence of solar models constructed with varying extent of overshoot below the CZ base. Using observed solar oscillation frequencies, we find an improved upper limit of 0.05Hp on the extent of overshoot. This technique also allows us to probe the composition profile at the CZ base, and we find that solar models with a sharp change in the composition gradients at the base of the CZ are ruled out from this study. It thus appears that there is some turbulent mixing just below the base of the CZ. The base of the CZ is also the region where the solar rotation rate changes from differential rotation in the CZ to nearly solid-body rotation in the radiative interior. Using modes that have their lower turning points near the transition region, we show that this transition occurs below the CZ base at a radial distance of 0.7050 ± 0.0027 R0 over a half width of 0.0098 ± 0.0026 R0 . We also find an upper limit of 0.3 MG on the toroidal magnetic field concentrated below the CZ base.

Hyperion: Rotation, Shape, and Geology from Voyager Images

Voyager 2 images have been used to measure the instantaneous rotation state of Hyperion during the period of the spacecraft's 1981 flyby of Saturn, to define the satellite's shape, and to map geological features. For the 38 hr of image coverage at resolutions better than 17 km/pixel, control point calculations yield a rotation rate of 72°/day, with a pole direction of RA = 226 ± 4°, Dec = 35 ± 4°. Rotation was essentially about the long axis of Hyperion. A shape model with 5° × 5° spacing is developed using stereo, limb, and terminator data. About 95% of the surface of Hyperion is constrained within 20 km by the control point and lower resolution images. An ellipsoidal fit to this model gives principal axes (radii) of 164, 130, and 107 km. The shape model has a mean radius of 133 ± 8 km; the model moments of inertia (I/MR 2) are A = 0.32 ± 0.02, B = 0.46 ± 0.02, and C = 0.52 ± 0.02. G. J. Black et al . (1995, Icarus) have used the shape model and the instantaneous rotation state to calculate the expected rotation of Hyperion throughout the Voyager 2 encounter. They predict significant changes in the rotation pole orientation, but only minor changes in rotation rate during the 18 days of low-resolution, disk-resolved imaging of Hyperion. We compare the Voyager-observed lightcurve of Hyperion to lightcurves predicted from the dynamical model. During this 18-day period the dynamical model matches the observed lightcurve very well; the best lightcurve fit is for a rotation rate of 72 + 3 - 4°/day (identical to the control point solution) at the time of the first of the high-resolution images. Much of the Hyperion lightcurve amplitude derives from wobble rather than from the spin. The good agreement of the dynamical model with observed behavior suggests that Hyperion's moments of inertia are well modeled by the shape and that it has no substantial internal density contrasts. The overall shape of Hyperion is typical for icy objects smaller than 200 km mean radius. Small icy satellites appear to have less structural control of their shapes than do rocky satellites and asteroids. A 300-km-long arcuate scarp and a more subdued, nearly parallel scarp suggest spallation of several kilometers of material from nearly 1/4 the area of the satellite due to the formation of a 140-km-diameter crater.

Fluctuations in rotation rate of the flagellar motor of Escherichia coli

The purpose of this work was to study the changes in rotation rate of the bacterial motor and to try to discriminate between various sources of these changes with the aim of understanding the mechanism of force generation better. To this end Escherichia coli cells were tethered and videotaped with brief stroboscopic light flashes. The records were scanned by means of a computerized motion analysis system, yielding cell size, radius of rotation, and accumulated angle of rotation as functions of time for each cell selected. In conformity with previous studies, fluctuations in the rotation rate of the flagellar motor were invariably found. Employing an exclusively counterclockwise rotating mutant ("gutted" RP1091 strain) and using power spectral density, autocorrelation and residual mean square angle analysis, we found that a simple superposition of rotational diffusion on a steady rotary motion is insufficient to describe the observed rotation. We observed two additional rotational components, one fluctuating (0.04-0.6 s) and one oscillating (0.8-7 s). However, the effective rotational diffusion coefficient obtained after taking these two components into account generally exceeded that calculated from external friction by two orders of magnitude. This is consistent with a model incorporating association and dissociation of force-generating units.

Ulysses observations of latitude gradients in the heliospheric magnetic field

Several parameters measured by Ulysses as it traveled southward to heliographic latitudes of −50° are presented and analyzed. The radial component of the magnetic field, averaged over 5° latitude increments and extrapolated back to 1 AU, is found to agree with baseline measurements provided by IMP-8. There is little, if any, evidence of a latitude gradient, a result consistent with the dominance of the magnetic field associated with the heliospheric current sheet and with recent models which include the effect of the current sheet as well as of source surface fields. Thus far, the spiral angle agrees with the Parker spiral assuming a rate of rotation of the field lines at the Sun equal to the equatorial value. No evidence is seen of either a change in rotation rate with latitude or an unwinding of the spiral as suggested by a recent analysis. Hourly variances in the field magnitude and in the sum of the variances in the components, normalized to the square of the observed field strength, show the former to be independent of latitude while the latter shows a strong increase with latitude. These two observations are shown to be associated with Alfvén waves that are continuously present at high latitudes. The waves have large amplitudes, extend to long periods, and have important implications for galactic cosmic rays and the solar wind.

Porphyrin [2]catenanes—dynamic control through protonation

Protonation of the previously reported porphyrin [2]catenanes in strongly acidic solutions results in electrostatic repulsion of their two components, and conformational reorientations and changes in rotation rates, which are dependent on the structural flexibility of the molecules.

Some effects of rotation rate on planetary-scale wave flows

A series of experiments were performed in a rotating annulus of fluid to study effects of rotation rate on planetary-scale baroclinic wave flows. The experiments reveal that change in rotation rate of fluid container causes variation in Rossby number and Taylor number in flows and leads to change in flow patterns and in phase and amplitude of quasi-stationary waves. For instance, with increasing rotation rate, amplitude of quasi-stationary waves increases and phase shifts upstream. On the contrary, with decreasing rotation rate, amplitude of quasi-stationary waves decreases and phase shifts downstream. In the case of the earth’s atmosphere, although magnitude of variation in earth’s rotation rate is very small, yet it causes a very big change in zonal velocity component of wind in the atmosphere and of currents in the ocean, and therefore causes a remarkable change in Rossby number and Taylor number determining regimes in planetary-scale geophysical flows. The observation reveals that intensity and geographic location of subtropic anticyclones in both of the Northern and Southern Hemispheres change consistently with the variation in earth’s rotation rate. The results of fluid experiments are consistent, qualitatively, with observed phenomena in the atmospheric circulation.

Precambrian climate: The effects of land area and Earth's rotation rate

Rotation rate and land area have changed significantly over the Earth's history. The associated climate changes are examined with a general circulation model (GCM) and compared with the current climate state. Unlike previous GCM studies, clouds in the model interact with the radiation field. We show that rotation rate changes can affect mean air temperatures by strongly affecting the cloud field. For example, an Earth day length of 14 hours causes the global mean cloud fraction to decrease 20%. There are also large changes in the wind field; indeed, at some mid‐latitudes the time‐averaged surface wind changes from westerlies to easterlies. If the land masses are removed from the model and with present‐day rotation, the global mean air temperature is 4 K higher than for the present‐day simulation; if in addition the day length is 14 hours, the global mean air temperature is 5.5 K. Thus the early atmosphere may not have contained the very large concentrations of CO2 thought to be necessary to prevent a frozen planet higher.

An examination of the change in the earth's rotation rate from ancient Chinese observations of lunar occultations of the planets

view Abstract Citations (4) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Examination of the Change in the Earth's Rotation Rate From Ancient Chinese Observations of Lunar Occultations of the Planets Hilton, James L. ; Seidelmann, P. K. ; Liu, Ciyuan Abstract Fifty-eight records of naked-eye observations of occultations of the planets by the moon chosen from the Chinese dynastic histories are studied. These records cover the period from 68 B.C. to 575 A.D. The observations are compared to topocentric ephemerides computed using Bretagnon's planetary theories VSOP82 and the Chapront-Touze lunar theory ELP2000-85. Overall, the check on the change in the rotation rate is very weak, but it represents the limit of what can be done with known, untimed occultation records. Publication: The Astronomical Journal Pub Date: December 1992 DOI: 10.1086/116401 Bibcode: 1992AJ....104.2250H Keywords: Earth Rotation; Lunar Occultation; Solar System; Acceleration (Physics); China; Planet Ephemerides; Astronomy; EARTH; ECLIPSES; TIME full text sources ADS |

Physics in Strong Magnetic Fields Near Neutron Stars

Electromagnetic phenomena occurring in the strong magnetic fields of neutron stars are currently of great interest in high-energy astrophysics. Observations of rotation rate changes and cyclotron lines in pulsars and gamma-ray bursts indicate that surface magnetic fields of neutron stars often exceed 10(12) gauss. In fields this strong, where electrons behave much as if they were in bound atomic states, familiar processes undergo profound changes, and exotic processes become important. Strong magnetic fields affect the physics in several fundamental ways: Energies perpendicular to the field are quantized, transverse momentum is not conserved, and electron-positron spin is important. Neutron stars therefore provide a unique laboratory for the study of physics in extremely high fields that cannot be generated on Earth.

Solar-cycle dependence of the Sun's deep internal rotation shown by helioseismology

HELIOSEISMOLOGY, the study of solar oscillations, yields information on the Sun's internal rotation and magnetism which is of great importance in understanding the 22-year solar cycle. We show here that helioseismic data suggest that the Sun's internal rotation rate, at depths greater than half the solar radius, has changed systematically during the most recent cycle. There is no variation, however, in the rotation over a range of intermediate solar radii covering the upper part of the Sun's radiative interior and the lower part of the convective zone; this intermediate region is where, according to the same helioseismic data, an abrupt change in rotation rate with depth accompanies the transition from convective to radiative structure. We suggest that the modulation of the rotation rate in the Sun's interior could be caused by a torsional oscillation, provided that a poloidal magnetic field of kilogauss strength exists in the radiative interior.

The global tracking networks for crustal dynamics

Highly accurate Satellite Laser Ranging (SLR) and Very-Long-Baseline Interferometry (VLBI) have been implemented by the NASA Crustal Dynamics Project and many cooperating groups in many countries to form global SLR and VLBI networks for geodetic measurements of global plate motion, plate deformation, regional deformations in areas of high earthquake activity, and accurate measurements of the Earth's polar motion and changes in rotation rate. These systems are measuring vector baselines between stations to an accuracy of 2–5 cm. New improvements being implemented will improve the accuracy to about 1 cm.