Precession Of Equinoxes Research Articles

Resonant obliquity of Mars?

The obliquity of Mars executes large-scale oscillations as a result of spin axis and orbit plane precessions. This motion is an important driver of the climate system and exhibits two dominant periodicities: (i) oscillations driven by the differential spin axis and orbit precession rates during which the obliquity may change by ≳20° over ∼10 5 years and (ii) amplitude modulations over ∼10 6 years due to changes in the orbital inclination. This paper discusses a third time scale for change involving a possible spin-orbit resonance. New work on secular orbit theory implies that Mars may have passed through such a resonance recently. The mechanism typically operates on a 10 7-year time scale and suggests an increase in the average obliquity of Mars of nearly 15° only ∼5 × 10 6 years ago. This could have important implications for the planet's climatic history.

Hagelberg and Doney take Ocean Science Student Honors

The Ocean Sciences Committee has announced the winners of Outstanding Student Paper and Outstanding Student Poster, for presentations given at the AGU held in San Francisco, December 3–7. In the Outstanding Student Paper category, Terri Hagelberg was honored for her examination of new ways of studying paleoclimate time series with high‐order spectral techniques. Scott Doney's results obtained from chlorofluorocarbon measurements made along a zonal hydrographic section extending from Iceland to the equator won the Outstanding Student Poster category.“Nonlinear response of Plio‐Pleistocene ice volume records to orbital forcing: initial results from bispectral analysis” was Hagelberg's paper. A Ph.D. student at Oregon State University, her use of bispectral and cross‐bispectral analysis provided evidence that variations in Pleistocene global ice volume are coupled to oscillations in the calculated record of orbital forcing. A surprising result was that apparent nonlinearity in the climate system may come largely from nonlinear coupling within the radiative forcing (the orbital system driving modulation of eccentricity, axial tilt, and precession of the equinoxes).

A Luni-Solar Precession and Nutation Analysis from Radio Astrometric Observations

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The ZMOA-1990 Nutation Series

AbstractWe present a new nutation series for the Earth (ZMOA-1990) based on (1) the rigid Earth nutation series developed by Zhu and Groten [1989], (2) the normalized response for an elastic, elliptical Earth with fluid-outer and solid-inner cores developed by Mathews et al. [1990], and (3) corrections for the effects of ocean tides and anelasticity, computed to be consistent with the Mathews et al. [1990] normalized response function. In deriving this series, only two parameters of the geophysical model for the Earth have been modified from their values computed with PREM: the dynamic ellipticities of the whole Earth, e, and of the fluid outer core, ef. The adopted values for these parameters, determined from the analysts of very long baseline interferometry (VLSI) data, are e=0.00328915 which is about 1% higher than the value obtained from PREM and 6×10−5 times larger than the IAU adopted value, and ef=0.002665 which is 4.6% higher than the PREM value. The above values were obtained from an adjustment of −0.3 ʺ/cent to the IAU-1976 luni-solar precession constant for e, and from the amplitude of the retrograde annual nutation for ef. The ZMOA-1990 nutation series agrees with estimates of the in-phase and the out-of-phase nutation amplitudes obtained from VLBI data to within 0.5 mas for the terms with 18.6 year period, and to better than 0.1 mas for terms at all other periods except for the out-of-phase terms with annual period (differences 0.39 mas, retrograde, and 0.13 mas, prograde), and for the in-phase term with prograde 13.66 day period (difference −0.25 mas).

Analysis and Synthesis of Catalogues of Extragalactic Radio Sources

AbstractRecent observation catalogues of extragalactic radio sources obtained by Very Long Baseline Interferometry agree in the mean to a few milliarcseconds (mas). Within this range the position differences show constant, linear and periodic offsets. To cast light on these offsets the differences between some of the representative observation catalogues are plotted. Especially, the periodic variations of declination differences of observation catalogues having significantly different epochs are tentatively explained by an uncertainty of the general precession in declination. In terms of the luni-solar precession this uncertainty is estimated to be of the order of −1to −2 mas per year.

On Precession and Nutation Values

AbstractThe results of research on the Earth’s theory of rotation are presented, comparing observed and theoretical values specially for the luni-solar precession and nutation. Investigations of geodynamics show the strong dependence of the nutation values on the adopted model for the structure of the Earth, while the values referring to the precession are not affected as much. The new observational techniques are able to determine some of these values with greater precision than the classical optical techniques, but it is essential that the observations should be done in a systematic and regular way for several decades.

Test of the linearity of quantum mechanics in optically pumped 201Hg.

Measurement of the free precession of nuclear spins in optically pumped ground-state $^{201}\mathrm{Hg}$ atoms has allowed a test of Weinberg's nonlinear generalization of quantum mechanics. Shifts among the three resolved precession frequencies in the spin-3/2 system were studied as a function of the projection of spin polarization along the precession axis. Our results set an upper limit on \ensuremath{\epsilon}, Weinberg's nonlinearity parameter, of \ensuremath{\Vert}\ensuremath{\epsilon}\ensuremath{\Vert}/2\ensuremath{\pi}\ensuremath{\Elzxh}3.8\ensuremath{\mu} Hz, which corresponds to 2.0\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}27}$ of the binding energy per nucleon. This is the most stringent such limit to date.

The rigid body obliquity history of Mars

The primary objective of this study is to explore the range of uncertainty in the obliquity history of Mars associated with the present uncertainty in the axial precession rate. The obliquity, or angular separation between the spin axis and the orbit normal, is the most important parameter for determining the seasonal and latitudinal pattern of insolation. Thus significant variations in obliquity are a likely source of major climatic variations on Mars. The present obliquity is well known, and the torques acting to reorient the spin axis of Mars can be readily calculated for time spans of order 107 years into the past (or future). The primary limitation to reconstructing the obliquity history is uncertainty in the mean moment of inertia of Mars, which governs its response to the applied torques. The range of axial precession rates corresponding to recent theoretical estimates of the moment of inertia is 8.29–8.77 arc sec/yr, but even the most recent observational limits are still much broader: 8–12 arc sec/yr. Nominal estimates of the axial precession rate suggest that resonant amplification of a number of small terms in the orbital inclination series will lead to significant variations in the obliquity of Mars, a behavior much different from the Earth. The major variations are on a 105 year time scale, with significant amplitude modulation on a 106 year time scale. Because of this resonant amplification, estimates of the obliquity history depend very sensitively on assumed values for the axial precession rate. Three different analytic techniques are applied to the obliquity problem. Both linear perturbation analysis and direct numerical integration of the governing differential equations can be used to obtain an obliquity time series, once a model value is selected for the moment of inertia. The linear solution, because of its simplicity, provides useful insight into the amplification of near‐resonant forcing, but fails in the case of exact resonance. The secular orbital theory of Laskar, which is complete to fifth order in eccentricity and inclination, has been used to integrate numerically a suite of 501 different obliquity histories, each spanning the 20‐m.y. interval centered on the present. Each of the computed histories corresponds to a different axial precession rate. Another approach, which utilizes the adiabatic invariance of action variables associated with the spin evolution, gives additional insight into the obliquity behavior expected during passage through resonance but does not yield an actual obliquity time series. On approach to resonance, the amplitude of obliquity oscillations increases dramatically, and on passage through resonance, the mean value about which the oscillations occur changes abruptly. Clearly, passage through a resonance involves either a change in the resonant frequency, which is determined by the internal mass distribution of Mars, or a change in the effective forcing frequency, due either to actual changes in the orbital configurations of the perturbing planets or merely to interference effects among closely spaced forcing frequencies. It has previously been hypothesized that the formation of Tharsis and/or core differentiation may have driven the spin axis precession rate through resonance with one of the orbital inclination eigenfrequencies early in the history of Mars, giving rise to very large obliquity oscillations. A major result of the present analysis is the observation that, within the plausible range of present axial precession rates, a very wide range of obliquity histories are possible, including some which involve resonance passages within the relatively recent past. As a result, obliquities as high as 51.4°, or as low as 0.2°, may have occurred within the last 10‐m.y.

Geodetic constraints on the composition of Mars

The mean density and mean moment of inertia are remotely accessible geodetic parameters which provide two integral constraints on the radial density profile of Mars. The mean density is presently well known, but until the axial precession rate is better determined, the moment of inertia will remain uncertain. Values anywhere in the interval from 0.345 MR2 to 0.365 MR2 can be obtained from the observed gravitational field, depending on how that field is partitioned into hydrostatic and nonhydrostatic components. Even if the moment were accurately known, a considerable degree of nonuniqueness would still remain concerning the density and composition. This nonuniqueness is illustrated by construction of a family of orthogonal polynomials in the normalized radius which make no contribution to either the mean density or the mean inertial moment. If the mean moment is near to the lower end of its plausible range, the nonuniqueness in density and composition is considerably diminished. In order to avoid unrealistically high densities in the deep interior, the Martian mantle must have a density appreciably lower than the terrestrial mantle and must consequently be significantly depleted in iron. On the other hand, if the mean moment is near the upper end of its plausible range, a much broader range of density profiles can be accommodated, including (but not restricted to) iron enriched mantles.

Geometric phase in neutron interferometry

We revisit a recent proposal by Wagh to test the dependence of spinor phase on the orientation of the precession axis. We identify the spinor phase shift originating from the misalignment between π-flippers in the two branches of a neutron interferometer with a geometric phase. We also interpret quantum beats in polarised neutron interferometry observed by Rauch's group as a manifestation of a time-dependent geometric phase shift.

Dependence of the spinor phase on the orientation of the precession axis

We examine the dependence of the phase acquired by a spinor during a precession, on the orientation of the precession axis. We suggest possible neutron interferometric experiments for investigating such a dependence.

Late Pleistocene variability of Arabian Sea summer monsoon winds and continental aridity: Eolian records from the lithogenic component of deep‐sea sediments

The modern Indian Ocean summer monsoon is driven by differential heating between the Asian continent and the Indian Ocean to the south. This differential heating produces a strong pressure gradient which drives southwest monsoon winds during June, July, and August. Satellite and meteorological observations, aerosol measurements, sediment trap studies, and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest Arabian Sea. Analyses of lithogenic grain size and mass accumulation rate (MAR) records from the Owen Ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr. Visual inspection shows that the MAR record is positively correlated with global ice volume as indicated by the marine δ18O record. In contrast, the grain‐size record varies at a much higher frequency, showing little correlation to either the MAR or the δ18O records. Spectral analyses confirm these relationships, indicating that the lithogenic grain‐size and MAR records are coherent only over the precession band whereby the grain size leads the MAR by 124° (∼8 kyr). We conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and MAR with independent eolian records. We use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic MAR as a paleoclimatic indicator of source‐area aridity. These interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength (Globigerina bulloides upwelling record) and aridity (a loess record from central China). Such comparisons indicate high coherence and zero phase relationships. Our work supports the findings of previous studies which have documented the link between monsoon strength and the Earth's axial precession cycles. Both the lithogenic MAR and the grain‐size records have high coherency with precessional insolation. Maximum lithogenic MAR (source‐area aridity) is in phase with δ18O (global ice volume) and leads maximum precessional insolation by 88° (∼6 kyr). We attribute this lead to the influence of glacial conditions on the aridity, and therefore the deflation potential, of the source areas. Maximum lithogenic grain size (summer monsoon wind strength) lags maximum precession by 148° (∼9 kyr). We attribute this lag both to the influence of global and/or local ice volume and to the availability of latent heat from the southern hemisphere Indian Ocean, the two of which combine to determine the strength of the Indian Ocean monsoon.

Corrections to the Luni-Solar Precession From Radio Positions of Extragalactic Objects

In an attempt of a realization of the radio reference frame a compilation catalogue of positions is derived from independent observation catalogues of extragalactic objects the coordinates of which had been determined by means of Very Long Baseline Interferometry. The compilation catalogue comprises 209 objects which are divided into a core consisting of 50 objects having mean positional accuracies of 0.5 milliseconds of arc (mas) and an extension with positional accuracies better than 2 mas. Comparison of this catalogue with an independent compilation catalogue led to confidence limits at the 1 mas level. - The compilation catalogue is supposed to represent a static reference frame of fixed extragalactic points. As the epochs of the contributing observations span nearly 10 years it was tried to interpret the apparent motion of the fixed points recognizable in the observation catalogues as an effect of luni-solar precession. The pilot study points at a reduction of the conventional value of about 2 mas per year.

The Status of the Dirbe Instrument on the COBE

AbstractThe Diffuse Infrared-Background Experiment (DIRBE) on the Cosmic Background Explorer (COBE) satellite is a 10-band absolute photometer covering the wavelengths 1–300 microns using photovoltaic, photoconductive, and bolometric detectors. The input is via a 19-cm, off-axis, highly-baffled Gregorian telescope, with the detectors located at a pupil plane so they share the same field of view (0.7 × 0.7 degrees). The whole assembly is mounted inside a 1.4 K; super-fluid, liquid-He dewar, which is shared with the Far Infrared Absolute Spectrometer (FIRAS) instrument. Each day half of the sky is surveyed, as the line-of-sight of the DIRBE is canted 30 degrees to the COBE spin axis. The whole sky is fully observed in 6 months, as the spin axis precesses at about 1 degree per day. At present each sky pixel has been observed at least once. The basic findings on the general brightness of the sky - Zodiacal light and galaxy - are provided, as well as a synopsis of the advantages and disadvantages associated with a space-borne observatory. The relationship of our experience and findings with respect to possible future missions and their scientific goals is presented.

Ichno-Sedimentological Record of Short-Term Climate-Controlled Redox Events and Cycles in Organic-Rich Strata: ABSTRACT

Reduced rates of biochemical degradation of organic matter in oxygen-depleted marine settings generally result in the accumulation of laminated strata with high hydrocarbon source potential. Periods of improved oxygenation, during which the quantity and quality of organic matter are effectively reduced, are reflected by interbedded bioturbated intervals. Such benthic redox excursions may reflect variable paleooceanographic responses to climatic events or cycles. The potential role of climate in the short-term modulation of source rock potential is exemplified by bioturbated intervals within three predominantly laminated organic-rich units. The Jurassic Posidonia Shale (Germany) contains bioturbated beds whose ichnologic characteristics reflect a spectrum from short, low-magnitude redox events to longer episodes of greater magnitude. The character and distribution of these event beds appear to be controlled by sea level mediated variations in the frequency and intensity of storm-induced basin turnover. Bioturbated beds of the Upper Cretaceous Niobrara Formation (Colorado) are characterized by four oxygen-related ichnocoenoses, the distribution of which reflects cyclic variations in redox conditions. Relationships between paleooxygenation and organic-carbon and carbonate contents, and estimated cycle periodicities, suggest that redox variations were controlled by wet-dry climatic cycles modulated by the Milankovitch cycle of axial precession. Bioturbated beds within slope and basinal facies of themore » Miocene Monterey Formation (California) are variable in character, reflecting differences in duration and magnitude of associated oxygenation episodes, and may be in response to short-term variations in wind-stress-induced upwelling and/or ice-volume-controlled eustatic sea level changes.« less

Lake levels and climate for the last 30,000 years in the fucino area (Abruzzo-Central Italy) — A review

Lake Fucino was in a closed basin that was drained in 1875. A review of published data as well as new geological and geomorphological studies are used to define changes in lake level over the last 30,000 years. The changes are summarized as follows: (1) a general rise of level between 33,000 and 18,000–20,000 yr B.P., (2) a general lowering between 18,000–20,000 and 7500–6500 yr B.P., (3) a rise between 6000-5000 yr B.P., (4) a lowering between 5000-2800 yr B.P., (5) a rise between 2800-2300 yr B.P., (6) lower between 2300-1800 yr B.P., (7) very low levels in the 16th century, and (8) a rise during the 1750–1861 period of the so-called Little Ice Age. Lake level fluctuations are attributed to climatic variations. In particular, there is a clear link between fluctuations and changes in seasonal insolation produced by the orbital parameters of the Earth (precession of the equinoxes and obliquity of the ecliptic) and average annual rainfall. The fluctuations of lake levels do not seem to have been influenced significantly by tectonic movements affecting the Fucino Plain, or by karst drainage pits present along the periphery.

Supplemental satellites and lunisolar precession

Two earth orbiting satellites with the same semimajor axes and eccentricities, but supplemental inclinations, define a direction — the bisector of their nodal lines — which is free from the secular motion due to the oblateness of the earth (Ciufolini 1986). We show that the “inclination” and the “longitude of the node” refer to the direction of the angular momentum of the earth. Because of the lunisolar precession and nutation, the longitude of the bisector so defined changes in a way dependent on the orientation of the angular momentum. If the relativistic Lense-Thirring precession is assumed, its measurement with two “supplemental satellites” will give information about the precessional and nutational constants.

A mathematical representation of the incident solar energy as a function of latitude and time

A simple mathematical representation of the incoming solar radiation as a function of latitude and time is introduced. The expression approximates the total zonally and daily averaged solar energy incident on the earth's surface before any is absorbed. It includes dependence on both the obliquity and the precession of the equinoxes and, within its accuracy limits, the representation is convenient for use in long-term climate modelling.

Numerical integration of precession and nutation of the rigid Earth

A numerical solution for the luni-solar precession and nutation of the rigid Earth is obtained and compared with the result from the analytical theories which are the basis of the current IAU precession and nutation formulas. We have developed a new scheme of numerical calculation by modifying the equations of motion, which enables us to avoid the numerical integration with a small step. Some errors are found in the long periodic region of nutation in the current IAU theory.

Layer-disordered wurtzite (ZnS-2H): diffuse X-ray scattering recorded by c-axis precession photography

A novel type of X-ray diffraction pattern results when a layer-disordered crystal is photographed by X-ray precession using the stacking direction as the precession axis and no layer-line screen. The 10l, 20l, 21l and symmetry-equivalent rows of diffuse scattering of layer-disordered wurtzite (ZnS-2H) are represented by compound loops superimposed on the zero-level hk0 diffraction pattern. Closed loops result because the reciprocal-lattice rows associated with diffuse scattering remain in contact with the sphere of reflection during the precession cycle. Formulae for dimensional parameters of the compound loops of diffuse scattering are derived from the sphere-of-reflection construction.