Effects Of Mass Redistribution Research Articles

Secular changes in length of day: Effect of the mass redistribution

In this paper the secular change in the length of day due to mass redistribution effects is revisited using the Hamiltonian formalism of the Earth rotation theories. The framework is a two-layer deformable Earth model including dissipative effects at the core–mantle boundary, which are described through a coupling torque formulated by means of generalized forces. The theoretical development leads to the introduction of an effective time-averaged polar inertia moment, which allows us to quantify the level of core–mantle coupling throughout the secular evolution of the Earth. Taking advantage of the canonical procedure, we obtain a closed analytical formula for the secular deceleration of the rotation rate, numerical evaluation of which is performed using frequency-dependent Love numbers corresponding to solid and oceanic tides. With this Earth modeling, under the widespread assumption of totally coupled core and mantle layers in the long term response, a secular angular acceleration of − 1328.6′′ cy−2 is obtained, which is equivalent to an increase of 2.418 ms cy−1 in the length of day. The ocean tides and the semidiurnal band of the mass-redistribution-perturbing potential, mostly induced by the Moon, constitute the main part of this deceleration. This estimate is shown to be in very good agreement with recent observational values, and with other theoretical predictions including comparable modeling features.

Dynamic scaling behavior of mica ripples produced by low energy Ar+ ion erosion

The scaling behavior of ion beam induced ripple patterns on mica surface is investigated by means of atomic force microscopy (AFM). The ripples were produced by 12 keV Ar+ ion beam erosion at an angle 60° with respect to the surface normal. Ripple wave-vectors are found to align parallel to the ion beam projection direction. The root-mean-square (rms) roughness and lateral correlation length of the rippled surface are observed to increase with ion fluence with a growth exponent β = 0.51 ± 0.04 and dynamic exponent 1/zx = 0.42 ± 0.07 along the ripple direction as well as 1/zy = 0.34 ± 0.09 normal to the ripple direction respectively. Ripple wavelength is also found to increase slowly with ion fluence upto ϕ ∼ 6 × 1017 ions.cm−2 and then shows a rapid coarsening behavior with an exponent n = 0.43 ± 0.04. The two different roughness exponents, αx and αy, along and normal to the ripple direction, are also calculated from their corresponding power spectral density function and found the values 1.25 ± 0.09 and 1.20 ± 0.08 respectively. The scaling properties of ripple growth for long time ion bombardment and the overall morphological changes are explored according to calculated erosive and redistribution coefficients in the framework of recently advanced continuum models of pattern formation by ion beam sputtering. The production of ripples is found to be driven by mass-redistribution effects rather than curvature dependent sputter erosion. This is an worth addition to the understanding of ion beam nanopatterning process as it ascertains mass redistribution as indispensable phenomena for pattern formation not only for ion energies less than 1 keV but also for ion irradiation of energy range 10 keV and above.

Changes in ice-shelf buttressing following the collapse of Larsen A Ice Shelf, Antarctica, and the resulting impact on tributaries

ABSTRACTThe dominant mass-loss process on the Antarctic Peninsula has been ice-shelf collapse, including the Larsen A Ice Shelf in early 1995. Following this collapse, there was rapid speed up and thinning of its tributary glaciers. We model the impact of this ice-shelf collapse on upstream tributaries, and compare with observations using new datasets of surface velocity and ice thickness. Using a two-horizontal-dimension shallow shelf approximation model, we are able to replicate the observed large increase in surface velocity that occurred within Drygalski Glacier, Antarctic Peninsula. The model results show an instantaneous twofold increase in flux across the grounding line, caused solely from the reduction in backstress through ice shelf removal. This demonstrates the importance of ice-shelf buttressing for flow upstream of the grounding line and highlights the need to explicitly include lateral stresses when modelling real-world settings. We hypothesise that further increases in velocity and flux observed since the ice-shelf collapse result from transient mass redistribution effects. Reproducing these effects poses the next, more stringent test of glacier and ice-sheet modelling studies.

An assessment of degree-2 Stokes coefficients from Earth rotation data

SUMMARY Variations in the degree-2 Stokes coefficients C20, C21 and S21 can be used to understand longandshort-termclimateforcing.Herewederivechangesinthesecoefficientsfortheperiod2003 January–2012 April using Earth rotation data. Earth rotation data contain contributions from motion terms (the effects of winds and currents) and contributions from the effects of mass redistribution. We remove the effects of tides, atmospheric winds and oceanic currents from our data. We compare two different models of atmospheric and oceanic angular momentum for removing the effects of winds and currents: (1) using products from the National Centers for Environmental Prediction and (2) using data from the European Centre for Medium-range Weather Forecasts (ECMWF). We assess the quality of these motion models by comparing the two resulting sets of degree-2 Stokes coefficients to independent degree-2 estimates from satellite laser ranging (SLR), GRACE and a geophysical loading model. We find a good agreementbetweenthecoefficientsfromEarthrotationandthecoefficientsfromothersources. Ingeneral,theagreementisbetterforthecoefficientsweobtainbyremovingwindsandcurrents effectsusingtheECMWFmodel.Inthiscase,wefindhighercorrelationswiththeindependent

The impact of Greenland melt on local sea levels: a partially coupled analysis of dynamic and static equilibrium effects in idealized water-hosing experiments

Local sea level can deviate from mean global sea level because of both dynamic sea level (DSL) effects, resulting from oceanic and atmospheric circulation and temperature and salinity distributions, and changes in the static equilibrium (SE) sea level configuration, produced by the gravitational, elastic, and rotational effects of mass redistribution. Both effects will contribute to future sea level change. To compare their magnitude, we simulated the effects of Greenland Ice Sheet (GIS) melt by conducting idealized North Atlantic “water-hosing” experiments in a climate model unidirectionally coupled to a SE sea level model. At current rates of GIS melt, we find that geographic SE patterns should be challenging but possible to detect above dynamic variability. At higher melt rates, we find that DSL trends are strongest in the western North Atlantic, while SE effects will dominate in most of the ocean when melt exceeds ~20 cm equivalent sea level.

Simultaneous inversion of deformation and gravity changes in a horizontally layered half-space: Evidences for magma intrusion during the 1982–1984 unrest at Campi Flegrei caldera (Italy)

A very large uplift (about 1.8 m) occurred in the period 1982–1984 at Campi Flegrei caldera, Italy, without culminating in an eruption. A still-standing controversy accompanies the interpretation of deformation and gravity changes recorded during the unrest, which were interpreted to result from the sub-surface magmatic reservoir by some authors and from the hydrothermal system or hybrid sources by others. Here for the first time we take into account crustal layering while inverting leveling, EDM, and gravity data using uniformly-pressurized sources, namely small vertical spheroids and finite horizontal penny-shaped sources. The weight of EDM data in the misfit function is chosen from a trade-off curve in order to balance the compromise between fitting the leveling and the EDM data well. Models using a homogeneous medium cannot give a good simultaneous fit to leveling and EDM deformation data of the 1982–1984 unrest, whereas incorporating a layered structure (determined from seismically derived estimates of the P wave speed for the crust, and not adjusted to improve the fit in any of the inversions) allows a significantly better fit. Also, layering affects the sub-surface mass redistribution effects on gravity changes, and we show that the retrieved intrusion density is in full agreement with densities for highly evolved magmas expected at the Campi Flegrei caldera for depths of 3 to 4 km, ruling out hydrothermal fluids as the primary cause of the 1982–1984 unrest. The source of the 1982–1984 CF unrest was probably a shallow (about 3-km deep) penny-shaped magma intrusion fed by a deeper magma chamber; source overpressure was few MPa.

Effects of crustal layering on the inversion of deformation and gravity data in volcanic areas: An application to the Campi Flegrei caldera, Italy

We study the effects of crustal layering on ground displacements and gravity changes due to a spheroidal expanding source. Soft superficial layers affect the deformation pattern (giving an apparent shallower source if layering is not taken into account), the ratio of horizontal to vertical displacements (biasing the source shape), and the subsurface mass redistribution effects on gravity changes. Retrieved intrusion density is biased toward very low values if the source is modelled as a penny‐shaped crack (point and finite) in a homogeneous half‐space and the resulting density misestimate can lead to a possibly incorrect assessment of volcanic hazard. As an application, we consider the 1982–1984 Campi Flegrei unrest. We show that the large discrepancy between densities of spherical and penny‐shaped sources, given in the literature and obtained inverting ground displacement and gravity data in a homogeneous half‐space, is at least partially a consequence of the homogeneous half‐space assumption.

Seasonal air and water mass redistribution effects on [the geodetic satellites] LAGEOS and Starlette : Gutierrez, Roberto and C.R. Wilson, 1987. Geophys. Res. Letts, 14(9):929–932. Center for Space Res., Univ. of Texas, Austin, TX 78759, USA

Seasonal air and water mass redistribution effects on [the geodetic satellites] LAGEOS and Starlette : Gutierrez, Roberto and C.R. Wilson, 1987. Geophys. Res. Letts, 14(9):929–932. Center for Space Res., Univ. of Texas, Austin, TX 78759, USA

Seasonal air and water mass redistribution effects on LAGEOS and Starlette

We computed zonal geopotential coefficients from average seasonal variations in global air and water mass distribution. These coefficients are used to predict the seasonal variations of LAGEOS' and Starlette's orbital node, δΩ, and the seasonal δJ3 for Starlette. A comparison of these predictions with the observed values indicates that air pressure and, to a lesser extent, water storage may be responsible for a large portion of the currently unmodeled variation in the earth's gravity field.

Observation of Rayleigh-Taylor-like Structures in a Laser-Accelerated Foil

The development of the Rayleigh-Taylor hydrodynamic instability was studied in laser-accelerated targets by introduction of mass thickness variations in foil targets. Observations made by side-on flash x radiography showed target structures and mass redistribution effects which resemble Rayleigh-Taylor bubbles and spikes, including not only advanced broadening of the spike tips on the laser-irradiated side of the foil but also projections of mass on the unirradiated side. The observations compare well with numerical simulations.

Rotational motion of a free body induced by mass redistribution

The effects of mass redistribution on the rotational motion of a free body, initially rotating uniformly about its axis of maximum moment of inertia, are studied using a simple three-body model composed of two points masses and a triaxial rigid body. An exact analytical solution for the motion of the original spin axis after redistribution of the masses is developed from the classical solution for the rotational motion of a free triaxial rigid body. Yhis motion in interpreted geometrically using the reciprocal inertia ellipsoid of the redistributed system and the angular momentum integral. Application of simple mass redistribution to the problem of spacecraft attitude control is discussed and results for a particular system are presented. T is a well-known fact1 that for a free, triaxial, rigid body, the condition of uniform rotation about its axis of in- termediate, principal moment of inertia is unstable. This in- stability manifests itself when small disturbances in the angular velocity components about the other principal axes occur; for then, the once-stationary axis of intermediate moment of inertia performs large-angle motions with respect to a nonrotating reference frame. Recently, Beachley and Dicker2 and Beachley,3 have suggested that this characteristic of rigid body rotational motion might be used to advantage to a spinning spacecraft in the sense that predictable large-angle motions of an axis fixed in the spacecraft might be induced by changing the mass distribution of the spacecraft.% A control system based on this idea might be more economical than a mass expulsion system which would rotate the angular momentum vector of the spacecraft. Changes in the mass distribution of the spacecraft may be accomplished by internal motion of control masses. The ef- fects of such internal mass motion on the rotational motion of a free system of bodies have been studied by several authors and a review of some of the work in this area is given by Lorell and Lange,5 who propose an automatic mass-trim system for spinning spacecraft which utilizes movable control masses. The primary purpose of this paper is not to study the effects of internal mass motion on the rotational motion of a free system of bodies, although these effects cannot be ignored en- tirely and will be considered. Our main goal is to obtain an analytical description of the spacecraft's rotational motion af- ter a redistribution of mass has occurred. Such a description has previously been obtained only in a limited way by numerical integration.3 We shall also provide geometrical in- terpretation of the analytical results and consider the use of simple mass redistribution as a means for spacecraft attitude control. In this paper we shall consider a system similar to those discussed in Ref. 3 and employ some results from the classical theory for the rotational motion of a free, triaxial, rigid body.