SUMMARYThe Earth’s rotation exhibits periodic variations as a result of gravitational torques exe... more SUMMARYThe Earth’s rotation exhibits periodic variations as a result of gravitational torques exerted by the Sun and the Moon and of angular momentum exchange of the solid Earth with the Earth’s atmosphere and hydrosphere. Here, we aim at determining the complementary effect of the deep interior on variations in the length-of-day (LOD) and focus on the influence of topography at the core–mantle boundary (CMB). For this purpose, we have developed an analytical approach for solving the Navier–Stokes equation for global rotational motions and inertial waves, based on and extending the approach of Wu & Wahr (1997). An advantage of the analytical approach is that it allows to identify the frequencies and topographic spherical harmonics degrees and orders where resonance can happen, as well as to quantify the total amplifications in the tidal effects on LOD variations. Although the resonances are found to be sometimes quite near tidal frequencies, we show that they are not sufficiently cl...
NEA's constitute a potential threat of collisions with the Earth in the future and in consequ... more NEA's constitute a potential threat of collisions with the Earth in the future and in consequence their study is fundamental. One of the most impressive phenomena related to these objects in the next decades is the close encounter of (99942) Apophis on April 13, 2029. This asteroid, with a diameter estimated at approximatively 300m, will approach the Earth at a distance of roughly 38 300 km from our planet. In this paper we present at first a detailed study of the orbital characteristics of Apophis and their changes during the 2029 encounter. Then we calculate the dramatic rotational effects undergone by the asteroid during the close encounter, depending on a few physical and geometrical parameters.
Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determin... more Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determine directly the celestial pole offsets (CPO). In this paper, we make use of the CPO derived from global VLBI solutions to estimate empirical corrections to the main lunisolar nutation terms included in the IAU 2006/2000A precession–nutation model. In particular, we pay attention to two factors that affect the estimation of such corrections: the celestial reference frame used in the production of the global VLBI solutions and the stochastic model employed in the least-squares adjustment of the corrections. In both cases, we have found that the choice of these aspects has an effect of a few μas in the estimated corrections.
This paper presents recent advances in Earth Orientation Parameters (EOP) determination and in th... more This paper presents recent advances in Earth Orientation Parameters (EOP) determination and in their modeling. These advances are related to the increase of the precision of the observation and the implementation of dedicated strategies to better obtain them. The advances are also related to the determination of Earth geophysical parameters from VLBI observations and better modeling of the phenomena within the Earth. Further improvement in the observation precision enhances our understanding of the interior of the Earth. In particular, we examine the coupling mechanisms at the core-mantle boundary: the electromagnetic coupling, the topographic coupling, and the viscous coupling. We also present future developments necessary for a better understanding of the Earth’s interior and its orientation parameters.
Very Long Baseline Interferometry (VLBI) is the only space geodesy technique that can directly ob... more Very Long Baseline Interferometry (VLBI) is the only space geodesy technique that can directly observe the celestial pole offsets. These values are time-dependent corrections to the IAU200A/2006 precession-nutation model that are estimated by different VLBI analysis centres. The celestial pole offsets, together with the rest of Earth Orientation Parameters (EOP) are combined by the IERS and disseminated in official series.
SUMMARYThe Earth’s rotation exhibits periodic variations as a result of gravitational torques exe... more SUMMARYThe Earth’s rotation exhibits periodic variations as a result of gravitational torques exerted by the Sun and the Moon and of angular momentum exchange of the solid Earth with the Earth’s atmosphere and hydrosphere. Here, we aim at determining the complementary effect of the deep interior on variations in the length-of-day (LOD) and focus on the influence of topography at the core–mantle boundary (CMB). For this purpose, we have developed an analytical approach for solving the Navier–Stokes equation for global rotational motions and inertial waves, based on and extending the approach of Wu & Wahr (1997). An advantage of the analytical approach is that it allows to identify the frequencies and topographic spherical harmonics degrees and orders where resonance can happen, as well as to quantify the total amplifications in the tidal effects on LOD variations. Although the resonances are found to be sometimes quite near tidal frequencies, we show that they are not sufficiently cl...
NEA's constitute a potential threat of collisions with the Earth in the future and in consequ... more NEA's constitute a potential threat of collisions with the Earth in the future and in consequence their study is fundamental. One of the most impressive phenomena related to these objects in the next decades is the close encounter of (99942) Apophis on April 13, 2029. This asteroid, with a diameter estimated at approximatively 300m, will approach the Earth at a distance of roughly 38 300 km from our planet. In this paper we present at first a detailed study of the orbital characteristics of Apophis and their changes during the 2029 encounter. Then we calculate the dramatic rotational effects undergone by the asteroid during the close encounter, depending on a few physical and geometrical parameters.
Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determin... more Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determine directly the celestial pole offsets (CPO). In this paper, we make use of the CPO derived from global VLBI solutions to estimate empirical corrections to the main lunisolar nutation terms included in the IAU 2006/2000A precession–nutation model. In particular, we pay attention to two factors that affect the estimation of such corrections: the celestial reference frame used in the production of the global VLBI solutions and the stochastic model employed in the least-squares adjustment of the corrections. In both cases, we have found that the choice of these aspects has an effect of a few μas in the estimated corrections.
This paper presents recent advances in Earth Orientation Parameters (EOP) determination and in th... more This paper presents recent advances in Earth Orientation Parameters (EOP) determination and in their modeling. These advances are related to the increase of the precision of the observation and the implementation of dedicated strategies to better obtain them. The advances are also related to the determination of Earth geophysical parameters from VLBI observations and better modeling of the phenomena within the Earth. Further improvement in the observation precision enhances our understanding of the interior of the Earth. In particular, we examine the coupling mechanisms at the core-mantle boundary: the electromagnetic coupling, the topographic coupling, and the viscous coupling. We also present future developments necessary for a better understanding of the Earth’s interior and its orientation parameters.
Very Long Baseline Interferometry (VLBI) is the only space geodesy technique that can directly ob... more Very Long Baseline Interferometry (VLBI) is the only space geodesy technique that can directly observe the celestial pole offsets. These values are time-dependent corrections to the IAU200A/2006 precession-nutation model that are estimated by different VLBI analysis centres. The celestial pole offsets, together with the rest of Earth Orientation Parameters (EOP) are combined by the IERS and disseminated in official series.
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Papers by Marta Folgueira