On High Frequency Polar Motion and Length of Day Variations

AbstractThe 0.042-day Earth rotation data (diurnal and semidiurnal) computed by the International GPS Service were used to analyze the daily/sub-daily variations of polar motion (PM) and length of day (LOD). Systematic and advanced spectral analytical investigations of the degree of periodic variability have been carried out. They show that the prominent periodical components can be found at the tidal frequencies of zonal, tesseral and sectorial waves. These investigations should give better insight into the physical processes, which influence Earth orientation (i.e. due to the atmospheric and oceanic motions, tidal forces etc.). It should be the basis for the detailed modeling of excitation functions in the sub-diurnal range of the high-frequency spectrum.

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Atmospheric Effects on Earth Rotation and Polar Motion

Symposium - International Astronomical Union ◽

10.1017/s0074180900135107 ◽

1988 ◽

Vol 129 ◽

pp. 401-410

Author(s):

David A. Salstein

Keyword(s):

Time Scales ◽

Earth Rotation ◽

Polar Motion ◽

Atmospheric Effects ◽

Length Of Day ◽

Wind Fields ◽

Wind Variability ◽

Body Tides ◽

Wind Distribution

The variability in the earth's rotation rate not due to known solid body tides is dominated on time scales of about four years and less by variations in global atmospheric angular momentum (M), as derived from the zonal wind distribution. Among features seen in the length of day (Δl.o.d.) record produced by atmospheric forcing are the strong seasonal cycle, quasi-periodic fluctuations around 40–50 days, and an interannual signal forced by a strong Pacific warming event, known as the El Niño. Momentum variations associated with these time scales arise in different latitudinal regions. Furthermore, winds in the stratosphere make a particularly important contribution to seasonal variability.Other related topics discussed here are (i) comparisons of the M series from wind fields produced at different weather centers, (ii) the torques that dynamically link the atmosphere and earth, and (iii) longer-term non-atmospheric effects that can be seen upon removal of the atmospheric signal. An interesting application for climatological purposes is the use of historical earth rotation series as a proxy for atmospheric wind variability prior to the era of upper-air data. Lastly, results pertaining to the role of atmospheric pressure systems in exciting rapid polar motion are presented.

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IGS Combined and Contributed Earth Rotation Parameter Solutions

International Astronomical Union Colloquium ◽

10.1017/s0252921100061418 ◽

2000 ◽

Vol 178 ◽

pp. 277-302

Author(s):

Jan Kouba ◽

Gerhard Beutler ◽

Markus Rothacher

Keyword(s):

Angular Momentum ◽

Earth Rotation ◽

Polar Motion ◽

Rotation Parameter ◽

Atmospheric Angular Momentum ◽

Length Of Day ◽

Earth Rotation Parameter ◽

Average Correlation ◽

Precision Level

AbstractSince January 1995 the International GPS Service (IGS) has been combining and analyzing daily polar motion (PM) series, produced and submitted by seven IGS analysis centers (ACs) for the IGS Final orbit/clock combinations. Since June 30, 1996 the IGS Earth Rotation Parameter (ERP) series that accompany the IGS combined orbits, also include combined PM rates. Furthermore, since March 1997, the IGS LOD (Length of Day) solutions are based on separate combinations of AC LOD solutions calibrated and weighted according to the IERS Bulletin A definite values. Similar to AC orbit solutions, the PM solutions have improved considerably since 1995, so that currently the IGS combined and the best AC PM solutions are at or below the 0.1 mas precision level, although PM biases may exceed .1 mas. Comparisons of AC ERP and PM rate solutions with the IGS Final combined ERP series revealed signals with 7 and 14-day periods for some AC solutions.During 1998, the IGS Final and the best AC PM rate solutions compared with Atmospheric Angular Momentum (AAM) at 0.3 mas/day (rms) with an average correlation of about 0.8 and 0.6 for the PM x and PM y rate components. The correlation varied considerably with time and frequency, though significant correlation already started from 6-day periods and reaching maxima within 10 to 50 day period bands. Most of the remaining signal in the PM rate solutions could likely be accounted for by Ocean Angular Momentum (OAM) as seen from the comparisons of combined OAM and AAM with the IGS PM series during 1995 and early 1996 when also OAM data were made available. During this period the IGS PM rates agreed with the combined OAM + AAM series with 0.3 and 0.2 mas/day (rms) for the PM x and y components and with an average correlation of about 0.8 for both PM components.

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New Definition for the Celestial Pole and the Celestial Origin in the ICRS

Highlights of Astronomy ◽

10.1017/s1539299600012971 ◽

2002 ◽

Vol 12 ◽

pp. 102-106

Author(s):

Nicole Capitaine

Keyword(s):

Earth Rotation ◽

High Frequency ◽

Reference System ◽

Polar Motion ◽

The Other ◽

General Assembly ◽

Practical Application ◽

Celestial Pole ◽

Definition Of ◽

Celestial Reference System

AbstractTwo Resolutions have been submitted to the 24thGeneral Assembly of the IAU concerning the definition and use of the celestial pole of reference and the celestial origin. The aim of both resolutions is to provide new parameters for Earth rotation which are consistent with the properties of the International Celestial Reference System (ICRS), adopted from 1 January 1998 as the IAU celestial reference system. The definition of the parameters have also to be consistent with the precision and the temporal resolution of the current Earth rotation measurements as well as with the theory for nutation and polar motion at the microarcsecond level. This paper explains the basis of the resolutions as well as their practical application. One of the resolutions defines the “Celestial Intermediate Pole” (CIP) in order to replace the “Celestial Ephemeris Pole” (CEP) for the new IAU precession-nutation model; its specifies the way for taking into account the constant offset from the ICRS and the high frequency terms in polar motion and nutation. The other resolution recommends the use of the “non-rotating origin” (Guinot 1979) on the moving equator, for defining Earth rotation and UT1; it also recommends the use of the celestial and terrestrial coordinates of the CIP in the transformation from the celestial to the terrestrial systems.

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Polar Motion and Earth Rotation from Lageos Laser Ranging

International Astronomical Union Colloquium ◽

10.1017/s0252921100002499 ◽

1981 ◽

Vol 63 ◽

pp. 123-124 ◽

Cited By ~ 1

Author(s):

B. D. Tapley

Keyword(s):

Earth Rotation ◽

Polar Motion ◽

Smoothing Parameter ◽

Laser Ranging ◽

Range Data ◽

Length Of Day ◽

Laser Range ◽

International Polar ◽

Short Arc

Laser ranging collected during the period from May 7 1976 through May 1981, has been used to determine polar motion and length of day (LOD) variations. Independent short-arc solutions of five days in length are used to obtain the polar motion and LOD results. The solutions obtained with these approaches are compared with BIH and Doppler solutions. With the Vondrak smoothing parameter of 10−7, the weighted RMS of the raw minus smoothed results is 0010 in x, 0008 in y and 0.28 msec in LOD. Finally, the results obtained during the MERIT campaign, an international polar motion intercomparison experiment, using both “quick-look” and the final processed laser range data are discussed.

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Assimilation of Earth rotation parameters into a global ocean model: excitation of polar motion

Nonlinear Processes in Geophysics ◽

10.5194/npg-18-581-2011 ◽

2011 ◽

Vol 18 (5) ◽

pp. 581-585 ◽

Cited By ~ 7

Author(s):

J. Saynisch ◽

M. Wenzel ◽

J. Schröter

Keyword(s):

Angular Momentum ◽

Mass Distribution ◽

Earth Rotation ◽

Polar Motion ◽

Ocean Model ◽

Current Speed ◽

Global Ocean ◽

Length Of Day ◽

Motion Generation ◽

Ocean Mass

Abstract. The oceanic contribution to Earth rotation anomalies can be manifold. Possible causes are a change of total ocean mass, changes in current speed or location and changes in mass distribution. To derive the governing physical mechanisms of oceanic Earth rotation excitation we assimilate Earth rotation observations with a global circulation ocean model. Before assimilation, observations of length of day and polar motion were transformed into estimates of ocean angular momentum. By using the adjoint 4D-VAR assimilation method we were able to reproduce these estimated time series. Although length of day was assimilated simultaneously the analysis in this paper focuses on the oceanic polar motion generation. Our results show that changes in mass distribution and currents contribute to oceanic polar motion generation. Both contributions are highly correlated and show similar amplitudes. The changes in the model done by the assimilation procedure could be related to changes in the atmospheric forcing. Since for geometrical reasons the change of total ocean mass does not project on polar motion, we conclude that the polar motion is mainly generated by a geostrophic response to atmospheric momentum forcing. In geostrophic currents mass displacement and current speed entail each other. This way the large similarity of mass and current generated ocean angular momentum can be explained.

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Earth Orientation since AD 1600

Highlights of Astronomy ◽

10.1017/s1539299600013708 ◽

2002 ◽

Vol 12 ◽

pp. 342-345

Author(s):

Dennis D. McCarthy

Keyword(s):

International Cooperation ◽

Geographic Distribution ◽

Additional Data ◽

Physical Processes ◽

Earth Orientation ◽

The Earth ◽

History Of ◽

Wide Geographic Distribution ◽

Insight Into

AbstractPast endeavors in the field of Earth orientation have provided both service to astronomical users of the data and insight into the physical processes of the planet Earth. Since the study of Earth orientation has required a wide geographic distribution of astronomical observing sites, it has been an area of research that has depended heavily on international cooperation over long intervals of time. Recently, IAU Colloquium 178 pointed out that the need exists to find and collect observations that may have been made before the establishment of the current operational services. Reanalysis of such data could be important in our understanding of the physical processes affecting the Earth. All of these observations need to be analyzed in one system consistent with current definitions and conventions. The history of available observations is reviewed along with the contributions that have been made possible using these data. Possible sources for additional data are suggested.

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Preferential acceleration of heavy ions from thermal velocities

Canadian Journal of Physics ◽

10.1139/p68-314 ◽

1968 ◽

Vol 46 (10) ◽

pp. S638-S641 ◽

Cited By ~ 1

Author(s):

D. B. Melrose

Keyword(s):

Frequency Spectrum ◽

High Frequency ◽

Heavy Ions ◽

Crab Nebula ◽

Low Frequency ◽

High Frequency Waves ◽

Hydromagnetic Waves ◽

The Crab Nebula ◽

Low Frequency Waves

The acceleration of ions from thermal velocities is analyzed to determine conditions under which heavy ions can be preferentially accelerated. Two accelerating mechanisms involving high-and low-frequency hydromagnetic waves respectively are considered. Preferential acceleration of heavy ions occurs for high-frequency waves if the frequency spectrum falls off faster than (frequency)−1. For the low-frequency waves heavy ions are less effectively accelerated than lighter ions. However, very heavy ions can be preferentially accelerated, the abundances of the very heavy ions being enhanced by a factor Ai over the thermal abundances. Acceleration of ions in the envelope of the Crab nebula is considered as an example.

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Analysis and Optimization of Conformal Patch Excited Wideband DRA of Several Shapes

Frequenz ◽

10.1515/freq-2017-0039 ◽

2018 ◽

Vol 72 (5-6) ◽

pp. 197-208 ◽

Cited By ~ 4

Author(s):

Pramod Kumar ◽

Santanu Dwari ◽

Shailendra Singh ◽

Ashok Kumar ◽

N. K. Agrawal ◽

...

Keyword(s):

Comparative Analysis ◽

Frequency Spectrum ◽

High Frequency ◽

Unit Volume ◽

Experimental Results ◽

Impedance Bandwidth ◽

High Frequency Structure Simulator ◽

Triangular Shape ◽

Operating Band ◽

Peak Gain

AbstractIn this paper various shapes of DR antennas excited by common feed have been proposed and successfully implemented for wideband applications. Proposed structures are Hemispherical, Arrow-shaped and Triangular DRA, while common excited feed is inverted trapezoidal conformal patch. These shapes of DR offer significant optimization in several parameters such as impedance bandwidth, peak gain and bandwidth per unit volume of the antenna. By using inverted trapezoidal patch feed mechanism an impedance bandwidth (VSWR<2) of about 63 % for hemispherical shape, 66 % for arrow shape, and 72 % for triangular shape DRA has been achieved with maximum bandwidth per unit volume. Proposed wideband DRAs i. e. triangular, hemispherical, and arrow shapes of DR antennas cover almost complete C-band (4 GHz–8 GHz) frequency spectrum of microwave. The average peak gain within the operating band for hemispherical, arrow, and triangular shape DRA are about 5, 5.4, and 5.5 dB respectively. A comparative analysis of proposed structures for various antenna parameters has been analyzed by HFSS (High-Frequency Structure Simulator) and validated by experimental results.

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