scholarly journals The phase difference between length of day and atmospheric angular momentum at subannual frequencies and the possible role of core-mantle coupling

1997 ◽  
Vol 24 (14) ◽  
pp. 1799-1802 ◽  
Author(s):  
Stephen Zatman ◽  
Jeremy Bloxham
Keyword(s):  
Angular Momentum ◽  
Phase Difference ◽  
Atmospheric Angular Momentum ◽  
Length Of Day

The short-term prediction of universal time and length of day using atmospheric angular momentum

1994 ◽  
Vol 99 (B4) ◽  
pp. 6981 ◽  
Author(s):  
A. P. Freedman ◽  
J. A. Steppe ◽  
J. O. Dickey ◽  
T. M. Eubanks ◽  
L.-Y. Sung
Keyword(s):  
Angular Momentum ◽  
Universal Time ◽  
Atmospheric Angular Momentum ◽  
Length Of Day ◽  
Short Term ◽  
Term Prediction ◽  
Short Term Prediction

scholarly journals The influence of global warming in Earth rotation speed

1999 ◽  
Vol 17 (6) ◽  
pp. 806-811 ◽  
Author(s):  
R. Abarca del Rio
Keyword(s):  
Angular Momentum ◽  
Surface Temperature ◽  
Earth Rotation ◽  
Rotation Speed ◽  
Atmospheric Angular Momentum ◽  
Time Interval ◽  
Dynamical Response ◽  
Earth System ◽  
Length Of Day ◽  
Data Set

Abstract. The tendency of the atmospheric angular momentum (AAM) is investigated using a 49-year set of monthly AAM data for the period January 1949-December 1997. This data set is constructed with zonal wind values from the reanalyses of NCEP/NCAR, used in conjunction with a variety of operationally produced AAM time series with different independent sources and lengths over 1976-1997. In all the analyzed AAM series the linear trend is found to be positive. Since the angular momentum of the atmosphere-earth system is conserved this corresponds to a net loss of angular momentum by the solid earth, therefore decreasing the Earth rotation speed and increasing the length of day (LOD). The AAM rise is significant to the budget of angular momentum of the global atmosphere-earth system; its value in milliseconds/century (ms/cy) is +0.56 ms/cy, corresponding to one-third of the estimated increase in LOD (+1.7 ms/cy). The major contribution to this secular trend in AAM comes from the equatorial Tropopause. This is consistent with results from a previous study using a simplified aqua-planet model to investigate the AAM variations due to near equatorial warming conditions. During the same time interval, 1949-1997, the global marine + land-surface temperature increases by about 0.79 °C/cy, showing a linear correspondence between surface temperature increase and global AAM of about 0.07 ms per 0.1 °C. These results imply that atmospheric angular momentum may be used as an independent index of the global atmosphere's dynamical response to the greenhouse forcing, and as such, the length of day may be used as an indirect indicator of global warming.Key words. Meteorology and atmospheric dynamics (general circulation) · Geodesy

Atmospheric angular momentum fluctuations, length-of-day changes and polar motion

1983 ◽  
Vol 387 (1792) ◽  
pp. 31-73 ◽  
Keyword(s):  
Angular Momentum ◽  
Solid Earth ◽  
Polar Motion ◽  
Meteorological Data ◽  
Liquid Core ◽  
Atmospheric Angular Momentum ◽  
Axial Component ◽  
Length Of Day ◽  
Momentum Exchange ◽  
Geophysical Research

Variations in the distribution of mass within the atmosphere and changes in the pattern of winds, particularly the strength and location of the major mid-latitude jet-streams, produce fluctuations in all three components of the angular momentum of the atmosphere on timescales upwards of a few days. In a previous study (Hide et al . 1980) it has been shown that variations in the axial component of atmospheric angular momentum during the Special Observing Periods in 1979 of the First GARP Global Experiment (FGGE, where GARP is the Global Atmospheric Research Program) are well correlated with changes in length-of-day. This would be expected if the total angular momentum of the atmosphere and ‘solid’ Earth were conserved on short timescales (allowing for lunar and solar effects) but not if angular momentum transfer between the Earth’s liquid core and solid mantle, which is accepted to be substantial and even dominant on timescales upwards of several years, were significant on timescales of weeks or months. Fluctuations in the equatorial components of atmospheric angular momentum should contribute to the observed wobble of the instantaneous pole of the Earth’s rotation with respect to the Earth’s crust, but this has not been shown conclusively by previous studies. In this paper we re-examine some aspects of the underlying theory of non-rigid body rotational dynamics and angular momentum exchange between the atmosphere and solid Earth. Since only viscous or topographic coupling between the atmosphere and solid Earth can transfer angular momentum, no atmospheric flow that everywhere satisfied inviscid equations (including, but not solely, geostrophic flow) could affect the rotation of a spherical solid Earth. Currently available meteorological data are not adequate for evaluating the usual wobble excitation functions accurately, but we show that partial integration leads to an expression involving simpler functions ─ here called ‘equatorial angular momentum functions’ ─ which can be reliably evaluated from available meteorological data. The length-of-day problem is treated in terms of a similar ‘axial angular momentum function’ ; and ‘effective angular momentum functions’ are defined in order to allow for rotational and surface loading deformation of the Earth. Daily values of these atmospheric angular momentum functions have been calculated from the ‘initialized analysis global database’ of the European Centre for Medium-Range Weather Forecasts (ECMWF). They are presented for the period 1 January 1981─30 April 1982, along with the corresponding astronomically observed changes in length-of-day and polar motion, published by the Bureau International de l’Heure (BIH). Changes in length-of-day during this period can be accounted for almost entirely by angular momentum exchange between the atmosphere and solid Earth, and the existence of a persistent fluctuation in this exchange, with a timescale of about 7 weeks, is confirmed. We also demonstrate that meteorological phenomena provide an important contribution to the excitation of polar motion. Our work offers a theoretical basis for future routine determinations of atmospheric angular momentum fluctuations for the purposes of meteorological and geophysical research, including the assessment of the extent to which movements in the solid Earth associated with very large earthquakes contribute to the excitation of the Chandlerian wobble.

scholarly journals IGS Combined and Contributed Earth Rotation Parameter Solutions

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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