scholarly journals Atmospheric Effects on Earth Rotation and Polar Motion

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.

scholarly journals On High Frequency Polar Motion and Length of Day Variations

2000 ◽  
Vol 178 ◽  
pp. 545-554
Author(s):  
K. Arfa-Kaboodvand ◽  
E. Groten
Keyword(s):  
Frequency Spectrum ◽  
Earth Rotation ◽  
High Frequency ◽  
Polar Motion ◽  
Length Of Day ◽  
Physical Processes ◽  
Earth Orientation ◽  
Tidal Forces ◽  
Diurnal Range ◽  
Insight Into

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.

scholarly journals Role of Low-Frequency Wind Variability in Inducing WWBs during the onset of super El Niños

2021 ◽  
Author(s):  
Yi-Kai Wu ◽  
Chi-Cherng Hong ◽  
Tim Li ◽  
An-Yi Huang
Keyword(s):  
El Niño ◽  
North Pacific ◽  
El Nino ◽  
Low Frequency ◽  
Wind Fields ◽  
Wind Variability ◽  
The Pacific ◽  
Sst Anomaly ◽  
Wind Bursts

Abstract In this study, the effect of multiple timescale wind fields on the westerly wind bursts (WWBs) was investigated during the onset of super (1982, 1997, and 2015) and moderate El Niño events. The results revealed that extreme WWBs during the onset of the super El Niño group were attributed to low-frequency westerly (≥90 days, LFW), medium-frequency westerly (20–90 days, MFW, or intraseasonal) and high-frequency westerly (≤10 days, HFW) components, accounting for approximately 51%, 33% and 16%, respectively. Thus, the extreme WWBs during the onset of super El Niños were primarily contributed by LFWs and MFWs. By contrast, the WWBs during the onset of moderate El Niños were determined primarily by MFWs (38%) and HFWs (35%), whereas the LFW contribution is relatively small (27%). A further analysis indicated that LFWs during the onset of the super El Niños were primarily a response to a positive SST anomaly in the tropical to eastern North Pacific resembling the Pacific Meridional Mode (PMM), which had persisted during the preceding 9–12 months in the extratropical eastern North Pacific. A significant lagged correlation between the tropical and extratropical North Pacific SST was identified, and their correlation has become stronger since the late 1980s. MFWs during the onset of the super El Niños were primarily associated with the Madden-Julian Oscillation.

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.

scholarly journals Polar Motion and Earth Rotation from Lageos Laser Ranging

1981 ◽  
Vol 63 ◽  
pp. 123-124 ◽  
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.

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

2011 ◽  
Vol 18 (5) ◽  
pp. 581-585 ◽  
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.

The Role of Interactions between Multiscale Circulations on the Observed Zonally Averaged Zonal Wind Variability Associated with the Madden–Julian Oscillation

2014 ◽  
Vol 71 (10) ◽  
pp. 3816-3836 ◽  
Author(s):  
Naoko Sakaeda ◽  
Paul E. Roundy
Keyword(s):  
Zonal Wind ◽  
Time Scale ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Wind Fields ◽  
Zonal Wind Anomaly ◽  
Wind Variability ◽  
Driving Mechanisms ◽  
Budget Analysis

Abstract The mechanisms driving the upper-tropospheric zonal mean intraseasonal zonal wind associated with the Madden–Julian oscillation are examined through budget analysis during boreal winter. To diagnose the role of nonlinear and cross-scale interactions, the wind fields are decomposed into three temporal bands, including the intraseasonal time scale (30–100 days), and periods shorter and longer than the intraseasonal time scales. The intraseasonal zonal mean circulation and its driving mechanisms are first examined based on the leading EOFs of the intraseasonal zonal wind. Consistent with previous studies of intraseasonal atmospheric angular momentum, the upper-troposphere zonal mean intraseasonal zonal wind anomaly begins in the tropics and propagates poleward. Results show that interaction between the background state and intraseasonal-time-scale zonally symmetric and asymmetric circulation helps drive changes in the tropical intraseasonal zonal wind and its poleward propagation. The intraseasonal anomalous circulation also modulates the characteristics of the transient eddies that induce anomalous momentum flux convergence that then helps to accelerate further the intraseasonal zonal wind in the extratropics. Results also suggest that feedbacks between the anomalous intraseasonal circulation and transient eddies have some sensitivity to event-to-event variability of the MJO.

scholarly journals Impact of tumor-parenchyma biomechanics on liver metastatic progression: a multi-model approach

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yafei Wang ◽  
Erik Brodin ◽  
Kenichiro Nishii ◽  
Hermann B. Frieboes ◽  
Shannon M. Mumenthaler ◽  
...  
Keyword(s):  
Time Scales ◽  
Constitutive Relations ◽  
Elastic Tissue ◽  
Metastatic Progression ◽  
Patient Death ◽  
Metastatic Growth ◽  
Tumor Parenchyma ◽  
Short Time ◽  
Model Approach

AbstractColorectal cancer and other cancers often metastasize to the liver in later stages of the disease, contributing significantly to patient death. While the biomechanical properties of the liver parenchyma (normal liver tissue) are known to affect tumor cell behavior in primary and metastatic tumors, the role of these properties in driving or inhibiting metastatic inception remains poorly understood, as are the longer-term multicellular dynamics. This study adopts a multi-model approach to study the dynamics of tumor-parenchyma biomechanical interactions during metastatic seeding and growth. We employ a detailed poroviscoelastic model of a liver lobule to study how micrometastases disrupt flow and pressure on short time scales. Results from short-time simulations in detailed single hepatic lobules motivate constitutive relations and biological hypotheses for a minimal agent-based model of metastatic growth in centimeter-scale tissue over months-long time scales. After a parameter space investigation, we find that the balance of basic tumor-parenchyma biomechanical interactions on shorter time scales (adhesion, repulsion, and elastic tissue deformation over minutes) and longer time scales (plastic tissue relaxation over hours) can explain a broad range of behaviors of micrometastases, without the need for complex molecular-scale signaling. These interactions may arrest the growth of micrometastases in a dormant state and prevent newly arriving cancer cells from establishing successful metastatic foci. Moreover, the simulations indicate ways in which dormant tumors could “reawaken” after changes in parenchymal tissue mechanical properties, as may arise during aging or following acute liver illness or injury. We conclude that the proposed modeling approach yields insight into the role of tumor-parenchyma biomechanics in promoting liver metastatic growth, and advances the longer term goal of identifying conditions to clinically arrest and reverse the course of late-stage cancer.

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