Causes of rapid motions of the Earth's pole

Eubanks, T. M.; Steppe, J. A.; Dickey, J. O.; Rosen, Richard D.; Salstein, David A.

doi:10.1038/334115a0

Cited by 96 publications

(75 citation statements)

References 25 publications

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“…Since the advent of space geodetic methods about 20 yeas ago, polar motion data are significantly above the noise level from periods of a few weeks to several years [see, e.g., Eubanks et al, 1988;Chao, 1993;Kuehne et al, 1996]. These modern data invite an accounting of the excitation spectrum across a broad continuous frequency band.…”

Section: ] Both Wilson and Haubrich [1976] And Wahrmentioning

confidence: 99%

Climate‐driven polar motion

Celaya¹,

Wahr²,

Bryan³

1999

J. Geophys. Res.

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Abstract. The output of a coupled climate system model provides a synthetic climate record with temporal and spatial coverage not attainable with observational data, allowing evaluation of climatic excitation of polar motion on timescales of months to decades. Analysis of the geodetically inferred Chandler excitation power shows that it has fluctuated by up to 90% since 1900 and that it has characteristics representative of a stationary Gaussian process. Our model-predicted climate excitation of the Chandler wobble also exhibits variable power comparable to the observed. Ocean currents and bottom pressure shifts acting together can alone drive the 14-month wobble. The same is true of the excitation generated by the combined effects of barometric pressure and winds. The oceanic and atmospheric contributions are this large because of a relatively high degree of constructive interference between seafloor pressure and currents and between atmospheric pressure and winds. In contrast, excitation by the redistribution of water on land appears largely insignificant. Not surprisingly, the full climate effect is even more capable of driving the wobble than the effects of the oceans or atmosphere alone are. Our match to the observed annual excitation is also improved, by about 17%, over previous estimates made with historical climate data. Efforts to explain the 30-year Markowitz wobble meet with less success. Even so, at periods ranging from months to decades, excitation generated by a model of a coupled climate system makes a close approximation to the amphtude of what is geodetically observed.

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Section: ] Both Wilson and Haubrich [1976] And Wahrmentioning

confidence: 99%

Climate‐driven polar motion

Celaya¹,

Wahr²,

Bryan³

1999

J. Geophys. Res.

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“…Fluctuations about the Earth's axis are observed as changes in the length of day; such motions have been very clearly related to changes in axial angular momentum, mostly due to the variations in zonal winds [e.g., Rosen, 1993]. Motions about the equatorial axes of the Earth are known as polar motion, and those on relatively rapid timescales, between 10 and 150 days, have been linked to fluctuations in the atmosphere as well, mostly through rearrangements in its mass, as noted in surface pressure field changes [Eubanks et al, 1988;Chao, 1993;Nastula, 1992Nastula, , 1995 Kosek et al, 1995;Kuehne et al, 1993]. The influence of the atmosphere on variations of polar motion in this spectral range is therefore presently not questioned, although the details of the phenomenon have not yet been fully explained, and may involve the contributions of ocean mass variation as well [Ponte et al, 1998].…”

Section: Introductionmentioning

confidence: 99%

Regional atmospheric angular momentum contributions to polar motion excitation

Nastula¹,

Salstein²

1999

J. Geophys. Res.

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Abstract. We focus on a regional analysis of equatorial components of the effective atmospheric angular momentum (EAAM) functions that measure the excitation of polar motion. These functions are computed from National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) reanalysis data both globally and in 108 geographic sectors for the period 1968-1997. We investigate the relationship between the regional sector EAAM and the global functions responsible for polar motion excitation. We examine two excitation terms in parallel, with and without the inverted barometer (lB) approximation, which adjusts the atmosphere to account for an isostatic equilibrium response of the ocean to overlying pressure. The previous results were based on rather limited periods and, furthermore, on series from operational meteorological centers, whose changes in character with time may make them too heterogeneous for a reliable long-term study. Given the 7347

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“…The polar motion AEFs ((4)- (7)) are weighted zonally following sine and cosine waves, which means that only zonally asymmetric wind and mass anomalies result in a net polar motion excitation. Consequently, subseasonal variations in polar motion are not generally excited by wind anomalies, which tend to cancel out in the zonal integral [Barnes et al, 1983;Eubanks et al, 1988], but rather by midlatitude anomalies in the atmospheric mass distribution. Mass anomalies in the middle troposphere are a common precursor of SSWs, because they excite upward propagating planetary waves that break and thereby weaken the vortex, and SSWs are often preceded by persistent northern European blocking anticyclones [Quiroz, 1986;Martius et al, 2009;Woollings et al, 2010] and positively correlated to warm ENSO events [Garfinkel and Hartmann, 2008].…”

Section: Neef Et Almentioning

confidence: 99%

“…On time scales from a few days to months, fluctuations in the angular momentum of the atmosphere, modified by the response of the sea levels to pressure loading from the atmosphere [Eubanks et al, 1988], dominate changes in both LOD [Rosen and Salstein, 1983;Rosen et al, 1990] and polar motion. The rest of this manuscript will examine only the atmospheric angular momentum excitation functions (AEFs hereafter), with the exception of some oceanic effects covered in section 4.1.…”

Section: Atmospheric Excitation Functionsmentioning

confidence: 99%

Observations of stratospheric sudden warmings in Earth rotation variations

et al. 2014

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Stratospheric sudden warmings (SSWs) are extreme events in the polar stratosphere that are both caused by and have effects on the tropospheric flow. This means that SSWs are associated with changes in the angular momentum of the atmosphere, both before and after their onset. Because these angular momentum changes are transferred to the solid Earth, they can be observed in the rate of the Earth's rotation and the wobble of its rotational pole. By comparing observed Earth rotation variations to reanalysis data, we find that an anomaly in the orientation of the Earth's rotational pole, up to 4 times as large as the annual polar wobble, typically precedes SSWs by 20-40 days. The polar motion signal is due to pressure anomalies that are typically seen before SSW events and represents a new type of observable that may aid in the prediction of SSWs. A decline in the length of day is also seen, on average, near the time of the SSW wind reversal and is found to be due to anomalous easterly winds generated in the tropical troposphere around this time, though the structure and timing of this signal seems to vary widely from event to event.

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Causes of rapid motions of the Earth's pole

Cited by 96 publications

References 25 publications

Climate‐driven polar motion

Climate‐driven polar motion

Regional atmospheric angular momentum contributions to polar motion excitation

Observations of stratospheric sudden warmings in Earth rotation variations

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