Excitations of length-of-day seasonal variations: Analyses of harmonic and inharmonic fluctuations

Luo, Jiangshui; Chen, Wei; Ray, Jim; Li, Jian Cheng

doi:10.1016/j.geog.2019.09.002

Cited by 3 publications

(3 citation statements)

References 18 publications

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“…The mathematical methods adopted in this study include the continuous wavelet transform (CWT) and the cross wavelet transform (XWT). The CWT of a time series xn ( n = 1, 2,..., N) is defined as (Grinsted et al., 2004):

W_{n}^{x} (normalS) = \sqrt{δ t / s} \sum_{n^{'} = 1}^{N} x_{n^{'}} ϕ_{italic0} [(n^{'} - n) \frac{δ t}{s}]

where

W_{n}^{x} (S)

is the wavelet coefficient,

δ t

is the uniform time step, s is the wavelet scale,

n^{'}

is the reversed time,

ϕ_{italic0}

is the mother function and we specially choose the Morlet wavelet (

w_{0}

= 6) as the month wavelet since it offers an optimal balance between frequency and time localization (Luo et al., 2019; Xu et al., 2020). The Morlet wavelet is defined as (Grinsted et al., 2004):

ψ_{0} (η) = π^{- 1 / 4} e^{i w_{0} η} e^{- η^{2} / 2}

where

w_{0}

and

η

are dimensionless frequency and time, respectively.…”

Section: Methodsmentioning

confidence: 99%

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A Reconstruction of Total Solar Irradiance Based on Wavelet Analysis

Lei

2021

Earth and Space Science

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The total solar irradiance (TSI) refers to the sum of the solar electromagnetic radiation energy of all wavebands reaching the top of the earth's atmosphere per unit area in unit time at the average distance between the sun and the earth (Biktash & Lilia, 2017). Although the solar radiation energy received by the earth is only one in two billion of the total radiation energy from the sun to the space, but it is the main energy source of the earth's atmospheric movement, it is the most important energy source of the earth's atmospheric movement and an important external driving factor of global climate change (Haigh, 2007;Kren, 2015;Solanki et al., 2013). Before Hickey-Frieden cavity radiator (HF) was used to observe the solar radiation in October 1978, TSI was regarded as a constant due to the low accuracy of ground observation equipment, so it was called "solar constant." Since HF was launched, TSI has been continuously observed by several radiometers. Due to the high accuracy of these space radiometers, it is recognized that the solar radiation varies from several minutes to several decades (Kopp, 2016). TSI produces the earth's radiation environment and affects the earth's temperature and atmosphere, even a small change in TSI will have a profound impact on the earth's climate (

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W_{n}^{x} (normalS) = \sqrt{δ t / s} \sum_{n^{'} = 1}^{N} x_{n^{'}} ϕ_{italic0} [(n^{'} - n) \frac{δ t}{s}]

where

W_{n}^{x} (S)

is the wavelet coefficient,

δ t

is the uniform time step, s is the wavelet scale,

n^{'}

is the reversed time,

ϕ_{italic0}

is the mother function and we specially choose the Morlet wavelet (

w_{0}

= 6) as the month wavelet since it offers an optimal balance between frequency and time localization (Luo et al., 2019; Xu et al., 2020). The Morlet wavelet is defined as (Grinsted et al., 2004):

ψ_{0} (η) = π^{- 1 / 4} e^{i w_{0} η} e^{- η^{2} / 2}

where

w_{0}

and

η

are dimensionless frequency and time, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…is the mother function and we specially choose the Morlet wavelet ( 0 E w = 6) as the month wavelet since it offers an optimal balance between frequency and time localization (Luo et al, 2019;Xu et al, 2020). The Morlet wavelet is defined as (Grinsted et al, 2004):…”

mentioning

confidence: 99%

A Reconstruction of Total Solar Irradiance Based on Wavelet Analysis

Lei

2021

Earth and Space Science

View full text Add to dashboard Cite

show abstract

“…Chao et al [35] analyzed PM excitation for the period 1900-2012 using wavelet analysis, found an ~8-year quasi-periodic signal and proved the existence of the ~26-year Markowitz wobble. Besides PM excitation, Luo et al [36] also applied wavelet analysis to the excitation of length-of-day (LOD) variations and found that consideration of wavelet-based inharmonic excitation can achieve a better match with the observed LOD time series.…”

mentioning

confidence: 99%

Excitations of Seasonal Polar Motions Derived from Satellite Gravimetry and General Circulation Models: Comparisons of Harmonic and Inharmonic Analyses

et al. 2022

Self Cite

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Due to the conservation of global angular momentum, polar motion (PM) is dominated by global mass redistributions and relative motions in the atmosphere, oceans and land water at seasonal time scales. Thus, accurately measured PM data can be used to validate the general circulation models (GCMs) for the atmosphere, oceans and land water. This study aims to analyze geophysical excitations and observed excitations obtained from PM observations from both the harmonic and wavelet analysis perspectives, in order to refine our understanding of the geophysical excitation of PM. The geophysical excitations are derived from two sets of GCMs and a monthly gravity model combining satellite gravity data and some GCM outputs using the PM theory for an Earth model with frequency-dependent responses, while the observed excitation is obtained from the PM data using the frequency-domain Liouville’s equation. Our results show that wavelet analysis can reveal the time-varying nature of all excitations and identify when changes happen and how strong they are, while harmonic analysis can only show the average amplitudes and phases. In particular, the monthly gravity model can correct the mismodeled GCM outputs, while the Earth’s frequency-dependent responses provide us with a better understanding of atmosphere–ocean–land water–solid Earth interactions.

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Madden-Julian oscillation winds excite an intraseasonal see-saw of ocean mass that affects Earth’s polar motion

Afroosa

Rohith

Paul

et al. 2021

Commun Earth Environ

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Strong large-scale winds can relay their energy to the ocean bottom and elicit an almost immediate intraseasonal barotropic (depth independent) response in the ocean. The intense winds associated with the Madden-Julian Oscillation over the Maritime Continent generate significant intraseasonal basin-wide barotropic sea level variability in the tropical Indian Ocean. Here we show, using a numerical model and a network of in-situ bottom pressure recorders, that the concerted barotropic response of the Indian and the Pacific Ocean to these winds leads to an intraseasonal see-saw of oceanic mass in the Indo-Pacific basin. This global-scale mass shift is unexpectedly fast, as we show that the mass field of the entire Indo-Pacific basin is dynamically adjusted to Madden-Julian Oscillation in a few days. We find this large-scale ocean see-saw, induced by the Madden-Julian Oscillation, has a detectable influence on the Earth’s polar axis motion, in particular during the strong see-saw of early 2013.

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Excitations of length-of-day seasonal variations: Analyses of harmonic and inharmonic fluctuations

Cited by 3 publications

References 18 publications

A Reconstruction of Total Solar Irradiance Based on Wavelet Analysis

A Reconstruction of Total Solar Irradiance Based on Wavelet Analysis

Excitations of Seasonal Polar Motions Derived from Satellite Gravimetry and General Circulation Models: Comparisons of Harmonic and Inharmonic Analyses

Madden-Julian oscillation winds excite an intraseasonal see-saw of ocean mass that affects Earth’s polar motion

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