The Experts below are selected from a list of 48 Experts worldwide ranked by ideXlab platform
George N Kiladis - One of the best experts on this subject based on the ideXlab platform.
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convectively coupled equatorial waves analysis of clouds and temperature in the wavenumber frequency domain
Journal of the Atmospheric Sciences, 1999Co-Authors: Matthew C Wheeler, George N KiladisAbstract:A Wavenumber-Frequency Spectrum analysis is performed for all longitudes in the domain 158S‐158N using a long (;18 years) twice-daily record of satellite-observed outgoing longwave radiation (OLR), a good proxy for deep tropical convection. The broad nature of the Spectrum is red in both zonal wavenumber and frequency. By removing an estimated background Spectrum, numerous statistically significant spectral peaks are isolated. Some of the peaks correspond quite well to the dispersion relations of the equatorially trapped wave modes of shallow water theory with implied equivalent depths in the range of 12‐50 m. Cross-Spectrum analysis with the satellite-based microwave sounding unit deep-layer temperature data shows that these spectral peaks in the OLR are ‘‘coupled’’ with this dynamical field. The equivalent depths of the convectively coupled waves are shallower than those typical of equatorial waves uncoupled with convection. Such a small equivalent depth is thought to be a result of the interaction between convection and the dynamics. The convectively coupled equatorial waves identified correspond to the Kelvin, n 5 1 equatorial Rossby, mixed Rossby-gravity, n 5 0 eastward inertiogravity, n 5 1 westward inertio-gravity (WIG), and n 5 2 WIG waves. Additionally, the Madden‐Julian oscillation and tropical depression-type disturbances are present in the OLR spectra. These latter two features are unlike the convectively coupled equatorial waves due to their location away from the equatorial wave dispersion curves in the Wavenumber-Frequency domain. Extraction of the different convectively coupled disturbances in the time‐longitude domain is performed by filtering the OLR dataset for very specific zonal wavenumbers and frequencies. The geographical distribution of the variance of these filtered data gives further evidence that some of the spectral peaks correspond to particular equatorial wave modes. The results have implications for the cumulus parameterization problem, for the excitation of equatorial waves in the lower stratosphere, and for extended-range forecasting in the Tropics.
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convectively coupled equatorial waves analysis of clouds and temperature in the wavenumber frequency domain
Journal of the Atmospheric Sciences, 1999Co-Authors: Matthew C Wheeler, George N KiladisAbstract:Abstract A Wavenumber-Frequency Spectrum analysis is performed for all longitudes in the domain 15°S–15°N using a long (∼18 years) twice-daily record of satellite-observed outgoing longwave radiation (OLR), a good proxy for deep tropical convection. The broad nature of the Spectrum is red in both zonal wavenumber and frequency. By removing an estimated background Spectrum, numerous statistically significant spectral peaks are isolated. Some of the peaks correspond quite well to the dispersion relations of the equatorially trapped wave modes of shallow water theory with implied equivalent depths in the range of 12–50 m. Cross-Spectrum analysis with the satellite-based microwave sounding unit deep-layer temperature data shows that these spectral peaks in the OLR are “coupled” with this dynamical field. The equivalent depths of the convectively coupled waves are shallower than those typical of equatorial waves uncoupled with convection. Such a small equivalent depth is thought to be a result of the interacti...
Matthew C Wheeler - One of the best experts on this subject based on the ideXlab platform.
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convectively coupled equatorial waves analysis of clouds and temperature in the wavenumber frequency domain
Journal of the Atmospheric Sciences, 1999Co-Authors: Matthew C Wheeler, George N KiladisAbstract:A Wavenumber-Frequency Spectrum analysis is performed for all longitudes in the domain 158S‐158N using a long (;18 years) twice-daily record of satellite-observed outgoing longwave radiation (OLR), a good proxy for deep tropical convection. The broad nature of the Spectrum is red in both zonal wavenumber and frequency. By removing an estimated background Spectrum, numerous statistically significant spectral peaks are isolated. Some of the peaks correspond quite well to the dispersion relations of the equatorially trapped wave modes of shallow water theory with implied equivalent depths in the range of 12‐50 m. Cross-Spectrum analysis with the satellite-based microwave sounding unit deep-layer temperature data shows that these spectral peaks in the OLR are ‘‘coupled’’ with this dynamical field. The equivalent depths of the convectively coupled waves are shallower than those typical of equatorial waves uncoupled with convection. Such a small equivalent depth is thought to be a result of the interaction between convection and the dynamics. The convectively coupled equatorial waves identified correspond to the Kelvin, n 5 1 equatorial Rossby, mixed Rossby-gravity, n 5 0 eastward inertiogravity, n 5 1 westward inertio-gravity (WIG), and n 5 2 WIG waves. Additionally, the Madden‐Julian oscillation and tropical depression-type disturbances are present in the OLR spectra. These latter two features are unlike the convectively coupled equatorial waves due to their location away from the equatorial wave dispersion curves in the Wavenumber-Frequency domain. Extraction of the different convectively coupled disturbances in the time‐longitude domain is performed by filtering the OLR dataset for very specific zonal wavenumbers and frequencies. The geographical distribution of the variance of these filtered data gives further evidence that some of the spectral peaks correspond to particular equatorial wave modes. The results have implications for the cumulus parameterization problem, for the excitation of equatorial waves in the lower stratosphere, and for extended-range forecasting in the Tropics.
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convectively coupled equatorial waves analysis of clouds and temperature in the wavenumber frequency domain
Journal of the Atmospheric Sciences, 1999Co-Authors: Matthew C Wheeler, George N KiladisAbstract:Abstract A Wavenumber-Frequency Spectrum analysis is performed for all longitudes in the domain 15°S–15°N using a long (∼18 years) twice-daily record of satellite-observed outgoing longwave radiation (OLR), a good proxy for deep tropical convection. The broad nature of the Spectrum is red in both zonal wavenumber and frequency. By removing an estimated background Spectrum, numerous statistically significant spectral peaks are isolated. Some of the peaks correspond quite well to the dispersion relations of the equatorially trapped wave modes of shallow water theory with implied equivalent depths in the range of 12–50 m. Cross-Spectrum analysis with the satellite-based microwave sounding unit deep-layer temperature data shows that these spectral peaks in the OLR are “coupled” with this dynamical field. The equivalent depths of the convectively coupled waves are shallower than those typical of equatorial waves uncoupled with convection. Such a small equivalent depth is thought to be a result of the interacti...
Charles Meneveau - One of the best experts on this subject based on the ideXlab platform.
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spatio temporal spectra in the logarithmic layer of wall turbulence large eddy simulations and simple models
Journal of Fluid Mechanics, 2015Co-Authors: Michael Wilczek, Richard J A M Stevens, Charles MeneveauAbstract:Motivated by the need to characterize the spatio-temporal structure of turbulence in wall-bounded flows, we study wavenumber–frequency spectra of the streamwise velocity component based on large-eddy simulation (LES) data. The LES data are used to measure spectra as a function of the two wall-parallel wavenumbers and the frequency in the equilibrium (logarithmic) layer. We then reformulate one of the simplest models that is able to reproduce the observations: the random sweeping model with a Gaussian large-scale fluctuating velocity and with additional mean flow. Comparison with LES data shows that the model captures the observed temporal decorrelation, which is related to the Doppler broadening of frequencies. We furthermore introduce a parameterization for the entire wavenumber–frequency Spectrum E11(k1,k2,ω;z), where k1, k2 are the streamwise and spanwise wavenumbers, ω is the frequency and z is the distance to the wall. The results are found to be in good agreement with LES data.
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spatio temporal spectra in the logarithmic layer of wall turbulence large eddy simulations and simple models
arXiv: Fluid Dynamics, 2014Co-Authors: Michael Wilczek, Richard J A M Stevens, Charles MeneveauAbstract:Motivated by the need to characterize the spatio-temporal structure of turbulence in wall-bounded flows, we study Wavenumber-Frequency spectra of the streamwise velocity component based on large-eddy simulation (LES) data. The LES data are used to measure spectra as a function of the two wall-parallel wavenumbers and the frequency in the equilibrium (logarithmic) layer. We then reformulate one of the simplest models that is able to reproduce the observations: the random sweeping model with a Gaussian large-scale fluctuating velocity and with additional mean flow. Comparison with LES data shows that the model captures the observed temporal decorrelation, which is related to the Doppler broadening of frequencies. We furthermore introduce a parameterization for the entire Wavenumber-Frequency Spectrum $E_{11}(k_1,k_2,\omega;z)$, where $k_1$, $k_2$ are the streamwise and spanwise wavenumbers, $\omega$ is the frequency and $z$ is the distance to the wall. The results are found to be in good agreement with LES data.
Michael Wilczek - One of the best experts on this subject based on the ideXlab platform.
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spatio temporal spectra in the logarithmic layer of wall turbulence large eddy simulations and simple models
Journal of Fluid Mechanics, 2015Co-Authors: Michael Wilczek, Richard J A M Stevens, Charles MeneveauAbstract:Motivated by the need to characterize the spatio-temporal structure of turbulence in wall-bounded flows, we study wavenumber–frequency spectra of the streamwise velocity component based on large-eddy simulation (LES) data. The LES data are used to measure spectra as a function of the two wall-parallel wavenumbers and the frequency in the equilibrium (logarithmic) layer. We then reformulate one of the simplest models that is able to reproduce the observations: the random sweeping model with a Gaussian large-scale fluctuating velocity and with additional mean flow. Comparison with LES data shows that the model captures the observed temporal decorrelation, which is related to the Doppler broadening of frequencies. We furthermore introduce a parameterization for the entire wavenumber–frequency Spectrum E11(k1,k2,ω;z), where k1, k2 are the streamwise and spanwise wavenumbers, ω is the frequency and z is the distance to the wall. The results are found to be in good agreement with LES data.
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spatio temporal spectra in the logarithmic layer of wall turbulence large eddy simulations and simple models
arXiv: Fluid Dynamics, 2014Co-Authors: Michael Wilczek, Richard J A M Stevens, Charles MeneveauAbstract:Motivated by the need to characterize the spatio-temporal structure of turbulence in wall-bounded flows, we study Wavenumber-Frequency spectra of the streamwise velocity component based on large-eddy simulation (LES) data. The LES data are used to measure spectra as a function of the two wall-parallel wavenumbers and the frequency in the equilibrium (logarithmic) layer. We then reformulate one of the simplest models that is able to reproduce the observations: the random sweeping model with a Gaussian large-scale fluctuating velocity and with additional mean flow. Comparison with LES data shows that the model captures the observed temporal decorrelation, which is related to the Doppler broadening of frequencies. We furthermore introduce a parameterization for the entire Wavenumber-Frequency Spectrum $E_{11}(k_1,k_2,\omega;z)$, where $k_1$, $k_2$ are the streamwise and spanwise wavenumbers, $\omega$ is the frequency and $z$ is the distance to the wall. The results are found to be in good agreement with LES data.
Lian Shen - One of the best experts on this subject based on the ideXlab platform.
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wind wave coupling study using les of wind and phase resolved simulation of nonlinear waves
Journal of Fluid Mechanics, 2019Co-Authors: Xuanting Hao, Lian ShenAbstract:We present a study on the interaction between wind and water waves with a broad-band Spectrum using wave-phase-resolved simulation with long-term wave field evolution. The wind turbulence is computed using large-eddy simulation and the wave field is simulated using a high-order spectral method. Numerical experiments are carried out for turbulent wind blowing over a wave field initialised using the Joint North Sea Wave Project Spectrum, with various wind speeds considered. The results show that the waves, together with the mean wind flow and large turbulent eddies, have a significant impact on the wavenumber–frequency Spectrum of the wind turbulence. It is found that the shear stress contributed by sweep events in turbulent wind is greatly enhanced as a result of the waves. The dependence of the wave growth rate on the wave age is consistent with the results in the literature. The probability density function and high-order statistics of the wave surface elevation deviate from the Gaussian distribution, manifesting the nonlinearity of the wave field. The shape of the change in the Spectrum of wind-waves resembles that of the nonlinear wave–wave interactions, indicating the dominant role played by the nonlinear interactions in the evolution of the wave Spectrum. The frequency downshift phenomenon is captured in our simulations wherein the wind-forced wave field evolves for peak wave periods. Using the numerical result, we compute the universal constant in a wave-growth law proposed in the literature, and substantiate the scaling of wind–wave growth based on intrinsic wave properties.
