On the Synoptic-Scale Lagrangian Autocorrelation Function

Daoud, Wessam Z.; Kahl, Jonathan D. W.; Ghorai, J. K.

doi:10.1175/1520-0450(2003)042<0318:otssla>2.0.co;2

Cited by 16 publications

(12 citation statements)

References 27 publications

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“…In their study of synoptic-scale Lagrangian autocorrelation function, Daoud et al (2003) analyzed a large database of modeled 10-day atmospheric trajectories, and they showed indeed an autocorrelation function whose shape is similar to that in our study (although in their case, it is the horizontal velocity autocorrelation). They also related this shape to wavelike motion of the particle in the atmosphere.…”

Section: Lagrangian Statisticssupporting

confidence: 88%

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Relating Eulerian and Lagrangian Statistics for the Turbulent Dispersion in the Atmospheric Convective Boundary Layer

Dosio

Arellano

Holtslag

et al. 2005

Journal of the Atmospheric Sciences

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Eulerian and Lagrangian statistics in the atmospheric convective boundary layer (CBL) are studied by means of large eddy simulation (LES). Spectra analysis is performed in both the Eulerian and Lagrangian frameworks, autocorrelations are calculated, and the integral length and time scales are derived. Eulerian statistics are calculated by means of spatial and temporal analysis in order to derive characteristic length and time scales. Taylor's hypothesis of frozen turbulence is investigated, and it is found to be satisfied in the simulated flow.Lagrangian statistics are derived by tracking the trajectories of numerous particles released at different heights in the turbulent flow. The relationship between Lagrangian properties (autocorrelation functions) and dispersion characteristics (particles' displacement) is studied through Taylor's diffusion relationship, with special emphasis on the difference between horizontal and vertical motion. Results show that for the horizontal motion, Taylor's relationship is satisfied. The vertical motion, however, is influenced by the inhomogeneity of the flow and limited by the ground and the capping inversion at the top of the CBL. The Lagrangian autocorrelation function, therefore, does not have an exponential shape, and consequently, the integral time scale is zero. If distinction is made between free and bounded motion, a better agreement between Taylor's relationship and the particles' vertical displacement is found.Relationships between Eulerian and Lagrangian frameworks are analyzed by calculating the ratio ␤ between Lagrangian and Eulerian time scales. Results show that the integral time scales are mainly constant with height for z/z i Ͻ 0.7. In the upper part of the CBL, the capping inversion transforms vertical motion into horizontal motion. As a result, the horizontal time scale increases with height, whereas the vertical one is reduced. Current parameterizations for the ratio between the Eulerian and Lagrangian time scales have been tested against the LES results showing satisfactory agreement at heights z/z i Ͻ 0.7.

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Section: Lagrangian Statisticssupporting

confidence: 88%

“…The Eulerian autocorrelation function is calculated as follows (Daoud et al 2003): The autocorrelation is then spatially averaged over all the fixed measurement positions. Spatial autocorrelation is calculated from the velocities u i measured at different positions along the wind direction (recorded every 10 min) as follows:…”

Section: A Eulerian Statisticsmentioning

confidence: 99%

Relating Eulerian and Lagrangian Statistics for the Turbulent Dispersion in the Atmospheric Convective Boundary Layer

Dosio

Arellano

Holtslag

et al. 2005

Journal of the Atmospheric Sciences

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“…The mean length scale L near the surface in midlatitudes is on the order of 10 000 km or greater in the zonal mean in all seasons. By contrast, the mixing length L 0 near the surface is on the order of 900 km, given an rms meridional velocity V ; 10 m s 21 and the measured Lagrangian integral time scale t ; 1 day (Swanson and Pierrehumbert 1997;Daoud et al 2003). Dividing synoptic potential temperature anomalies u 0 near the surface by mean gradients › y u also gives similar mixing lengths (KeppelAleks et al 2011(KeppelAleks et al , 2012.…”

Section: Theory a Potential Temperature Variancesupporting

confidence: 80%

“…Note that the Lagrangian mixing length L 0 need not be equal to Eulerian eddy length scales. It generally is smaller, particularly near the surface, where strong thermal coupling to the surface leads to Lagrangian integral time scales t that are smaller (about 1 day) than eddy time scales (several days) (Swanson and Pierrehumbert 1997;Daoud et al 2003).…”

Section: Theory a Potential Temperature Variancementioning

confidence: 99%

Physics of Changes in Synoptic Midlatitude Temperature Variability

2015

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This paper examines the physical processes controlling how synoptic midlatitude temperature variability near the surface changes with climate. Because synoptic temperature variability is primarily generated by advection, it can be related to mean potential temperature gradients and mixing lengths near the surface. Scaling arguments show that the reduction of meridional potential temperature gradients that accompanies polar amplification of global warming leads to a reduction of the synoptic temperature variance near the surface. This is confirmed in simulations of a wide range of climates with an idealized GCM. In comprehensive climate simulations (CMIP5), Arctic amplification of global warming similarly entails a large-scale reduction of the near-surface temperature variance in Northern Hemisphere midlatitudes, especially in winter. The probability density functions of synoptic near-surface temperature variations in midlatitudes are statistically indistinguishable from Gaussian, both in reanalysis data and in a range of climates simulated with idealized and comprehensive GCMs. This indicates that changes in mean values and variances suffice to account for changes even in extreme synoptic temperature variations. Taken together, the results indicate that Arctic amplification of global warming leads to even less frequent cold outbreaks in Northern Hemisphere winter than a shift toward a warmer mean climate implies by itself.

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“…The problem, therefore, persists regardless of the size of ensemble used. These results are analogous to the results presented by Salman et al for the more realistic double gyre flow in which the EnKF diverged for t assim > T L where T L is the Lagrangian autocorrelation time-scale (Daoud et al, 2003). The results presented in Figures 4(a,b) for our hybrid filter, therefore, show a substantial improvement over the results of the EnKF.…”

Section: Resultsmentioning

confidence: 58%

A hybrid grid/particle filter for Lagrangian data assimilation. II: Application to a model vortex flow

Salman

2008

Quart J Royal Meteoro Soc

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ABSTRACT:We apply our hybrid filter to a regularised vortex model of a co-rotating vortex pair. To illustrate the main advantages of our formulation over existing filters, we compare our method to the perturbed observation Ensemble Kalman filter and a particle filter with Gaussian resampling. Our numerical simulations show that both the hybrid and particle filters can track the true vortex positions even when tracer position data is assimilated infrequently into our model. In contrast, the Ensemble Kalman filter diverges in this parameter range as was recently observed in the more realistic shallow-water model simulations of Salman et al. We have found that our hybrid method can track the true system with as few as 20 members for the vortex model flow. The particle filter on the other hand requires an ensemble comprising in excess of 160 members. The hybrid filter, therefore, provides one solution to the filter divergence problem that has been identified in recent work on Lagrangian data assimilation.

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On the Synoptic-Scale Lagrangian Autocorrelation Function

Cited by 16 publications

References 27 publications

Relating Eulerian and Lagrangian Statistics for the Turbulent Dispersion in the Atmospheric Convective Boundary Layer

Relating Eulerian and Lagrangian Statistics for the Turbulent Dispersion in the Atmospheric Convective Boundary Layer

Physics of Changes in Synoptic Midlatitude Temperature Variability

A hybrid grid/particle filter for Lagrangian data assimilation. II: Application to a model vortex flow

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