scholarly journals Spectral evolution of two-layer weak geostrophic turbulence. Part I: Typical scenarios

1996 ◽  
Vol 3 (3) ◽  
pp. 166-195 ◽  
Author(s):  
T. Soomere
Keyword(s):  
Large Scale ◽  
Rossby Waves ◽  
Initial Conditions ◽  
Local Equilibrium ◽  
Zonal Flow ◽  
Underlying Mechanism ◽  
Wave System ◽  
Spectral Evolution ◽  
Initial State ◽  
Geostrophic Turbulence

Abstract. Long-time evolution of large-scale geophysical flows is considered in a β-plane approximation. Motions in an infinite 2-layer model ocean are treated as a system of weakly nonlinear Rossby waves (weak geostrophic turbulence). The evolution of the energy spectrum of the barotropic and the baroclinic modes is investigated on the basis of numerical experiments with the kinetic equation for baroclinic Rossby waves. The basic features of free (nonforced inviscid) spectral evolution of baroclinic flows are similar to those of the barotropic motions. A portion of the energy is transferred to a sharp spectral peak while the rest of it is isotropically distributed. The peak corresponds to an intensive nearly zonal barotropic flow. Typically, this well-defined barotropic zonal anisotropy inhibits the reinforcement of its baroclinic analogy. For a certain set of initial conditions (in particular, if the barotropic zonal flow is not present initially), a zonal anisotropy of both modes is generated. The interplay between the multimodal nearly zonal flow components leads to the excitation of large-scale (several times exceeding the scale of the initial state), mostly meridional, baroclinic motions at the expense of the barotropic nearly zonal flow. The underlying mechanism is explained on the level of elementary mixed-triad interaction. The whole wave field retains its essentially baroclinic as well as spectrally broad nature. It evidently tends towards a thermodynamically equilibrated final state, consisting of the superposition of a (usually barotropic, but occasionally multimodal) zonal flow and a wave system with a Raleigh-Jeans spectrum. This evolution takes place as a multi-staged process, with fast convergence of the modal spectra to a local equilibrium followed by a more gradual adjustment of the energy balance between the modes.

scholarly journals Dynamics of Convectively Driven Banded Jets in the Laboratory

2007 ◽  
Vol 64 (11) ◽  
pp. 4031-4052 ◽  
Author(s):  
Peter L. Read ◽  
Yasuhiro H. Yamazaki ◽  
Stephen R. Lewis ◽  
Paul D. Williams ◽  
Robin Wordsworth ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flows ◽  
Large Scale ◽  
Zonal Flow ◽  
Inertial Range ◽  
Instability Criterion ◽  
Rossby Wave Breaking ◽  
Outer Planets ◽  
Zonal Jets ◽  
Geostrophic Turbulence

Abstract The banded organization of clouds and zonal winds in the atmospheres of the outer planets has long fascinated observers. Several recent studies in the theory and idealized modeling of geostrophic turbulence have suggested possible explanations for the emergence of such organized patterns, typically involving highly anisotropic exchanges of kinetic energy and vorticity within the dissipationless inertial ranges of turbulent flows dominated (at least at large scales) by ensembles of propagating Rossby waves. The results from an attempt to reproduce such conditions in the laboratory are presented here. Achievement of a distinct inertial range turns out to require an experiment on the largest feasible scale. Deep, rotating convection on small horizontal scales was induced by gently and continuously spraying dense, salty water onto the free surface of the 13-m-diameter cylindrical tank on the Coriolis platform in Grenoble, France. A “planetary vorticity gradient” or “β effect” was obtained by use of a conically sloping bottom and the whole tank rotated at angular speeds up to 0.15 rad s−1. Over a period of several hours, a highly barotropic, zonally banded large-scale flow pattern was seen to emerge with up to 5–6 narrow, alternating, zonally aligned jets across the tank, indicating the development of an anisotropic field of geostrophic turbulence. Using particle image velocimetry (PIV) techniques, zonal jets are shown to have arisen from nonlinear interactions between barotropic eddies on a scale comparable to either a Rhines or “frictional” wavelength, which scales roughly as (β/Urms)−1/2. This resulted in an anisotropic kinetic energy spectrum with a significantly steeper slope with wavenumber k for the zonal flow than for the nonzonal eddies, which largely follows the classical Kolmogorov k−5/3 inertial range. Potential vorticity fields show evidence of Rossby wave breaking and the presence of a “hyperstaircase” with radius, indicating instantaneous flows that are supercritical with respect to the Rayleigh–Kuo instability criterion and in a state of “barotropic adjustment.” The implications of these results are discussed in light of zonal jets observed in planetary atmospheres and, most recently, in the terrestrial oceans.

scholarly journals The Dynamics of Baroclinic Zonal Jets*

2015 ◽  
Vol 72 (3) ◽  
pp. 1137-1151 ◽  
Author(s):  
Paul D. Williams ◽  
Christopher W. Kelsall
Keyword(s):  
Root Mean Square ◽  
Power Law ◽  
Zonal Flow ◽  
Small Scale ◽  
Mean Square ◽  
Initial State ◽  
Zonal Jets ◽  
Rotation Periods ◽  
Inverse Energy Cascade ◽  
Geostrophic Turbulence

Abstract Multiple alternating zonal jets are a ubiquitous feature of planetary atmospheres and oceans. However, most studies to date have focused on the special case of barotropic jets. Here, the dynamics of freely evolving baroclinic jets are investigated using a two-layer quasigeostrophic annulus model with sloping topography. In a suite of 15 numerical simulations, the baroclinic Rossby radius and baroclinic Rhines scale are sampled by varying the stratification and root-mean-square eddy velocity, respectively. Small-scale eddies in the initial state evolve through geostrophic turbulence and accelerate zonally as they grow in horizontal scale, first isotropically and then anisotropically. This process leads ultimately to the formation of jets, which take about 2500 rotation periods to equilibrate. The kinetic energy spectrum of the equilibrated baroclinic zonal flow steepens from a −3 power law at small scales to a −5 power law near the jet scale. The conditions most favorable for producing multiple alternating baroclinic jets are large baroclinic Rossby radius (i.e., strong stratification) and small baroclinic Rhines scale (i.e., weak root-mean-square eddy velocity). The baroclinic jet width is diagnosed objectively and found to be 2.2–2.8 times larger than the baroclinic Rhines scale, with a best estimate of 2.5 times larger. This finding suggests that Rossby wave motions must be moving at speeds of approximately 6 times the turbulent eddy velocity in order to be capable of arresting the isotropic inverse energy cascade.

scholarly journals Solitary Rossby Waves in the Lower Tropical Troposphere

2013 ◽  
Vol 2013 ◽  
pp. 1-8
Author(s):  
Andre Lenouo ◽  
Francois Kamga Nkankam
Keyword(s):  
West Africa ◽  
Large Scale ◽  
Rossby Waves ◽  
Initial Conditions ◽  
Nonlinear Approximation ◽  
Tropical Storm ◽  
Weakly Nonlinear ◽  
African Easterly Jet ◽  
Tropical Troposphere ◽  
Cascade Method

Weakly nonlinear approximation is used to study the theoretical comportment of large-scale disturbances around the intertropical midtropospheric jet. We show here that the Korteweg de Vries (KdV) theory is appropriated to describe the structure of the streamlines around the African easterly jet (AEJ) region. The introduction of the additional velocity of the soliton C1 permits to search the stage where the configuration of the wave structures is going to emerge out of specified initial conditions and this is the direct and inverse cascade method. It was also shown that the configurations of disturbances can be influenced by this parameter so that we can look if the disturbances are in the control or not of their dispersive effects. This permits to explain the evolution of initial conditions of the Tropical Storm (TS) Debby over West Africa from 20 to 24 August 2006.

scholarly journals Sensitivity of High-Resolution Forecasts Using the Adjoint Technique at the 10-km Scale

2006 ◽  
Vol 134 (3) ◽  
pp. 772-790 ◽  
Author(s):  
Cornel Soci ◽  
Claude Fischer ◽  
András Horányi
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Initial Conditions ◽  
Nonlinear Flow ◽  
Gradient Field ◽  
Adjoint Model ◽  
Initial State ◽  
Gradient Computation ◽  
Sensitivity Studies ◽  
The One

Abstract This paper provides an experimental framework designed to assess the performance and the evolution of the diabatic Aire Limitée Adaptation Dynamique Développement International (ALADIN) adjoint model at 10-km grid size. Numerical experiments are carried out with the goal of evaluating the adjoint model solutions and the benefit of employing a complex linearized physical parameterization package in the gradient computation. Sensitivity studies with respect to initial conditions at high resolution on real meteorological events are performed. Numerical results obtained in the gradient computations show that, at high resolution, a strong nonlinear flow over complex orography might be a potential source of numerical instability in the absence of a robust dissipative physics employed in the adjoint model. Also, the scheme of the linearized large-scale precipitation is a source of noise in precipitating areas. The results on one particular case suggest that on the one hand the adjoint model is able to capture the dynamically sensitive area, but on the other hand the subsequent sensitivity forecast is more sensitive to the sign and the amplitude of the initial state perturbation rather than the structure of the gradient field.

The nonlinear properties of a large-scale dynamo driven by helical forcing

2002 ◽  
Vol 456 ◽  
pp. 219-237 ◽  
Author(s):  
FAUSTO CATTANEO ◽  
DAVID W. HUGHES ◽  
JEAN-CLAUDE THELEN
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Initial Conditions ◽  
Spatial Scales ◽  
Mean Field ◽  
Forced Flow ◽  
Small Scale ◽  
Dynamo Action ◽  
Initial State ◽  
The Magnetic Field

By considering an idealized model of helically forced flow in an extended domain that allows scale separation, we have investigated the interaction between dynamo action on different spatial scales. The evolution of the magnetic field is studied numerically, from an initial state of weak magnetization, through the kinematic and into the dynamic regime. We show how the choice of initial conditions is a crucial factor in determining the structure of the magnetic field at subsequent times. For a simulation with initial conditions chosen to favour the growth of the small-scale field, the evolution of the large-scale magnetic field can be described in terms of the α-effect of mean field magnetohydrodynamics. We have investigated this feature further by a series of related numerical simulations in smaller domains. Of particular significance is that the results are consistent with the existence of a nonlinearly driven α-effect that becomes saturated at very small amplitudes of the mean magnetic field.

An Analog Method for Real-Time Forecasting of Summer Monsoon Subseasonal Variability

2007 ◽  
Vol 135 (12) ◽  
pp. 4149-4160 ◽  
Author(s):  
Prince K. Xavier ◽  
B. N. Goswami
Keyword(s):  
Real Time ◽  
Summer Monsoon ◽  
Large Scale ◽  
Initial Conditions ◽  
Empirical Orthogonal Functions ◽  
Initial Condition ◽  
Analog Method ◽  
Initial State ◽  
Orthogonal Functions ◽  
Modeling Data

Abstract A physically based empirical real-time forecasting strategy to predict the subseasonal variations of the Indian summer monsoon up to four–five pentads (20–25 days) in advance has been developed. The method is based on the event-to-event similarity in the properties of monsoon intraseasonal oscillations (ISOs). This two-tier analog method is applied to NOAA outgoing longwave radiation (OLR) pentad averaged data that have sufficiently long records of observation and are available in nearly real time. High-frequency modes in the data are eliminated by reconstructing the data using the first 10 empirical orthogonal functions (EOFs), which together explain about 75% of the total variance. In the first level of the method, the spatial analogs of initial condition pattern are identified from the modeling data. The principal components (PCs) of these spatial analogs, whose evolution history of the latest five pentads matches that of the initial condition pattern, are considered the temporal PC analogs. Predictions are generated for each PC as the average evolution of PC analogs for the given lead time. Predicted OLR values are constructed using the EOFs and predicted PCs. OLR data for 1979–99 are used as the modeling data and independent hindcasts are generated for the period 2000–05. The skill of anomaly predictions is rather high over the central and northern Indian region for lead times of four–five pentads. The phases and amplitude of intraseasonal convective spells are predicted well, especially the long midseason break of 2002 that resulted in large-scale drought conditions. Skillful predictions can be made up to five pentads when started from an active initial state, whereas the limit of useful predictions is about two–three pentads when started from break initial conditions. An important feature of this method is that unlike some other empirical methods to forecast monsoon ISOs, it uses minimal time filtering to avoid any possible endpoint effects and hence may be readily used for real-time applications. Moreover, as the modeling data grow with time as a result of the increased number of observations, the number of analogs would also increase and eventually the quality of forecasts would improve.

scholarly journals Hurricane Intensity Predictability

2016 ◽  
Vol 97 (10) ◽  
pp. 1847-1857 ◽  
Author(s):  
Chanh Q. Kieu ◽  
Zachary Moon
Keyword(s):  
Large Scale ◽  
Initial Conditions ◽  
Numerical Models ◽  
Absolute Intensity ◽  
Limited Range ◽  
Mature Stage ◽  
Lead Times ◽  
Initial State ◽  
Hurricane Intensity ◽  
Chaotic Nature

Abstract Weather has long been projected to possess limited predictability due to the inherent chaotic nature of the atmosphere; small changes in initial conditions could lead to an entirely different state of the atmosphere after some period of time. Given such a limited range of predictability of atmospheric flows, a natural question is, how far in advance can we predict a hurricane’s intensity? In this study, it is shown first that the predictability of a hurricane’s intensity at the 4–5-day lead times is generally determined more by the large-scale environment than by a hurricane’s initial conditions. This result suggests that future improvement in hurricane longer-range intensity forecasts by numerical models will be most realized as a result of improvement in the large-scale environment rather than in the storm’s initial state. At the mature stage of a hurricane, direct estimation of the leading Lyapunov exponent using an axisymmetric model reveals, nevertheless, the existence of a chaotic attractor in the phase space of the hurricane scales. This finding of a chaotic maximum potential intensity (MPI) attractor provides direct information about the saturation of a hurricane’s intensity errors around 8 m s−1, which prevents the absolute intensity errors at the mature stage from being reduced below this threshold. The implication of such intensity error saturation to the limited range of hurricane intensity forecasts will be also discussed.

scholarly journals Scale Effects of Footings on Geocell Reinforced Sand Using Large-Scale Tests

2018 ◽  
Vol 4 (3) ◽  
pp. 497
Author(s):  
A. Shadmand ◽  
Mahmoud Ghazavi ◽  
Navid Ganjian
Keyword(s):  
Large Scale ◽  
Initial Conditions ◽  
Scale Effects ◽  
Friction Angle ◽  
Full Scale ◽  
Small Scale ◽  
Granular Soils ◽  
Initial State ◽  
The Difference ◽  
Mean Stresses

The scale effect on bearing capacity of shallow footings supported by unreinforced granular soils has been evaluated extensively. However, the subject has not been addressed for shallow footings on geocell-reinforced granular soils. In this study, load-settlement characteristic of large square footings is investigated by performing large-scale loading tests on unreinforced and geocell-reinforced granular soils. The effects of footing width (B), soil relative density of soil (Dr), and reinforcement depth (u) have been investigated. The test results show that the scale effects exist in geocell-reinforced soils, like unreinforced soils, and the behavior of small-scale models of footings cannot be directly related to the behavior of full-scale footings due to the difference between initial conditions of tests and the initial state of mean stresses in the soil beneath the footings having different dimensions. Large footings create higher mean stresses in the soil, resulting in low soil friction angle and initial conditions of the test approach to the critical state lines. The results of tests indicate that model experiments should be conducted on low-density soil for better prediction of the behavior of full-scale footings, otherwise, the predicted behavior of full-scale footings does not seem conservative.

Nonlinear interaction of small‐scale Rossby waves with an intense large‐scale zonal flow

1994 ◽  
Vol 6 (3) ◽  
pp. 1158-1167 ◽  
Author(s):  
Dmitrii Yu. Manin ◽  
Sergey V. Nazarenko
Keyword(s):  
Nonlinear Interaction ◽  
Large Scale ◽  
Rossby Waves ◽  
Zonal Flow ◽  
Small Scale

The emergence of isolated coherent vortices in turbulent flow

1984 ◽  
Vol 146 ◽  
pp. 21-43 ◽  
Author(s):  
James C. Mcwilliams
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Large Scale ◽  
Initial Conditions ◽  
Turnaround Time ◽  
Large Reynolds Number ◽  
Two Dimensional ◽  
Dominant Component ◽  
Geostrophic Turbulence ◽  
Large Scale Flow

A study is made of some numerical calculations of two-dimensional and geostrophic turbulent flows. The primary result is that, under a broad range of circumstances, the flow structure has its vorticity concentrated in a small fraction of the spatial domain, and these concentrations typically have lifetimes long compared with the characteristic time for nonlinear interactions in turbulent flow (i.e. an eddy turnaround time). When such vorticity concentrations occur, they tend to assume an axisymmetric shape and persist under passive advection by the large-scale flow, except for relatively rare encounters with other centres of concentration. These structures can arise from random initial conditions without vorticity concentration, evolving in the midst of what has been traditionally characterized as the ‘cascade’ of isotropic, homogeneous, large-Reynolds-number turbulence: the systematic elongation of isolines of vorticity associated with the transfer of vorticity to smaller scales, eventually to dissipation scales, and the transfer of energy to larger scales. When the vorticity concentrations are a sufficiently dominant component of the total vorticity field, the cascade processes are suppressed. The demonstration of persistent vorticity concentrations on intermediate scales - smaller than the scale of the peak of the energy spectrum and larger than the dissipation scales - does not invalidate many of the traditional characterizations of two-dimensional and geostrophic turbulence, but I believe it shows them to be substantially incomplete with respect to a fundamental phenomenon in such flows.

Sign in / Sign up

Export Citation Format

Share Document