scholarly journals Baroclinic Eddy Equilibration under Specified Seasonal Forcing

2010 ◽  
Vol 67 (8) ◽  
pp. 2632-2648 ◽  
Author(s):  
Yang Zhang ◽  
Peter H. Stone
Keyword(s):  
Time Scale ◽  
Late Spring ◽  
Time Interval ◽  
External Forcing ◽  
Moist Convection ◽  
Mean Flow ◽  
Seasonal Behavior ◽  
Eddy Activity ◽  
Late Fall ◽  
Baroclinic Adjustment

Abstract Baroclinic eddy equilibration under a Northern Hemisphere–like seasonal forcing is studied using a modified multilayer quasigeostrophic channel model to investigate the widely used “quick baroclinic eddy equilibration” assumption and to understand to what extent baroclinic adjustment can be applied to interpret the midlatitude climate. Under a slowly varying seasonal forcing, the eddy and mean flow seasonal behavior is characterized by four clearly divided time intervals: an eddy inactive time interval in summer, a mainly dynamically determined eddy spinup time interval starting in midfall and lasting less than one month, and a quasi-equilibrium time interval for the zonal mean flow available potential energy from late fall to late spring, with a mainly external forcing determined spindown time interval for eddy activity from late winter to late spring. The baroclinic adjustment can be clearly observed from late fall to late spring. The sensitivity study of the eddy equilibration to the time scale of the external forcing indicates that the time scale separation between the baroclinic adjustment and the external forcing in midlatitudes is only visible for external forcing cycles one year and longer. In spite of the strong seasonality of the eddy activity, similar to the observations, a robust potential vorticity (PV) structure is still observed through all the seasons. However, it is found that baroclinic eddy is not the only candidate mechanism to maintain the robust PV structure. The role of the boundary layer thermal forcing and the moist convection in maintaining the lower-level PV structure is discussed. The adjustment and the vertical variation of the lower-level stratification play an important role in all of these mechanisms.

Amplitudes of Composition Fluctuations in the Simplest Chemical Reaction Equilibrium

2004 ◽  
Vol 218 (9) ◽  
pp. 1033-1040 ◽  
Author(s):  
M. Šolc ◽  
J. Hostomský
Keyword(s):  
Random Walk ◽  
Discrete Time ◽  
Continuous Time ◽  
Time Scale ◽  
Numerical Study ◽  
Mean Amplitude ◽  
Time Interval ◽  
The Mean ◽  
Composition Fluctuations ◽  
Number Of Particles

AbstractWe present a numerical study of equilibrium composition fluctuations in a system where the reaction X1 ⇔ X2 having the equilibrium constant equal to 1 takes place. The total number of reacting particles is N. On a discrete time scale, the amplitude of a fluctuation having the lifetime 2r reaction events is defined as the difference between the number of particles X1 in the microstate most distant from the microstate N/2 visited at least once during the fluctuation lifetime, and the equilibrium number of particles X1, N/2. On the discrete time scale, the mean value of this amplitude, m̅(r̅), is calculated in the random walk approximation. On a continuous time scale, the average amplitude of fluctuations chosen randomly and regardless of their lifetime from an ensemble of fluctuations occurring within the time interval (0,z), z → ∞, tends with increasing N to ~1.243 N0.25. Introducing a fraction of fluctuation lifetime during which the composition of the system spends below the mean amplitude m̅(r̅), we obtain a value of the mean amplitude of equilibrium fluctuations on the continuous time scale equal to ~1.19√N. The results suggest that using the random walk value m̅(r̅) and taking into account a) the exponential density of fluctuations lifetimes and b) the fact that the time sequence of reaction events represents the Poisson process, we obtain values of fluctuations amplitudes which differ only slightly from those derived for the Ehrenfest model.

The Variability of the Atlantic Storm Track and the North Atlantic Oscillation: A Link between Intraseasonal and Interannual Variability

2011 ◽  
Vol 68 (3) ◽  
pp. 577-601 ◽  
Author(s):  
Dehai Luo ◽  
Yina Diao ◽  
Steven B. Feldstein
Keyword(s):  
North Atlantic Oscillation ◽  
Interannual Variability ◽  
North Atlantic ◽  
Storm Track ◽  
Positive Phase ◽  
Negative Phase ◽  
Time Interval ◽  
European Continent ◽  
Eddy Activity ◽  
Nao Index

Abstract The winter-mean North Atlantic Oscillation (NAO) index has been mostly positive since the 1980s, with a linear upward trend during the period from 1978 to 1990 (P1) and a linear downward trend during the period from 1991 to 2009 (P2). Further calculations show that the Atlantic storm-track eddy activity is more intense during P2 than during P1, which is statistically significant at the 90% confidence level for a t test. This study proposes a hypothesis that the change in the trend of the positive NAO index from P1 to P2 may be associated with the marked intensification of the Atlantic storm track during P2. A generalized nonlinear NAO model is used to explain the observed trend of the positive NAO index within P2. It is found that even when the Atlantic storm-track eddies are less intense, a positive-phase NAO event can form under the eddy forcing if the planetary-scale wave has an initial value with a low-over-high dipole structure during P1 and P2. A blocking flow can occur in the downstream side (over Europe) of the Atlantic basin as a result of the energy dispersion of Rossby waves during the decay of the positive-phase NAO event. This blocking flow does not strictly correspond to a negative-phase NAO event because the blocking stays mainly over the European continent. However, when the Atlantic storm-track eddies are rather strong, the blocking flow occurring over the European continent is enhanced and can retrograde into the Atlantic region and finally become a long-lived negative-phase NAO event. In this case, the NAO event can transit from the positive phase to the negative phase. Thus, the winter-mean NAO index during P2 will inevitably decline because of the increase in days of negative-phase NAO events in winter because the Atlantic storm track exhibits a marked intensification in the time interval. The transition of the NAO event from the positive phase to the negative phase can also be observed only when the downstream development of the Atlantic storm-track eddy activity is rather prominent. Thus, it appears that there is a physical link between intraseasonal and interannual time scales of the NAO when the Atlantic storm track exhibits an interannual variability.

Barotropic and Baroclinic Eddy Feedbacks in the Midlatitude Jet Variability and Responses to Climate Change–Like Thermal Forcings

2016 ◽  
Vol 74 (1) ◽  
pp. 111-132 ◽  
Author(s):  
D. Alex Burrows ◽  
Gang Chen ◽  
Lantao Sun
Keyword(s):  
Climate Change ◽  
Time Scale ◽  
Climate Models ◽  
Atmospheric Model ◽  
Finite Amplitude ◽  
Mean Flow ◽  
Annular Mode ◽  
Flow Interactions ◽  
Jet Variability ◽  
Vertically Propagating

Abstract Studies have suggested that the persistence in the meridional vacillation of the midlatitude jet (i.e., annular mode time scale) in comprehensive climate models is related to the model biases in climatological jet latitude, with important implications for projections of future climates and midlatitude weather events. Through the use of the recently developed finite-amplitude wave activity formalism and feedback quantifying techniques, this paper has quantified the role of barotropic and baroclinic eddy feedbacks in annular mode time scales using an idealized dry atmospheric model. The eddy–mean flow interaction that characterizes the persistent anomalous state of the midlatitude jet depends on processes associated with the lower-tropospheric source of vertically propagating Rossby waves, baroclinic mechanisms, and processes associated with upper-tropospheric wave propagation and breaking, barotropic mechanisms. A variety of climate change–like thermal forcings are used to generate a range of meridional shifts in the midlatitude eddy-driven jet. The idealized model shows a reduction in annular mode time scale associated with an increase in jet latitude, similar to comprehensive climate models. This decrease in time scale can be attributed to a similar decrease in the strength of the barotropic eddy feedback, which, in the positive phase of the annular mode, is characterized by anomalous potential vorticity (PV) mixing on the equatorward flank of the climatological jet. The decrease in subtropical PV mixing is, in turn, associated with a stronger subtropical jet as the eddy-driven jet is more distant from the subtropics. These results highlight the importance of subtropical eddy–mean flow interactions for the persistence of an eddy-driven jet.

Decadal variability of the Kuroshio Extension

2020 ◽  
Author(s):  
Guidi Zhou ◽  
Xuhua Cheng
Keyword(s):  
Decadal Variability ◽  
Kuroshio Extension ◽  
Relaxation Oscillation ◽  
Mesoscale Eddy ◽  
Height Anomaly ◽  
Intrinsic Variability ◽  
Mean Flow ◽  
The Real ◽  
Eddy Activity ◽  
The Kuroshio

<p>The decadal variability of the Kuroshio Extension (KE) is investigated using altimeter observations (AVISO) and the output of an ocean model (OFES). It is shown that the KE decadal variability is manifested in its strength, latitudinal position, and zonal extent, as well as the associated mesoscale eddy activity. Two differences between the two datasets are identified: (a) In OFES, the eddy activity positively correlates with the KE mode index when it leads by a few years, whereas in AVISO the two are negatively and concurrently correlated. (b) In OFES, the positive KE mode is associated with large meanders of the Kuroshio south of Japan, but in AVISO they are irrelevant. These differences indicate that the generation mechanism of KE's decadal variability is different in OFES and the real ocean. The sea surface height anomaly (SSHA) is then decomposed into major components including the wind-driven Rossby waves and residual (intrinsic) variability. The relationship between the two components are virtually the same in OFES and in AVISO, showing a negative correlation when the wind-driven part leads by a few years. Further diagnostics based on OFES reveals that the residual SSHA originates from the downstream region over the Shatsky Rise, slowly propagates westward, and is driven by eddy potential energy transfer. The OFES results partly conform to the intrinsic relaxation oscillation theory put forth by idealized model analyses, but in the latter the SSHA signal originates from the upstream Kuroshio. A new mechanism is then proposed for OFES: the decadal variability of the KE is first a result of the intrinsic relaxation oscillation probably excited by wind forcing, which regulates the strength of the KE’s inflow and thus modulates the downstream topography interaction, resulting in different downstream mesoscale eddy activity that further feeds back on the mean-flow. The mechanism for the real ocean is also reassessed.</p>

Statistical Tests of Taylor’s Hypothesis: An Application to Precipitation Fields

2009 ◽  
Vol 10 (1) ◽  
pp. 254-265 ◽  
Author(s):  
Bo Li ◽  
Aditya Murthi ◽  
Kenneth P. Bowman ◽  
Gerald R. North ◽  
Marc G. Genton ◽  
...  
Keyword(s):  
Correlation Analysis ◽  
Time Scale ◽  
Statistical Tests ◽  
Spatial Scales ◽  
Statistical Significance ◽  
Time Lag ◽  
Mean Flow ◽  
Spatial Covariance ◽  
Simple Correlation ◽  
Taylor’S Hypothesis

Abstract The Taylor hypothesis (TH) as applied to rainfall is a proposition about the space–time covariance structure of the rainfall field. Specifically, it supposes that if a spatiotemporal precipitation field with a stationary covariance Cov(r, τ) in both space r and time τ moves with a constant velocity v, then the temporal covariance at time lag τ is equal to the spatial covariance at space lag r = vτ that is, Cov(0, τ) = Cov(vτ, 0). Qualitatively this means that the field evolves slowly in time relative to the advective time scale, which is often referred to as the frozen field hypothesis. Of specific interest is whether there is a cutoff or decorrelation time scale for which the TH holds for a given mean flow velocity v. In this study, the validity of the TH is tested for precipitation fields using high-resolution gridded Next Generation Weather Radar (NEXRAD) reflectivity data produced by the WSI Corporation by employing two different statistical approaches. The first method is based on rigorous hypothesis testing, while the second is based on a simple correlation analysis, which neglects possible dependencies between the correlation estimates. Radar reflectivity values are used from the southeastern United States with an approximate horizontal resolution of 4 km × 4 km and a temporal resolution of 15 min. During the 4-day period from 2 to 5 May 2002, substantial precipitation occurs in the region of interest, and the motion of the precipitation systems is approximately uniform. The results of both statistical methods suggest that the TH might hold for the shortest space and time scales resolved by the data (4 km and 15 min) but that it does not hold for longer periods or larger spatial scales. Also, the simple correlation analysis tends to overestimate the statistical significance through failing to account for correlations between the covariance estimates.

scholarly journals Optimal Surface Excitation of the Thermohaline Circulation

2008 ◽  
Vol 38 (8) ◽  
pp. 1820-1830 ◽  
Author(s):  
Laure Zanna ◽  
Eli Tziperman
Keyword(s):  
Surface Temperature ◽  
Time Scale ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Initial Conditions ◽  
Singular Problem ◽  
Mean Flow ◽  
L2 Norm ◽  
Basin Scale ◽  
The Mean

Abstract The amplification of thermohaline circulation (THC) anomalies resulting from heat and freshwater forcing at the ocean surface is investigated in a zonally averaged coupled ocean–atmosphere model. Optimal initial conditions of surface temperature and salinity leading to the largest THC growth are computed, and so are the structures of stochastic surface temperature and salinity forcing that excite maximum THC variance (stochastic optimals). When the THC amplitude is defined as its sum of squares (equivalent to using the standard L2 norm), the nonnormal linearized dynamics lead to an amplification with a time scale on the order of 100 yr. The optimal initial conditions have a vanishing THC anomaly, and the complex amplification mechanism involves the advection of both temperature and salinity anomalies by the mean flow and of the mean temperature and salinity by the anomaly flow. The L2 characterization of THC anomalies leads to physically interesting results, yet to a mathematically singular problem. A novel alternative characterizing the THC amplitude by its maximum value, as often done in general circulation model studies, is therefore introduced. This complementary method is shown to be equivalent to using the L-infinity norm, and the needed mathematical approach is developed and applied to the THC problem. Under this norm, an amplification occurs within 10 yr explained by the classic salinity advective feedback mechanism. The analysis of the stochastic optimals shows that the character of the THC variability may be very sensitive to the spatial pattern of the surface forcing. In particular, a maximum THC variance and long-time-scale variability are excited by a basin-scale surface forcing pattern, while a significantly higher frequency and to some extent a weaker variability are induced by a smooth and large-scale, yet mostly concentrated in polar areas, surface forcing pattern. Overall, the results suggest that a large THC variability can be efficiently excited by atmospheric surface forcing, and the simple model used here makes several predictions that would be interesting to test using more complex models.

Isotopic variations in primitive meteorites

1981 ◽  
Vol 303 (1477) ◽  
pp. 339-349 ◽  
Keyword(s):  
Solar System ◽  
Time Scale ◽  
Decay Product ◽  
Common Source ◽  
Time Interval ◽  
Crystal Formation ◽  
Ordinary Chondrites ◽  
Gas Reservoir ◽  
Oxygen Isotopic ◽  
Isotopic Variations

Oxygen isotopic variations in carbonaceous chondrites and in ordinary chondrites can each be interpreted as mixtures of two isotopically different reservoirs, one consisting of solids, enriched in 16 O , the other of a gas, depleted in 16 O relative to terrestrial abundances. The data suggest a common source of the solids for each of the two classes of meteorites, but a different gas reservoir for each. These conditions might prevail in gaseous protoplanets. Radiogenic 26 Mg is variable in abundance among some classes of Allende inclusions, implying either nebular heterogeneity with respect to 26 A1/ 27 Al ratios, or time differences of crystal formation of 1 or 2 x 10 6 a. The presence of excess 107 Ag from decay of extinct 107 Pd supports the evidence from 26 Mg for a time interval of at most a few million years between the last nucleosynthetic event and accretion of substantial bodies in the Solar System. The widespread small excess of 50 Ti in Allende inclusions is tantalizing, but unexplained. An exceptional hibonite-rich inclusion from Allende contains strongly fractionated isotopes of oxygen and calcium, but isotopically normal magnesium. Its trace elements imply association with a hot, oxidized gas. Among the volatile elements, neon-E has been shown to be essentially pure 22 Ne, and appears to be the decay product of extinct 22 Na. If so, condensation of some stellar ejecta must take place on a time scale of a year or so. The problem of reconciling the 26 A1 time scale of about 10 6 years between nucleosynthesis and Solar System condensation with the 10 8 year scale implied by the decay of 129 I to 129 Xe and fission of 244 Pu requires that at most a small fraction of the 129 I and 244 Pu be formed in the most recent event. Progress has been made in establishing the carrier phases of isotopically anomalous xenon and krypton. The apparent location of anomalous xenon and 14 N-rich nitrogen in identical carriers supports the notion that nucleosynthetic anomalies in nitrogen are also present in Allende.

Timing of Soil-Residual Herbicide Applications for Control of Giant Ragweed (Ambrosia trifida)

2015 ◽  
Vol 29 (4) ◽  
pp. 771-781 ◽  
Author(s):  
R. Joseph Wuerffel ◽  
Julie M. Young ◽  
Joseph L. Matthews ◽  
Vince M. Davis ◽  
William G. Johnson ◽  
...  
Keyword(s):  
Field Experiments ◽  
Early Spring ◽  
Late Spring ◽  
Weed Species ◽  
Southern Illinois ◽  
Application Timing ◽  
Late Fall ◽  
Emergence Patterns ◽  
Giant Ragweed ◽  
Residual Control

Fall-applied residual and spring preplant burn-down herbicide applications are typically used to control winter annual weeds and may also provide early-season residual control of summer annual weed species such as giant ragweed. Field experiments were conducted from 2006 to 2008 in southern Illinois to (1) assess the emergence pattern of giant ragweed, (2) evaluate the efficacy of several herbicides commonly used for soil-residual control of giant ragweed, and (3) investigate the optimal application timing of soil-residual herbicides for control of giant ragweed. Six herbicide treatments were applied at four application timings: early fall, late fall, early spring, and late spring. Giant ragweed first emerged in mid- and late-March in 2007 and 2008, respectively. The duration of emergence varied by year, with 95% of emergence complete in late May of 2008, but not until early July in 2007. Giant ragweed emergence occurred more quickly in plots that received a fall application of glyphosate + 2,4-D compared with the nontreated. Fall-applied residual herbicides did not reduce giant ragweed emergence in 2007 when compared with the nontreated, with the exception of chlorimuron + tribenuron applied in late fall. Giant ragweed control from early- and late-spring herbicide applications was variable by year. In 2007, saflufenacil (50 and 100 g ai ha−1) and simazine applied in early spring reduced giant ragweed densities by 95% or greater through mid-May; however, in 2008, early-spring applications failed to reduce giant ragweed emergence in mid-April. The only treatments that reduced giant ragweed densities by > 80% through early July were late-spring applications of chlorimuron + tribenuron or saflufenacil at 100 g ha−1. Thus, the emergence patterns of giant ragweed in southern Illinois dictates that best management with herbicides would include late-spring applications of soil-residual herbicides just before crop planting and most likely requires subsequent control with foliar or soil-residual herbicides after crop emergence.

DNS of the thermal effects of laser energy deposition in isotropic turbulence

2010 ◽  
Vol 654 ◽  
pp. 387-416
Author(s):  
SHANKAR GHOSH ◽  
KRISHNAN MAHESH
Keyword(s):  
Shock Wave ◽  
Time Scale ◽  
Energy Deposition ◽  
Isotropic Turbulence ◽  
Radial Distance ◽  
Working Fluid ◽  
Shock Propagation ◽  
Mean Flow ◽  
Turbulent Reynolds Number ◽  
The Mean

The interaction of a laser-induced plasma with isotropic turbulence is studied using numerical simulations. The simulations use air as the working fluid and assume local thermodynamic equilibrium. The numerical method is fully spectral and uses a shock-capturing scheme in a corrector step. A model problem involving the effect of energy deposition on an isolated vortex is studied as a first step towards plasma/turbulence interaction. Turbulent Reynolds number Reλ = 30 and fluctuation Mach numbers Mt = 0.001 and 0.3 are considered. A tear-drop-shaped shock wave is observed to propagate into the background, and progressively become spherical in time. The turbulence experiences strong compression due to the shock wave and strong expansion in the core. This behaviour is spatially inhomogeneous and non-stationary in time. Statistics are computed as functions of radial distance from the plasma axis and angular distance across the surface of the shock wave. For Mt = 0.001, the shock wave propagates on a much faster time scale compared to the turbulence evolution. At Mt of 0.3, the time scale of the shock wave is comparable to that of the background. For both cases the mean flow is classified into shock formation, shock propagation and subsequent collapse of the plasma core, and the effect of turbulence on each of these phases is studied in detail. The effect of mean vorticity production on the turbulent vorticity field is also discussed. Turbulent kinetic energy budgets are presented to explain the mechanism underlying the transfer of energy between the mean flow and background turbulence.

A Laser Dual-Beam Method for Flow Measurements in Turbomachines

1974 ◽  
Author(s):  
R. Schodl
Keyword(s):  
Signal To Noise Ratio ◽  
Time Interval ◽  
Mean Flow ◽  
Mean Velocity ◽  
Supersonic Wind Tunnel ◽  
Flow Measurements ◽  
Flow Angle ◽  
Plane Normal ◽  
Doppler Probe ◽  
The Mean

Similar to the Doppler technique the principle of this method is also based on light scattered by small particles as they are normally contained in every fluid. Two light beams (laser beams are not necessary) are focused in two very small light spots in the measuring volume. Particles passing both the spots emit two light pulses which can be detected by a photomultiplier. From the time interval between these two pulses and from the known spots distance the flow velocity can be calculated. A statistical analysis of many signals, taken at the same treasuring point, allows calculation of the mean velocity, the mean flow angle and the turbulence degree of the velocity components in a plane normal to the beam axis. Due to the light intensity of the light spots (102 to 103 times higher than the intensity in a Doppler probe volume under similar conditions) a sufficient signal-to-noise ratio is achieved so that velocity measurements even in unseeded air flows are possible up to 500 m/s in backscattering by using a 5 mW laser. Tests were carried out in a supersonic wind tunnel up to a Mach number of 2.2. For measurements in the rotor blade channels of turbomachines a specific trigger optic has been installed.

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