What controls probability distribution of local wave activity in the midlatitudes?

2021 ◽  
Author(s):  
Noboru Nakamura ◽  
Claire Valva
Keyword(s):  
Probability Distributions ◽  
Wave Activity ◽  
Skewed Distribution ◽  
Vertical Shear ◽  
Wave Flow ◽  
Transient Eddy ◽  
Layer Model ◽  
Speed Increase ◽  
Local Wave ◽  
Two Layer Model

<p>We examine probability distributions of <em>local wave activity</em> (LWA), a measure of the jet stream's meander, and factors that control them.  The observed column-mean LWA distributions exhibit significant seasonal, interhemispheric, and regional variations but are always positively skewed in the extratropics, and their tail often involves disruptions of the jet stream.  A previously derived 1D traffic flow model driven by observed spectra of transient eddy forcing qualitatively reproduces the shape of the observed LWA distribution.  It is shown that the skewed distribution emerges from nonlinearity in the zonal advection of LWA even though the eddy forcing is symmetrically distributed.  A slower jet and stronger transient and stationary eddy forcings, when introduced independently, all broaden the LWA distribution and increase the probability of spontaneous jet disruption.  Quasigeostrophic two-layer model also simulates skewed LWA distributions in the upper layer.  However, in the two-layer model both transient eddy forcing and the jet speed increase with an increasing shear (meridional temperature gradient), and their opposing influence leaves the frequency of jet disruptions insensitive to the vertical shear.  When the model's nonlinearity in the zonal flux of potential vorticity is artificially suppressed, it hinders wave-flow interaction and virtually eliminates reversal of the upper-layer zonal wind.  The study underscores the importance of nonlinearity in the zonal transmission of Rossby waves to the frequency of jet disruptions and associated weather anomalies. </p>

scholarly journals The Influence of Stratification on the Instabilities in an Idealized Two-Layer Ocean Model

2014 ◽  
Vol 44 (10) ◽  
pp. 2718-2738 ◽  
Author(s):  
R. L. Irwin ◽  
F. J. Poulin
Keyword(s):  
Stability Analysis ◽  
Linear Stability Analysis ◽  
Nonlinear Evolution ◽  
Ocean Model ◽  
Vertical Shear ◽  
General Context ◽  
Layer Model ◽  
Different Types ◽  
Two Layer Model ◽  
Rotating Shallow Water

Abstract This work investigates the instability of a two-layer Bickley jet in the context of the rotating shallow water (RSW) model. This provides a general context in which the instability of oceanographic jets with simple stratification can be investigated. The three objectives of this work are as follows: First, the study investigates the morphology of unstable modes that can occur in this two-layer model. This is done by performing a linear stability analysis to investigate different types of flows both with and without vertical shear. Second, the authors study how the growth rates of the unstable modes are affected by changes in the stratification. Third, this study looks at the nonlinear evolution of some of these instabilities to determine how easy it is for nonprimary instabilities to develop. This is motivated by the fact that in the literature there have been many investigations that have found a multitude of unstable modes in this model, and it is not evident as to how easily they can be generated in oceanographic flows.

Baroclinic instability of quasi-geostrophic flows localized in a thin layer

1995 ◽  
Vol 288 ◽  
pp. 175-199 ◽  
Author(s):  
E. S. Benilov
Keyword(s):  
Baroclinic Instability ◽  
Vertical Shear ◽  
Layer Model ◽  
Effective Time ◽  
Sufficient Stability ◽  
Geostrophic Flows ◽  
Characteristic Spatial Scale ◽  
Northern Pacific ◽  
Two Layer Model ◽  
Layer I

This paper examines the baroclinic instability of a quasi-geostrophic flow with vertical shear in a continuously stratified fluid. The flow and density stratification are both localized in a thin upper layer. (i) Disturbances whose wavelength is much smaller than the deformation radius (based on the depth of the upper layer) are demonstrated to satisfy an ‘equivalent two-layer model’ with properly chosen parameters. (ii) For disturbances whose wavelength is of the order of, or greater than, the deformation radius we derive a sufficient stability criterion. The above analysis is applied to the subtropical and subarctic frontal currents in the Northern Pacific. The effective time of growth of disturbances (i) is found to be 16–22 days, the characteristic spatial scale is 130–150 km.

scholarly journals Blocking Statistics in a Varying Climate: Lessons from a “Traffic Jam” Model with Pseudostochastic Forcing

2019 ◽  
Vol 76 (10) ◽  
pp. 3013-3027 ◽  
Author(s):  
Adiv Paradise ◽  
Cesar B. Rocha ◽  
Pragallva Barpanda ◽  
Noboru Nakamura
Keyword(s):  
Wave Amplitude ◽  
Stationary Wave ◽  
Reanalysis Data ◽  
Wave Activity ◽  
Future Trend ◽  
Boreal Winter ◽  
Stationary Waves ◽  
Transient Eddy ◽  
Dominant State ◽  
Local Wave

Abstract Recently Nakamura and Huang proposed a semiempirical, one-dimensional model of atmospheric blocking based on the observed budget of local wave activity in the boreal winter. The model dynamics is akin to that of traffic flow, wherein blocking manifests as traffic jams when the streamwise flux of local wave activity reaches capacity. Stationary waves modulate the jet stream’s capacity to transmit transient waves and thereby localize block formation. Since the model is inexpensive to run numerically, it is suited for computing blocking statistics as a function of climate variables from large-ensemble, parameter sweep experiments. We explore sensitivity of blocking statistics to (i) stationary wave amplitude, (ii) background jet speed, and (iii) transient eddy forcing, using frequency, persistence, and prevalence as metrics. For each combination of parameters we perform 240 runs of 180-day simulations with aperiodic transient eddy forcing, each time randomizing the phase relations in forcing. The model climate shifts rapidly from a block-free state to a block-dominant state as the stationary wave amplitude is increased and/or the jet speed is decreased. When eddy forcing is increased, prevalence increases similarly but frequency decreases as blocks merge and become more persistent. It is argued that the present-day climate lies close to the boundary of the two states and hence its blocking statistics are sensitive to climate perturbations. The result underscores the low confidence in GCM-based assessment of the future trend of blocking under a changing climate, while it also provides a theoretical basis for evaluating model biases and understanding trends in reanalysis data.

Coherent structures of nonlinear barotropic-baroclinic interaction in unequal depth two-layer model

2021 ◽  
Vol 408 ◽  
pp. 126347
Author(s):  
Jiaqi Zhang ◽  
Ruigang Zhang ◽  
Liangui Yang ◽  
Quansheng Liu ◽  
Liguo Chen
Keyword(s):  
Coherent Structures ◽  
Layer Model ◽  
Two Layer Model

Propagation and localization of Rossby waves over random topography (two-layer model)

Wave Motion ◽  
1998 ◽  
Vol 28 (4) ◽  
pp. 333-352 ◽  
Author(s):  
V.I. Klyatskin ◽  
N.V. Gryanik ◽  
D. Gurarie
Keyword(s):  
Rossby Waves ◽  
Layer Model ◽  
Two Layer Model
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