Showing papers on "Rossby radius of deformation published in 1991"

Can Reflected Extra-equatorial Rossby Waves Drive ENSO?

Abstract: The possibility that the evolution of the ENSO phenomenon is determined by the reflection of extra-equatorial Rossby waves from the western boundary into the equatorial waveguide has been a subject of recent debate. Observations and some wind-driven models suggest an apparent continuity of off-equatorial signals and subsequent waveguide anomalies. On the other hand, coupled model results show that ENSO-like behavior can be simulated with no involvement of the extra-equatorial regions. Linear equatorial wave theory shows that significant reflection can only occur within about 8° of the equator, with a sharp fall-off in the reflectivity poleward of this latitude. Although the amplitude of the thermocline anomalies associated with observed ENSO-forced extra-equatorial Rossby waves can be large, it is the net zonal transport of these waves that is crucial to the reflectivity, and this net transport decreases rapidly as Rossby waves occur farther from the equator. The zonal geostrophic flows associate...

Analysis of remotely forced oceanic Rossby waves off California

Abstract: Complex empirical orthogonal function (CEOF) analysis is used to investigate the coastal Kelvin wave driven Rossby wave response in the northeast Pacific. Using CEOF analysis, a spatial structure function is obtained from model upper layer thickness data. The model is a nonlinear, reduced gravity model of the northeast Pacific forced by coastal Kelvin waves originating in the equatorial Pacific. The spatial structure function is used to extract the interannual Rossby wave response from observed 300-m-depth temperature anomalies. The observed Rossby wave signal is termed the projection mode. Rossby wavelike features observed in the projection mode are order 1000 km long with most periods ranging between 2 and 4 years. The wave numbers and frequencies found are consistent with Rossby dynamics. The mean phase speed of the Rossby wavelike features within the projection mode is 1.3 cm s−1, in agreement with the theoretical Rossby wave phase speed at 40°N. Large amplitude nearshore and decreasing amplitude away from shore suggests nearshore generation of these waves. An important source of sea level variability along the east coast of North America at periods of 2–4 years was identified by Pares-Sierra and O'Brien (1989) as poleward propagating Kelvin waves. Since the Rossby wavelike features observed in the projection mode have a majority of their periods ranging between 2 and 4 years, their forcing can be attributed to long-period Kelvin waves. Spectral comparisons between the nearshore values in the projection mode and coastal sea level show greater than 90% coherence in the period band 3–4.4 years. The high coherence between coastal sea level variations and the projection mode shows that there is a strong correlation between the Rossby wavelike features within the projection mode and coastal Kelvin wave propagation. It is concluded that the Rossby waves within the projection mode are forced by coastal Kelvin wave propagation. The projection mode accounts for 47.5% of the variance in the 300-m-depth temperature anomalies. The implication of this result is that the physical mechanism of the numerical model, i.e., Rossby waves excited by coastal Kelvin wave propagation, accounts for 47.5% of the variance in the observed 300-m depth temperature anomalies.

The Mean Zonal Flow Response to Rossby Wave and Gravity Wave Forcing in the Equatorial Lower Stratosphere: Relationship to the QBO

Abstract: Observations show that the westerly acceleration of the equatorial quasi-biennial oscillation (QBO) can be accounted for by Kelvin waves, but that there is a deficiency in the easterly acceleration due to Rossby-gravity waves. Rossby waves and westward propagating gravity waves have been suggested as alternative sources for the easterly acceleration. The possible role of these two wave modes has been tested in a two-dimensional model of the QBO. When the easterly acceleration is due to Rossby waves, the zonal-mean response is steady; when it is due to gravity waves, an oscillation with some features similar to the QBO occurs, but it is of short period and weak amplitude. A similar result occurs when a standing-wave forcing pattern is imposed. These results suggest that Rossby waves play only a minor role in the QBO, and that while the Rossby-gravity mode is essential, other gravity modes may also be important for the easterly phase.

Computational Dispersion Properties of Horizontal Staggered Grids for Atmospheric and Ocean Models

Abstract: The computational dispersion properties of horizontally and time-horizontally staggered grids utilizing corresponding centered-difference techniques for approximation of the adjustment, or gravity wave equations, are examined in terms of their group velocity characteristics. Results are acquired for oceanic and atmospheric models, the former being characterized by a much smaller Rossby radius of deformation. For all grids considered additional filtering is required to control and even eliminate waves with poor computational dispersion characteristics. Computational dispersion properties along with other computational characteristics and requirements give some guidance for an optimal selection of an appropriate grid for an ocean or atmospheric model.

Nonlinear schrodinger equation in the rotational barotropic atmosphere and atmospheric blocking

Abstract: In this paper,the WKB method is used to obtain the nonlinear Schr(?)dinger equation satisfied by nonlinearRossby wave in the rotational barotropic atmosphere.It is found that the nonlinear Schr(?)dinger equation hasan envelope solitary wave solution under the condition 1≤m≤2(m the zonal wavenumber),and the phasespeed of envelope solitary Rossby wave in the atmosphere is related to the square of its amplitude linearly,thatis,the larger the amplitude of envelope solitary Rossby wave,the smaller its propagation speed.Farthermore,the blocking high and cut-off low pressures which are consistent with the observations of blocking in the atmo-sphere are obtained by calculating envelope solitary Rossby wave,and the blocking structures persist more thanfive days,the results demonstrate that the envelope solitary Rossby wave is a possible mechanism about theformation,maintenance and breakout of blocking in the atmosphere.

Rossby waves in a fluctuating zonal mean flow

Abstract: The effects of the zonal mean wind variability on the energy propagation of a stationary Rossby wave in a barotropic non-divergent atmosphere are studied. It is shown that the random nature of the zonal wind fluctuations do not allow Rossby wave energy to propagate from its energy source. The mechanism for this effect is strongly dependent on the spatial resolution at which the zonal mean flow is assumed to be known. Some speculations are offered on the relation between this mechanism and the systematic error of some low-resolution climate models. DOI: 10.1034/j.1600-0870.1991.t01-3-00001.x

Coastal-trapped waves in elliptical lakes and around elliptical islands

Abstract: The propagation of low-frequency waves, trapped around the shelves of lakes and islands, is investigated. A two-layer model with a simple step topography is used to study the combined effects of depth changes and stratification. The lake or island boundary and corresponding shelf break are modelled as confocal ellipses and analytical solutions for the barotropic streamfunction, interface displacement and dispersion relation are found. Results show the presence of a topographically modified internal Kelvin wave and a stratification-modified topographic Rossby wave. The model is applied to the small, elongated northern basin of Lake Lugano. Although the Rossby wave frequency is close to its barotropic value the two mode 1 dispersion curves “kiss” for very weak stratification with important effects on the wave structures and velocities. The velocity field of the observed 74th oscillation more closely resembles that of an internal Kelvin wave than a topographic Rossby wave.

Numerical Study Of The Nonlinear Barotropic Instability Of Rossby Wave Motion

Abstract: Using β-plane geometry the non-linear barotropic, non-divergent vorticity equation is solved numerically over a long time period to test for stability Rossby’s original wave solution of the equation. This equation represents a simple model of the dynamics of the atmosphere. The numerical results show that the initial growth rate of the solution (when unstable) is correctly predicted by the linearized analysis of the problem conducted by Lorenz (1972) but that eventually the solution settles into a bounded oscillating state (which contrasts with the unbounded growth predicted by linear theory). This eventual bounded oscillating behaviour is shown to occur for all values of the basic wave amplitude, A which extends the result of the weakly nonlinear analysis of the problem by Loesch (1978) and Deininger and Loesch (1982) who showed similar behaviour for values of A slightly in access of AC (the critical amplitude for instability determined by linear theory). Significantly, the numerical results show that AC is not an accurate indicator of stability/instability for the nonlinear solution.

The effects of zonal flow on nonlinear Rossby waves

Abstract: In this paper, we using phase plane method have derived the stability criteria of linear and nonlinear Rossby waves under the conditions of semi-geostrophic approximation and have gotten the solutions and geostrophic vorticity of corresponding solitary Rossby waves. It is pointed out that the wave stability is connected with the distri-bution of zonal flow and when the zonal flow is different the solitary wave trough or ridge is formed.