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The influence of Rossby waves emitted in the northeastern Pacific Ocean on the Northern Hemisphere’s atmosphere during summer is analysed using ERA5 reanalysis and a new large ensemble performed with the EC-Earth3 model. The Rossby Wave Sources (RWS) trigger wave-like patterns arising from the upper troposphere of the north-eastern Pacific region, causing a response around the Northern Hemisphere with alternating regions of positive and negative correlation values between RWS and geopotential height at 500 hPa. Increased RWS intensity during summer is related to negative temperature anomalies over western North America, and positive temperature anomalies over eastern North America, concurrently with increased precipitation over the western subtropical Atlantic and Northern Europe during summer. Colder than normal conditions on the North Pacific Ocean intensify the RWS and its impact on the global atmospheric circulation. Different warm or cold states in the Pacific and Atlantic Oceans modify the atmospheric response to RWS, showing a change in the middle troposphere (500 hPa) towards a more-wavy structure with cold Pacific conditions, and towards a less-wavy structure with a warm Pacific Ocean. Furthermore, the North Atlantic plays a very important role in hindering (in the case of warm water) or permitting (cold water) that Rossby waves generated in the Pacific modulate the atmospheric conditions over Europe.

We study the possibility of having resonant interactions between three Rossby modes on a coast or channel of arbitrary orientation. A Rossby mode comprises two propagating Rossby waves (RWs) to satisfy the no normal flow through the boundary(ies). In each geometry, we state the conditions, degrees of freedom and RWs of the primary two modes that could force a third mode. We discuss differences between zonal and non-zonal orientations. Resonant interactions are only possible if all RWs participate in the zonal case, while only three RWs participate in the non-zonal case. The non-zonality reduces the degrees of freedom of the resonance conditions, and the solutions are more restrictive for more meridional orientations. In particular, there are no solutions if the coast or channel is meridional. For the non-zonal coast, we find a family of solutions for given periods of the primary modes. Using multiple scales, we obtain a uniformly valid solution of the quasi-geostrophic potential vorticity equation (QGPVE), with the resonant modes exchanging energy in space. There are no degrees of freedom for the non-zonal channel, and we develop a graphical method to seek resonant solutions, finding some. We provide a bounded solution of the QGPVE in case the primary modes excite one RW, not a channel mode, and the modes do not exchange energy either in time or space. Regarding possible oceanographic applications, we show solutions for the Hawaiian Ridge and inquire if there are solutions in the Mozambique Channel, Tasman Sea, Denmark Strait and the English Channel.

The influence of Rossby wave sources (RWS) emitted on the Northeastern Pacific Ocean in the Northern Hemisphere during summer is analysed in the ERA5 reanalysis and new large ensemble performed with the EC-Earth3 model. Using extreme years composites of precipitation, surface temperature, geopotential height, we found a causal influence of the Rossby waves generated over the Northeastern Pacific Ocean, on a global climate response. Both the reanalysis ERA5 and the EC-Earth3 model show that RWS triggers wave-like patterns arising from the upper troposphere Northeastern Pacific region. We show that an increased Rossby wave sources intensity is related with negative temperature anomalies over western North America, and positive temperature anomalies over eastern North America concurrently increased precipitation over Northern Europe during summer and sea-ice concentration decrease in the Arctic. We also show that the North Atlantic plays a very important role hindering or permitting that Rossby waves generated in the Pacific reach the Atlantic and modulate the atmospheric conditions over Europe. Such conditions were found in ERA5 and SMHI-LENS during colder and icier conditions over the North Atlantic.

Seasonal precipitation forecast over Mexico based on a hybrid statistical-dynamical approach

The free Rossby wave (RW) solutions in an ocean with a straight coast when the offshore wavenumber of incident ( l 1 ) and reflected ( l 2 ) wave are equal or complex are discussed. If l 1 = l 2 the energy streams along the coast and a uniformly valid solution cannot be found; if l 1,2 are complex it yields the sum of an exponentially decaying and growing (away from the coast) Rossby wave. The channel does not admit these solutions as free modes. If the wavenumber vectors of the RWs are perpendicular to the coast, the boundary condition of no normal flow is trivially satisfied and the value of the streamfunction does not need to vanish at the coast. A solution that satisfies Kelvin's theorem of time-independent circulation at the coast is proposed. The forced RW solutions when the ocean's forcing is a single Fourier component are studied. If the forcing is resonant, i.e. a free Rossby wave (RW), the linear response will depend critically on whether the wave carries energy perpendicular to the channel or not. In the first case, the amplitude of the response is linear in the direction normal to the channel, y , and in the second it has a parabolic profile in y . Examples of these solutions are shown for channels with parameters resembling the Mozambique Channel, the Tasman Sea, the Denmark Strait and the English Channel. The solutions for the single coast are unbounded, except when the forcing is a RW trapped against the coast. If the forcing is non-resonant, exponentially decaying or trapped RWs could be excited in the coast and both the exponentially “decaying” and exponentially “growing” RW could be excited in the channel.

The Mediterranean California Border Region (MCBR) rainfall's relationship with El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) is reexamined for the period 1951–2014. When stratifying data by ENSO events we found that strong events of either sign yield the highest ENSO–rainfall correlation; but when the stratification was done by rainfall the wet seasons yield the highest ENSO–rainfall correlation. Most strong ENSO events have the same sign as PDO; but the ENSO–rainfall correlation for all ENSO–PDO same-sign events is almost undistinguishable from the full-record's correlation. Timewise stratification shows that 30-year climatological values (MCBR precipitation, PDO and ENSO) and ENSO–rainfall correlations have decreased in recent years.

The spreading of n particles simultaneously released is modeled numerically and analytically using a Langevin’s equation. In the numerical experiments, particles are dispersed utilizing the random walk technique plus advection caused by a vortex with rigid-body rotation (RV) or irrotational (IV). In each vortex, the dispersion is described analyzing the statistical behavior of the particles’ position as a function of time t. In the RV case, analytical expressions for the statistics indicate (like the numerical experiments) that the dispersion or variance is linear in t and the diffusion coefficient D depends on the angular speed Ω of the vortex. If the time scale of the random walk is much smaller than the rotation period (i.e., Δt ≪ 2π/Ω), then D decreases lightly if Ω increases relative to a pure two-dimensional (2D) random walk. In the experiments of the IV in which all particles start at the same point, we observe an asymmetric dispersion (the cloud becomes a comet and then a spiral), which leads to a...

An ensemble of future climate projections performed with the regional climate model RegCM4 is used to assess changes in inter-annual variability of precipitation over Southern Mexico and Central America (SMECAM). Two different Global Climate Models (GCMs) from the coupled model intercomparison project phase 5 are used to provide boundary conditions for two different RegCM4 configurations. This results in four regional climate projections extending from 1970 to 2100 for the greenhouse gas representative concentration pathway RCP8.5. The precipitation variability over the SMECAM region and its dependence on the gradient between Atlantic and Pacific sea surface temperature (SST) anomalies are verified by reproducing SST anomaly patterns during wettest and driest years similar to those seen in observational datasets. RegCM4 does a comparably better job than the driving GCMs. This strong relationship between precipitation and SST anomalies does not appear to change substantially under future climate conditions. For the rainy season, June to September, we find a future change in inter-annual variability of precipitation towards a much greater occurrence of very dry seasons over the SMECAM region, with this change being more pronounced in the regional than in the global model projections. A greater warming of the Tropical Northeastern Pacific (TNP) compared to the Tropical North Atlantic (TNA), which causes stronger wind fluxes from the TNA to the TNP through the Caribbean Low Level Jet, is identified as the main process responsible for these drier conditions.

The skill of a regional climate model (RegCM4) in capturing the mean patterns, interannual variability and extreme statistics of daily-scale temperature and precipitation events over Mexico is assessed through a comparison of observations and a 27-year long simulation driven by reanalyses of observations covering the Central America CORDEX domain. The analysis also includes the simulation of tropical cyclones. It is found that RegCM4 reproduces adequately the mean spatial patterns of seasonal precipitation and temperature, along with the associated interannual variability characteristics. The main model bias is an overestimation of precipitation in mountainous regions. The 5 and 95 percentiles of daily temperature, as well as the maximum dry spell length are realistically simulated. The simulated distribution of precipitation events as well as the 95 percentile of precipitation shows a wet bias in topographically complex regions. Based on a simple detection method, the model produces realistic tropical cyclone distributions even at its relatively coarse resolution (dx = 50 km), although the number of cyclone days is underestimated over the Pacific and somewhat overestimated over the Atlantic and Caribbean basins. Overall, it is assessed that the performance of RegCM4 over Mexico is of sufficient quality to study not only mean precipitation and temperature patterns, but also higher order climate statistics.

Maximum and minimum surface air temperatures (Tmax, Tmin) throughout Mexico were analysed to look for a regional sign of climate change. Temperature (T) records were divided into two periods: early (1940–1969) and recent (1970–2004); and the analysis was performed for the four seasons plus the annual average. For these 20 cases, and for each of ∼1400 selected stations, time series were constructed and their linear trends (m) were obtained. The statistical significance of m was tested by posing the null hypothesis m = 0, i.e. that there was no trend. The length of the time series (n) considered for this test was the n-effective (neff) that takes into account the fact that consecutive values of T have non-zero correlation. The null hypothesis was rejected in less than 25% of the stations in all cases. The principal findings are: (1) Mexico warmed up during the recent period, and this warming was more generalized in Tmax than in Tmin and in summer than in the other seasons; (2) Mexico cooled down during the early period, and this cooling was more generalized in winter than in the other seasons; (3) In neither of these two cases El Nino-Southern Oscillation (ENSO) seems to play any direct role; (4) In contrast to ENSO, the trends and phases of the Pacific Decadal Oscillation (PDO) are consequent in both cases: a warming trend at the beginning of the 1970s and a warm PDO phase prevailing during the recent warming period; as well as a cooling trend at the beginning of the 1940s and a cold PDO phase prevailing during the early cooling period; and (5) north-western and central Mexico temperature trends often contrast with those of the rest of the country. Copyright © 2008 Royal Meteorological Society

The role of the Pacific decadal oscillation (PDO) in El Niño–Southern Oscillation (ENSO)-related Mexican climate anomalies during winter and summer is investigated. The precipitation and mean temperature data of approximately 1000 stations throughout Mexico are considered. After sorting ENSO events by warm phase (El Niño) and cold phase (La Niña) and prevailing PDO phase: warm or high (HiPDO) and cold or low (LoPDO), the authors found the following: 1) For precipitation, El Niño favors wet conditions during summers of LoPDO and during winters of HiPDO. 2) For mean temperature, cooler conditions are favored during La Niña summers and during El Niño winters, regardless of the PDO phase; however, warmer conditions are favored by the HiPDO during El Niño summers.

In this work, recent (1948‐2001) rainfall data in a southwestern California station (San Diego) and a northwestern Baja California station (Ensenada) within a region called Mediterranean California, around 33 8N, 1178W, are studied. Cumulative annual means are used as indicators of climatological variability; but the entire datasets are analyzed by modeling the histogram of each set as a Weibull distribution probability density function, f . The climatology of both stations, defined simply as the arithmetic average, is compared with their theoretical mean; that is, the first moment of f . It is assumed that this comparison would be indicative of the reliability of the available rainfall climatologies. If these assumptions hold, in particular if the data is indeed Weibull distributed, it can be concluded that the climatological annual mean precipitation in this region is slightly overestimated at this time.

We study the weakly nonlinear self-interaction of a single Rossby mode in a straight channel of arbitrary orientation on a β -plane. As in the problem of reflection from a single wall [Graef, F., 1993. First order resonance in the reflection of baroclinic Rossby waves. J. Fluid Mech., 251, 515–532], resonance is possible only if 0 α |≤1/3, where α is the angle between east and the direction along the channel. However, in contrast to the problem of a single wall, the straightforward expansion yields a uniformly valid solution in the flow domain in the resonant case, so there is no need of using multiple scales. The three waves (two belonging to the mode and the excited one), although in resonance, do not exchange energy in time due to the additional constraint on the motion imposed by the boundary conditions at the channel walls. A full solution to the first order equations is given in both the resonant and non-resonant cases. We also inquire if resonance is possible in the self-interaction of a Rossby mode in a gulf. Since a mode in a gulf can be physically conceived as the reflection of a channel mode impinging at the gulf's head, the above necessary condition for resonance in the channel holds for the gulf. However there is another possibility of resonant interaction for which the condition 0 α |≤1/3 applies. Therefore, in a gulf is easier to find resonance.

This paper examines the motion of an isolated lenslike eddy using the reduced-gravity shallow-water equations (SWE) on a β plane. In contrast to previous studies the author uses a correct first-order β-plane approximation of the SWE that posseses the same integrals of motion as the original system. The approximation includes terms proportional to (1 − y tanθ0/r0)−1, where y is the northward coordinate, θ0 the reference latitude, and r0 the earth’s mean radius. The center of mass of the eddy is found to oscillate meridionally and zonally with the inertial frequency f0 and drift westward at the same speed as in the case of the conventional β-plane approximation. The new terms arising from the non-Cartesian metric cancel each other. Therefore, the ad hoc procedure of replacing f0 by f0 + βy in the f-plane shallow-water equations does give the correct answer for the bulk motion of the eddy.

The collision of anticyclonic, lens-like eddies with a meridional western boundary is investigated as a function of two independent, nondimensional numbers: ß = ß0 R/f o and e = ¿/f o, where f 0 and ß0 are the Coriolis parameter and its rate of change with latitude, respectively, both evaluated at the reference latitude. R is the eddy's radius, and ¿ is its angular frequency. The numerical experiments show that in all cases there is a southward expulsion of mass proportional to both ß and e. which is estimated during the eddy-boundary interaction. The eddies are invariably deformed with the initial collision, but afterward, they reacquire a new circular shape. There is a meridional translation of the eddy along the boundary which depends exclusively on the initial ratio r = e/ß. If r > 1, the eddy goes southward, but if r

In this study we investigate which conditions are needed to assure uniqueness of solutions of the barotropic QG model, and, how these conditions are related to the conservation laws of mass, vorticity and energy. Uniqueness and conservation laws are analyzed for a simply connected domain (a closed basin) and for a doubly connected domain (a periodic or re-entrant channel). For the multiply connected domain we find, besides the model proposed by McWilliams in 1977, another consistent model whose solutions satisfy the conservation laws. The additional conditions in our model are: (a) the sum of the circulations around all closed solid walls is time-independent; (b) the value of the QG streamfunction (Φ) is the same at all closed walls. McWilliams' model and ours are not equivalent. As a simple application we study the free Rossby normal modes in a channel. For a non-zonal channel on a β-plane there are solutions (modes) that are independent of the coordinate along the channel. These are used to compare the modes and frequencies obtained from three different, but well posed, models. Solutions that are independent of the along-channel coordinate do not exist for the planetary geostrophic and for the shallow water equations on a β-plane.

The reflection of weakly nonlinear Rossby waves (RWs) from a vertical wall is examined analytically through perturbation methods, with the β-Rossby number (ϵ) as the small parameter. A uniformly valid solution up to O(ϵ3) is constructed using multiple scales. At O(ϵ), the nonlinear interaction between an incident and the reflected RW leads to 1) an Eulerian steady flow, us(1), parallel to the (nonzonal) wall and 2) a transient flow oscillating with a frequency twice (2ω) that of the RW pair. The steady forcing, whose response is us(1), can never be resonant, which implies, under the weak nonlinear regime, that us(1) is stable to the driving RWs. At the next order, the nonlinear interaction between the incident-reflected RW pair and us(1) plus the transient flow produces, in general, resonant forcing leading to a modification of the RWs’ phases: a shift in their offshore wavenumber. The steady flow that occurs at O(ϵ3) is driven by the modified RWs as well as through interactions of several compon...

The nonlinear interaction between an incident and a reflected Rossby wave produces a steady flow parallel to the (non-zonal) reflecting wall and a transient flow oscillating at twice the frequency of the incident-reflected pair. If the transient forcing is resonant, i.e. a free Rossby wave, the resonant response must have zero amplitude at the wall in order to fulfil the boundary condition there; a straightforward expansion predicts a linear growth of its amplitude in the offshore direction y. Resonance is possible only if 0 < |sin α| ≤ $\frac13$, where α is the angle between the wall and the easterly direction. This requirement is met by several boundaries in the ocean. A simple graphical method to find a resonant triad is described.Using the method of multiple scales, it is shown that the wave amplitudes of the triad are slowly varying periodic functions of y, such that the energy flux of the triad through any plane parallel to the wall vanishes, as required by energy conservation. The waves participating in the resonant triad become wave packets. The three waves do not exchange energy in time due to the additional constraint on the motion imposed by the boundary condition at the wall. It is shown that the wave amplitudes cannot be slowly varying functions of v and time.As a possible oceanic application of the theoretical findings, the distance from the wall where one would expect to find large semi-annual amplitudes if annual Rossby waves are impinging on the boundary is of the order of 100 km. Motivated by similar studies (Plumb 1977; Mysak 1978), there are speculations on what would happen if three incident-reflected Rossby wave pairs (or modes) are taken, allowing each mode amplitude to be slowly varying in time.

A free Rossby normal mode in a rectangular gulf of arbitrary orientation is constructed by considering the reflection of a Rossby mode in a channel at the head of the gulf. Therefore, it is the superposition of four Rossby waves in an otherwise unbounded ocean with the same frequency and wavenumbers perpendicular to the gulf axis whose difference is equal to 2 mπ / W , where m is a positive integer and W the gulf's width. The lower (or higher) modes with small m (or large m ) are oscillatory (evanescent) in the coordinate along the gulf; these are elucidated geometrically. However for oceanographically realistic parameter values, most of the modes are evanescent. When the gulf is forced at the mouth with a single Fourier component, the response is in general an infinite sum of modes that are needed to match the value of the streamfunction at the gulf's entrance. The dominant mode of the response is the resonant one, which corresponds to forcing with a frequency ω and wavenumber normal to the gulf axis η appropriate to a gulf mode: η =− β sin α /(2 ω ) ± Mπ / W , where α is the angle between the gulf's axis and the eastern direction (+ve clockwise) and M the resonant's mode number. For zonal gulfs ω drops out of the resonance condition. For the special cases η = 0 in which the free surface goes up and down at the mouth with no flow through it, or a flow with a sinusoidal profile, resonant modes can get excited for very specific frequencies (only for non-zonal gulfs in the η = 0 case). The resonant mode is around the annual frequency for a wide range of gulf orientations α ∈ [40°, 130°] or α ∈ [220°, 310°] and gulf widths between 150 and 200 km; these include the Gulf of California and the Adriatic Sea. If η is imaginary, i.e. a flow with an exponential profile, there is no resonance. In general less modes get excited if the gulf is zonally oriented.

Los remolinos oceánicos de mesoescala (con radios de decenas a cientos de kilómetros) tienen la capacidad de dispersar diversas propiedades físicas, químicas y biológicas a lo largo de distancias mucho mayores a su propio tamaño. En esta tesis se estudia la dispersión de partículas en tres vórtices bidimensionales: Rankine, monopolar no aislado y el dipolo de Chaplygin-Lamb. La dispersión se modela numéricamente usando una ecuación estocástica cinemática, en la que la velocidad total de una partícula es igual a la del vórtice más una velocidad estocástica (caminata aleatoria), que representa una turbulencia homogénea. Para cada vórtice se hacen experimentos con miles de partículas y se calcula la varianza respecto al centro de masa en función del tiempo. Se compara la varianza obtenida entre un vórtice monopolar no aislado y un vórtice de Rankine por la semejanza entre sus perfiles de velocidad azimutal. Si las partículas se posicionan inicialmente cerca del punto máximo de velocidad azimutal, la varianza se comporta como en un vórtice irrotacional. En el caso del dipolo de Chaplygin-Lamb se usa el método de Runge-Kutta de 4o orden para resolver la ecuación estocástica. Debido a la geometría del dipolo conformado por un flujo interior y exterior, la varianza tiene un comportamiento diferente dependiendo en qué región se dispersen las partículas. El primer comportamiento se da en el flujo exterior, donde las partículas no sienten el corte de velocidad del flujo interior, resultando en una varianza que crece linealmente en el tiempo, análoga a la caminata aleatoria (dispersión estándar). El segundo ocurre cuando las partículas interactúan con la separatriz (frontera entre el flujo interior y exterior), ocasionando que la curva de la varianza se deforme creando una oscilación. El tercero es cuando las partículas inician en el interior (en uno de los polos): ahí se crean múltiples oscilaciones en la varianza debido a las elongaciones de las líneas de corriente y la circulación del flujo interior. Mesoscale ocean eddies (with radius of tens to hundreds of kilometers) have the ability to disperse various physical, chemical, and biological properties over distances much greater than their own size. The dispersion of particles in three two-dimensional vortices: Rankine, non-isolated monopolar and Chaplygin-Lamb dipole is studied in this thesis. The dispersion is modeled numerically by using a kinematic stochastic equation, in which the total particle’s velocity is equal to the vortex one, plus a stochastic velocity (random walk), representing homogeneous turbulence. For each vortex, experiments are carried out with thousands of particles and the variance relative to center of mass as a function of time is calculated. The variance obtained for a non-isolated monopolar vortex and a Rankine vortex are compared because of the similarity between their azimuthal velocity profiles. If the particles are initially positioned near the point of maximum azimuthal velocity, the variance behaves as in an irrotational vortex. In the case of the Chaplygin-Lamb dipole, the Runge-Kutta 4th order method is used to solve the stochastic equation. Due to the dipole’s geometry formed by an internal and external flow, the variance has different behavior depending on which region the particles are dispersed in. The first behavior occurs at the external flow, where the particles do not feel the velocity shear of the internal flow, resulting in a variance that grows linearly as a function of time, analogous to the random walk (standard dispersion). The second occurs when the particles interact with the separatrix (the boundary between the internal and external flow), this causes a deformation in the variance creating an oscillation. The third is when the particles start in the internal flow (at one of the poles), there are created multiple oscillations in the variance due to the elongations of the streamlines and the circulation of the internal flow.

El esparcimiento de n partículas liberadas instantáneamente en un tiempo inicial t₀ (con n tal que la concentración de las partículas para todo tiempo t > t₀ es descrita por una distribución gaussiana) es modelado numérica y analíticamente usando una ecuación de Langevin. Se realizan experimentos numéricos, con diferentes condiciones inicial y de frontera, en que las partículas son esparcidas por difusión molecular, simulada con la técnica de caminata aleatoria, y por advección debida a la presencia de un vórtice: a) con rotación de cuerpo rígido; b) irrotacional. Se describe la cinemática de la difusión en cada tipo de vórtice mediante el análisis del comportamiento estadístico de las partículas en función del tiempo, para lo cual se calculan la media y la desviación estándar correspondientes a la posición de las partícuals en toda iteración de tiempo. Las simulaciones y consideraciones sobre la ecuación de difusión en un sistema en rotación para el caso de un vórtice con rotación de cuerpo rígido indican que la advección no tiene ningún efecto en el esparcimiento de las partículas. En el caso de difusión en un vórtice irrotacional, las simulaciones y la solución de la ecuación de difusión demuestran que, una vez que las partículas se distribuyen uniformemente alrededor del origen de la advección, el efecto del vórtice en el esparcimiento de las partículas es nulo para todo tiempo posterior; si en t₀ las partículas están distribuidas de manera uniforme en un anillo cuyo centro es el origen del vórtice , ubicado en el radio r = 0, entonces la concentración máxima se presenta en r = 0 una vez que transcurre cierto tiempo. Al comparar las soluciones numérica y analítica de las ecuaciones de Langevin y de difusión-advección, la solución analítica de la ecuación de Langevin constituyó el mejor método para simular el proceso difusivo en un vórtice, debido a su sencillez y a aspectos de eficiencia computacional. The spreading of n particles instantaneously released at an initial time t₀ (n such that the particles' concentration for any time t > t₀ is described by a Gaussian distribution) is modeled numerically and analytically using a Langevin's equation. Numerical experiments with different initial and boundary conditions are set up; particles are spread by molecular diffusion, simulated by means of the random walk technique, and by advection caused by a vortex: a) with rigid-body rotation; b) irrotational. The kinematics of diffusion in each one of these vortices is described analyzing the statistical behavior of the particles for every iteration of time. Simulations and considerations on the diffusion equation in a rotational system for a vortex with rigid-body rotation show that the advection has no effect on the spreading of the particles. With respect to diffusion in an irrotational vortex, simulations and the advection-diffusion equation demonstrate that, once the particles are uniformly distributed around the advection's origin, the vortex has no effect for any subsequent time; if at t₀ the particles are uniformly distributed in a ring whose center is the vortex's origin, then after certain time the maximum concentration occurs there. Comparing the analytical and numerical solutions of the advection-diffusion and Langevin's equations, the analytical solution of Langevin's equation proved to be the best method to simulate a diffusive process in a vortex, considering its simplicity and its computational efficiency.

Se estudia la auto-interaccion de un modo normal de Rossby en una cuenca rectangular por medio de un modelo analítico y uno numérico. La auto-interacción a primer orden produce un forzamiento transitorio con el doble de la frecuencia del modo y un forzamiento estacionario. El forzamiento estacionario tiene como respuesta la presencia de dos giros: uno anticiclónico en la parte norte de la cuenca y el otro ciclónico en la parte sur. La respuesta directa al forzamiento transitorio no satisface la condición a la frontera de flujo normal cero en las paredes meridionales. El fluido se ajusta generando ondas de Rossby, de tal forma que la suma de la función corriente de estas ondas (solución homogénea) y la función corriente forzada resulte nula en las paredes. Entre las componentes de la solución perturbativa a primer orden, la que tiene mayor importancia es la solución estacionaria. Los términos advectivos juegan un papel decisivo en la circulación de la cuenca si ésta es relativamente pequeña; por el contrario, para cuencas grandes los términos alineales tienen poco peso. En los resultados del modelo numérico se aprecia un desfase en la función corriente respecto a la solución analítica, presumiblemente por el efecto de la discretización en el modelo numérico. La solución numérica alineal difiere apreciablemente de la solución analítica a primer orden conforme la amplitud de la condición inicial se incrementa, indicándonos que la solución analítica es válida para números de B-Rossby pequeños. No contiene