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A steady-state barotropic model, linearized about a GCM-derived 500 hPa basic state, is driven by a sample of \"observed\" forcing fields. lt tums out that the leading mode (LEOF) obtained from the sample of linear solutions matches weil with the leading EOF of low-frequency atmospheric variability actually occurring in the GCM. The response ofthe linear model is analysed in tenns of the singular modes of the model\'s linear operator. lt is found that about 50 percent ofthe spatial variance of the LEOF can be explained in tenns of the leading two singular modes. This finding is reflected also in the linear barotropic energy balance of the LEOF which shows that the mode is maintained through nearly equal contributions from i) the kinetic energy conversion of basic state kinetic energy (which is primarily due to the action of the singular modes) and ii) the forcing. The linear simulation of the GCM EOF fails if the linear model is linearized about a 300 hPa basic. This is explained by the fact that in this case the structure of the leading singular modes, which have a strong impact on the linear response, is much more dissimilar to the structure of the GCM EOF than in the 500 hPa case. / Ein stationäres barotropes Modell, das bezüglich eines (aus einem GCM Experiment abgeleiteten) 500 hPa Grundzustandes linearisiert ist, wird für einen Satz von "beobachteten" Antriebsfeldern gelöst. Dabei zeigt sich, daß die führende Mode der langperiodischen atmosphärischen Variabilität (EOF) im GCM Experiment durch das lineare Modell sehr gut simuliert wird. Weiterhin stellt sich heraus, daß hierfür die Antriebsfelder und die singulären Moden des linearen Modelloperators die gleiche Bedeutung besitzen. Auf die Wichtigkeit der Anwendung des Modells bezüglich des äquivalentbarotropen Niveaus wird hingewiesen.

The movement of tropical cyclones (TC) is studied numerically based on a two-dimensional barotropic model, using a previously developed non-oscillatory balanced scheme. The model of TC used here takes an exponential form, and its size and strength are selected to be of a middle scale. Without a background flow, TCs move in the northwest direction due to the beta effect. The amplitudes of high wavenumber modes of the asymmetric flow, that are believed to be responsible for the TC drift, are computed using Fourier analysis. The amplitude of wavenumber one and two modes are dominant, so they are indicators of beta conversion of energy. Also, the effect of the monsoon trough on the TC movement is investigated. The results show a sudden change of the TC propagation path, consistent with earlier work. These two studies correspond to previous works. Here, the effect of equatorially trapped waves such as Kelvin, Rossby, and Mixed Rossby Gravity, on the TC path is newly studied by varying the wavenumber and wave speed of the underlying waves. The effect of the waves is considered because they are believed to contribute to cyclogenesis. For studying the effect, the barotropic flow induced by these waves via momentum transport and its variation were simulated for 50 days, and some patterns are found in the change of maximum wind speed. At a given time during the simulation, a TC is injected and the effect of the background wave is analyzed. Using the wavefield of 11 cases from 10 days to 30 days, the trajectories are calculated, and their patterns appear to be stochastic. So, the patterns are identified by calculating the mean path and its spread. The trajectories of TCs are different for different time of the waves. Kelvin waves make small variations on the length and direction of the trajectory of TCs. On the contrary, Rossby waves cause a dramatic change in the TC path and yield longer trajectories. Meanwhile, TCs in MRG waves keep fairly the same direction and usually have longer traveling distance. These changes vary by wave conditions. Therefore, the three kinds of waves have different effects on the trajectories of the TC. For some peculiar cases, the movements are explained based on wavefields. / Graduate

A steady-state barotropic model, linearized about a GCM-derived 500 hPa basic state, is driven by a sample of \'observed\' forcing fields. lt tums out that the leading mode (LEOF) obtained from the sample of linear solutions matches weil with the leading EOF of low-frequency atmospheric variability actually occurring in the GCM. The response ofthe linear model is analysed in tenns of the singular modes of the model\''s linear operator. lt is found that about 50 percent ofthe spatial variance of the LEOF can be explained in tenns of the leading two singular modes. This finding is reflected also in the linear barotropic energy balance of the LEOF which shows that the mode is maintained through nearly equal contributions from i) the kinetic energy conversion of basic state kinetic energy (which is primarily due to the action of the singular modes) and ii) the forcing. The linear simulation of the GCM EOF fails if the linear model is linearized about a 300 hPa basic. This is explained by the fact that in this case the structure of the leading singular modes, which have a strong impact on the linear response, is much more dissimilar to the structure of the GCM EOF than in the 500 hPa case. / Ein stationäres barotropes Modell, das bezüglich eines (aus einem GCM Experiment abgeleiteten) 500 hPa Grundzustandes linearisiert ist, wird für einen Satz von 'beobachteten' Antriebsfeldern gelöst. Dabei zeigt sich, daß die führende Mode der langperiodischen atmosphärischen Variabilität (EOF) im GCM Experiment durch das lineare Modell sehr gut simuliert wird. Weiterhin stellt sich heraus, daß hierfür die Antriebsfelder und die singulären Moden des linearen Modelloperators die gleiche Bedeutung besitzen. Auf die Wichtigkeit der Anwendung des Modells bezüglich des äquivalentbarotropen Niveaus wird hingewiesen.