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Steven J. Lambert

Abstract

The cyclone event climatology is presented for a five-year simulation by the Canadian Climate Centre general circulation model. Winter season results are given for the extratropical regions of both the Northern and the Southern hemispheres and the results are compared to an event climatology based on five years of observed data.

In the Northern Hemisphere, classification of the simulated and the observed 1000 mb lows as a function of central height shows that the model has a deficiency of weak cyclones and an excess of intense cyclones while the number of cyclones of medium intensity is well simulated. The geographical distribution of the cyclone events shows that those features of the observed climatology which are thermal in nature, such as a preference for lows to form and move over relatively warm underlying surfaces, are reasonably well simulated, but the topographical features such as lee cyclogenesis and the avoidance of high terrain by lows are poorly simulated.

The Southern Hemisphere also shows a deficiency of simulated cyclones although less pronounced than the Northern Hemisphere. The number of weak and strong cyclones are well simulated, and the paucity of Southern Hemisphere lows results from a deficiency of cyclones of moderate intensity. The observed climatology, which is nearly free of mountain influences, is well simulated and only a few minor problems are evident, such as a poor simulation of the winter cyclogenesis in the lee of the Andes and a tendency for model cyclones to be present over high terrain.

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Steven J. Lambert

Abstract

The intraseasonal divergent and rotational kinetic energy (KE) budgets for the 30–60 day interval are calculated from the analyses of the European Centre for Medium Range Weather Forecasts/World Meteorological Organization (ECMWF/WMO) dataset, and from simulations by the Canadian Climate Centre (CCC) General Circulation Model (GCM). Comparison of the results indicates that the model simulates the rotational KE well but there are differences in the observed and simulated rotational KE budgets. In the observed budget, the most important term is the nonlinear interaction term indicating that the atmosphere draws on energy produced over a wide range of spatial and temporal scales to maintain the rotational KE maximum in the intraseasonal time scales. The model, on the other hand, uses a more direct approach in that it tends to maintain the simulated rotational KE maximum by using KE generated at spatial scales similar to those of the KE maximum.

Both the divergent KE and its budget are reasonably well simulated by the model. Most of the divergent KE in the intraseasonal time scales is a result of the Madden-Julian Oscillation (MJO). Even though the model simulates the intraseasonal divergent KE and its budget well, it has problems in simulating the MJO. The simulated MJO-like phenomenon in the model does not display well-organized spectral peaks concentrated in a single octave of the spectrum as seen in the observations, but displays much more random behavior with the variance spread out over a wide range of frequencies.

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Steven J. Lambert

Abstract

Using time series of simple statistics, the homogeneity of a long-term Northern Hemisphere 500-mb dataset is assessed. Several discontinuities coinciding with major analysis changes were found which indicate that care must be exercised in the use of this dataset in studies where homogeneous data are required.

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Steven J. Lambert

Abstract

The extratropical winter cyclone climatologies for the Northern and Southern Hemispheres are presented for a control, or 1 × CO2 simulation, and an enhanced greenhouse warming, or 2 × CO2 simulation, using the second generation Canadian Climate Centre general circulation model. When compared to the control climatology, the 2 × C02 simulation exhibits a significant reduction in the total number of lows in both winter hemispheres. Although the total number of cyclones decreases, the frequency of intense cyclones increases, with this behavior being more significant in the Northern Hemisphere. Examination of the storm tracks in both simulations indicates that there is little change in their geographical positions with global warming.

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