Observed and Simulated Intraseasonal Energetics

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.