The energy budget of an extratropical cyclone system which traversed North America and intensified through the period 9-1 1 January 1975 is presented. The objectives of the study are (1) to document the complete energy budget of a significant winter cyclone event. and (2) to comment on the significance of latent heat release (LHR) in the cyclone's evolution. Results reveal an overall increase in both kinetic ( K ) and available potential energy ( A ) . K increases are accounted for by boundary flux convergence of K , while A increases are due to generation by LHR and K to A conversion. In addition, the general A increase is accompanied by a 24 h oscillation that is explained largely by the flux quantity in the A budget equation and is correlated with a similar fluctuation in the K to A conversion.LHR does not appear to be critical in the development of this cyclone system. Rather. LHR acts to increase the intensity of the event. It is hypothesized that the direct influence that LHR had on the deepening cyclone's reduced mass was augmented by an indirect influence, in which pre-existing dry dynamical forcing was enhanced by diabatic heating. thus leading to accelerated cyclone development at a later time.
The winters of 1976-77 and 1977-78 were severe by virtually any standard. In this study, heating degree day (HDD) accumulations for these two winters as well as for the 1941-70 normals are examined at 31 National Weather Service stations in Indiana, Wisconsin, Michigan, Illinois, Ohio, and Kentucky. In addition, a modified heating degree day (MHDD) based on wind chill temperature is accumulated. In both cases, the winter is defined as consisting of the months of December, January, and February. Three-month and one-month accumulations are plotted and analyzed to gain a view of spatial and temporal distributions of both HDD and MHDD. Both parameters are shown to be influenced markedly by the presence of the Great Lakes, an influence that diminishes as an extensive ice cover forms on the lakes. The winter of 1976-77 is found to have greater accumulations of both HDD and MHDD. A comparative ratio also is calculated in order to give an impression of the extent to which the wind's influence is felt. The ratio values show that for 1976-77 the inclusion of wind data gives the impression of a more intense winter than would be given by temperature data alone. However, the reverse is true for 1977-78; the inclusion of wind data gives the impression of a less intense winter.
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