Available potential energy and extratropical cyclone activity during the FGGE year

Available potential energy quantities derived using twice daily Northern Hemisphere data are compared to extratropical cyclone activity during the First GARP Global Experiment (FCGE) year. The so-called exact (isentropic) available potential energy formulations are employed, both for the entire hemisphere and within limited regions.

Good agreement is indicated between cyclone tracks and hemispheric distributions of the time mean and standard deviations or eddy available potential energy contributions by individual 5° latitude—longitude areas during each season of the FGGE year. The regional available potential energies in climatologically active east coast cyclogenetic regions are shown to exceed values from less active eastern ocean regions during active periods of cyclogenesis. Also, regional available potential energy values from four Northern Hemisphere quadrants suggest that asymmetries in the land—ocean distributions of the hemisphere may be responsible for the diurnal variation in hemispheric available energy values reported in previous work. As indicated by these results, it is important to use limited region calculations when studying atmospheric features that derive their energy on scales smaller than the entire hemisphere.