The Seasonal Cycle over the United States and Mexico

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Abstract The annual cycle occupies a unique position in the spectra of meteorological time series. This cycle and its first three harmonics are extracted from the series as a seasonal cycle. The distributions of the annual and seasonal cycles are studied for the United States and its immediate surroundings, using four years of data. The results show that the annual and seasonal cycles are extremely important contributors to be observed temperature and wind fields at the 850, 500 and 250 mb levels. In winter, the annual cycle establishes a west wind maximum in the subtropics, quite akin to the winter-average jet stream. The annual cycle in horizontal wind constitutes a trough over the central parts of the United States in winter and a ridge in the same area in summer.