Some observations on climate variability as seen in daily temperature structure

Distinctive annual cycles of daily maximum and minimum temperature and temperature range are observed across the United States when averaging daily data for multiple decades. In some cases, abrupt changes in the range between daily maximum and minimum temperatures are observed within annual cycles. Such discontinuities, or steps, of 5°C may occur within a week, despite the fact that the daily data are averaged over several decades. Discontinuities are most pronounced in the fall and spring, and display differing characteristics of timing, rapidity, magnitude and direction of change across the nation. In northern and central portions of the eastern U.S., a winter minimum and summer maximum in temperature range is observed, while in the southern U.S. the opposite is found. Abrupt discontinuities are observed in early November in the Northeast and in late spring and early summer in the Southeast and Southwest. ences in mean daily temperature cycles between various portions of this century are a function of variations in maximum and minimum temperatures. The central U.S. had higher maximum and minimum temperatures during the 1930ʹs than at other times this century, with little affect on daily temperature range. In the Northeast, the temperature range was lower in the 1930ʹs, as a result of decreased maximum and increased minimum temperatures. namics responsible for changes within the annual cycle or between different periods have not yet been unequivocally identified. The location of the polar front jet stream and its associations with solar radiation, clouds, snow cover and other atmospheric and surface variables are certainly involved. We believe that the identification of the climate system dynamics responsible for the structure of the annual cycle of daily temperature is a necessary first step in the study of potential human-induced climate change.