Variability in the Atmospheric Annual Cycle

Seasonal and intraseasonal variability in the extratropical annual cycle is examined from the perspective of largbe-scale dynamical and energetics descriptors: horizontal atmospheric motion, kinetic energy, and horizontal temperature gradients. Time series of daily data from a ten-year global observational data set (ECMWF initialization fields) for selected regional means of these descriptors illustrate significant intraseasonal variability in magnitudes and fluctuations. This variability, which includes abrupt changes in the overall time-series characteristics and marked differences from year to year, highlights the nonlinear character of the atmospheric system and the challenges for extended range prediction.

Definitions of the four seasons based on the characteristics of these descriptors are compared to those based on astronomical and temperature conditions. Results provide a range of perspectives for the forcing of the annual cycle, the role of ocean-continent contrasts, monsoons, and other global-scale features. Results also demonstrate the large interannual and intraseasonal variability in the seasonal cycle that will compound the task of detecting anthropogenic impacts on regional climater