Noguchi, S., H. Mukougawa, T. Hirooka, M. Taguchi, and S. Yoden, 2014: Month-to-month predictability variations of the winter-time stratospheric polar vortex in an operational one-month ensemble prediction system. J. Meteor. Soc. Japan, 92, 543-558.
- The predictability variation of the stratospheric polar vortex in the northern hemisphere winter is examined based on the systematic error and the ensemble spread using a seven-year archive of the operational ensemble one-month forecast dataset provided by the Japan Meteorological Agency.
- In early winter, the north pole temperature in the stratosphere has a significant warm bias due to the significant underestimation of the equatorward propagation of planetary waves in the upper stratosphere (Fig. 1).
- An upper bound of the predictable period of the north pole temperature is assessed by applying the logistic equation, which describes the evolution of small initial errors proposed by Lorenz, to the monthly averaged ensemble spread.
- The estimated predictable period in the stratosphere attains a maximum value of 35 days in early winter, gradually decreases with the seasonal march to 20 days in late winter, which is considerably longer than that in the troposphere (Fig. 2).