The dynamics and predictability of a downward migration event of the negative Northern Annular Mode (NAM) anomaly following a stratospheric sudden warming (SSW) occurring in January 2003 are examined using the operational 1-month ensemble forecast data set provided by the Japan Meteorological Agency. It is found that the predictable period of the tropospheric negative NAM anomaly is at most 6 days, which is much shorter than that of the precedent SSW event. The tropospheric NAM anomaly is caused by the E-P flux convergence associated with zonal wavenumber 2 planetary waves at the tropopause level, of which propagating property is affected by the zonal-mean zonal wind there. Our results suggest that even large stratospheric circulation changes associated with the SSW event have only limited influence on the predictability of the tropospheric circulation.
All Science Journal Classification (ASJC) codes
- Atmospheric Science