Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.a21c0175i&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #A21C-0175
Mathematics
Logic
3334 Middle Atmosphere Dynamics (0341, 0342), 3389 Tides And Planetary Waves
Scientific paper
The predictability of stratospheric circulations in Northern Hemisphere winters from 2001 to 2006 is examined by the use of ensemble 1-month forecast data produced by the Japan Meteorological Agency. In the current study, we examine time variations of Root Mean Square Error (RMSE) and Anomaly Correlation (AC), a pattern correlation between forecast and analysis anomalies of 10-hPa height, along with the spread among ensemble forecast members of 10-hPa zonal-mean temperature. Stratospheric circulations in the winter season largely vary with stratospheric sudden warming (SSW) events which are caused by enhanced planetary waves propagating from the troposphere (e.g., Andrews et al. 1987); in such phases, the RMSE tends to be large. The predictable limit can be defined as the time when the RMSE value surpasses a climatological standard deviation of the analyzed height field. The resultant limit during SSW events ranges from 3 to 19 days according to the case, and the mean value is about 10 days. On the other hand, we can also define the predictability based on the time when the AC first reaches a critical value, say, 0.6. The result is similar to that on the basis of the RMSE. Moreover, it is found that such forecast errors are caused by poor predictability of both zonal mean and planetary-wave fields. Specifically examined is the predictability for warming peaks of SSWs based on the spread in terms of 10-hPa zonal-mean temperature averaged over latitudes north of 80°N. Most warming peaks are roughly predictable from one to two weeks in advance, while SSW events in Dec 2001 and in Jan 2006 have a long predictable period of more than 2 weeks. These results are consistent with the predictability estimated by the RMSE and AC.
Hirooka Toshihiko
Ichimaru T.
Mukougawa Hitoshi
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