We investigate the feasibility of dynamical seasonal predictions of the interannual variability of the mean location of typhoon formation in the western North Pacific and its physical mechanisms during the active typhoon season from June to October. We performed seven-month integrations for 28 years starting from late April using the El Nino Southern Oscillation (ENSO) prediction system of the Japan Meteorological Agency. Typhoons detected with an objective method using model outputs are verified with best track data from the Regional Specialized Meteorological Center, Tokyo.
|Number of Typhoon Formation|
The climatological number of typhoon formation during the active typhoon season
June to October, is 19.6 per year in observation and 18.5 per year in seasonal
prediction experiment. We focus on the inverannual variability number of typhoon
As seen in Fig. 1, the correlation coefficient of the interannual variability of the number of typhoon formation during the active typhoon season is low (0.36) for the whole period (1979 to 2006) with 90% statistical significance level, comparable to that of AGCM simulations forced with the observed SST (Camargo et al. 2005).
|Mean location of Typhoon Formation|
The mean location of typhoon formation is correlated with El Nino Southern
Oscillation phenomena (ENSO)
Wang and Chan). ENSO is one of the most predictable phenomena in the seasonal
predictions. Then, is the mean location related to ENSO predictable?
The good overall deterministic skill in predicting the interannual variability of the mean location of typhoon formation (Fig. 2) fundamentally stems from the ability to predict the interannual variability of the atmospheric circulation in the western North Pacific influenced by ENSO. The interannual variability of indices representing a latitudinal shift of the atmospheric circulation in the western North Pacific is better predicted than that of indices representing a longitudinal shift in this experiment. This difference in skill among these indices provides a physical basis for the difference in prediction skill between the mean latitude and longitude regarding the interannual variability of typhoon formation (Fig. 3). The correlation coefficients for mean longitude and latitude are 0.36 and -0.82, respectively.