Analysis Of The Forecasting Errors And The Mechanisms Of Sudden Typhoon Track Changes

The multi-time scale environmental flow interactions on sudden typhoon track changes in the western North Pacific were examined in this study. Analysis of the National Meteorological Center of China Meteorological Administration operational forecasts indicated that the mean24h and48h forecast errors for the sudden west-turning cases from2005to2010were close to the average forecasting errors. For the sudden northward change, the mean24h and48h forecast errors were145.6km and317.3km, increasing by29.3%and68.3%, respectively, compared to the average forecast errors. Further composite analysis of Madden-Julian oscillation (MJO), quasi-biweekly oscillation (QBW), and synoptic scale components of the environmental flow showed that there were clear differences in the westward extension of the low-frequency component of the subtropical high, the features of low-frequency components of the monsoon gyre, and the synoptic-scale wind fields associated with the typhoons. The sudden north-turning typhoons underwent a coalescence process first with a QBW-scale cyclonic gyre and then with the MJO-scale cyclonic gyre. The coalescence enhanced the synoptic-scale southerly winds on the east side of typhoons. The enhanced winds shifted the typhoons northward and placed them in a northward or northeastward orbit under the steering of the flows associated with the Pacific subtropical high. The sudden west-turning typhoons underwent a coalescence process with a QBW-scale cyclonic gyre, but the MJO-scale cyclonic gyre was not obvious or did not coalesce with the typhoons. With the symmetrical winds in synoptic-scale the typhoons placed in a westward obit under the easterly steering of the flows associated with the Pacific subtropical high. Observations and simulations had proved that the enhanced synoptic-scale southwesterly winds on the southeast side of typhoons were produced by the Rossby energy depression. And it proved that the reduced synoptic-scale northeasterly winds on the northwest side of sudden north-turning typhoons and the steady synoptic-scale northeasterly winds on the northwest side of sudden west-turning typhoons mainly caused by the advection of the low-frequency vorticity by the synoptic-scale winds and the advection of the typhoon vorticity by the synoptic-scale winds.