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A diagnosis study of the persistent cold anomaly in North Taiwan during boreal wintertime from 1958-2008.
Abstract
This study aimed at the persistent winter (November~March) cold events in Northern Taiwan during 1958-2008. The relationship between the persistent cold events and the large scale circulation and the tropical sea surface temperature (SST) anomalies is explored by analyzing the NCEP/NCAR.reanalysis global data of CWB (central weather bureau ) data.
Eight persistent cold events are identified during 1958-2008, which occurs generally in January (4 events) and December (3 events). It shows that the occurrence of the persistent cold events is significantly affected by the global warming, most of the persistent cold events occurs before 1980s. Though the occurrence of the persistent cold event drops after 1980s, the change of the strength (amplitude) of persistent cold is insignificant.
It revealed that the following large scale conditions are favors for the developing of the persistent cold events: 1) an enhanced Siberia High, 2) a significant wave-like pattern upstream the upper atmosphere of the Siberia High, 3) a persistent low level meridional wind anomalies over Southeast Asia, 4) a barotropic wave pattern emigrated from the Atlantic over the subtropical jet stream, 5) La Nina type SST anomaly in equatorial eastern Pacific, 6) the eastward propagation of the tropical intraseasonal oscillation (MJO). Most of the above factors are fitted for each of the persistent cold event. The persistent cold event becomes particularly stronger if all the six factors are satisfied.
Key words: persistent cold anomaly 、wave chain 、 ENSO 、 MJO
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