Large-scale processes modulating the frequency of typhoons affecting Taiwan during 1900 - 1945

  • Annual and monthly typhoon numbers were lower during 1900–1945 than 1970–2015
  • TC-more years tended to have warm SST anomalies in the tropical central Pacific
  • The ISO had a positive effect to steer typhoon movements toward Taiwan

The typhoons affecting Taiwan during 1900–1945 are defined as those with a low-pressure center making a landfall in Taiwan or moving near Taiwan and included in disaster reports. The annual and monthly numbers of typhoons were lower during 1900–1945 than during 1970–2015, which might be attributed to the colder environment, a weakened western North Pacific subtropical high with the eastward retreat and lack of satellite detection techniques during 1900–1945. However, the monthly percentages of typhoons were comparable in the high-frequency months of July–September during the two periods. In contrast to the warm period, the cold period had fewer total typhoon numbers but more concentrated occurrence during May–October. During 1900–1945, an interannual variability of the typhoon frequency affecting Taiwan was observed. During the typhoon-more (typhoon-less) years, the significant sea surface temperature patterns were dominated by warm (cold) anomalies elongating the tropical central-eastern Pacific with a maximum center in the central Pacific and cold (warm) anomalies over the tropical western Pacific. The anticyclonic (cyclonic) circulation around Taiwan that responds to a divergent (convergent) centerin the Maritime Continents tended to provide a favorable (unfavorable) steering flow to force typhoons over the east of the Philippines moving westward/northwestward (eastward) toward (away from) Taiwan. The modulations of intraseasonal oscillations on typhoon movements under the westward/northwestward and northward tracks of typhoons affecting Taiwan exerted a positive but different effect on steering the typhoon toward or near Taiwan.

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