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Evidence for the significant role of sea surface temperature distributions over remote tropical oceans in tropical cyclone intensity

 The role of remote ocean sea surface temperature (SST) in regulating tropical cyclone (TC) characteristics has been examined by performing numerical experiments with a regional scale model. Model simulations have been carried out to simulate typhoon Man-yi (July 2007), in our case study, under a range of SST conditions over the Indian Ocean and the South China Sea.
 The intensity and track of the cyclone have been systematically changed in sensitivity simulations of cool and warm SSTs over that region, following its peak phase. Warm oceans can substantially reduce the intensification of western North Pacific cyclones, whereas cool oceans can enhance their strength. This is intimately associated with the enhancement/weakening of the moisture supply through the moisture conveyor belt (MCB) in the lower troposphere, from the Indian Ocean and South China Sea into the vicinity of the cyclone center.
 When the MCB is interrupted over the South China Sea in warm SST occurrences, the large-scale transport of moisture into the cyclone system is significantly reduced, leading to the weakening of the cyclone intensity and to the eastward shift of its track. This study shows that changes in remote tropical ocean SST can also modulate TCs and thus can help in improving the forecasting of TC intensities and tracks.

 領域気象モデルを用いて、遠隔海域の海面水温が熱帯低気圧(台風)の強度や進路に与える影響を調査した。 台風Man-yi (2007)を典型事例として、インド洋および南シナ海の観測された海面水温(SST)分布に正負の偏差を 与えたSST感度実験を行った。
 遠隔海域の高温・低温SST実験の結果から、台風の最盛期以降に台風の強度と進路が系統的に変化することが見出された。 具体的には、インド洋および南シナ海のSSTが高いと、北西太平洋の台風の発達が抑制され、対照的に、同海域のSSTが 低いと台風の強度が増大することがわかった。このような系統的な差異は、インド洋・南シナ海から台風中心近傍へと 延びる、対流圏下層の水蒸気コンベアベルト(moisture conveyor belt: MCB)(下図参照)を介した水蒸気供給の強化・弱化と 密接に関連していた。
 SSTが高い状態ではMCBが南シナ海上で断裂してしまい、遠隔海域から台風システム内に流入する水蒸気量が減少する。 その結果、台風の強度は弱化し、台風の進路も東偏する。本研究は遠隔海域のSST変化もまた台風の強度や進路に実質的な 影響を与えている証拠を始めて示したもので、台風の強度予測および進路予測の改善に貢献することが期待される。  

*Please refer to the following manuscript.
Hegde, A. K., R. Kawamura, and T. Kawano (2016): Evidence for the significant role of sea surface temperature distributions over remote tropical oceans in tropical cyclone intensity. Climate Dynamics, 47, 623-635, doi:10.1007/s00382-015-2859-8.


Fig. 6: Spatial patterns of SLP (contours), vertically integrated moisture flux (green vectors), and its magnitude (shaded) for the CNTL experiment at 0000 and 1200 UTC on July 10, 0000 and 1200 UTC on July 11, 0000 and 1200 UTC on July 12. The contoured interval is 5 hPa. The reference arrow is 6000 kg m-1 s-1. Fluxes of less than 700 kg m-1 s-1 have been suppressed.