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Remote thermodynamic impact of the Kuroshio Current on a developing tropical cyclone over the western North Pacific in boreal fall

To examine the remote linkage between tropical cyclone (TC) development and moisture transport from the Kuroshio Current toward the TC, we conducted sensitivity experiments that modified the surface latent heat flux (LHF) over the Kuroshio, applying a cloud‐resolving regional model and Lagrangian diagnostics to Typhoon Chaba as it approached Japan in October 2010.

The synoptic environment was characterized by a combination of an anticyclone of continental origin around Japan and the northward‐migrating TC, bringing about low‐level northeasterlies over the Kuroshio through an enhanced meridional pressure gradient. When the LHF over the Kuroshio was artificially reduced or removed under this environmental flow, the intensity of the TC, which was fully away from the domain in which the LHF is modified, appreciably attenuated during its developing stage, implying the importance of moisture influx due to the environmental flow in TC development. Since dry air of midlatitude origin could receive little of the moisture supply from the Kuroshio in the sensitivity experiments, the values of equivalent potential temperature within the inflow layer tend to decrease, thus facilitating the weakening of convective updrafts and downdrafts around the eyewall of the TC. It is suggested that such changes act as an inhibitory factor for TC development.

The Kuroshio has the potential to remotely influence the TC intensity over the western North Pacific if favorable synoptic conditions are satisfied.

  熱帯低気圧(台風)の発達と黒潮から台風へ向かう水蒸気輸送との遠隔結合を調査するために、 黒潮の海面潜熱フラックス(LHF)改変実験を行った。具体的には、2010年10月に日本に接近した台風Chabaの典型事例に 雲解像領域モデル並びにラグランジュ診断解析を適用した。
 日本付近には大陸起源の移動性高気圧が存在し、北進する台風との間で南北気圧傾度が強まることで、 黒潮上では下層北東風が卓越する総観場になっていた。この環境場の下で黒潮のLHFを人為的に減少させる、あるいは除去すると、 LHF改変領域から十分遠距離に台風が位置しているにもかかわらず、台風の発達が明らかに抑制された。これは環境風による水蒸気流入フラックスが台風発達に重要であることを意味している。 LHF感度実験では、中緯度起源の乾燥空気は黒潮からの水蒸気供給をほとんど受け取れないので、 境界層のインフロー内の相当温位は減少傾向にあり、台風の壁雲付近の対流による上昇流・下降流の弱化を促進させる。 そのような変化は台風発達の抑制因子として作用すると考えられる。 

*Please refer to the following manuscript.
Fujiwara, K., R. Kawamura, and T. Kawano (2020): Remote thermodynamic impact of the Kuroshio Current on a developing tropical cyclone over the western North Pacific in boreal fall. J. Geophys. Res. Atmos., 125, e2019JD031356.


Fig. 5: (a) Horizontal distributions of latent heating rates (shaded) at a height of 6 km at 1300 UTC on 28 October 2010. The open red circle indicates Chaba's inner core, as defined by a radius of 150 km from its center. (b) Frequency distribution of the trajectories of air parcels (based on each box of 0.2° latitude by 0.2° longitude) that are imported into the inner core, which are calculated by a backward trajectory analysis. See text for details. The closed green circle denotes the location of the typhoon at 1300 UTC on 28 October 2010. (c) Same as in the panel (b) except for the frequency distribution of the parcel trajectories that pass through the 29°N latitude line (blue thick line). The domain where the latent heat flux is modified in sensitivity experiments is enclosed by a black line.