著者

Kenji YOSHIDA Hisanori ITOH

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.90, no.3, pp.377-401, 2012-06-25 (Released:2012-06-30)

参考文献数

46

被引用文献数

12 17

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This study examines the indirect effect of tropical cyclones (TCs) on cases of heavy rainfall during the Baiu season in Kyushu, Japan using data analyses and numerical experiments. A detailed analysis of the heavy rainfall event that occurred on 7 June 1999 (JST) is performed. This event was remotely affected by Typhoon Maggie (9903), which was located approximately 2000 km from Kyushu at the time. As Typhoon Maggie passed close to Taiwan, a high potential vorticity (PV) zone appeared to the north of Taiwan. A low PV region formed simultaneously to the east of Taiwan, corresponding to a northwestward extension of the Pacific high. These dynamical changes induced an enhanced southerly moisture flux between the high PV zone and the low PV region, leading to moisture convergence and heavy rain in the vicinity of Kyushu. During this time, Typhoon Maggie also caused the northward advection of a separate tropical disturbance.The high PV zone to the north of Taiwan was produced by diabatic heating associated with interplay between the circulation of Typhoon Maggie and the topography of Taiwan. In contrast, the low PV region was formed through the advection of low-PV air from low latitudes by Typhoon Maggie. A piecewise PV inversion diagnostic shows that the low PV region was the largest contributor to the southerly moisture flux, although both Typhoon Maggie and the high PV zone also made positive contributions. Numerical experiments reveal that the precipitation in and around Kyushu was enhanced by both the topography of Taiwan and the northward advection of the additional tropical disturbance.This study identifies a new mechanism as an indirect effect of TCs. The core element of this mechanism is a large moisture flux south of Kyushu, which is termed “moisture road,” and the difference from “atmospheric river” is discussed. This mechanism is not unique to Typhoon Maggie, as other cases of heavy rainfall in and around Kyushu are associated with similar situations.

著者

Hiroki TSUJI Hisanori ITOH Kensuke NAKAJIMA

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.94, no.3, pp.219-236, 2016 (Released:2016-07-02)

参考文献数

29

被引用文献数

15

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To understand the basic mechanism governing the size evolution of tropical cyclones (TCs), we systematically perform numerical experiments using the primitive equation system on an f-plane. A simplified, TC-like vortex is initially given and an external forcing mimicking cumulus heating is applied to an annular region at a prescribed distance from the vortex center. Moist process and surface friction are excluded for simplification. We focus on the sensitivity of size evolution to the location of the forcing. The vortex size is defined as the radius of 15 m s-1 lowest-level wind speed (R15). The evolution of R15 depends on the forcing location, and its dependence can be understood by considering radial transport of the absolute angular momentum (AAM) at R15 due to the heat-induced secondary circulation (SC), whose structure is governed by the distribution of inertial stability. When the forcing is applied to the outer part of a vortex but still inside R15, where inertial stability is weak, the SC extends to the outside of R15 and carries AAM inward. Thus, R15 increases. Conversely, when the forcing is applied near the center of the vortex, where inertial stability is strong, the SC closes inside R15 and R15 hardly increases. These results indicate that extension of the heat-induced SC to the outside of R15 is important for the evolution of the vortex size. Moreover, the further beyond R15 the SC extends, the more the vortex size increases. This relationship is consistent with the result of the parcel trajectory analysis; the larger the extent of SC, the longer distances the parcels cover, conserving larger AAM. Finally, when the forcing is applied to the outside of R15, smaller AAM is carried outward by the SC on the inward side of the heating location, resulting in the decrease of R15.

著者

Sam Sherriff-Tadano Hisanori Itoh

出版者

(公社)日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.9, pp.115-119, 2013 (Released:2013-08-23)

参考文献数

13

被引用文献数

1

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Teleconnection patterns in boreal winter were sought by using the streamfunction based on one-point covariance analysis. As a result, five patterns with two new patterns, i.e., the North and South Pacific Oscillation pattern (PO) and the Middle Atlantic pattern (MA), were obtained. The PO is an interhemispheric pattern with major centers in the Pacific, related to the El Niño/La Niña. The MA has a similar structure with the East Atlantic pattern (EA), though the orientation of the pattern and the difference in the sustaining mechanism, as well as a relatively low correlation between the two indices, distinguish the MA from the EA, with the primary importance of the MA from several pieces of evidence. The PO and MA have significant relations to the surface air temperature mostly through the temperature advection. By comparing the result of the combined EOF for the zonal and meridional winds, the appropriateness of the use of the streamfunction in association with wind variations was also confirmed.