著者

TOCHIMOTO Eigo YOKOTA Sho NIINO Hiroshi YANASE Wataru

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2022-007, (Released:2021-10-06)

被引用文献数

1

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Ensemble forecasts with 101 members (including one ensemble mean) using ensemble Kalman filter analysis were performed to understand the atmospheric conditions favorable for the development of a meso-β-scale vortex (MBV) that caused shipwrecks as a result of sudden gusty winds in the southwestern part of the Sea of Japan on 1 September 2015. A composite analysis was performed to reveal differences in the structure of the MBV and atmospheric conditions around the MBV between the strongest eight (STRG) and weakest ten (WEAK) ensemble members, where two of the strongest ten members that developed the MBV much earlier than the other members were excluded from the analysis. The analysis shows that near-surface cyclonic horizontal shear to the northeast and the south of the MBV was stronger for STRG than for WEAK. In addition, larger low-level water vapor and its horizontal flux for STRG contribute to greater convective available potential energy to the southeast of the MBV, resulting in stronger convection around the MBV. The results of the composite analysis are also statistically supported by an ensemble-based sensitivity analysis. Differences in near-surface horizontal shear were closely related to the structure of the extratropical cyclone in which the MBV was embedded. Although the strength of the extratropical cyclone for STRG was comparable with that for WEAK, the cyclonic horizontal shear of winds in the northeastern quadrant of the extratropical cyclone was greater for STRG than for WEAK.

著者

TOCHIMOTO Eigo NIINO Hiroshi

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2018-043, (Released:2018-04-27)

被引用文献数

7

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This study used the JRA-55 reanalysis dataset to analyze the structure and environment of extratropical cyclones (ECs) that spawned tornadoes (tornadic ECs: TECs) between 1961 and 2011 in Japan. Composite analysis indicated that the differences between the structure and environment of TECs and those of ECs that did not spawn tornadoes (non-tornadic ECs: NTECs) vary with the seasons. In spring (March–May), TECs are associated with stronger upper-level potential vorticity and colder mid-level temperature than NTECs. The colder air at the mid-level contributes to the increase in convective available potential energy (CAPE) of TECs. TECs in winter (December–February: DJF) and those northward of 40°N in autumn (September–November: SON) are accompanied by larger CAPE than are NTECs. The larger CAPE for TECs in DJF is caused by larger moisture and warmer temperature at low levels, and that for TECs northward of 40°N in SON (NSON) is caused by the colder mid-level temperature associated with an upper-level trough. The distribution of the energy helicity index also shows significant differences between TECs and NTECs for DJF and NSON. On the other hand, the distribution of the 0–1 km storm relative environmental helicity (SREH) shows no significant differences between TECs and NTECs in most seasons except DJF. A comparison of TECs between Japan and the United States (US) shows that SREH and CAPE are noticeably larger in the US. It is suggested that these differences occur because TECs in the US (Japan) develop over land (ocean), which exerts more (less) surface friction and diurnal heating.

著者

TOCHIMOTO Eigo KAWANO Tetsuya

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

pp.2017-005, (Released:2017-01-13)

被引用文献数

10

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This work investigates development processes of Baiu frontal depressions (BFDs) using a numerical model. To investigate the effects of upper-level disturbances, latent heating, and baroclinicity on the development of BFDs, case-study numerical simulations are performed. In the present study, two typical cases were selected from BFDs that appeared in June and July, 2000-2007: a BFD that developed in the western part of the Baiu frontal zone (W-BFD) from 26 to 27 June 2003 and a BFD that had formed in the eastern part of the Baiu frontal zone (E-BFD) from 1 to 3 July 2003. An available potential energy (APE) diagnosis shows that the effect of latent heating is dominant during the W-BFD development, while baroclinicity as well as latent heating is important to the E-BFD development. A sensitivity experiment excluding upper-level potential vorticity (PV) anomalies shows that upper-level disturbances are important contributors to the development of E-BFDs. The low-level PV and its production associated with latent heating suggest that the W-BFD has a development mechanism driven by latent heating. In the early developmental stage, PV near the W-BFD center is enhanced. This feature is consistent with the nonlinear conditional instability of the second kind mechanism. In the later developmental stage, PV is produced in front of the W-BFD center, in which low-level baroclinicity is large. This process is consistent with a diabatic Rossby vortex. In contrast, the E-BFD develops through a baroclinic instability-like mechanism in the moist atmosphere.