- Issue 6 Pages 435-
- Issue 5 Pages 371-
- Issue 4 Pages 233-
- Issue 3 Pages 175-
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Yasuhiro KAWABATA, Udai SHIMADA, Munehiko YAMAGUCHI2023 Volume 101 Issue 6 Pages 435-443
Published: 2023
Released on J-STAGE: October 04, 2023
Advance online publication: July 19, 2023JOURNAL OPEN ACCESS FULL-TEXT HTMLThe trend of strong typhoons over the recent 30 years was analyzed using Dvorak reanalysis data from 1987 to 2016 produced by the Japan Meteorological Agency. The strong typhoons were defined in this study as tropical cyclones equivalent to Category 4 and 5 on the Saffir-Simpson scale. The temporal homogeneity of the Dvorak reanalysis data is expected to be much better than that of best track data. Results showed no statistically significant increasing trend in strong typhoons with large inter-annual and multi-year scale variations. Meanwhile, the spatial distribution of the genesis locations of tropical cyclones, which could influence whether or not they develop into strong typhoons, varied locally during the analysis period. The changes in genesis locations may have influenced the overall trend of strong typhoons during the analysis period. The results with the new Dvorak reanalysis data highlight the need for the accumulation of high-quality data over time as well as for careful interpretation of trend analysis results seen in previous studies.
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Kunihiko KODERA, Tomoe NASUNO, Seok-Woo SON, Nawo EGUCHI, Yayoi HARADA2023 Volume 101 Issue 6 Pages 445-459
Published: 2023
Released on J-STAGE: October 31, 2023
Advance online publication: August 23, 2023JOURNAL OPEN ACCESS FULL-TEXT HTMLModulation of tropical convection by the stratospheric quasi-biennial oscillation (QBO) during the austral summer has become evident in recent studies. In this study, we show that the QBO affects the seasonal migration of the tropical convection from the equatorial Indian Ocean to the Western Pacific: large-scale convection over the Maritime Continent (MC) and western Pacific strengthens and moves eastward more effectively during easterly QBO (QBO–E) austral summers than during westerly QBO counterparts. This relationship is consistent with an enhanced Madden–Julian Oscillation (MJO) in the QBO–E. The monsoonal active convection over the Sumatra–Borneo region in December produces Kelvin wave-like low temperature anomalies in the tropical tropopause layer (TTL) over the eastern MC. These temperature anomalies strengthen when the lower stratospheric wind is easterly. We propose a hypothesis that the anomalous cooling associated with Kelvin wave-like response produces a favorable condition for the development of penetrating convection into the TTL over the eastern MC and a more effective seasonal march of deep convection across the MC occurs under the QBO–E. The implication of this process for the QBO modulation of the MJO crossing the MC is also discussed.
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Hideaki ISHIZAKI, Takatoshi SAKAZAKI, Keiichi ISHIOKA2023 Volume 101 Issue 6 Pages 461-469
Published: 2023
Released on J-STAGE: October 23, 2023
Advance online publication: August 25, 2023JOURNAL OPEN ACCESS FULL-TEXT HTMLInspired by two recent studies on the Pekeris mode, one of which first detected the Pekeris mode in satellite data after the eruption of the Hunga Tonga-Hunga Ha'apai (HTHH) volcano in January 2022, and the other of which obtained the theoretical equivalent depth of the Pekeris mode under the vertical temperature profile of the US Standard Atmosphere, the present manuscript calculates the theoretical equivalent depths of the Pekeris and Lamb modes under the realistic vertical temperature profile of the atmosphere after the eruption of the HTHH and longer period averages using global reanalysis data. The obtained equivalent depths depend to some extent on the location and range of the horizontal mean used to determine the vertical temperature profile, as well as the time and length of the temporal mean, but the equivalent depth of the Lamb mode is about 10.1 km, and that of the Pekeris mode is about 6.5 km. The reason why the equivalent depth of the Pekeris mode differs from the values obtained in the two recent studies mentioned above is also discussed.
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