著者

Kohei Fukuda Kazuaki Yasunaga Ryo Oyama Akiyoshi Wada Atsushi Hamada Hironori Fudeyasu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2020-019, (Released:2020-05-25)

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This study examined the diurnal cycles of brightness temperature (TB) and upper-level horizontal winds associated with tropical cyclones (TCs) over the western North Pacific basin, making use of data retrieved from geostationary-satellite (Himawari-8) observations that exhibited unprecedented temporal and spatial resolutions. The results of a spectral analysis revealed that diurnal cycles prevail in TB variations over the outer regions of TCs (300-500 km from the storm center). The dominance of the diurnal cycle was also found in variations in the radial wind (Vr) in intensive TCs, although there was no dominant cycle in tangential wind variation. In addition, coherence spectra demonstrated that the diurnal cycles of TB and Vr are significantly coherent in intensive TCs. The migration speed of TB and Vr anomalies exceeded the time-mean Vr, and it was speculated that diurnal cycle signals propagate (i.e., are not advected) toward the outer regions of TCs.

著者

Kohei Fukuda Kazuaki Yasunaga Ryo Oyama Akiyoshi Wada Atsushi Hamada Hironori Fudeyasu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.109-114, 2020 (Released:2020-07-01)

参考文献数

22

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This study examined the diurnal cycles of brightness temperature (TB) and upper-level horizontal winds associated with tropical cyclones (TCs) over the western North Pacific basin, making use of data retrieved from geostationary-satellite (Himawari-8) observations that exhibited unprecedented temporal and spatial resolutions. The results of a spectral analysis revealed that diurnal cycles prevail in TB variations over the outer regions of TCs (300-500 km from the storm center). The dominance of the diurnal cycle was also found in variations in the radial wind (Vr) in intensive TCs, although there was no dominant cycle in tangential wind variation. In addition, coherence spectra demonstrated that the diurnal cycles of TB and Vr are significantly coupled in intensive TCs. The migration speed of TB and Vr anomalies exceeded the time-mean Vr, and it was speculated that diurnal cycle signals propagate (i.e., are not advected) toward the outer regions of TCs.

著者

Akiyoshi WADA Ryo OYAMA

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.96, no.6, pp.489-509, 2018 (Released:2018-11-22)

参考文献数

52

被引用文献数

8

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Typhoon Lionrock (2016) made landfall in the Pacific side of northern Japan. One of the intriguing events was consecutive deep convections (convective bursts, CBs) occurred before making landfall on 31 August. Lionrock paused the decay of the intensity of the storm, although sea surface cooling (SSC) was induced distinctly by Lionrock along the track. To examine the influence of CBs on changes in storm intensity during the decay phase, numerical simulations were conducted with a 3 km mesh coupled atmosphere-wave-ocean model. The coupled model successfully simulated the occurrence of CBs north of the near-surface-convergence area, which was formed by the confluent of the storm's tangential winds with near-surface frictional spiral inflow from the surrounding region where the significant wave height was high. Simultaneously, the relatively fast translation and asymmetric tropical cyclone (TC) structure were maintained. Lower tropospheric horizontal moisture fluxes have enhanced around the convergence area, although SSC resulted in reduction of the air-sea latent heat fluxes within the storm's inner core. Local occurrences of upward moisture fluxes associated with CBs increased the mid-to-upper tropospheric condensational heating on the upstream side. This caused local increase in lower-tropospheric pressure gradient on the upstream side. This was favorable for pausing the decay of the simulated storm intensity even during the decay phase. Sensitivity experiments regarding the execution time of the coupled model showed that the vertical moisture fluxes and number of CBs could increase around the surface frictional convergence area ahead of the storm when the coupled model was not used. This suggests that the storm in mid-latitude could locally increase the maximum surface wind speed under favorable oceanic conditions. The number and distribution of CBs are indeed sensitive to oceanic conditions and are considered to affect the storm-track simulation and maximum surface wind speeds.

著者

Kotaro BESSHO Kenji DATE Masahiro HAYASHI Akio IKEDA Takahito IMAI Hidekazu INOUE Yukihiro KUMAGAI Takuya MIYAKAWA Hidehiko MURATA Tomoo OHNO Arata OKUYAMA Ryo OYAMA Yukio SASAKI Yoshio SHIMAZU Kazuki SHIMOJI Yasuhiko SUMIDA Masuo SUZUKI Hidetaka TANIGUCHI Hiroaki TSUCHIYAMA Daisaku UESAWA Hironobu YOKOTA Ryo YOSHIDA

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.94, no.2, pp.151-183, 2016 (Released:2016-04-28)

参考文献数

66

被引用文献数

143 885

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Himawari-8/9—a new generation of Japanese geostationary meteorological satellites-carry state-of-the-art optical sensors with significantly higher radiometric, spectral, and spatial resolution than those previously available in the geostationary orbit. They have 16 observation bands, and their spatial resolution is 0.5 or 1 km for visible and near-infrared bands and 2 km for infrared bands. These advantages, when combined with shortened revisit times (around 10 min for Full Disk and 2.5 min for sectored regions), provide new levels of capacity for the identification and tracking of rapidly changing weather phenomena and for the derivation of quantitative products. For example, fundamental cloud product is retrieved from observation data of Himawari-8 operationally. Based on the fundamental cloud product, Clear Sky Radiance and Atmospheric Motion Vector are processed for numerical weather prediction, and volcanic ash product and Aeolian dust product are created for disaster watching and environmental monitoring. Imageries from the satellites are distributed and disseminated to users via multiple paths, including Internet cloud services and communication satellite services.

著者

Ryo OYAMA Masahiro SAWADA Kazuki SHIMOJI

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.96B, pp.3-26, 2018 (Released:2018-03-16)

参考文献数

56

被引用文献数

9

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The high temporal and spatial resolutions of geostationary satellite observations achieved by recent technological advancements have facilitated the derivation of atmospheric motion vectors (AMVs), even in a tropical cyclone (TC) wherein the winds abruptly change. This study used TCs in the western North Pacific basin to investigate the ability of upper tropospheric AMVs to estimate the TC intensity and structure. We first examined the relationships between the cloud-top wind fields captured by 6-hourly upper tropospheric AMVs derived from images of the Multi-functional Transport Satellite (MTSAT) and the surface maximum sustained wind (MSW) of the Japan Meteorological Agency's best-track data for 44 TCs during 2011-2014. The correlation between the maximum tangential winds of the upper tropospheric AMVs (UMaxWinds) and MSWs was high, approximately 0.73, suggesting that the cyclonic circulation near the cloud top was intensified by the upward transport of absolute angular momentum within the TC inner core. The upper tropospheric AMVs also revealed that the mean radii of UMaxWinds and the maximum radial outflows shifted inward as the TC intensification rate became large, implying that the low-level inflow was strong for TCs undergoing rapid intensification. We further examined the possibility of estimating the MSW using 30-min-interval UMaxWinds derived from Himawari-8 target observations, which have been used to track TCs throughout their lifetimes. A case study considering Typhoon Lionrock (1610) showed that the UMaxWinds captured the changes in the cyclonic circulation near the cloud top within the inner core on a timescale shorter than 1 day. It was apparent that the increase in the UMaxWind was associated with the intensification of the TC warm core and the shrinkage of UMaxWind radius. These results suggest that Himawari-8 AMVs include useful information about TC intensification and related structural changes to support the TC intensity analysis and structure monitoring.