- 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)
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
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
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
- Akiyoshi Wada Johnny C. L. Chan
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- pp.17A-005, (Released:2021-01-11)
- 被引用文献数
- 9
In the 2019 tropical cyclone season in the western North Pacific, Typhoons FAXAI and HAGIBIS made landfall in Japan while keeping the intensity, resulting in serious disasters. This study addresses the influences of an increasing trend and variations in the upper ocean heat content above 26°C (tropical cyclone heat potential: TCHP) from January 1982 to June 2020 on FAXAI and HAGIBIS. TCHP underneath FAXAI and HAGIBIS in 2019 was higher than the climatological mean except for a part of mature phase of HAGIBIS due to HAGIBIS-induced sea surface cooling. TCHP significantly increased with the interannual oceanic variations (IOVs) in the subtropical (15-20°N, 140-150°E) and midlatitude (30-35°N, 130-140°E) areas where FAXAI and HAGIBIS intensified or kept the intensity. From an empirical orthogonal function (EOF) analysis of TCHP, we demonstrate that the leading three EOF modes of TCHP explains approximately 76.8% of total variance, but the increase in TCHP along the tracks of FAXAI and HAGIBIS particularly in the early intensification of HAGIBIS cannot be explained only by the IOVs included in the leading three EOF modes but rather by the warming trend irrespective of the IOVs.
- 著者
- Akiyoshi Wada Johnny C. L. Chan
- 出版者
- Meteorological Society of Japan
- 雑誌
- SOLA (ISSN:13496476)
- 巻号頁・発行日
- vol.17A, no.Special_Edition, pp.29-32, 2021 (Released:2021-03-18)
- 参考文献数
- 18
- 被引用文献数
- 9
In the 2019 tropical cyclone season in the western North Pacific, Typhoons FAXAI and HAGIBIS made landfall in Japan while keeping the intensity, resulting in serious disasters. This study addresses the influences of an increasing trend and variations in the upper ocean heat content above 26°C (tropical cyclone heat potential: TCHP) from January 1982 to June 2020 on FAXAI and HAGIBIS. TCHP underneath FAXAI and HAGIBIS in 2019 was higher than the climatological mean except for a part of mature phase of HAGIBIS due to HAGIBIS-induced sea surface cooling. TCHP significantly increased with the interannual oceanic variations (IOVs) in the subtropical (15°N-20°N, 140°E-150°E) and midlatitude (30°N-35°N, 130°E-140°E) areas where FAXAI and HAGIBIS intensified or kept the intensity. From an empirical orthogonal function (EOF) analysis of TCHP, we demonstrate that the leading three EOF modes of TCHP explain approximately 76.8% of total variance, but the increase in TCHP along the tracks of FAXAI and HAGIBIS particularly in the early intensification of HAGIBIS cannot be explained only by the IOVs included in the leading three EOF modes but rather by the warming trend irrespective of the IOVs.
- 著者
- Akiyoshi WADA Hiroshige TSUGUTI Kozo OKAMOTO Naoko SEINO
- 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.97, no.3, pp.553-575, 2019 (Released:2019-06-05)
- 参考文献数
- 62
- 被引用文献数
- 4
The September 2015 Kanto-Tohoku heavy rainfall event occurred in a stationary linear convective system between Typhoons Kilo and Etau. We investigated the influence of sea surface temperature (SST) on the local heavy rainfall event using a regional air-sea strongly coupled data assimilation system based on the local ensemble transform Kalman filter (LETKF) and a nonhydrostatic atmosphere model (NHM) coupled with an ocean-surface wave model and a multilayer ocean model with an Advanced Microwave Scanning Radiometer 2 (AMSR2) level 2 (L2) SST product. From the validation of SST analyzed by the coupled data assimilation system with the Japanese geostationary multi-functional transport satellite 2 hourly SST product and in-situ observations at a moored buoy, we demonstrated that the coupled system with the AMSR2 L2 SST led to an improvement in the SST analysis. Based on the verification using radiosonde observations and radar-rain gauge rainfall analysis, the analysis of the lower-atmospheric components was improved by the air-sea coupled NHM-LETKF. The local torrential rainfall event that occurred around 37°N in the Tochigi prefecture was embedded in a stationary linear convective system. The location of the linear convective system corresponded to the synoptic-scale convergence area between the cyclonic circulation associated with Etau and easterly lower-tropospheric winds. Strong southerly winds associated with Etau caused a periodic enhancement of local convection along the convergence area on the upwind side of the linear convective system and resulted in a wave-like train of the total water content around an altitude of 4-8 km on the leeward side. The improvement of SST analysis could not only change the transition of Etau to the extratropical cyclone but also the lower-tropospheric wind field and thereby the location of the stationary linear convective system with embedded local torrential rain.