著者

Ryohei MISUMI Namiko SAKURAI Takeshi MAESAKA Shin-ichi SUZUKI Shingo SHIMIZU Koyuru IWANAMI

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.96A, pp.51-66, 2018 (Released:2018-02-19)

参考文献数

26

被引用文献数

4

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Convective storms are frequently initiated over mountains under weak synoptic forcing conditions. However, the initiation process of such convective storms is not well understood due to a lack of observations, especially the transition process from non-precipitating cumuli to precipitating convective clouds. To investigate the initiation process, we conducted observations around the mountains in the Kanto region, Japan on 18 August 2011 using a 35 GHz (Ka-band) Doppler radar and a pair of digital cameras. The evolution of convective clouds was classified into three stages: convective clouds visible but not detected by the Ka-band radar (stage 0), convective clouds detectable by the Ka-band radar with reflectivity below 15 dBZ (stage 1), and convective clouds accompanied by descending echoes corresponding to precipitation (stage 2). During the transition process from stage 1 to stage 2, weak radar echoes rose to the higher level and reflectivity rapidly increased. This phenomenon suggests that drizzle particles produced in a preexisting convective cloud were lifted by a newly developed updraft, and raindrops were formed rapidly by coalescence of the drizzle particles and cloud droplets. This hypothetical process explains the precipitation echo formation in the lower layer frequently observed in the mountainous area in the Kanto region.

著者

FUJIBE Fumiaki

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.2018-021, (Released:2018-01-23)

被引用文献数

1

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Climatological features of surface air temperature variations on time scales of a few minutes to one hour were examined using one-minute data, spanning a four-year period, from 917 automated stations in Japan. The temperature time series was spectrally analyzed after the application of a Gaussian high-pass filter, and the variances with periods of 64 minutes or less were statistically analyzed as sub-hourly temperature variations. The result obtained shows that daytime temperature variation is observed throughout the country with relatively small regional differences. The amplitudes of daytime temperature variations were larger during spring and summer than those during autumn and winter, and under high temperature and sunny weather than under low temperature, no sunshine, and precipitation. A cross spectral analysis of temperature and wind speed reveals that temperature peaks tend to coincide with or lag behind wind speed minima. The variation is likely to correspond to the convective motion in the mixing layer. On the other hand, the intensity of nighttime temperature variation showed a large amount of scatter among stations, with exceptionally large variations during winter at some stations in northern and eastern Japan. Nighttime temperature variation tends to be in-phase with wind speed variation, with longer periods than daytime temperature variation, and is more intense under low temperature and low wind speed than under high temperature, high wind speed, and precipitation. Stations with large winter nighttime temperature variations tend to be located on a col or a slope, where the surface inversion layer is likely to be easily disturbed by any kind of atmospheric motion.

著者

MURAZAKI Kazuyo TSUJINO Hiroyuki MOTOI Tatsuo KURIHARA Kazuo

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.93, no.2, pp.161-179, 2015

被引用文献数

12

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We performed a 20-year numerical experiment over the period 1985 to 2004 using a high-resolution North Pacific Ocean General Circulation Model (NPOGCM) and a 20 km-resolution regional climate model (RCM20) to clarify the impact of the Kuroshio large meander (LM) on the climate around Japan. The NPOGCM reproduced the two primary quasi-stationary states, straight path (SP), and large meander (LM), although the periods during which each state prevailed differed from those indicated in the observational data. The NPOGCM result also showed that the Kuroshio LM causes a cold sea surface temperature anomaly to the south of the Pacific coast of the central Japan. Using the result as a lower boundary condition, a continuous numerical integration was performed by the RCM20. An 8-year composite analysis of the atmospheric circulations of the RCM20 simulation for the Kuroshio LM and SP showed that, in both winter and summer, substantial decreases in the upward surface turbulent heat flux, the frequency of precipitation, and the frequency of steep horizontal gradients in equivalent potential temperature over the ocean are caused by the cold sea surface temperature anomaly. Similar effects are evident over the land area of Japan, although they are less intense, at most 20-50 % of magnitude over the cold sea surface temperature anomaly area, and limited to the coastal region on the Pacific Ocean side in the central part of the country.

著者

Tsuyoshi Thomas SEKIYAMA Mizuo KAJINO Masaru KUNII

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.95, no.6, pp.447-454, 2017 (Released:2017-11-14)

参考文献数

26

被引用文献数

17

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We investigated the predictability of plume advection in the lower troposphere and the impact of AMeDAS surface wind data assimilation by using radioactive cesium emitted by the Fukushima nuclear accident in March 2011 as an atmospheric tracer. We conducted two experiments of radioactive plume predictions over eastern Japan for March 15, 2011 with a 3-km horizontal resolution using the Japan Meteorological Agency non-hydrostatic weather forecast model and local ensemble transform Kalman filter (JMANHM-LETKF) data assimilation system. The assimilated meteorological data were obtained from the standard archives collected for the Japan Meteorological Agency operational numerical weather prediction and the AMeDAS surface wind observations. The standard archives do not contain land-surface wind observations. The modeled radioactive cesium concentrations were examined for plume arrival times at 40 observatories. The mean error of the plume arrival times for the standard experiment (assimilating only the standard archives) was 82.0 min with a 13-h lead-time on an average. In contrast, the mean error of the AMeDAS experiment (assimilating both the standard archives and AMeDAS surface wind observations) was 72.8 min, which was 9.2 min (11 %) better than that of the standard experiment. This result indicates that the plume prediction has a reasonable accuracy for the environmental emergency response and the prediction can be significantly improved by the surface wind data assimilation.

著者

Tomoe NASUNO Kazuyoshi KIKUCHI Masuo NAKANO Yohei YAMADA Mikiko IKEDA Hiroshi TANIGUCHI

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.95, no.6, pp.345-368, 2017 (Released:2017-11-14)

参考文献数

79

被引用文献数

7

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By comparison with satellite and field observations, the comprehensive performance and potential utility of near real-time forecasts using Nonhydrostatic Icosahedral Atmospheric Model (NICAM) are demonstrated by exploiting the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY2011) / Dynamics of the Madden–Julian Oscillation (DYNAMO) campaign. A week-long forecast was run each day using a regionally stretched version of NICAM, with the finest mesh size of 14 km over the tropical Indian Ocean (IO), throughout the intensive observation period (IOP).  The simulated precipitation time series fairly represented the evolution and propagation of the observed Madden-Julian Oscillation (MJO) events, although a 30 % overprediction of precipitation over the IO domain (60–90°E, 10°S–10°N) was found on average. Frequencies of strong (> 40 mm day−1) precipitation were overpredicted, while those of weak precipitation were underpredicted against satellite observations. Compared with the field observations at Gan Island, the biases in precipitation frequency were less obvious, whereas the growth of lower to middle tropospheric dry (∼ 1 g kg−1) and warm (∼ 1 K) biases were found. Despite these mean biases, temporal variations of the moisture and zonal wind profiles including the MJO events were reasonably simulated. Using the forecast data the moisture and energy budgets during the IOP were investigated. The diagnosis using the 7-day-mean fields captured the observed features of the MJO events. Meanwhile, significant upward transport of moisture by the grid-resolved high-frequency variability was detected throughout the IOP. The relationship between these high-frequency effects and the simulated MJO or mean biases is also discussed.

著者

竹村 和人 向川 均 前田 修平

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.99, no.4, pp.879-897, 2021 (Released:2021-08-20)

参考文献数

47

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現在気候及び将来気候を対象とする大気大循環モデルによる大規模アンサンブルシミュレーションの結果を用いて、8月の北太平洋中央部におけるロスビー波の砕波頻度の将来変化、及びそれに関連する大気循環場の特徴を調べた。現在気候実験における北太平洋中央部での砕波頻度は、再解析データと同様に、エルニーニョ・南方振動と関連することが相関解析より示された。将来気候実験における北太平洋中央部での砕波頻度は、現在気候実験と比べて顕著に減少することが分かった。将来気候実験では、アジアモンスーン循環が顕著に弱化し、その結果としてアジアジェット気流が南偏する傾向が見られた。このアジアジェット気流の将来変化に伴って、北太平洋中央部ではジェット気流の分流・減速が弱化し、それは砕波頻度の減少と関連していた。また将来気候実験では、ユーラシア大陸及び北太平洋の中緯度でロスビー波の波束伝播が弱化する傾向が明瞭であり、このことは砕波頻度の減少と整合的である。相関解析及び頻度分布の解析より、将来気候実験における砕波頻度の減少は、フィリピンの東海上での積雲対流活動の弱化と関連することが示された。さらに、ω方程式を用いた診断より、砕波頻度の減少は、中部太平洋トラフの弱化及びそれに伴う力学的上昇流の弱化を通して、フィリピンの東海上での積雲対流活動の弱化に影響を及ぼすことが示された。

著者

Hidehiko MURATA Kotaro SAITOH Yasuhiko SUMIDA

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.211-238, 2018 (Released:2018-11-15)

参考文献数

22

被引用文献数

10 12

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The combination of three visible bands of the Advanced Himawari Imager (AHI) aboard Japan Meteorological Agency's (JMA) new-generation Himawari-8 and Himawari-9 geostationary meteorological satellites enables the production of true color imagery. True color is intuitively understandable to human analysts and beneficial for monitoring surface and atmospheric features. It is particularly useful when applied to frequent observations from a geostationary platform. In this article, we report on an application of a color reproduction approach based on the International Commission on Illumination (CIE) 1931 XYZ color system to imagery rendering. This approach allows the consideration of primary color (RGB) differences among satellite and output devices, which in turn cause differences in the colors reproduced. The RGB signals observed by the AHI are converted to XYZ tristimulus values, which are independent of the devices themselves, and then reconverted to RGB signals for output devices via the application of 3 × 3 conversion matrices. This article also covers an objective technique for the evaluation of the accuracy of XYZ values. The evaluation indicated that the combination of AHI native RGB bands is suboptimal for obtaining XYZ values as is, whereas a combination in which the green band is replaced by a pseudo band with a central wavelength of around 0.555 μm is optimal. The pseudo band is generated via regression with existing visible and near-infrared bands as predictor variables. The imagery produced using this approach was termed True Color Reproduction (TCR). This approach is applicable to other satellites that have several bands in the visible to near-infrared spectral range, and it has the potential for development toward the production of standardized sensor-independent true color imagery.

著者

WANG Chung-Chieh CHEN George Tai-Jen NGAI Chi-Hong TSUBOKI Kazuhisa

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.2018-051, (Released:2018-07-31)

被引用文献数

5

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There exists a minor, secondary early-morning peak in mei-yu rainfall climatology along the western coast of Taiwan, and this work investigates one such event on 8 June 2012 in southwestern Taiwan under weak synoptic conditions through both observational analysis and numerical modeling, with the main focus on the triggering mechanism of the convection. Observations show that the convection developed offshore around midnight near the leading edge of a moderate low-level southwesterly wind surge of 15-20 kts, and intensified and moved onshore to produce rainfall. The cold outflow from precipitation also led to new cell development at the backside, and the rain thus lasted for several hours till about 0700 LST. Numerical simulation using a cloud-resolving model at a grid size of 0.5 km successfully reproduced the event development with close agreement with the observations, once a time delay in the arrival of the southwesterly wind surge in initial/boundary conditions (from global analyses) is corrected. Aided by two sensitivity tests, the model results indicate that the convection breaks out between two advancing boundaries, one from the onshore surge of the prevailing southwesterly wind and the other from the offshore land/mountain breeze, when they move to about 40 km from each other. Also, both boundaries are required, as either one alone does not provide sufficient forcing to initiate deep convection in the model. These findings on the initiation of offshore convection in the mei-yu season, interestingly, are qualitatively similar to some cases in Florida with two approaching sea breeze fronts (in daytime over land).

著者

Hisaki EITO Teruyuki KATO Masanori YOSHIZAKI Ahoro ADACHI

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.83, no.4, pp.551-576, 2005 (Released:2005-10-07)

参考文献数

32

被引用文献数

23 26

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On 16 January 2001 during the field experiment named WMO-01, a meso-β-scale snowband extending eastward from Toyama Bay was observed in the coastal area of eastern Hokuriku district, middle part of Japan. This snowband stagnated for about half a day and brought a snowfall of about 50 cm in this region.Numerical simulations of this snowband are performed using a nonhydrostatic cloud resolving model (NHM), with a horizontal grid size of 1 km. The NHM well reproduces many characteristics of the observed snowband. The snowband forms over the convergence zone between a cold southerly land breeze and a northwesterly winter monsoon, to which heat and moisture is supplied from relatively warm sea surface. Convective snow cells with the horizontal scale of a few km successively form at the northern part of the snowband and propagate east-southeastward. Meso-γ-scale convective snow systems are organized, consisting of developed snow cells in the snowband. A cold pool forms under the snowband. The diabatic cooling due to the sublimation of snow is responsible for the formation of the cold pool. After the land breeze became weak, the cold pool contributes to the maintenance of the horizontal convergence with the northwesterly winter monsoon at the northern edge of the snowband by compensating for the weakened land breeze. Therefore, the formation of the cold pool is significant for the maintenance of thesnowband.

著者

ISHIOKA Keiichi YAMAMOTO Naoto FUJITA Masato

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.2022-022, (Released:2021-12-28)

被引用文献数

1

---

In the discretization of the primitive equations for numerical calculations, a formulation of a three-dimensional spectral model is proposed that uses the spectral method not only in the horizontal direction but also in the vertical direction. In this formulation, the Legendre polynomial expansion is used for the vertical discretization. It is shown that semi-implicit time integration can be efficiently done under this formulation. Then, a numerical model based on this formulation is developed and several benchmark numerical calculations proposed in previous studies are performed to show that this implementation of the primitive equations can give accurate numerical solutions with a relatively small degrees of freedom in the vertical discretization. It is also shown that, by performing several calculations with different vertical degrees of freedom, a characteristic property of the spectral method is observed in which the error of the numerical solution decreases rapidly when the number of vertical degrees of freedom is increased. It is also noted that an alternative to the sponge layer can be devised to suppress the reflected waves under this formulation, and that a “toy” model can be derived as an application of this formulation, in which the vertical degrees of freedom are reduced to the minimum.

著者

TOHJIMA Yasunori NIWA Yosuke TSUBOI Kazuhiro SAITO Kazuyuki

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.2022-021, (Released:2021-12-28)

被引用文献数

2

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Synoptic-scale variabilities of atmospheric CO2 and CH4 observed at Yonagunijima (Yonaguni Island, YON, 24.47°N, 123.01°E) during winter (from January to March) in 1998-2020 were examined. The monthly mean variability ratios (ΔCO2/ΔCH4) based on correlation slopes within 24-hour time windows showed a clear increasing trend, which is mainly attributed to the unprecedented increase in the fossil fuel-derived CO2 (FFCO2) emissions from China. A similar increasing trend of the ΔCO2/ΔCH4 ratio had been reported for the observation at Hateruma Island (HAT, 24.06°N, 123.81°E), located at about 100 km east of YON. However, the absolute values for YON were 34 % larger than those for HAT. In addition, the monthly average in February 2020 for YON showed no marked change, while that for HAT showed an abrupt considerable decrease associated with the FFCO2 emission decrease in China presumably caused by the COVID-19 lockdown. Investigating the diurnal variations, we found that the local influences were larger at YON, especially during daytime, than at HAT. Using nighttime data (20-6 LST) and a longer time window (84-hour), we succeeded in reducing the local influences and the resulting monthly mean ΔCO2/ΔCH4 ratio showed considerable similarity to that observed at HAT including the abrupt decrease in February 2020. These results convinced us that the ΔCO2/ΔCH4 ratio could be successfully used to investigate the relative emission strength in the upwind region.

著者

Adam H. Sobel 堀之内 武

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.78, no.2, pp.167-173, 2000-04-25 (Released:2009-09-15)

参考文献数

29

被引用文献数

11 12

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ITCZやモンスーントラフ域で観測される回転性の総観規模風速擾乱の幾つかの側面は、大きなメソスケール対流システムに特徴的な振幅や時・空間スケールを持つパルス的加熱に対する、乾燥・静止大気の線形応答を考えることで理解できることを議論する。その鍵は、短波長のロスビー波の平均流から見た群速度、位相速度は小さいことと、加熱が赤道上よりも赤道から少し離れた位置にあるほうがロスビーモードの応答は遥かに大きなエネルギーを持つことである。故に、観測される擾乱に似た特徴を持つ総観規模ロスビー波は、大きなメソスケール積雲システムが発達する赤道を少し離れた領域に存在するということになる。

著者

SISWANTO Siswanto SCHRIER Gerard van der HURK Bart van den

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.2022-023, (Released:2022-02-08)

被引用文献数

4

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Sub-daily extreme precipitation in Jakarta exhibits trends related to local temperature, seasonal tropical monsoon circulations, and other environmental drivers. Analysis of 81 years of hourly rainfall between 1900-2010 shows a significant increase of about doubling the number of short-duration rainfall events in the wet season. In recent decades, rainfall is found to be higher in intensity and shorter in duration relative to preceding decades. These short-duration rain showers develop typically between afternoon and late night or during early morning hours. Changing short-duration rainfall characteristics throughout the last century are partly attributed to changes in the surface environment of urban Jakarta. A recent temperature increase and land surface drying in the city, in combination with a small increase of the atmospheric moisture content, promote intensified atmospheric convection. A combination of rain gauge data with upper-air observations collected during 2002-2016 reveals that surface warming in the urbanized city accompanied by enhanced availability of moisture results in an increase of convective available potential energy (CAPE), which contributes to enhanced intense precipitation. Super Clausius-Clapeyron scaling (CC) of high-intensity rainfall is attributed to high near-surface temperature and atmospheric moisture content in the morning. This super CC scaling is present in a relatively small range of surface temperature values. Results of this study are in agreement with earlier findings exploring the intensification of extreme morning precipitation and a temporal shift of the diurnal convective maximum from late afternoon to late night/early morning in response to local warming. For a delta city such as Jakarta with abundant convection and heavy precipitation, a well-maintained rainfall database is crucial to assist urban flood early warning.

著者

増山 元三郎

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.15, no.6, pp.215-223, 1937-06-05 (Released:2009-02-05)

参考文献数

8

被引用文献数

1 1

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Je suppose que les postulates fondamentaux en hydrodynamique sont K. I.....K. 10 (§ 1), qui soot été employés par nombreux auteurs explicitement on implicitement pour deduire l'équation de NAVIER-STOKES (1.17).Il y a en § 2 quelques critiques pour les postulates K. I.....K. 10, et on obtient un nonvel terme turbulent fr (2.3). Il faut en conséquence développer le tenseur de viscosité Zrs en série des gradients de vitesse vr, s comme (2.5). Dans le cas du médium isotrope le coefficient de viscosité _??_rsmn n'est pas nécessairement symétrique, et on a un nouvel terme kr (2.7) additivement à côté droit de l'équation (2.11). Si on l'écrit vectoriellement, on obtient (2.9) pour kr comme l'expression vectorielle. J.y donne de plus une nouvelle expression (2.12), qui peut être employée au lieu de relation “Austausch” de Prandtl.On a quelques explications à phenomènes hydrodynamiques biers connues mais non expliqués jusqu'ici (§ 3). Enfin j'étudie sur la fondation d'équation (3.2) quand tourbillon se mouvoit le long de son axe, et explique géométriquement sa condition nécessaire et suffisante.

著者

KUSAKA Hiroyuki NAKAMURA Yusuke ASANO Yuki

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2022-035, (Released:2022-05-13)

被引用文献数

1

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Ultra Violet (UV) parasols are a reasonable countermeasure against heat stress as they are portable and inexpensive. This study compared the heat stress mitigation effect of a UV parasol with that of street trees and dry-mist spraying on a hot and humid summer day in Japan. We observed meteorological elements and calculated the universal thermal climate index (UTCI) and wet-bulb globe temperature (WBGT) under UV parasol, street trees, dry-mist spraying, and direct sunlight. The observed UTCI and WBGT under the UV parasol were lower than those in direct sunlight by 4.4 and 1.3°C, respectively, because of the decrease in black globe temperature caused by the reduced downward shortwave radiation. This demonstrated that UV parasol reduced heatstroke risk by one level. The effect of the UV parasol was equal to or greater than 75 % of that of the street trees from the perspective of UTCI. The street trees reduced the UTCI and WBGT by 5.9 and 1.9°C, respectively, compared to those in direct sunlight, resulting in the reduction of heatstroke risk by one level. In contrast, dry-mist spraying did not mitigate heat stress in conditions with moderate winds. Although the results of this study were obtained from observations on a single day, comparison with earlier studies confirms that the values observed in this study are representative results on summer days in Japan.

著者

伊藤 耕介

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.100, no.2, pp.321-341, 2022 (Released:2022-04-13)

参考文献数

46

被引用文献数

4

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気象庁の全球日別海面水温解析の準リアルタイム版(以下、R-MGD)では、解析時間の前に得られた観測データに短時間スケールの変動を落とすようなフィルタを適用している。そのため、台風の通過に伴う急激な海面水温の変化がバイアスを生むと考えられる。本研究では、R-MGDの現場観測に対するバイアスを、北西太平洋における台風の通過に沿って定量化した。初めに、2020年8月~9月にかけて立て続けに接近した3つの台風に関し、事例解析を行った。R-MGDは3つの台風の通過直後では2℃以上もの正バイアスを生じており、最後の台風が通過して1週間以上経過したのち負バイアスが観測された。R-MGDと係留ブイの比較を行ったところ、短時間スケールを落とすフィルタリングと解析時間の前に得られたデータを用いていることで、バイアスが説明できた。次に、2015年5月から2020年10月の期間でコンポジット解析を行ったところ、台風最接近の1日前から4日後までに統計的に有意な正バイアス、台風最接近の7日後から14日後までに統計的に有意な負バイアスが、台風から500 kmの範囲内で検出された。正バイアスは、冷たい亜表層の水と激しい台風の通過に伴って生じやすく、とりわけ、黒潮と黒潮続流域を除く中緯度帯で大きくなっていた。また、R-MGDの解析時間の72時間前までに得られた現場観測を追加の最適内挿法で同化することにより、バイアスは軽減されることが分かった。これは、この過程により短周期の変動が復元されたためである。台風予報への影響評価および最適内挿法の独立な観測に対する検証も実施した。

著者

宮本 佳明 筆保 弘徳 和田 章義

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.100, no.1, pp.181-196, 2022 (Released:2022-02-22)

参考文献数

48

被引用文献数

6

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中心気圧が960hPaで関東地方に上陸した台風Faxai (1915)に関して、非静力学モデルを用いて格子間隔1kmでの数値シミュレーションを行なった。Faxaiは上陸まで軸対称的な構造を維持し、強風により甚大な被害をもたらした。シミュレーションの結果、上陸前後の48時間の現実的な経路・強度が再現された。計算された強度は上陸まで強く、渦の水平方向の大きさは小さかった。計算されたFaxaiの構造は、熱帯海洋上における発達した熱帯低気圧(TC)のように、軸対称的で目の壁雲が存在していた。中心付近で海面の潜熱フラックスは上陸まで300W m-2を超えていて、高度1.5-12 kmでの鉛直シアーは中緯度としては比較的弱く、9m s-1よりも低かった。 台風の環境場パラメータからポテンシャル強度(MPI)を算出した。計算されたTCの強度もベストトラックの強度も、上陸12時間前からMPIよりも大きいsuperintense状態にあった。これは、内部コア域で超傾度風化していたことによるもので、強い強度や軸対称な構造が原因と考えられる。計算されたTCは、成熟期において傾度風平衡を除いたMPIの式に必要な近似を良く満たしており、これはTCの構造が熱帯で発達したものと類似していたためと考えられる。 今回の解析から、Faxaiは、好ましい環境条件と渦構造によって強い強度を維持したと考えられる。

著者

YULIHASTIN Erma HADI Tri Wahyu ABDILLAH Muhammad Rais FAUZIAH Irineu Rakhmah NINGSIH Nining Sari

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.2022-005, (Released:2021-10-04)

被引用文献数

7

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Early morning precipitation (EMP) events occur most frequently during January and February over the northern coast of West Java and are characterized by propagating systems originating from both inland and offshore. The initial location, direction, and speed of the propagating precipitating system determine the timing of EMP. This study explores processes that characterize such propagating precipitation systems by performing composite analysis and real-case numerical simulations of selected events using the Weather and Research Forecasting (WRF) model with a cloud-permitting horizontal resolution of 3 km. In the composite analysis, EMP events are classified according to the strength of the northerly background wind (VBG), defined as the 925-hPa meridional wind averaged over an area covering western Java and the adjacent sea. We find that under both strong northerly (SN) and weak northerly (WN) wind conditions, EMP is mainly induced by a precipitation system that propagates from sea to land. For WN cases, however, precipitating systems that propagate from inland areas to the sea also play a role. The WRF simulations suggest that mechanisms akin to cold pool propagation and advection by prevailing winds are responsible for the propagating convection that induces EMP, which also explains the dependence of EMP frequency on the strength of VBG. Based on the WRF simulations, we also discuss the roles of sea breeze and gravity waves in the initiation of convection.

著者

松野 太郎

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.44, no.1, pp.25-43, 1966 (Released:2008-05-27)

参考文献数

10

被引用文献数

1371 1997

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コリオリの力が働かなくなる赤道近辺での大規模運動の特性を理論的に検討してみた。自由表面をもった単層の流体-いわゆる発散順圧モデル-について線型化された運動方程式を扱い東西方向に動く自由波動の解を求めると,一定のスケールに対して3つの解が得られた。これらは振動数解の形(圧力及び運動の場)から夫々東向きおよび西向きの慣性重力波およびロスビー波であることがわかる.但し南北スケール最小のものに関してはその区別は明瞭でなく一方の型から他方の型に連続的にかわる。ロスビー波に相当する解は風と圧力の関係が高緯度でほぼ地衡風的であるごと,および赤道近くで特異なふるまいをするのが特徴である。次に同じモデル熱冷源に相当するものとして東西に周期的なmass source,sinkを与え,定常解と求めた。熱源に相当する所は低圧になるが赤道で分断され,赤道のごく近くはやや逆センスになり,これに伴って高緯度と逆向きの強い流れが生ずることが分った。

著者

ROH Woosub SATOH Masaki HOHENEGGER Cathy

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.2021-070, (Released:2021-08-24)

被引用文献数

12

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We intercompared the cloud properties of the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) simulation output over the Atlantic Ocean. The domain averaged outgoing long-wave radiation (OLR) is relatively similar across the models, but the net shortwave radiation at the top of the atmosphere (NSR) shows large differences among the models. The models capture the triple modes of cloud systems corresponding to shallow, congestus, and high clouds, even though their partition in these three categories is strongly model dependent.The simulated height of the shallow and congestus peaks is more robust than the peak of high clouds, whereas cloud water content exhibits larger intermodel differences than cloud ice.  Furthermore, we investigated the resolution dependency of the vertical profiles of clouds for NICAM (Nonhydrostatic ICosahedral Atmospheric Model), ICON (Icosahedral Nonhydrostatic), and IFS (Integrated Forecasting System). We found that the averaged mixing ratio of ice clouds consistently increased with finer grid spacing. Such a consistent signal is not apparent for the mixing ratio of liquid clouds for shallow and congestus clouds. The impact of the grid spacing on OLR is smaller than on NSR and also much smaller than the intermodel differences.