著者

TAKAMURA Tamio IRIE Hitoshi

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.2019-059, (Released:2019-08-09)

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The accurate aerosol optical thickness is indispensable for estimating the radiative forcing of aerosols in the atmosphere. Sun photometry is one of the most popular methods, which is simple and easy to use, but it should be noted that some errors due to forward scattering effect can be introduced in the observation of the direct normal irradiance. Consequently, the estimated optical thickness of aerosols can be under-estimated even if the calibration constant is correct. This possibility depends on an optical geometry of the measuring instrument as well as aerosol characteristics. This report assesses these effects by assuming several aerosol types and instrumental parameters quantitatively. Forward scattering ratio γλfwd, which is defined as a ratio of the forward scattering part to the true direct normal irradiance (Iλ), by Iλobs=Iλ(1+γλfwd), is approximately proportional to the product of the optical thickness (τλaer) and the single scattering albedo (ωλ) of aerosols and the relative air mass (m), γλfwd≈ελωλτλaerm. The coefficient ελ is a proportional constant which is dependent on the opening angle of the instrument as well as the optical characteristics of aerosols. The variation of ελ is tabulated for several aerosol types and opening angles. Then the error for the estimate of τλaer can be approximately expressed by Δτλ≈ -ελωλτλaer.

出版者

社団法人 日本気象学会

雑誌

氣象集誌. 第1輯 (ISSN:00261165)

巻号頁・発行日

vol.10, no.7, pp.361-365, 1891 (Released:2009-02-05)

著者

VITANOVA Lidia Lazarova KUSAKA Hiroyuki DOAN Van Quang NISHI Akifumi

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.2019-013, (Released:2018-11-16)

被引用文献数

6

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This study investigates the impact of urbanization on surface air temperature and the urban heat island (UHI) for Sendai City. We estimate the impacts of the urbaniza-tion during the 150-year period by comparing the 1850s to the 2000s case. We use the Weather Research and Forecasting (WRF) model with 1-km horizontal resolution and three land-use datasets, one for potential natural vegetation (PNV) data, the other two for realistic land-use data (the 1850s and 2000s). Results from the control simulation (2000s land-use case) are firstly verified against observations. The results show that the WRF model reasonably well reproduces the diurnal variation of the observed surface air temperatures in the 2000s land-use case at six stations in Miyagi prefecture. The model mean biases range from −0.29 to −1.18°C in August (10-year average) and from −0.44 to −1.50°C in February (10-year average). Secondly, the impacts of urbanization on the surface air temperature distribution in and around Sendai City are evaluated. In the 1850s land-use case, the very small urban area of Sendai City results in a negligible UHI. This case gives nearly the same surface air temperatures as experiments using the PNV. Comparing the simulated monthly mean surface air temperatures in the central part of Sendai City between the 1850s and 2000s land-use cases, we find that the monthly mean temperature for February in the 2000s is 1.40°C higher than that in the 1850s, whereas that for August is 1.30°C. Similarly, we find considerable nocturnal (1800–0500 JST) average surface air temperature increases of 2.20°C in February and 2.00°C in August.

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

ITO Takahiro NISHIMOTO Shusuke KANEHISA Hirotada

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.2018-055, (Released:2018-09-07)

被引用文献数

1

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In this study, we show analytically that vortex Rossby waves (VRWs) with azimuthal wavenumber m =1 in a basic axisymmetric vortex can grow exponentially in a quasi-geostrophic system, although they cannot do so in a barotropic system. VRWs grow exponentially if Rayleigh’s condition and Fjørtoft’s condition are satisfied. Satisfying Rayleigh’s condition means that two horizontally aligned VRWs at two different radii propagate (here and hereafter “propagate” refers to propagation relative to the fluid) azimuthally counter to each other. Satisfying Fjørtoft’s condition means that the cyclonic advective angular velocity of the basic vortex is distributed radially so as to enable the VRWs to be phase-locked with each other. Under these conditions, a strong mutual interaction between the VRWs becomes possible, and thus they grow exponentially. In a barotropic system, even if Rayleigh’s condition is satisfied, the azimuthal counter propagation of VRWs with azimuthal wavenumber m =1 is so strong that phase-locking between them cannot occur, and thus they cannot grow exponentially. In a quasi-geostrophic system, however, the upper and lower VRWs of the first baroclinic vertical mode are equal in magnitude and have opposite signs. Because of this baroclinic structure, the azimuthal counter propagation of the horizontally aligned VRWs is suppressed by the vertical interactions between the upper and lower VRWs. Consequently, horizontally aligned VRWs with azimuthal wavenumber m =1 may become phase-locked, and hence they may grow exponentially. By analytically solving the linear problem of VRWs in a quasi-geostrophic system, we show that this is indeed the case.

著者

KADOYA Toshiki MASUNAGA Hirohiko

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.2018-054, (Released:2018-08-24)

被引用文献数

11

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A new observational measure, or the morphological index for convective self-aggregation (MICA), is developed to objectively detect the signs of convective self-aggregation on the basis of a simple morphological diagnosis of convective clouds in the satellite imagery. The proposed index is applied to infrared imagery from the Meteosat-7 satellite and is assessed with the sounding-array measurements in the tropics from Cooperative Indian Ocean experiment on Intraseasonal variability in the Year of 2011 (CINDY2011)/Dynamics of the Madden-Julian Oscillation (MJO) (DYNAMO)/Atmospheric Radiation Measurements (ARM) MJO Investigation Experiment (AMIE). The precipitation events during the observational period are first classified by MICA into “aggregation events” and “non-aggregation events”. The large-scale thermodynamics implied from the sounding-array data are then examined with focus on the difference between the two classes. The composite time series show that a drying proceeds over 6-12 hours as precipitation intensifies in the aggregation events. Such a drying is unclear in the non-aggregation events. The moisture budget balance is maintained in very different manners between the two adjacent sounding arrays for the aggregation events, in contrast to the non-aggregation events which lack such apparent asymmetry. These results imply the potential utility of the proposed metrics for future studies in search of convective self-aggregation in the real atmosphere.

著者

OTSUKA Michiko SEKO Hiromu SHIMOJI Kazuki YAMASHITA Koji

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.2018-034, (Released:2018-03-23)

被引用文献数

11

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Rapid scan atmospheric motion vectors (RS-AMV) were derived with an algorithm developed by the Meteorological Satellite Center of the Japan Meteorological Agency (JMA) from Himawari-8 rapid scan imagery over the area around Japan. They were computed every 10 min for seven different channels, namely, the visible channel (VIS), near infrared and infrared channels (IR), three water vapor absorption channels (WV), and CO2 absorption channel (CO2), from image triplets with time intervals of 2.5 min for VIS and 5 min for the other six channels. In June 2016, the amount of data was increased by more than 20 times compared to the number of routinely used AMVs. To exploit these high-resolution data in mesoscale data assimilation for the improvement of short-range forecasts, data verification and assimilation experiments were conducted. The RS-AMVs were of sufficiently good quality for assimilation and consistent overall with winds from JMA’s mesoscale analyses, radiosonde, and wind profiler observations. Errors were slightly larger in WV than in VIS and IR channels. Significant negative biases relative to sonde winds were seen at high levels in VIS, IR, and CO2, while slightly positive biases were noticeable in WV at mid- to high levels. Data assimilation experiments with the JMA’s non-hydrostatic model based Variational Data Assimilation System (JNoVA) on a cold vortex event in June 2016 were conducted using RS-AMVs from seven channels. The wind forecasts improved slightly in early forecast hours before 12 hours in northern Japan, over which the vortex passed during the assimilation period. They also showed small improvement at low levels when averaged over the whole forecast period. The results varied slightly depending on the channels used for assimilation, which might be caused by different error characteristics of RS-AMVs in different channels.

著者

MISUMI Ryohei UJI Yasushi TOBO Yutaka MIURA Kazuhiko UETAKE Jun IWAMOTO Yoko MAESAKA Takeshi IWANAMI Koyuru

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.2018-040, (Released:2018-04-13)

被引用文献数

7

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Continuous observations of cloud droplet size distributions (DSDs) in low-level stratiform clouds have been conducted at a height of 458 m from Tokyo Skytree (a 634-m high broadcasting tower in Tokyo) using a cloud droplet spectrometer. In this report, the characteristics of cloud parameters related to the cloud DSD from June to December 2016 are presented. The mean cloud droplet number concentration (Nc), average diameters, and effective diameters of cloud droplets in non-drizzling clouds were 213 cm-3, 7.3 μm, and 9.5 μm, respectively, which are close to the reported values for continental stratiform clouds. The relationship between the liquid water content (LWC; g m-3), Nc (cm-3) and radar reflectivity (Z; mm6 m-3) was estimated as LWC = 0.17Nc0.50 Z0.45, with a coefficient of determination ( R 2) of 0.93. The observed cloud DSDs were well fitted by a lognormal distribution and the average median diameter of the fitted DSD was 6.6 μm.

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

Stéphane BÉLAIR Sylvie LEROYER Naoko SEINO Lubos SPACEK Vanh SOUVANLASSY Danahé PAQUIN-RICARD

出版者

Meteorological Society of Japan

雑誌

Journal of the Meteorological Society of Japan. Ser. II (ISSN:00261165)

巻号頁・発行日

pp.2018-011, (Released:2017-12-21)

被引用文献数

20

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Heavy precipitation fell over Tokyo in the afternoon of 26 August 2011, leading to flooding and major disruptions for the population, businesses, and authorities. Over 150 mm of precipitation was observed over the city center on that day, with hourly accumulations reaching values as high as 90 mm in late afternoon. Numerical forecasts of this case were performed with a 250-m grid spacing version of the Global Environmental Multi-scale (GEM) model in the context of the Tokyo Metropolitan Area Convection Study (TOMACS). Although initialized only from a global 25-km upper-air analysis, results indicate that GEM is able to produce the intense precipitation over Tokyo at about the right location and time. A sensitivity test in which the urban surface scheme is switched off and replaced with tall grass suggests that the urban environment might have had considerable impact on precipitation intensity, but not on its occurrence or its timing. Based on diagnostics from the GEM integrations, the increased intensity of precipitation seems more related to an enhancement of lateral inflow of low-level moist static energy from Tokyo Bay than to augmented surface fluxes of heat and humidity from the city itself. The existence of low-level bands with locally high values of equivalent potential temperature indicates that the additional moist energy is distributed unevenly through the Tokyo area, an aspect of the simulation which is speculated to have directly contributed to the increase in precipitation intensity over the city.

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

菊地 勝弘 吉沢 深雪 遊馬 芳雄 上田 博

出版者

社団法人日本気象学会

雑誌

Journal of the Meteorological Society of Japan. Ser. II (ISSN:00261165)

巻号頁・発行日

vol.73, no.1, pp.47-58, 1995-02-25

被引用文献数

2

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1991年1月1日から3月31日まで札幌市の北西部に位置する北海道大学農学部付属農場で降雪、積雪、融雪過程を通しての酸性度の特徴を調査した。降雪は総観場から季節風及び季節風末期と低気圧に分類した。低気圧による降雪は更に、石狩湾上で発生する小低気圧、北海道の北側、北海道の南側を通過するものに分けられた。これによって降雪をもたらす風系の影響を見ることができる。降雪粒子は、比較的雲粒の付かない雪結晶、雲粒付雪結晶、霰、雨または霙に分類しポリ袋でサンプリングし測定した。積雪の酸性度は、降雪のサンプリング地点付近にトレンチを掘って、全積雪層と各降雪に伴う積雪層をサンプリングすることにより測定した。融雪の酸性度は同じ地点に底にノズルをつけた直径52cmの大型のポリ容器に自然の状態で降雪が積もったものの融雪水をポリ袋に貯めて測定した。これまで1シーズンに1〜2回の積雪のサンプリングで酸性度を議論するケースが多かったが、今回のように、各降雪毎、積雪全層及び各積雪層、さらに融雪を通して細かな変動の特徴を明らかにしたのは、これが最初のケースである。測定の結果、季節風に伴う降雪は比較的低いpHを示した。また、全積雪層の酸性度は融雪期の始まる前まではそれ程変化をしなかった。各積雪層の酸性度は積雪各層の変態に依存していた。融雪水の酸性度は融雪初期に大きく変動することが明らかになった。

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

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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.