著者
Shinya KOBAYASHI Yukinari OTA Yayoi HARADA Ayataka EBITA Masami MORIYA Hirokatsu ONODA Kazutoshi ONOGI Hirotaka KAMAHORI Chiaki KOBAYASHI Hirokazu ENDO Kengo MIYAOKA Kiyotoshi TAKAHASHI
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.93, no.1, pp.5-48, 2015 (Released:2015-03-18)
参考文献数
128
被引用文献数
213 or 0

The Japan Meteorological Agency (JMA) conducted the second Japanese global atmospheric reanalysis, called the Japanese 55-year Reanalysis or JRA-55. It covers the period from 1958, when regular radiosonde observations began on a global basis. JRA-55 is the first comprehensive reanalysis that has covered the last half-century since the European Centre for Medium-Range Weather Forecasts 45-year Reanalysis (ERA-40), and is the first one to apply four-dimensional variational analysis to this period. The main objectives of JRA-55 were to address issues found in previous reanalyses and to produce a comprehensive atmospheric dataset suitable for studying multidecadal variability and climate change. This paper describes the observations, data assimilation system, and forecast model used to produce JRA-55 as well as the basic characteristics of the JRA-55 product. JRA-55 has been produced with the TL319 version of JMA’s operational data assimilation system as of December 2009, which was extensively improved since the Japanese 25-year Reanalysis (JRA-25). It also uses several newly available and improved past observations. The resulting reanalysis products are considerably better than the JRA-25 product. Two major problems of JRA-25 were a cold bias in the lower stratosphere, which has been diminished, and a dry bias in the Amazon basin, which has been mitigated. The temporal consistency of temperature analysis has also been considerably improved compared to previous reanalysis products. Our initial quality evaluation revealed problems such as a warm bias in the upper troposphere, large upward imbalance in the global mean net energy fluxes at the top of the atmosphere and at the surface, excessive precipitation over the tropics, and unrealistic trends in analyzed tropical cyclone strength. This paper also assesses the impacts of model biases and changes in the observing system, and mentions efforts to further investigate the representation of low-frequency variability and trends in JRA-55.
著者
SAITO Kazuo KUNII Masaru ARAKI Kentaro
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
(Released:2018-02-11)

Local heavy rainfall of about 100 mm h-1 occurred in Tokyo and Kanagawa Prefecture on 26 August 2011. This rain was brought by a mesoscale convective system (MCS) that developed near a stationary front that slowly moved southward. In an analysis using geostationary multi-purpose satellite rapid scan images and dense automated weather station networks, development of the MCS occurred after the merging of sea breezes from the east (Kashima-nada) and the south (Tokyo Bay). Numerical experiments by the Japan Meteorological Agency (JMA) nonhydrostatic model (NHM) with horizontal resolutions of 10 km and 2 km using mesoscale 4D-VAR analysis of JMA for initial conditions tended to predict the position of intense rainfall areas west of observed positions. In the mesoscale ensemble forecast using perturbations from JMA’s one-week global ensemble prediction system (EPS) forecast, some ensemble members showed enhanced precipitation around Tokyo, but false precipitation areas appeared north of the Kanto and Hokuriku Districts. As an attempt to improve the model forecast, we modified the model, reducing the lower limit of subgrid deviation of water vapor condensation to diagnose the cloudiness for radiation. In the modified model simulation, surface temperatures around Tokyo increased by about 1°C and the position of the intense precipitation was improved, but the false precipitation areas in the Hokuriku District were also enhanced in the ensemble member which brought a better forecast than the control run. We also conducted ensemble prediction using a singular vector method based on NHM. One of the ensemble members unstabilized the lower atmosphere on the windward side of the Kanto District and suppressed the false precipitation in the Hokuriku District, and observed characteristics of the local heavy rainfall were well reproduced by NHM with a horizontal resolution of 2 km. A conceptual model of the initiation of deep convection by the formation of a low-level convergence zone succeeding merging of the two sea breezes from the east and south is proposed based on observations, previous studies, and numerical simulation results. In this event, the northerly ambient wind played an important role on the occurrence of the local heavy rainfall around Tokyo by suppressing the northward intrusion of the sea breeze from the south.
著者
Axel GABRIEL Dieter PETERS
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.86, no.5, pp.613-631, 2008 (Released:2008-11-13)
参考文献数
16
被引用文献数
19 or 26

The long-term behavior of Rossby wave breaking (RWB) events is investigated by a diagnosis separating in different asymmetric types of RWB, i.e., cyclonically sheared waves breaking predominantly pole-ward (P1) or equatorward (LC2) and anticyclonically sheared waves breaking predominantly poleward (P2) or equatorward (LC1). Generally, RWB can be identified by meridional overturning of potential vorticity (PV) on specific isentropes, but a separation in poleward or equatorward asymmetry is too difficult based on PV maps alone. For this paper, we use that northward or southward direction of the meridional wave flux component for quasi-stationary Rossby waves indicates cyclonically or anticyclonically sheared RWB. We demonstrate that the magnitude of the meridional wave fluxes gives a reliable measure of the asymmetric types of RWB when combining with PV diagnostics as well as with the geometry of large-scale diffluent/ confluent flow. Based on 45 winter periods of ECMWF Reanalysis (ERA-40), we found two pronounced regions for P1- and LC2-type events, over the northern North Pacific and the northern North Atlantic, and two extended belts of P2- and LC1-type RWB events, over the North Pacific/North America region and the North Atlantic/European-West Asian region. The results reveal that the long-term mean occurrence of poleward RWB is generally as large as that of equatorward RWB with local differences. Since poleward or equatorward RWB events influence different regions efficiently, e.g., by associated cut-off cyclones or anticyclones, the proposed diagnosis gives an important tool for interpreting long-term general circulation patterns and large-scale weather regimes.
著者
Youichi KAMAE Wei MEI Shang-Ping XIE
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.411-431, 2017 (Released:2017-11-14)
参考文献数
76

Eddy transport of atmospheric water vapor from the tropics is important for rainfall and related natural disasters in the middle latitudes. Atmospheric rivers (ARs), intense moisture plumes that are typically associated with extratropical cyclones, often produce heavy precipitation upon encountering topography on the west coasts of mid-latitude North America and Europe. ARs also occur over the northwestern Pacific and sometimes cause floods and landslides over East Asia, but the climatological relationship between ARs and heavy rainfall in this region remains unclear. Here we evaluate the contribution of ARs to the hydrological cycle over East Asia using high-resolution daily rainfall observations and an atmospheric reanalysis during 1958-2007. Despite their low occurrence, ARs account for 14-44 % of the total rainfall and 20-90 % of extreme heavy-rainfall events during spring, summer, and autumn. AR-related extreme rainfall is especially pronounced over western-to-southeastern slopes of terrains over the Korean Peninsula and Japan, owing to strong orographic effects and a stable direction of low-level moisture flows. A strong relationship between warm-season AR heavy rainfall and preceding-winter El Niño is identified since the 1970s, suggesting the potential of predicting heavy-rainfall risk over Korea and Japan at seasonal leads.
著者
Toshinori AOYAGI Nobuyuki KAYABA Naoko SEINO
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.90B, pp.11-31, 2012 (Released:2012-06-09)
参考文献数
32
被引用文献数
10 or 4

We investigated a warming trend in the Kanto-Koshin area during a 30-year period (1976-2006). The warming trends at AMeDAS stations were estimated to average a little less than 1.3°C/30 years in both summer and winter. These warming trends were considered to include the trends of large-scale and local-scale warming effects. Because a regional climate model with 20-km resolution without any urban parameterization could not well express the observed warming trends and their daily variations, we investigated whether a mesoscale atmospheric model with an urban canopy scheme could express them.To make the simulations realistic, we used 3 sets of real data: National Land Numerical Information datasets for the estimation of the land use area fractions, anthropogenic heat datasets varying in space and time, and GIS datasets of building shapes in the Tokyo Metropolis for the setting of building aspect ratios. The time integrations over 2 months were executed for both summer and winter. A certain level of correlation was found between the simulated temperature rises and the observed warming trends at the AMeDAS stations. The daily variation of the temperature rises in urban grids was higher at night than in the daytime, and its range was larger in winter than in summer. Such tendencies were consistent with the observational results.From factor analyses, we figured out the classic and some unexpected features of urban warming, as follows: (1) Land use distribution change (mainly caused by the decrease of vegetation cover) had the largest daytime warming effect, and the effect was larger in summer than in winter; (2) anthropogenic heat had a warming effect with 2 small peaks owing to the daily variation of the released heat and the timing of stable atmospheric layer formation; and (3) increased building height was the largest factor contributing to the temperature rises, with a single peak in early morning.
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

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

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

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
UCHIYAMA Akihiro CHEN Bin YAMAZAKI Akihiro SHI Guangyu KUDO Rei NISHITA-HARA Chiharu HAYASHI Masahiko HABIB Ammara MATSUNAGA Tsuneo
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
(Released:2018-02-05)

The aerosol optical characteristics in the East Asian cities of Fukuoka and Beijing were measured from 2010 to 2014. These long-term season-crossing data were compared to understand the differences between the aerosol characteristics at a source and a downstream region. Previously, few long-term, season-crossing observations have been reported. Using a method developed by one of the present authors, the measurement data were analyzed so that the retrieved optical properties can be more accurate than those obtained in previous studies. Using these data, the aerosol characteristics and their frequency distributions were reliably obtained. In Fukuoka, the annual means of the extinction, scattering, and absorption coefficients Cext (525 nm), Csca (525 nm), and Cabs (520 nm) were 74.6, 66.1, and 8.1 M m−1, respectively, whereas those in Beijing were 412.1, 367.2, and 42.4 M m−1, respectively. The coefficients in Fukuoka were approximately one-fifth of those in Beijing. The single-scattering albedos ω 0 (525 nm) in Fukuoka and Beijing were 0.877 and 0.868, respectively. The asymmetry factors G (525 nm) in the two cities were 0.599 and 0.656, respectively. The extinction Ångström exponents αext in the two cities were 1.555 and 0.855, respectively. The absorption Ångström exponents αabs in the two cities were 1.106 and 0.977, respectively. The fine and coarse mode volume fractions in Fukuoka were approximately 80 % and 20 %, and those in Beijing were both approximately 50 % except in the summer. The Cext , Csca , and Cabs showed seasonal variation in both cities. Some other properties showed also seasonal variation. In particular, the seasonal variation in αabs was clear in both cities; it tended to be small in the summer and large in the winter. The frequency distributions of various parameters were also investigated. The frequency of Cext >500 M m−1 in Fukuoka was very low, and large Cext values were recorded more frequently in the spring than in other seasons. In Beijing, Cext > 1000 M m−1 values were recorded more frequently, and the frequency of 10 M m−1 ≤ Cabs ≤ 60 M m−1 was high in the spring and summer. Furthermore, αabs < 1.0 values were recorded frequently, which cannot be explained by the simple external mixture of absorbing aerosols. To demonstrate the usefulness of the data obtained in this study, the relationships among αabs , αext , the volume size distribution, the imaginary part of the refractive index and ω 0 were investigated, and two characteristic cases in Beijing (winter) and Fukuoka (spring) were preliminarily analyzed.
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
26 or 0

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
TERASAKI Koji MIYOSHI Takemasa
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
(Released:2017-09-15)

An observation operator to assimilate satellite radiances with the Non-hydrostatic Icosahedral Atmospheric Model (NICAM)-based Local Ensemble Transform Kalman Filter (LETKF) is newly developed using the radiative transfer model RTTOV (Radiative Transfer for the TOVS (TIROS Operational Vertical Sounder)) version 11.1. Here we assimilate the Advanced Microwave Sounding Unit-A (AMSU-A) brightness temperature observations which are known to bring a large improvement to global numerical weather prediction. We apply the online estimation of bias correction for both airmass and scan biases, or the biases originating from the atmospheric state and scan position. Comparing the two experiments with and without the AMSU-A radiances, we find that the adaptive bias correction methods work appropriately, and that the analysis is significantly improved by assimilating the AMSU-A radiances. This is an important step toward assimilating different types of satellite radiances with NICAM-LETKF.
著者
Nurfiena Sagita PUTRI Tadahiro HAYASAKA Kim Dionne WHITEHALL
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.391-409, 2017 (Released:2017-11-14)
参考文献数
30

A mesoscale convective system (MCS) is organized thunderstorms with connected anvils, which has a significant impact on the global climate. By focusing on MCSs over the Maritime Continent of Indonesia, this study aims to gain a better understanding on the properties of the MCSs over the study area. The “Grab ‘em Tag ‘em Graph ‘em” (GTG) tracking algorithm is applied to hourly Multi-functional Transport Satellite-1R data for two years to observe the distribution of MCSs and the evolution of MCSs along their lifetime. The results of MCS identification by using GTG are combined with CloudSat data products to study the vertical structure of the MCSs at various MCS life stages: developing, mature, and dissipating. The distribution of MCSs over Indonesia has a seasonal variation and distinct diurnal cycle. The life stages of the observed MCSs are characterized by distinct cloud microphysics at each stage. In the developing stage, the upper level of the MCS raining region shows the presence of precipitating ice particles. As the MCS progresses to the mature stage, the proportion of the raining area becomes small and the intensity of rain is reduced, accompanied by increasing occurrence of small-sized ice particles at the upper level. In the dissipating stage, large hydrometeors no longer exist at the upper part of the raining region. Within the MCS anvils, the dissipating stage shows a more uniform distribution of ice-particle effective radius compared to that shown by the developing and mature stages. MCS characteristics over the land and ocean differ on the basis of the minimum brightness temperature, the equivalent radius, the maximum rain rate, and the rain fraction that varies along the MCS evolution.
著者
ROH Woosub SATOH Masaki
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
(Released:2017-09-29)

As an alternative approach to the previous multisensor satellite evaluation method of cloud system resolving models, a method is presented using combined infrared and microwave channels for precipitation clouds in cloud system resolving models over the ocean. This method determines characteristics of cloud-top temperatures and ice scatterings for clouds using infrared 11-μm and microwave high frequencies (89.0 GHz) brightness temperatures (TBs). The threshold of the TB at low frequencies (18.7 GHz) is also used to identify precipitation regions. This method extends the previous approach via the wider swath of the passive microwave sensor and sensitivities to ice clouds compared to the previous Tropical Rainfall Measuring Mission (TRMM)-based analysis method using the narrower coverage of the Precipitation Radar. The numerical results of the non-hydrostatic icosahedral atmospheric model (NICAM) with two cloud microphysics schemes are evaluated over the tropical open ocean using this method. The intensities of the scatterings in the two simulations at 89.0 GHz are different due to the parameterizations of the snow and graupel size distributions. A bimodal size distribution of the snow improved the underestimation of the TBs at 89.0 GHz. These results have a similar structure to the joint histograms of cloud-top temperatures and precipitation-top heights in the previous method: the overestimated intensity of scattering and the frequencies of high precipitation-top heights above 12 km in the control experiment. We find that the change in the snow size distribution in the cloud microphysics scheme can lead to better agreements of simulated TBs at 89.0 GHz with observations. We further investigate impacts of non-spherical assumptions for snow using a satellite simulator. The effect of a non-spherical shape of snow in the radiative transfer model causes a smaller change of TBs at 89.0 GHz compared to the difference between the TBs of the two simulations without non-spherical assumptions.
著者
Eigo TOCHIMOTO Tetsuya KAWANO
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.4, pp.217-237, 2017 (Released:2017-07-04)
参考文献数
39

In Part I of this study, the development processes of Baiu frontal depressions (BFDs) have been examined through case-study numerical experiments. The numerical simulations revealed that latent heating is dominant for the development of BFDs in the western part of the Baiu frontal zone (W-BFDs), west of approximately 140°E, while both latent heating and baroclinicity are important for the development of BFDs in the eastern part of the zone (E-BFDs), east of approximately 140°E. In this study, idealized numerical simulations with zonally homogeneous basic fields are conducted to obtain a more generalized perspective of the development processes of BFDs. The basic fields for the idealized simulations are made from the composites of the environments under which 28 W-BFDs and 43 E-BFDs developed. The idealized simulations successfully reproduce a realistic W-BFD and E-BFD. The W-BFD has a slightly westward-tilted vertical structure, modulated by latent heating at low levels of the atmosphere. In contrast, the E-BFD has a westward-tilted structure through the troposphere, similar to the well-known baroclinic wave structure. Results of available potential energy diagnosis for the effects of latent heating and baroclinicity on the BFD development are consistent with those in Part I. The W-BFD has a mechanism mainly driven by latent heating yielding strong convection, while the E-BFD develops through baroclinic instability in moist atmosphere.
著者
Yasuko OKADA Tetsuya TAKEMI Hirohiko ISHIKAWA Shoji KUSUNOKI Ryo MIZUTA
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.4, pp.239-260, 2017 (Released:2017-07-04)
参考文献数
45

This study investigates future changes in atmospheric circulation during the Baiu in Japan using 20-km-mesh atmospheric general circulation model (AGCM) simulations for the present-day (1979-2003) and the future (2075-2099) climates under the Representative Concentration Pathways 8.5 scenario. The simulated future climates include the outputs obtained with one control sea surface temperature (SST) and three different SST patterns. The Baiu frontal zone, defined as the meridional gradient of equivalent potential temperature, gradually moves northward during June–July–August in the present-day climate. In the future climate simulations using the control SST, the Baiu frontal zone is projected to stay to the south of Japan in June. Thus, precipitation is projected to increase over this region, while decreasing in the western part of Japan. Future changes in precipitation and atmospheric circulations in June are consistent across all four SST patterns. However, precipitation and atmospheric circulation in July and August in the future climate simulation depends on the SST patterns as follows: in non-El Niño-like SST pattern, the Baiu terminates in late July, similar to that of the present-day climate; a result with an El Niño-like SST pattern shows that sufficient amount moisture is transported to the Japanese islands and leads in a delay of the Baiu termination until August; and in the SST pattern with strong warming in the western North Pacific (WNP), a sufficient amount of moisture is transported to the south of Japan from June until August. The difference in the SST pattern leads to a variation in sea-level pressure in the WNP and affects a variation of the Northern Pacific subtropical high around the Japanese islands in July and August.
著者
Seiji KATO Norman G. LOEB David A. RUTAN Fred G. ROSE
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.93, no.6, pp.597-612, 2015 (Released:2016-01-13)
参考文献数
107

NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project integrates CERES, Moderate Resolution Imaging Spectroradiometer (MODIS), and geostationary satellite observations to provide top-of-atmosphere (TOA) irradiances derived from broadband radiance observations by CERES instruments. It also uses snow cover and sea ice extent retrieved from microwave instruments as well as thermodynamic variables from reanalysis. In addition, these variables are used for surface and atmospheric irradiance computations. The CERES project provides TOA, surface, and atmospheric irradiances in various spatial and temporal resolutions. These data sets are for climate research and evaluation of climate models. Long-term observations are required to understand how the Earth system responds to radiative forcing. A simple model is used to estimate the time to detect trends in TOA reflected shortwave and emitted longwave irradiances.
著者
土屋 清
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.47, no.6, pp.457-465, 1969 (Released:2008-05-27)
参考文献数
14

約4時間の時間間隔で撮影した気象衛星エッサ7号と8号の写真に現われた済州島風下のKarman鋤うず列状の雲を解析した結果,次のことがわかった.雲のうず列から得られた無次元パラメーターは,これまで2次元流の流体実験から得られたKarman鋤うず列発生の限界値を満足しており,Karmanうず列の理論で説明できる.島の抵抗とうず列のwakeによる抵抗を考慮して,うず列の間隔と個々のうずの間隔の比だけから,うず列の移動速度を求める計算式を導いた.結果実況とかなりよく合い,比が0.332のとき.一般流の約76%であった.済州島の風下に,このような雲のうず列のできるのは,晩秋から初春にかけて,比較的強い(10ノット以上)北風が持続し,1000m付近(島の中央部の山の高さの半分)に顕著な逆転のある時である.
著者
Hiroshige TSUGUTI Teruyuki KATO
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.92, no.2, pp.163-183, 2014 (Released:2014-05-16)
参考文献数
32
被引用文献数
4 or 0

On 20 October 2010, a heavy rainfall event occurred on Amami-Oshima Island, Japan, delivering a record 622 mm of rainfall in one day. To clarify the factors underlying this event, the supply mechanism and formation process of low-level humid air and the formation and maintenance mechanisms of the precipitation systems causing the heavy rainfall were examined using observation data, objective analysis data, and numerical simulation results. These investigations showed that low-level humid air, carried to Amami-Oshima Island during the rainfall event by strong east-northeasterly winds, originated more than 500 km to the east-northeast as low-level dry air on the northern side of a stationary front. This dry air was transformed into humid air on the way to the island by receiving large latent heat flux from the sea surface (air-parcel transformation). Warm sea surface temperatures around Amami-Oshima Island, about 2°C higher than the annual mean, contributed to this air-parcel transformation. At Amami-Oshima Island, the collision of the humid flows with a cold pool formed under earlier precipitation systems contributed significantly to the formation and maintenance of the precipitation systems, supplemented by topographic effects of the island.