著者

PUTRI Nurfiena Sagita IWABUCHI Hironobu HAYASAKA Tadahiro

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.2018-020, (Released:2018-01-23)

被引用文献数

12

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Two case studies of Mesoscale Convective System (MCS) in Indonesian region were conducted by applying an improved GTG tracking algorithm and ICAS algorithm to Himawari-8 AHI infrared data. The first case over Java Island showed a land-originating MCS in the boreal winter, which coincided with a wet phase of Madden-Julian Oscillation (MJO) over the Maritime Continent. The second case showed the evolution of MCS under the influence of a strong vertical wind shear during the boreal summer. The cloud top height (CTH) of deep convective part in the first case was larger than that in the second case, while the temporal evolution of CTH was similar between two cases. For the anvil part, the median CTH of the second case was relatively stable at around 13 km, while that of the first case showed a considerable temporal variation ranging from 14 to 16 km. The cloud-particle effective radius (CER) of anvil increased after the period of maximum deep convective CTH in both cases, although the CER was slightly larger in the second case than in the first case. These differences in cloud properties between two cases were attributable to the background wind profiles.

著者

Keisuke MORI Tomonori SATO

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.92, no.4, pp.327-346, 2014 (Released:2014-09-26)

参考文献数

39

被引用文献数

3 9

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This study investigated the spatiotemporal characteristics of high-temperature events in Hokkaido, Japan, using observational data of 26 years. Statistical analyses revealed that the annual mean frequency of these events was lower (higher) at stations on the western (eastern) side of Hokkaido. The frequency of these events showed clear seasonal variation with two distinct peaks occurring in January and May. In addition, the local time of the high-temperature onset was strongly dependent on the season; the onset occurred more frequently from 1600 to 0400 Japan Standard Time (JST) in January and from 0700 to 1300 JST in May. The seasonal dependence mechanism of the high-temperature onset was investigated in eastern Hokkaido, where the frequencies of both January and May high-temperature events were the highest. In January, an extratropical cyclone passage caused intensified warm advection and increased precipitable water vapor, leading to weakened radiative cooling during the night. In May, the high-temperature events were triggered by two different mechanisms related to solar insolation. The first mechanism is explained by dynamic foehn, which forms the subsidence of the high potential temperature layer on the lee of mountains. However, the nocturnal inversion layer prevented vertical mixing of the foehn-induced warm air aloft and cold air near the ground. The surface air temperature dramatically increased after sunrise when the nocturnal inversion layer disappeared. The second mechanism is explained by the combination of airflow diabatically heated by surface sensible heat flux and dynamic foehn. Therefore, solar insolation is the key factor that controlled the diurnal variation in high-temperature events in May.

著者

ODA Mayuko 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.2019-006, (Released:2018-10-29)

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A simple conceptual model of the resonant interaction in a typhoon-like vortex between vortex Rossby waves (VRWs) and gravity waves (GWs), which are caused by the VRWs, is presented. It is well known that the VRWs in the central region of the vortex can grow by the interaction with the GWs in the outer region, but a simple conceptual model for their interaction has not yet been proposed. The proposed conceptual model is based on the buoyancy-vorticity formulation (BV-thinking), and is different from that for the barotropic and baroclinic instabilities based on PV interactions (PV- thinking). We consider disturbances of the first baroclinic mode on a basic barotropic vortex. The disturbance vertical vorticity ζ of the VRW in the central region has a large amplitude on the upper and lower levels. While, the disturbance buoyancy b and radial vorticity η of the GW have a large amplitude on the middle level. The central VRW propagates (relative to the fluid) anticy-clonically, but moves cyclonically because of the strong cyclonic advection by the vortex. The outer cyclonically propagating GW is weakly advected also cyclonically by the vortex. As a result, the counter-propagating VRW and GW (satisfying Rayleigh's condition) may be phase-locked with each other (satisfying Fjørtoft's condition). By the counter-propagation and phase-lock, the circulation around ζ of the VRW enhances b of the GW, which in turn enhances η. At the same time, the circulation around η of the GW enhances ζ of the VRW. As a result, the VRW and GW grow simultaneously. We analytically show the possibility of the resonant interaction, and numerically obtain the growing solution in the system linearized about the basic vortex.

著者

KAWAI Yoshimi NISHIKAWA Hatsumi OKA Eitarou

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.2019-024, (Released:2018-12-13)

被引用文献数

8

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Previous modeling studies have indicated that the Oyashio front in the subarctic Pacific Ocean significantly affects the atmosphere on meso- to basin-scales, but there were no in situ observations that captured oceanic imprints on the atmosphere in this region as far as the authors know. We present in situ evidence of atmospheric responses to the Oyashio front by using a total of 103 radiosondes launched around the Oyashio front in April 2013 with continuous surface meteorology and ceilometer observations. Composite profiles showed that the low-level atmosphere below 1000 m was statically stable on the cold side of the Oyashio front, but unstable and mixed on the warm side. In the atmosphere on the warm side, relative humidity dropped sharply at an altitude of around 1000 m, an indication that the mean cloud top was at this altitude. While the frequency of cloud base height peaked at 50–100 m in the cold areas, cloud bases were distributed at higher altitudes in the warm areas. These differences in the atmospheric boundary layer and cloud base heights across the front were clearer under conditions of southerly winds compared with those of northerly winds. Above a local sea surface temperature minimum with a width of approximately 400 km, where the ocean mixed layer depth is known to reach a local maximum, a large horizontal air temperature gradient was observed below an altitude of 1000 m. This horizontal gradient corresponded to a sea level pressure (SLP) anomaly of 1.2 hPa, comparable to observations of SLP anomalies in the Kuroshio Extension region. Furthermore, we found that narrow warm ocean streamers moistened the overlying atmosphere, affecting downward longwave radiation. Over the wide streamer located between 146.4°E and 147.0°E on 5 April, near-surface atmospheric properties were largely different between over the western half and the eastern half.

著者

FUKUI Shin IWASAKI Toshiki SAITO Kazuo SEKO Hiromu KUNII Masaru

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.2018-056, (Released:2018-09-14)

被引用文献数

10

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The feasibility of regional reanalysis assimilating only conventional observations was investigated as an alternative to dynamical downscaling to estimate the past three-dimensional high-resolution atmospheric fields with long-term homogeneity over about 60 years. The two types of widely applied dynamical downscaling approaches have problems. One with a serial long-term time-integration often fails to reproduce synoptic-scale systems and precipitation patterns. The other with frequent reinitializations underestimates precipitation due to insufficient spin-up. To address these problems maintaining long-term homogeneity, we proposed the regional reanalysis assimilating only the conventional observations. We examined it paying special attention to summer precipitation, through one-month experiment before conducting a long-term reanalysis. The system is designed to assimilate surface pressure and radiosonde upper-air observations, using the Japan Meteorological Agency's nonhydrostatic model (NHM) and the local ensemble transform Kalman filter (LETKF). It covers Japan and its surrounding area with a 5-km grid spacing and East Asia with a 25-km grid spacing, applying one-way double nesting in the Japanese 55-year reanalysis (JRA-55). The regional reanalysis overcomes the problems with both types of dynamical downscaling approaches. It reproduces actual synoptic-scale systems and precipitation patterns better. It also realistically describes spatial variability and precipitation intensity. The 5-km grid spacing regional reanalysis reproduces frequency of heavy precipitation and describes anomalous local fields affected by topography such as circulations and solar radiation better than the coarser reanalyses. We optimized the NHM-LETKF for long-term reanalysis by sensitivity experiments. The lateral boundary perturbations derived from an empirical orthogonal function analysis of JRA-55 brings stable analysis, saving computational costs. The ensemble size of at least 30 is needed because further reduction significantly degrades the analysis. The deterministic run from non-perturbed analysis is adopted as first guess in LETKF, instead of the ensemble mean of perturbed runs, enabling reasonable simulation of spatial variability in the atmosphere and precipitation intensity.

著者

YAMASHITA Yousuke NAOE Hiroaki INOUE Makoto TAKAHASHI Masaaki

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.2018-057, (Released:2018-10-05)

被引用文献数

9

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We investigate the effects of the stratospheric equatorial quasi-biennial oscillation (QBO) on the extratropical circulation in the Southern Hemisphere (SH) from SH winter to early summer. The Japanese 55-year Reanalysis (JRA-55) dataset is used for 1960–2010. The factors important for the variation of zonal wind of the SH polar vortex are identified via multiple linear regression, using Equivalent effective stratospheric chlorine (EESC), middle- and lower-stratospheric QBO, solar cycle, El Niño-Southern Oscillation (ENSO), and volcanic aerosol terms as explanatory variables. The results show that the contributions to the SH polar vortex variability of ENSO are important in SH early winter (June) to mid-winter (July), while that of middle-stratospheric QBO is important from spring (September to November) to early summer (December). Analyses of the regression coefficients associated with both middle- and lower-stratospheric QBO suggest an influence on the SH polar vortex from SH winter through early summer in the seasonal evolution. One possible pathway is that the middle-stratospheric QBO results in the SH low-latitudes stratospheric response through the QBO-induced mean meridional circulation, leading to a high-latitude response. This favours delayed downward evolution of the polar-night jet (PNJ) at high latitudes (around 60°S) from late winter (August) to spring (September–November) during the westerly phase of the QBO, consequently tending to strengthen westerly winds from stratosphere to troposphere in SH spring. The other possible pathway involves the response to lower-stratospheric QBO that induces the SH late winter increase in upward propagation of planetary waves from the extratropical troposphere to stratosphere, which is consistent with weakening of the PNJ.

著者

TAKAHASHI Hiroshi G.

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.2018-046, (Released:2018-05-25)

被引用文献数

2

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This study investigated the absolute values of column-integrated water vapor (precipitable water; PW) in the climate models used in the Coupled Model Intercomparison Project Phase 5 (CMIP5), in terms of the relationships between PW and precipitation characteristics. We identified that global mean PW values are systematically much lower in CMIP5 models than in observations. This dry bias is most profound over the tropical ocean. The dry bias is partly due to biases in sea surface temperatures in the CMIP5-coupled climate models. However, the dry bias is also present in Atmospheric Model Intercomparison Project (AMIP) experiments, which implies the existence of other factors. The relationship between PW and rainfall characteristics shows that rainfall occurs when water vapor levels are lower than in observations, particularly in models with a relatively strong dry bias. This suggests that the reproducibility of rainfall characteristics may be associated with the dry bias.

著者

川畑 幸夫 藤戸 誠

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯

巻号頁・発行日

vol.29, no.2, pp.37-44, 1951

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本報文は,單に實用的見地から,台風接近の際に起る海面の上昇量と,最高水位の時刻を手輕に豫報せんとするもので,第5圖に示す如く,上昇量は大體其の季節の標準氣壓と台風の経路中の最低氣壓の差に比例し,同時に又台風が最も接近した時刻の距岸距離に逆比例する.それらを推定することにより豫報は量的に可成り正確に出來る.最高水位の時刻は本文中の表に示す如く,其の港で最低氣壓が起るときと殆んど同時と考えてよい.尤も距岸距離が著しく近く,&gamma;&rarr;0の場合には,單に圖からは上昇量が無限大となることになるが,丁度うまい場合の資料がまだないのでよくわからない.最高水位の時刻は外洋に面した港では上述の如くなるが,大阪灣,東京灣等の如く灣口の狭い灣の奥では最低氣壓の起時より10數時間早いこともあり,おそいこともある.<br>災害の面から見ると,暴風に伴う風浪が亦極めて大切なものであるが,このような短周期の波を自記せしめる測器は現在まだないので,やむを得ず檢潮儀り記録を資料とした.このため上の結果には風浪が一切除外されている.換言すれば風津浪の高さの最低限を與えてあることになり,實際には,いつでも第5圖の高さ以上の波が押寄せるわけである.<br>台風又は低氣壓に伴う海面の上昇量は,台風が洋上遙が遠方にある場合,或はそれらの中心示度が弱い場合には主として靜水力學的吸上げの影響として量的に殆んど完全に説明せられ,風の影響は全く認められない.ビユ〓フォ〓ト階級4以下の風が何日間吹き續いても影響は殆んどない.台風が接近し風力がビユーフォート階級5以上になると風による吹寄せは急速に増大し,遂に吸上げの効果を遙かに上廻るようになる.最高水位の場合の風向は第4圖に示した.<br>然しながら長週期の海面の昇降に關しては,之等の台風の場合と違ひ,風の影響は決して無視出來ないものゝようであり,これについては別途に報告したい.

著者

TAKAHASHI Hiroshi G. DADO Julie Mae B.

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.2018-031, (Released:2018-03-09)

被引用文献数

5

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We offer a new perspective on a relationship between sea surface temperature (SST) over the windward region of the Philippines and rainfall in the western Philippines during the Asian summer monsoon season, which has been known as the negative correlation, using observational daily SST, rainfall, and atmospheric circulation datasets. This study focuses on the local SST effect rather than the remote effect. A warmer local SST results in greater rainfall over the western Philippines under similar monsoon westerlies conditions, particularly during moderate and relatively stronger monsoon regimes. This result is obtained after selecting only the moderate or relatively stronger monsoon days, because the positive effect of SST on rainfall is masked by the apparent negative correlation between SST and rainfall. The warmer SSTs being associated with less rainfall correspond to weaker cooling by weaker monsoon westerlies and the cooler SSTs being associated with more rainfall correspond to stronger cooling by stronger monsoon westerlies. The cooler SSTs are the result of stronger monsoon cooling and are not the cause of the greater rainfall, which is the apparent statistical relationship. This also implies that the monsoon westerly is the primary driver of the variation in rainfall in this region. We conclude that the local SST makes a positive contribution toward rainfall, although it does not primarily control rainfall. This conclusion can be applicable to coastal regions where, climatologically, rainfall is controlled by winds from the ocean.

著者

OKAMOTO Kozo ISHIBASHI Toshiyuki ISHII Shoken BARON Philippe GAMO Kyoka TANAKA Taichu Y. YAMASHITA Koji KUBOTA Takuji

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.2018-024, (Released:2018-02-05)

被引用文献数

7

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This study evaluated the impact of a future space-borne Doppler wind lidar (DWL) on a super-low-altitude orbit using an observing system simulation experiment (OSSE) based on a sensitivity observing system experiment (SOSE) approach. Realistic atmospheric data, including wind and temperature, was provided as “pseudo-truth” (PT) to simulate DWL observations. Hourly aerosols and clouds that are consistent with PT winds were also created for the simulation. A full-scale lidar simulator, which is described in detail in the companion paper, simulated realistic line-of-sight wind measurements and observation quality information, such as signal-to-noise-ratio (SNR) and measurement error. Quality control (QC) procedures in the data assimilation system were developed to select high-quality DWL observations based on the averaged SNR from strong backscattering in the presence of aerosols or clouds. Also, DWL observation errors used in the assimilation were calculated using the measurement error estimated by the lidar simulator. The forecast impacts of DWL onboard polar- and tropical-orbiting satellites were assessed using the operational global data assimilation system. Data assimilation experiments were conducted in January and August in 2010 to assess overall impact and seasonal dependence. It is found that DWL on either polar- or tropical-orbiting satellites is overall beneficial for wind and temperature forecasts, with greater impacts for the January experiments. The relative forecast error reduction reaches almost 2 % in the tropics. An exception is a degradation in the southern hemisphere in August, suggesting a need to further refine observation error assignment and QC. A decisive conclusion cannot be drawn of the superiority of polar- or tropical-orbiting satellites due to their mixed impacts. This is probably related to the characteristics of error growth in the tropics. The limitations and possible underestimation of the DWL impacts, for example due to a simple observation error inflation setting, in the SOSE-OSSE are 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

pp.2018-026, (Released:2018-02-05)

被引用文献数

1

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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

LONG Jingchao WANG Yuqing ZHANG Suping

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.2018-018, (Released:2018-01-15)

被引用文献数

1

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The cloud variability and regime transition from-stratocumulus-to-cumulus across the sea surface temperature front in the Kuroshio region over the East China Sea are important regional climate features and may affect the earth’s energy balance. However, because of large uncertainties among available cloud products, it is unclear which cloud datasets are more reliable for use in studying the regional cloud features and to validate cloud simulations in the region by climate models. In this study, the monthly low cloud amount (LCA) and total cloud amount (TCA) datasets in the region from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), Moderate-resolution Imaging Spectroradiometer (MODIS) and International Comprehensive Ocean-Atmosphere Data Set (ICOADS) are validated against the combined product of CloudSat+CALIPSO (CC) in terms of the consistency and discrepancy in the climatologically mean, seasonal cycle, and interannual variation. The results show that LCA and TCA derived from MODIS and CALIPSO present relatively high consistency with CC data in the climatological annual mean and show similar behavior in seasonal cycle. The consistency in LCA between the three datasets and the CC is generally good in cold seasons (winter, spring and fall) but poor in summer. MODIS shows the best agreement with CC in fall with the correlation coefficient of 0.77 at the confidence level over 99%. CALIPSO and MODIS can provide competitive description of TCA in all seasons while ICOADS is good in terms of the climatological seasonal mean of TCA in winter only. Moreover, the interannual variation of LCA and TCA from all datasets is highly correlated with that from CC in both winter and spring with the Matching Score ranging between 2/3 and 1. Further analysis with long-term data suggests that both LCA and TCA from ICOADS and MODIS can be good references for the studies of cloud interannual variability in the region.

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

pp.2017-028, (Released:2017-09-15)

被引用文献数

18

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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

被引用文献数

11

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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

pp.2018-002, (Released:2017-09-29)

被引用文献数

10

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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

被引用文献数

4

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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

被引用文献数

19

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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

被引用文献数

11

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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.

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.1-2, 2015 (Released:2015-03-18)

参考文献数

5

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

被引用文献数

26

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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.