著者
KUJI Makoto MURASAKI Atsumi HORI Masahiro SHIOBARA Masataka
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.2018-025, (Released:2018-02-05)

Cloud fractions were observed during research cruises onboard the research vessel (R/V) Shirase between Japan and Antarctica using a whole-sky camera and a ceilometer. The cruises, Japanese Antarctic Research Expeditions (JARE) 55 and 56, took place from November 2013 to April 2014 and November 2014 to April 2015, respectively. Cloud fractions were estimated from the whole-sky camera based on the sky brightness and spectral characteristics, while the ceilometer recorded the cloud occurrence frequency. According to the comparison of daily-averaged cloud fractions from the whole-sky camera with the ceilometer observations over the open ocean between Japan and Antarctica, the correlation coefficients were 0.87 and 0.93 for JARE 55 and 56, respectively. Overall, the results from both observation methods were consistent over the open ocean. Nevertheless, it was necessary to take surface conditions into consideration, particularly for the estimated cloud fractions from the whole-sky camera, because the contrast in brightness and spectral properties between cloudy and clear skies was lower over the sea ice region, owing to the higher surface albedo. Hence, the classification parameter was expressed as a function of sun elevation over the sea ice region in this study. This parameter was determined from part of the data over the sea ice region during JARE 55 and then applied to JARE 56 as well as to remaining data from JARE 55. As a result, the daily-averaged cloud fractions over the sea ice region were approximately 84% and 57% from JARE 55 and 56, respectively. The daily-averaged cloud fractions estimated from the whole-sky camera were also consistent with the ceilometer observations where the correlation coefficients with the sea ice region were 0.93 and 0.96 for JARE 55 and 56, respectively.
著者
Jing XU Yuqing WANG
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.2018-014, (Released:2017-12-26)

The dependence of intensification rate (IR) of a tropical cyclone (TC) on its initial structure, including the radius of maximum wind (RMW) and the radial decay rate of tangential wind outside the RMW, is examined based on ensemble of simulations using a nonhydrostatic axisymmetric cloud-resolving model. It is shown that the initial spinup period is shorter and the subsequent IR is larger for the storm with the initially smaller RMW or with the initially more rapid radial decay of tangential wind outside the RMW. The results show that the longevity of the initial spinup period is determined by how quickly the inner-core region becomes nearly saturated in the middle and lower troposphere and thus deep convection near the RMW is initiated and organized. Because of the larger volume and weaker Ekman pumping, the inner-core of the initially larger vortex takes longer time to become saturated and thus experiences a longer initial spinup period. The vortex initially with the larger RMW (with the slower radial decay of tangential wind outside the RMW) has lower inertial stability inside the RMW (higher inertial stability outside the RMW) develops more active convection in the outer-core region and weaker boundary-layer inflow in the inner-core region and thus experiences lower IR during the primary intensification stage.
著者
Guanghua CHEN Ke WANG
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.96, no.2, pp.97-110, 2018 (Released:2018-03-23)
参考文献数
38

Although both the tropical cyclone (TC) peak seasons in 2016 and 1998 are in the decaying stage of a super El Niño, TC activities over the western North Pacific (WNP) exhibit vast differences. The TCs in 2016 were greater in number and intensity and had distinct monthly variations in TC activity in contrast to those in 1998. The detailed comparison shows that the warm sea surface temperature anomaly over the WNP in 2016 had higher magnitude and a more eastward extension than that in 1998. In August, coincident with the enhanced Madden–Julian oscillation westerly phase, more TCs clustered within the eastward-extending convective belt caused by the southwesterly surge. The mean longitude of TC genesis in 2016 shifted more eastward, which is favorable for the longer lifetime and greater intensity of the TCs. In terms of the extratropical influences, the cyclonic circulation anomaly associated with the Silk Road Pattern from the middle latitude penetrated southward and split the WNP subtropical high (WNPSH) into two components in August of 2016, thus causing deep-tropospheric southerly steering flows in between and TC northward-prone tracks. During the boreal autumn in 2016, the WNPSH strengthened and stretched westward, producing the robust easterly steering flows that led to successive TCs affecting the coastal areas of East Asia.
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)

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
Yuhei YAMAMOTO Hirohiko ISHIKAWA Yuichiro OKU Zeyong HU
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.59-76, 2018 (Released:2018-03-16)
参考文献数
53
被引用文献数
1

This paper presents a method for estimating the land surface temperature (LST) from Himawari-8 data. The Advanced Himawari Imager onboard Himawari-8 has three thermal infrared bands in the spectral range of 10-12.5 μm. We developed a nonlinear three-band algorithm (NTB) that makes the best use of these bands to estimate the LST. The formula of the algorithm includes 10 coefficients. The optimum values of these coefficients were derived using a statistical regression method from the simulated data, as obtained by a radiative transfer model. The simulated data sets correspond to a variety of values of LST, as well as surface emissivity, type and season of temperature and water vapor profiles. Viewing zenith angles (VZAs) from 0° to 60° were considered. For the coefficients obtained in this way, we verified the root-mean-square error (RMSE) in terms of the VZA, LST and precipitable water dependence. We showed that the NTB can accurately estimate the LST with an RMSE less than 0.9 K compared with the nonlinear split-window algorithm developed by Sobrino and Romaguera (2004). Moreover, we evaluated the sensitivities of the LST algorithms to the uncertainties in input data by using the dataset independent of the dataset used to obtain coefficients. Consequently, we showed that the NTB has the highest robustness against the uncertainties in input data. Finally, the stepwise LST retrieval method was constructed. This method includes a simple cloud mask procedure and the land surface emissivity estimation. The LST product was evaluated using in-situ data over the Tibetan Plateau, and the validity was confirmed.
著者
Yuhei YAMAMOTO Hirohiko ISHIKAWA
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.43-58, 2018 (Released:2018-03-16)
参考文献数
32
被引用文献数
1

Land surface emissivity (LSE) in the thermal infrared (TIR) is an essential parameter in the retrieving land surface temperature (LST) from space. This paper describes the LSE maps in three TIR bands (centered at 10.4, 11.2 and 12.4 μm) used for retrieving the LST from Himawari-8. Himawari-8, a next-generation geostationary satellite has high spatial and temporal resolutions compared to previous geostationary satellites. Because of these improvements, the Himawari-8 LST product is expected to contribute to the observation of small-scale environments in high-frequency. In this study, the LSE is estimated by a semi-empirical method, which is a combination of the classification based method and the normalized difference vegetation index (NDVI) thresholds method. The land cover classification information is taken from the Global Land Cover by National Mapping Organizations version3 (GLCNMO 2013). Material emissivities of soil, vegetation and others are taken from the MODIS UCSB emissivity library and the ASTER spectral library. This method basically follows the semi-empirical methods developed by the previous studies, but advanced considerations are added. These considerations are the phenology of vegetation, flooding of paddy fields, snow/ice coverage, and internal reflections (cavity effect) in urban areas. The average cavity effect on LSE in urban canopies is approximately 0.01, but it reaches 0.02 in built-up areas. The sensitivity analysis shows that the total LSE errors for the three bands are less than 0.02. The LSE estimation is especially stable at the vegetation area, where the error is less than 0.01.
著者
Ryo OYAMA Masahiro SAWADA Kazuki SHIMOJI
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.3-26, 2018 (Released:2018-03-16)
参考文献数
56

The high temporal and spatial resolutions of geostationary satellite observations achieved by recent technological advancements have facilitated the derivation of atmospheric motion vectors (AMVs), even in a tropical cyclone (TC) wherein the winds abruptly change. This study used TCs in the western North Pacific basin to investigate the ability of upper tropospheric AMVs to estimate the TC intensity and structure. We first examined the relationships between the cloud-top wind fields captured by 6-hourly upper tropospheric AMVs derived from images of the Multi-functional Transport Satellite (MTSAT) and the surface maximum sustained wind (MSW) of the Japan Meteorological Agency's best-track data for 44 TCs during 2011-2014. The correlation between the maximum tangential winds of the upper tropospheric AMVs (UMaxWinds) and MSWs was high, approximately 0.73, suggesting that the cyclonic circulation near the cloud top was intensified by the upward transport of absolute angular momentum within the TC inner core. The upper tropospheric AMVs also revealed that the mean radii of UMaxWinds and the maximum radial outflows shifted inward as the TC intensification rate became large, implying that the low-level inflow was strong for TCs undergoing rapid intensification. We further examined the possibility of estimating the MSW using 30-min-interval UMaxWinds derived from Himawari-8 target observations, which have been used to track TCs throughout their lifetimes. A case study considering Typhoon Lionrock (1610) showed that the UMaxWinds captured the changes in the cyclonic circulation near the cloud top within the inner core on a timescale shorter than 1 day. It was apparent that the increase in the UMaxWind was associated with the intensification of the TC warm core and the shrinkage of UMaxWind radius. These results suggest that Himawari-8 AMVs include useful information about TC intensification and related structural changes to support the TC intensity analysis and structure monitoring.

1 0 0 0 OA Editorial

出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.96, no.1, pp.1-2, 2018 (Released:2018-02-28)
参考文献数
6
著者
Woosub ROH Masaki SATOH
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
vol.96, no.1, pp.55-63, 2018 (Released:2018-02-08)
参考文献数
34

As an alternative approach to previous multisensor satellite evaluations for cloud system resolving models (CSRMs), a technique for precipitation clouds over the ocean of CSRMs is presented using combined infrared and microwave channels. This method quantitatively analyzes precipitation clouds using cloud-top temperatures and ice scatterings from infrared 11 μm and high frequency microwave (89.0 GHz) brightness temperatures (TBs). The TB threshold at low frequencies (18.7 GHz) is used to identify precipitation regions. This method extends a previous approach based on tropical rainfall measuring mission (TRMM) precipitation radar which uses a narrow coverage, by incorporating a wide passive microwave sensor swath and ice cloud sensitivity.  The numerical results of the non-hydrostatic icosahedral atmospheric model, NICAM, with two cloud microphysics schemes were evaluated over the tropical open ocean using this method. The scattering intensities in both simulations at 89.0 GHz were different due to the parameterizations of the snow and graupel size distributions. A bimodal snow size distribution improved the TB underestimation at 89.0 GHz. These results exhibited similar structures to the joint histograms of cloud-top temperatures and precipitation-top heights generated using the previous method; the frequencies of overestimated scattering intensities in this study and the frequencies of high precipitation-top heights above 12 km in the previous study. It was observed 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. Furthermore, we investigated the impacts of nonspherical snow assumptions using a satellite simulator. The effect of a nonspherical snow shape in the radiative transfer model caused a smaller change in TBs at 89.0 GHz compared to the difference between the TBs of the two simulations without nonspherical assumptions.
著者
Katsuyuki V. Ooyama
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
vol.60, no.1, pp.369-380, 1982 (Released:2007-10-19)
参考文献数
23
被引用文献数
48 126

航空機観測の進歩に伴ない,台風の一般構造およびエネルギー収支については,1960年代の初めごろまでに.かなりよくわかってきた。しかし,これらの知識を力学的に統一して台風の生成発達を説明する理論は容易に生れなかった。現在の台風理解の因となった最初の発達理論が出るためには,力学的問題としての台風の認識,特に種々の要因の相対的重要度,を再考する必要があった。雲のパラメータ化が成功の原因のように云われるが,実は,問題認識上の変化がそのような雲の扱いを一応許されるものとした。雲のパラメータ化を技術的にのみ応用すると,その後の種々の線型理論(いわゆるCISK)に見られるような物理的混乱を引きおこす。一方,台風の理解のためには,線型理論は不充分であり,理論の概念としての妥当性および限度は非線型数値モデルによる実験によってのみ評価されることとなった。数値モデルの進歩により,台風成生の理解のためには,雲のパラメータ化を取り除く必要があることもわかってきた。この論文は,歴史を逆転するかの如く見える最近の発展の裏にある真の進歩を概念的に解明することを目的とする。
著者
Michio Yanai Chengfeng Li Zhengshan Song
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
vol.70, no.1B, pp.319-351, 1992-02-25 (Released:2009-03-31)
参考文献数
127
被引用文献数
170 330

客観解析したFGGE II-b高層観測データを用いて、1978年12月から1979年8月までの9ヶ月間のチベット高原及びその周辺領域の大規模循環場と熱・水蒸気収支の解析を行った。客観解析には、FGGEデータに加えて1979年5月-8月に中国が行った「チベット高原特別気象観測」データも用いた。夏季アジアモンスーンの始まりにつながる冬から夏にかけての顕著な季節変化を同定するために、大規模循環、温度、外向き長波放射(OLR)および鉛直循環の時間的発展を記述した。チベット高原は、熱的に駆動された大規模垂直循環を維持しているが、この循環は地球規模のモンスーン循環とはもともとは別なものである。上昇流は冬には西部高原だけに限られているが、季節の進行とともに高原全域に広がる。アジアモンスーンの始まりは高原が誘導する循環と、北上する主要な降雨帯に伴う循環との相互作用によってもたらされる。冬の期間、高原は冷源となっているが、周囲はさらに強い冷源域となっている。春には高原は熱源となるが、周辺域は引続き冷源である。高原上での主要な熱源は地表からの顕熱輸送である。しかし、その他に凝結熱の貢献も、西部高原では年間を通して、更にもっと重要なことには東部高原ではとりわけ夏に観測されている。持ち上げられた高原表面の顕熱加熱と周辺域の放射冷却によって水平温度傾度が維持され、それが熱的直接循環を生じている。夏季アジアモンスーンへの2つの移行期間-5月の東南アジアのモンスーンの始まりと6月のインドモンスーンの始まり-の上部対流圏の昇温過程を詳しく調べた。その結果、最初のオンセット時の東部高原での気温上昇は、主に、非断熱加熱の結果であるが、次のオンセット時直前のイラン-アフガニスタン-西部高原の気温上昇は、強い下降流によってもたらされていることがわかった。高原上の境界層や垂直循環には大きな日変化が存在する。地表からの加熱によって、高原上では夕方(1200 UTC)に温位がほぼ一様な深い混合層がみられる。このことは熱の垂直輸送に果たす熱対流の役割の重要性を示唆している。しかし、水蒸気は垂直方向にあまり混合しておらず、また、境界層には大きな水平温度傾度がある。晩春から夏にかけて、境界層は乾燥対流に対してより安定となる。一方、晩春以降の相当温位の垂直分布は、下層の水蒸気量の増加に伴って、湿潤対流に対して条件付き不安定な成層を示す。
著者
石田 雅生
出版者
METEOROLOGICAL SOCIETY OF JAPAN
雑誌
氣象集誌. 第1輯 (ISSN:00261165)
巻号頁・発行日
vol.31, no.7, pp.203-210, 1912
著者
SU Shih-Hao KUO Hung-Chi HSU Li-Huan YANG Yi-Ting
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.90, no.5, pp.721-736, 2012
被引用文献数
14

We studied the temporal and spatial characteristics of extreme typhoon rainfall in Taiwan using Central Weather Bureau hourly precipitation data from 21 surface stations during the past 51 years (1960-2010). Extreme rainfall is defined as 95th percentile intensity of total rain events, or equivalently, rain events greater than 9 mm hr<sup>-1</sup> which contribute 40% to the total rain amount in Taiwan. It was found that approximately 70% (20%) of extreme rain is in the typhoon season (Mei-Yu) from July to October (from May to June). There are significant variations of typhoon extreme rainfall over the annual and decadal time scales, with larger extreme rainfall values and events in the periods of 1960-1976 and 1994-2010, and less in the 1977-1993 period. The recent 1994-2009 period has the most extreme rainfall and events, as well as, inter-annual variability. In contrast, there are strong inter-annual variations of Mei-Yu extreme rainfall, but no significant decadal variations. The averaged typhoon rain intensity, however, is about the same, being 19 mm hr<sup>-1</sup> in all these three periods. Our analysis indicates that the typhoon extreme rainfall spatial pattern is phased locked with the Central Mountain Range, Taiwan. In general, the amount of extreme rainfall was related to the typhoon translation speed and duration time, but not typhoon intensity. Slower speeds and longer duration time lead to larger extreme rainfall values. Our analysis also indicate that the mean duration time of Taiwan landfall typhoons with northern tracks (tracks north of 23 degrees latitude) is about 3 hours longer than that of southern track typhoons in the last 51 years, and is more likely to produce three times as much extreme rainfall. The interactions of summer or winter monsoons with typhoons are also important factors that may contribute to the extreme rainfall in Taiwan. Examples of extreme rainfall due to typhoon circulation interaction with summer and winter monsoon flows are presented. Monsoon water vapor supply, typhoon slow translation speed, and mesoscale convection due to typhoon-monsoon flow interactions are the key factors in extreme precipitation events.
著者
朝倉 慶吉
出版者
METEOROLOGICAL SOCIETY OF JAPAN
雑誌
氣象集誌. 第1輯 (ISSN:00261165)
巻号頁・発行日
vol.16, no.4, pp.178-184, 1897
著者
和田 雄治
出版者
METEOROLOGICAL SOCIETY OF JAPAN
雑誌
氣象集誌. 第1輯 (ISSN:00261165)
巻号頁・発行日
vol.31, no.8, pp.261-277, 1912
著者
和田 雄治
出版者
METEOROLOGICAL SOCIETY OF JAPAN
雑誌
氣象集誌. 第1輯 (ISSN:00261165)
巻号頁・発行日
vol.29, no.3, pp.81-87, 1910
著者
鹿角 義助
出版者
METEOROLOGICAL SOCIETY OF JAPAN
雑誌
氣象集誌. 第1輯 (ISSN:00261165)
巻号頁・発行日
vol.17, no.5, pp.215-220, 1898
著者
馬塲 信倫
出版者
METEOROLOGICAL SOCIETY OF JAPAN
雑誌
氣象集誌. 第1輯 (ISSN:00261165)
巻号頁・発行日
vol.10, no.9, pp.465-474, 1891
著者
Takahiro ITO Hirotada KANEHISA
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.91, no.6, pp.775-788, 2013
被引用文献数
3

The initial value problem of vortex Rossby waves (VRWs) is analytically solved in a linearized barotropic system on an <i>f</i> plane. The basic axisymmetric vorticity <span style="text-decoration: overline;"><i>q</i></span> is assumed to be piecewise uniform in the radial direction so that the radial gradient <i>d<span style="text-decoration: overline;"><i>q</i></span>/dr</i> and the disturbance vorticity <i>q</i> are expressed in terms of Dirac delta functions. After Fourier transformation in the azimuthal direction with the wavenumber <i>m</i>, the linearized vorticity equation becomes a system of ordinary differential equations with respect to time; these can be analytically solved to give a closed-form solution with a prescribed initial value.<br> For a monopolar <span style="text-decoration: overline;"><i>q</i></span>, the solution of <i>q</i> starting from the innermost radius exhibits the outward propagation of VRWs. As the outer disturbances are generated, the inner disturbance is diminished. On the other hand, in the case of a solution forced at the innermost radius, the inner disturbance is not diminished, and the outward propagation of VRWs forms a distribution of spiral-shaped disturbance vorticity.<br> For a basic vorticity <span style="text-decoration: overline;"><i>q</i></span> with a moat, and if the radial distribution of <span style="text-decoration: overline;"><i>q</i></span> satisfies a certain additional condition, the solution of <i>q</i> with |<i>m</i>| ≠ 1 grows exponentially or linearly in time as a result of the interaction of counterpropagating VRWs near the moat. Although the solution of <i>q</i> with |<i>m</i>| = 1 cannot grow exponentially for any <span style="text-decoration: overline;"><i>q</i></span>, it can grow as a linear function of time. This linear growth may be regarded as a result of resonance between two internal modes of the system.