著者

A GETTELMAN P.M. de F FORSTER

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.80, no.4B, pp.911-924, 2002 (Released:2002-10-10)

参考文献数

28

被引用文献数

205 243

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The tropical tropopause layer (TTL) is a transition region between the troposphere and the stratosphere. In this study the vertical extent of the TTL is diagnosed from radiosonde and ozonesonde profiles in the tropics and a climatology of this layer is presented. The radiative balance in the TTL is also characterized. The TTL is locally defined as extending from the level of the lapse rate minimum at 10-12 km to the cold point tropopause (CPT) at 16-17 km. The minimum in lapse rate represents the level of maximum convective impact on upper tropospheric temperatures, which is found to closely correspond to a minimum in ozone. Variations in this level are correlated with convective activity as measured by satellite brightness temperatures and Outgoing Longwave Radiation (OLR). At the cold point, the TTL height is nearly uniform throughout the tropics, and has a pronounced annual cycle. There are regional variations in the altitude of the lower boundary of the TTL. Interannual variations of the TTL result from changes in the large scale organization of convective activity, such as from the El-Niño Southern Oscillation (ENSO). Over the last 40 years, records indicate an increase (200-400 m) in the height of both the cold point tropopause and the level of minimum lapse rate. To better understand vertical transport in the TTL, the clear sky radiative heating rate is diagnosed using a sophisticated radiative transfer scheme. The level of zero radiative heating occurs roughly 1 km below the CPT, implying that convection needs to loft air 4-5 km above the base of the TTL if the air is to eventually enter the stratosphere.

著者

真鍋 淑郎

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.33, no.2, pp.76-88, 1955 (Released:2009-02-05)

参考文献数

7

被引用文献数

2 2

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Using 2-layer model which is the special case of the multiple layer model defined by Charney and Phillips, investigation is made, from the view point of numerical weather prediction, on the role of the tilt of trough relative to the vertical for the development of the pressure pattern. At the same time, the mechanism of the transition between the tilted and the non-tilted trough is discussed. Finally, corresponding to the above development, the energetics of westerly wave, i. e., the energy exchange between the potential and the kinetic energy is investigated. Here, the simple expression for the change of these energies is obtained.

著者

KODERA Kunihiko EGUCHI Nawo UEYAMA Rei FUNATSU Beatriz M. GAETANI Marco TAYLOR Christopher M.

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-055, (Released:2021-05-14)

被引用文献数

1

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Previous studies have suggested that the recent increase in tropical extreme deep convection, in particular over Asia and Africa during the boreal summer, has occurred in association with a cooling in the tropical lower stratosphere. The present study is focused on the Sahel region of West Africa, where an increased occurrence of extreme precipitation events has been reported over recent decades. The results show that the changes over West Africa since the 1980s involve a cooling trend in the tropical lower stratosphere and tropopause layer, combined with a warming in the troposphere. This feature is similar to that which might result from increased greenhouse gas levels, but is distinct from the interannual variation of precipitation associated with the transport of water vapor from the Atlantic Ocean. It is suggested that the decrease in the vertical temperature gradient in the tropical tropopause region enhances extreme deep convection over the Sahel, where penetrating convection is frequent, whereas tropospheric warming suppresses the shallower convection over the Guinea Coast. The essential feature of the recent changes over West Africa is therefore the depth of convection, rather than the total amount of surface precipitation.

著者

SONG Jinjie KLOTZBACH Philip J. DUAN Yihong

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-051, (Released:2021-04-27)

被引用文献数

3

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This study shows that the impact of El Niño-Southern Oscillation (ENSO) Modoki on boreal summer tropical cyclone (TC) formation over the western North Pacific (WNP) has experienced decadal changes during the past few decades. The correlation between the ENSO Modoki index (EMI) and TC frequency over the WNP is weak between 1975-1989, becomes strong and significant between 1990-2004, and becomes weak again between 2005-2019. Over the eastern part of the WNP, ENSO Modoki enhanced TC formation during 1990-2004 but did not significantly impact on the TC formation during 1975-1989 and 2005-2019. The difference in correlation strength primarily results from changes in large-scale features related to ENSO Modoki among the three sub-periods (1975-1989, 1990-2004 and 2005-2019). El Niño Modoki from 1990-2004 was characterized by a tripole SST pattern with maximum SST anomalies in the equatorial central Pacific, while from 1975-1989 and 2005-2019, the maximum SST anomalies were located over the subtropical northeastern Pacific. The two primary environmental variables likely leading to these observed relationships between ENSO Modoki and TCs were mid-level moisture (RH600) and low-level vorticity (VOR850). From 1990-2004, TC formation was enhanced both south of 20°N and north of 20°N. The increase in TC activity during El Niño Modoki south of 20°N was likely tied to greater RH600 and north of 20°N to larger cyclonic VOR850. In contrast, ENSO Modoki's impacts on both VOR850 and RH600 were weak from 1975-1989 and 2005-2019.

著者

SHIBUYA Ryosuke NAKANO Masuo KODAMA Chihiro NASUNO Tomoe KIKUCHI Kazuyoshi SATOH Masaki MIURA Hiroaki MIYAKAWA Tomoki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-046, (Released:2021-04-08)

被引用文献数

5

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In this study, we assessed the prediction skill of the Boreal Summer Intra-Seasonal Oscillation (BSISO) mode of one-month simulations using a global non-hydrostatic atmospheric model (NICAM) with explicit cloud microphysics and with a grid spacing of 14 km. The simulations were run as a series of hindcast experiments every day of August during 2000-2014; a total of 465 simulations were run with a 13950-day integration. On using forecast skill scores for statistical measurements, it was found that the model showed an overall BSISO prediction skill of approximately 24 days. The prediction skill tended to be slightly higher (∼ 2 days) when BSISO events began in the initial phases 7 to 1, which corresponded to the re-initiation phase of the BSISO, where a major convective center over the Philippine Sea decayed and a new convective envelope began aggregating over the western Indian Ocean. The phase speed and the evolution of the amplitude of the BSISO were well simulated by the model with a clear northwestward-southeastward tilted outgoing longwave radiation (OLR) structure over the Maritime continent and the western Pacific. However, the propagation speed was slower during phases 6-7, and the amplitude of the BSISO largely decayed during phases 8-1, which was likely to have been associated with the stagnant behavior of the convective cells over the Philippines. This stagnation of the propagation over the Philippines may be largely attributed to the small background southerlies bias in the model over the Philippines based on regression coefficient analysis using the moist static energy. The bias in the large-scale circulation was likely to have been associated with the bias in the moisture field and the associated background monsoonal circulation. We concluded that the model physics controlling the background fields are important factors for improving the BSISO prediction skill.

著者

KIKUCHI Kazuyoshi

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-045, (Released:2021-03-30)

被引用文献数

44

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The boreal summer intraseasonal oscillation (BSISO) is among the most pronounced subseasonal variability in the tropics during boreal summer. Compared to its wintertime counterpart, the so-called Madden-Julian oscillation (MJO), the BSISO convection displays more complicated spatio-temporal evolution, characterized by northward propagation over the northern Indian Ocean and western North Pacific as well as eastward propagation along the equator. It exerts a strong influence on a broad range of tropical weather and climate phenomena such as tropical cyclogenesis, monsoon onset and active/break cycles, among others. Our fundamental understanding of the BSISO has steadily advanced: so far various aspects of the BSISO have been described and several theories aiming to explain its northward propagation have been proposed. Yet, our skill to simulate the BSISO by general circulation models remains unsatisfactory, though it has been improved. This paper reviews some fundamental aspects of the BSISO from the viewpoint of observation, theory, and modeling.

著者

Prashant KUMAR Rakesh GAIROLA 久保田 拓志 Chandra KISHTAWAL

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.3, pp.741-763, 2021 (Released:2021-06-14)

参考文献数

69

被引用文献数

9

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インド夏季モンスーン(ISM)期間中の正確な降雨量推定はインド亜大陸およびその周辺で最も重要な活動の一つである。宇宙航空研究開発機構(JAXA)は、Global Satellite Mapping of Precipitation(GSMaP)降雨プロダクトとして、全球客観解析データ等を補助データとして用いて計算した衛星プロダクトであるGSMaP_MVKや全球地上雨量計データで調整したGSMaP_Gaugeを提供している。本研究では、2016~2018年のISM期間で、インド南西部の州の1つであるカルナータカ州における高密度地上雨量計ネットワークを基準として、GSMaP降雨プロダクト(バージョン7)の日降雨量を検証する。さらに、本研究の主目的として、これらの高密度地上雨量計観測を、ハイブリッド同化法を用いてGSMaP降雨量に同化することで、最終的な降雨推定を改善する。ここで、ハイブリッド同化法は二次元変分(2D-Var)法とKalmanフィルタの組合せであり、2D-Var法を用いて地上雨量計観測を統合し、Kalmanフィルタを用いて2D-Var法の背景誤差を更新する。準備としての検証結果は、GSMaP_Gauge降雨量が北部内陸カルナータカ州(NIK)と南部内陸カルナータカ州(SIK)地域で十分な精度を持ち、西ガーツ山脈の地形性豪雨領域で大きな誤差を持つことを示唆する。これらの誤差はGSMaP_MVK降雨量の地形性豪雨領域でより大きかった。ランダムに選択した地上雨量計観測を用いたハイブリッド同化結果は、独立した地上雨量計観測と比較して、GSMaP_GaugeとGSMaP_MVK降雨量の精度を改善した。これらの日雨量における改善は地形性豪雨領域でより顕著である。GSMaP_MVK降雨プロダクトは、JAXAの運用処理において地上雨量計による調整が含まれていないので、より大きな改善を示した。また本研究は、Cressman法や最適内挿法と比較して、用いられた雨量計の数のインパクトに対するハイブリット同化法の優位性を示す。

著者

NAKAMURA Kenji

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-035, (Released:2021-03-12)

被引用文献数

11

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The Tropical Rainfall Measuring Mission (TRMM) satellite was launched in 1997 and the observations continued for more than 17 years. The features of TRMM observation were as follows: (a) it followed a non-sun synchronized orbit that enabled diurnal variation of precipitation to be investigated, (b) it carried a precipitation radar and microwave and infrared radiometers, along with two instruments of opportunity in the form of a lighting sensor and a radiation budget sensor, and (c) it worked as a standard reference for precipitation measurements for other spaceborne microwave radiometers, which enabled global rain maps to be developed. For science, TRMM provided precise and accurate rain distributions over tropical and subtropical regions. The rainfall results are primarily important for the study of the precipitation climatologies, while the three-dimensional images of precipitation systems enabled the study of the global characteristics of precipitation systems. Technologically, the spaceborne rain radar onboard TRMM demonstrated the effectiveness of radars in space, while the combination with other rain observation instruments showed its effectiveness as a calibration source. Multi-satellite rain maps in which TRMM was the reference standard have been developed, and they became prototypes of the multi-satellite Earth observation systems. Based on the great success of TRMM, the Global Precipitation Measurement (GPM) was designed to expand TRMM's coverage to higher latitudes. The core satellite of GPM is equipped with a dual frequency precipitation radar (DPR) and a microwave radiometer. DPR consists of a Ku-band radar (KuPR) and a Ka-band radar (KaPR) and has a capability to discriminate solid from liquid precipitation. The period of the precipitation measurement with spaceborne radars extended to more than 23 years which may make it possible to detect the change of precipitation climatology related to change in the global environment. While TRMM's and GPM's accomplishments are very broad, this paper tries to highlight Japan's contributions to the science of these missions.

著者

YAMAJI Moeka KUBOTA Takuji YAMAMOTO Munehisa K.

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-033, (Released:2021-02-17)

被引用文献数

8

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Reliability information of satellite precipitation products is required for various applications. This study describes and evaluates a reliability flag of the Global Satellite Mapping of Precipitation Near-Real-Time precipitation product (GSMaP_NRT). This flag was developed to characterize the reliability of GSMaP_NRT data simply and qualitatively by considering its algorithm characteristics. The reliability at each pixel is represented by any one of ten levels (10 being the best and 1 the worst) by considering three major factors: 1) “surface type reliability”—which takes into account that estimation of rainfall using passive microwave sensors is better over the oceans than over land and coastal areas; 2) “low-temperature reliability”—which takes into account the lower reliability due to surface snow cover in low-temperature conditions; and 3) “Moving Vector with Kalman Filter (MVK) propagation reliability”—which means that the reliability gets worse with the increase in time since the last overpass of the passive microwave sensor. To evaluate the utility of the reliability flag, statistical indices are calculated for each reliability level using gauge-calibrated ground radar data around Japan. It is found that the reliability flag represents the differences in GSMaP accuracy: the accuracy worsens as the reliability decreases. The GSMaP errors exhibit seasonal changes that are well represented by the ten levels of the reliability flag, indicating that the reliability flag can be used to catch seasonal variations in GSMaP accuracy due to changes in environmental factors. This study also raises the possibility of improving the reliability flag by using information related to heavy orographic rainfall. It is shown how the error features of heavy orographic rainfall differ from those of the total rainfall, and it is suggested that heavy orographic rainfall information can be utilized to further improve the reliability flag.

著者

CHENG Chiu Tung SUZUKI Kentaroh

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-031, (Released:2021-02-18)

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The transport and removal processes of aerosol particles, as well as their potential impacts on clouds and climate, are strongly dependent on the particle sizes. Recent advances in computational capabilities enable us to develop sectional aerosol schemes for general circulation models and chemical transport models. The sectional aerosol modeling framework provides a capacity to explicitly simulate the variations in size distributions due to microphysical processes such as nucleation and coagulation, based on the mechanisms suggested from laboratory studies and field observations. Here, we develop a two-moment sectional aerosol scheme for Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS-bin) for use in NICAM (Nonhydrostatic ICosahedral Atmospheric Model) as an alternative to the original mass-based (single-moment) SPRINTARS-orig aerosol module. NICAM-SPRINTARS is a seamless multiscale model that has been used for regional-to-global simulations of different resolutions based on the same model framework. In this study, we performed global simulations with NICAM-SPRINTARS-bin at typical climate model resolution (Δx ∼ 230 km) with nudging to a meteorological re-analysis. We compared our results with equivalent simulations for the original model (NICAM-SPRINTARS-orig) and observations including 500 nm aerosol optical depth and 440-870 nm Angstrom Exponent in AErosol RObotic NETwork (AERONET) measurements, particle number concentrations measured at Global Atmospheric Watch (GAW) sites and size-resolved number concentrations measured at European Supersites for Atmospheric Aerosol Research (EUSAAR) and German Ultrafine Aerosol Network (GUAN) sites. We found that compared to NICAM-SPRINTARS-orig, NICAM-SPRINTARS-bin demonstrates the long-range transport of ultra-fine particles to high latitudes and predicts higher Angstrom Exponent and total number concentrations that better agrees with observations. The latter underscores the importance of resolving the microphysical processes that determine concentrations of ultra-fine aerosol particles and explicitly represent size-dependent deposition in predicting these properties. However, number concentrations of coarse particles are still underestimated by both the original mass-based and the new microphysical schemes. Further efforts are needed to understand the reasons for the differences with the observed size distributions, including testing different emission and secondary organic aerosol production schemes, incorporating inter-species coagulation and black carbon aging, as well as performing simulations with higher spatial resolutions.

著者

平山 操

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.16, no.11, pp.421-430, 1938-11-05 (Released:2009-02-05)

参考文献数

6

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Recently, Dellinger's phenomena which make the transmission of short waves impossible, attract the attentions of those who are engaged in the wireless-communication or in the observation of the earth's magnetic field and many studies have been made in the ionospheric conditions and magnetic and electric fields. The author investigated the magnetic field of the phenomena occurred during 1935-36, and found that the disturbance in the ionosphere not far from Japan causes the magnetic changes (De) so as to increase the amplitude of the diurnal variation. On comparatively quiet days, we obtained 0.2-0.9 for the ratio De/Ω0, where Ω0 is the departure from the preceding and following midnight.The author calc_??_lated the magnetic potential of the disturbing field by the increase of electrons in the ionosphere. When the increase is constant in the area Se, where σ0+σs and σ0 are the total conductivities when the ionosphere is disturbed and when it is not disturbed respectively, where [φ0]m is the mean normal current function in Se, α the ratio of current in the external and internal portions (Si) induced in the earth-core, and ωe or ωi are the solid angles subtended by Se and Si respectively. From these studies we see that the dynamo-theory is appropriate for interpreting De and the drift current and diamagnetic theories are not, since De is always produced in the sense to decrease the permanent field in the latter theories

著者

前田 修平 竹村 和人 小林 ちあき

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.2, pp.449-458, 2021 (Released:2021-04-14)

参考文献数

17

被引用文献数

3

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本研究では、ユーラシアパターン―ユーラシア北部において冬季に卓越するテレコネクションパターン―に関連する惑星波の変調を、JRA-55を使用した合成図分析により解析し、波―平均流相互作用を含むユーラシアパターンの力学的メカニズムを明らかにする。 平年偏差の点からは、ユーラシアパターンは、北ヨーロッパ、中西部シベリア、および日本に作用中心を持つ、等価順圧な鉛直構造をした定常ロスビー波型のテレコネクションとして知られている。一方、帯状平均からのずれの観点では、ユーラシアパターンは、東アジアの冬季モンスーンに関連する惑星波の活動度を変調する。 強化された東アジア冬季モンスーンに対応するユーラシアパターンの正位相では、対流圏のユーラシア中部から北太平洋において東方・上方に伝播する惑星波が平年より強まる。この惑星波の強化には、東アジアにおける帯状平均から擾乱への傾圧エネルギー変換が寄与する。強化され東方・上方に伝播した惑星波は、上部対流圏で収束し、それにより中高緯度の直接循環偏差と、中緯度下部対流圏への寒気流出を引き起こす。これらの結果は、ユーラシアパターンは主に惑星波の活動に関係する全球的な力学モードの1つであることを示す。

著者

Peter VOELGER Peter DALIN

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.2, pp.497-504, 2021 (Released:2021-04-26)

参考文献数

24

被引用文献数

2

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A case study of the occurrence of polar stratospheric clouds (PSCs) on February 13th, 2017, in northern Sweden is reported in this paper. For the first time, a quasistationary edge of a bright and extended PSC layer (∼ 600-km long) on the eastern side of the Scandinavian mountain range was photographed and registered using lidar observations. Both lidar measurements and model simulations demonstrated that atmospheric conditions were fairly unchanged for several hours during the presence of the PSC. Strong winds across the Scandinavian mountain range were responsible for triggering the formation of mountain lee waves in the Kiruna area, which induced the formation of the quasistationary long and straight edge of the PSCs.

著者

JAIN Shipra CHHIN Rattana DOHERTY Ruth M. MISHRA Saroj K. YODEN Shigeo

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-021, (Released:2021-01-13)

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Equilibrium climate sensitivity (ECS) is defined as the change in global-mean surface air temperature due to the doubling or quadrupling of CO2 in a climate model simulation. This metric is used to determine the uncertainty in future climate projections, and therefore the impact of model changes on ECS is of large interest to the climate modeling community. In this paper, we propose a new graphical method, which is an extension of the Gregory's linear regression method, to represent the impact of model changes on ECS, climate forcing and climate feedbacks in a single diagram. Using this visualization method, one can quantify (a) whether the model- or process-change amplifies, reduces, or has no impact on global warming, and evaluate (b) the percentage changes in ECS, climate forcing and climate feedbacks and (c) ranges of the uncertainties in the estimated changes. We demonstrate this method using an example of climate sensitivity simulations with and without interactive chemistry. This method can be useful for multi-model assessments where the response of multiple models for the same model experiment (e.g., usage of interactive chemistry as compared to the prescribed chemistry as shown here) can be assessed simultaneously, which is otherwise difficult to compare and comprehend. We also demonstrate how this method can be used to examine the spread in ECS, climate forcing and climate feedbacks with respect to the multi-model mean (or one benchmark model) for multi-model frameworks like Coupled Model Intercomparison Project Phase 5 or for different ensemble members in a large ensemble of simulations carried out using a single model.

著者

JIAN Hong-Wen CHEN Wei-Ting CHEN Peng-Jen WU Chien-Ming RASMUSSEN Kristen L.

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-013, (Released:2020-12-02)

被引用文献数

5

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This study investigates the synoptic scale flows associated with extreme rainfall systems over the Asian-Australian monsoon region (90-160°E and 12°S-27°N). Based on statistics of the 17-year Precipitation Radar observations from Tropical Rainfall Measurement Mission, a total of 916 extreme systems with both the horizontal size and maximum rainfall intensity exceeding the 99.9th percentiles of the tropical rainfall systems are identified over this region. The synoptic wind pattern and rainfall distribution surrounding each system are classified into four major types: Vortex, Coastal, Coastal with Vortex, and None of above, with each accounting for 44 %, 29 %, 7 %, and 20 %, respectively. The vortex type occurs mainly over the off-equatorial areas in boreal summer. The coast-related types show significant seasonal variations in their occurrence, with high frequency in the Bay of Bengal in boreal summer and on the west side of Borneo and Sumatra in boreal winter. The None-of-the-above type occurs mostly over the open ocean, and in boreal winter these events are mainly associated with the cold surge events. The environment analysis shows that coast-related extremes in the warm season are found within the areas where high total water vapor and low-level vertical wind shear occur frequently. Despite the different synoptic environments, these extremes show a similar internal structure, with broad stratiform and wide convective core rain. Furthermore, the maximum rain rate locates mostly over convective area, near convective-stratiform boundary in the system. Our results highlight the critical role of the strength and direction of synoptic flows in the generation of extreme rainfall systems near coastal areas. With the enhancement of the low-level vertical wind shear and moisture by the synoptic flow, the coastal convection triggered diurnally has a higher chance to organize into mesoscale convective systems and hence a higher probability to produce extreme rainfall.

著者

清木 達也

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.2, pp.379-402, 2021 (Released:2021-04-12)

参考文献数

61

被引用文献数

7

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本研究では全球降水観測計画主衛星(GPM)に搭載された二周波降水レーダー(DPR)を利用して雹の三次元分布を全球規模で検出する手法を提案した。雹の検出にはKu帯におけるレーダー反射因子(ZKu)に加え、Ku帯とKa帯のレーダー反射因子の比率(DFR)、そして再解析データから得られる気温分布を利用した。検証には地上レーダーの粒子種判別プロダクトを利用した。本研究では、雹粒子が雨との衝突によって急速に成長する事に着目し、二粒子衝突モデルによって雹の成長を特徴づけられると仮定した。ここで、本研究で取り扱う雹はKu帯とKa帯の散乱特性に基づいて定義されており、一般的に定義される雹の他に高密度の霰や小さい凍結雨滴を含んでいる事が考えられる。 まず初めに、降雹の一事例を基にZKuとDFRの散布図の特徴を抽出したところ、二粒子衝突モデルに則った成長曲線は雹の分布をよく捉えられることが分かった。気温に依存して雹の密度が変化する事から、本研究では五つの温度帯で雹を検出するためのZKuとDFRの閾値を定義した。この閾値を用いて地上レーダーとGPM-DPRがマッチングする74の雹事例を抽出し、雹の検出精度を検証した。この検証を通じて、本研究では雹の誤検出を低減する融解雪除去フィルター及び雨除去フィルターを提案した。これら雹閾値と誤検出除去フィルターを準全球観測データに適用したところ、雹は陸上と海上の収束帯に広く存在することが分かった。特に海洋上の雹は凍結高度付近に薄く(厚さ1500m以下)広く存在しており、その存在は従来の地上レーダー網では見逃されていたことが示唆された。最後に、凍結高度付近の薄い雹層を除去するフィルターを追加したところ、特に陸上の雹を伴う深い対流を選択的に捉えられた。

著者

SEIKI Ayako YOKOI Satoru KATSUMATA Masaki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-007, (Released:2020-11-12)

被引用文献数

7

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The impact of diurnal precipitation over Sumatra Island, the Indonesian Maritime Continent (MC), on synoptic disturbances over the eastern Indian Ocean is examined using high-resolution rainfall data by the Global Satellite Mapping of Precipitation project and the Japanese 55-year Reanalysis data during the rainy season from September to April for the period 2000-2014. When the diurnal cycle is strong, the high precipitation area observed over Sumatra in the afternoon migrates offshore during night-time and reaches 500 km off the coast on average. The strong diurnal events are followed by the development of synoptic disturbances over the eastern Indian Ocean for several days, and apparent twin synoptic disturbances straddling the equator develop only when the convective center of the Madden-Julian Oscillation (MJO) lies over the Indian Ocean (MJO-IO). Without the MJO, the synoptic disturbances develop mainly south of the equator. The differences in the locations and behaviors of active synoptic disturbances are related to the strength of mean horizontal winds in the lower troposphere. During the MJO-IO, the intensification of mean northeasterly winds in the northern hemisphere blowing into the organized MJO convection in addition to mean southeasterly winds in the southern hemisphere facilitate the formation of the twin disturbances. These results suggest that seed disturbances arising from the diurnal offshore migration of precipitation from Sumatra develop differently depending on the mean states over the eastern Indian Ocean. Furthermore, it is shown that the MJO events with the strong diurnal cycle tend to have longer duration and continuing eastward propagation of active convection across the MC whereas the convective activities of the other MJO events weaken considerably over the MC and develop again over the western Pacific. These results suggest that the strong diurnal cycle over Sumatra facilitates the smooth eastward propagation of the intraseasonal convection across the MC.

著者

大東 忠保 前坂 剛 鈴木 真一 出世 ゆかり 櫻井 南海子 岩波 越

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.1, pp.101-112, 2021 (Released:2021-02-28)

参考文献数

50

被引用文献数

2

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本研究では、非降水雲を検出することのできるKaバンド(波長8.6mm)偏波雲レーダーを用い、2016年5月21日に日本の首都圏に出現した晴天エコーの偏波パラメータを調べた。Kaバンド偏波雲レーダー観測において、晴天エコーと雲形成初期における雲・降水エコーを識別する可能性を確立することが目的である。対象とした日には晴天エコーは明瞭な日変化を示した。日の出前には晴天エコーは見られなかった。日の出以降、等価レーダー反射因子(Ze)は時間とともに増大し、現地時間の正午過ぎにはレーダー観測範囲内において水平方向に広範囲に広がったエコー(最大で>−15dBZ)が生じた。日没以降夜の早い時間帯に、Zeは急激に減少した。RHI(距離高度断面)観測によると晴天エコーは高度1.5kmより下層に限定されていた。晴天エコーのレーダー反射因子差(ZDR)は、現地時間18:00には大きな正の値(1.8dB)を示し標準偏差も大きかった。これは同時に観測された雲や弱い降水のエコーのZDR(0.4dB)と比較するとかなり大きい。雲・降水エコーと比べると偏波間相関係数(ρhv)は小さく(< 0.9)、合計の偏波間位相差(ΨDP)の距離方向の変動は大きかった。Zeの上限値、およびZDRとρhvの分布は、先行研究におけるSバンド(波長10cm)レーダーによって観測されたブラッグ散乱の特徴と矛盾していた。一方で、水平方向に広範囲に広がったエコー、大きなZDRと小さなρhvの値、ψDPの距離方向の大きな変動は昆虫エコーの特徴と一致する。ZDRとρhvを用いて定義される偏波抑圧比は、この種の晴天エコーと雲・降水エコーの識別に有効であると思われる。Kaバンド偏波雲レーダーによって取得される偏波パラメータは、晴天エコーと雲・降水エコーの識別に有用である。

著者

Bjorn STEVENS Claudia ACQUISTAPACE Akio HANSEN Rieke HEINZE Carolin KLINGER Daniel KLOCKE Harald RYBKA Wiebke SCHUBOTZ Julia WINDMILLER Panagiotis ADAMIDIS Ioanna ARKA Vasileios BARLAKAS Joachim BIERCAMP Matthias BRUECK Sebastian BRUNE Stefan A. BUEHLER Ulrike BURKHARDT Guido CIONI Montserrat COSTA-SURÓS Susanne CREWELL Traute CRÜGER Hartwig DENEKE Petra FRIEDERICHS Cintia Carbajal HENKEN CATHY Hohenegger Marek JACOB Fabian JAKUB Norbert KALTHOFF Martin KÖHLER Thirza W. van LAAR Puxi LI Ulrich LÖHNERT Andreas MACKE Nils MADENACH Bernhard MAYER Christine NAM Ann Kristin NAUMANN Karsten PETERS Stefan POLL Johannes QUAAS Niklas RÖBER Nicolas ROCHETIN Leonhard SCHECK Vera SCHEMANN Sabrina SCHNITT Axel SEIFERT Fabian SENF Metodija SHAPKALIJEVSKI Clemens SIMMER Shweta SINGH Odran SOURDEVAL Dela SPICKERMANN Johan STRANDGREN Octave TESSIOT Nikki VERCAUTEREN Jessica VIAL Aiko VOIGT Günter ZÄNGL

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.98, no.2, pp.395-435, 2020 (Released:2020-05-08)

参考文献数

131

被引用文献数

12 84

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More than one hundred days were simulated over very large domains with fine (0.156 km to 2.5 km) grid spacing for realistic conditions to test the hypothesis that storm (kilometer) and large-eddy (hectometer) resolving simulations would provide an improved representation of clouds and precipitation in atmospheric simulations. At scales that resolve convective storms (storm-resolving for short), the vertical velocity variance becomes resolved and a better physical basis is achieved for representing clouds and precipitation. Similarly to past studies we found an improved representation of precipitation at kilometer scales, as compared to models with parameterized convection. The main precipitation features (location, diurnal cycle and spatial propagation) are well captured already at kilometer scales, and refining resolution to hectometer scales does not substantially change the simulations in these respects. It does, however, lead to a reduction in the precipitation on the time-scales considered – most notably over the ocean in the tropics. Changes in the distribution of precipitation, with less frequent extremes are also found in simulations incorporating hectometer scales. Hectometer scales appear to be more important for the representation of clouds, and make it possible to capture many important aspects of the cloud field, from the vertical distribution of cloud cover, to the distribution of cloud sizes, and to the diel (daily) cycle. Qualitative improvements, particularly in the ability to differentiate cumulus from stratiform clouds, are seen when one reduces the grid spacing from kilometer to hectometer scales. At the hectometer scale new challenges arise, but the similarity of observed and simulated scales, and the more direct connection between the circulation and the unconstrained degrees of freedom make these challenges less daunting. This quality, combined with already improved simulation as compared to more parameterized models, underpins our conviction that the use and further development of storm-resolving models offers exciting opportunities for advancing understanding of climate and climate change.

著者

Masuo NAKANO Teruyuki KATO Syugo HAYASHI Sachie KANADA Yoshinori YAMADA Kazuo KURIHARA

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.90A, pp.339-350, 2012 (Released:2012-06-07)

参考文献数

32

被引用文献数

14 34

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A 5-km-mesh nonhydrostatic cloud-system-resolving regional climate model (NHM-5km) has been developed at the Meteorological Research Institute (MRI) of the Japan Meteorological Agency (JMA) by improving upon the JMA operational mesoscale model (MSM). Three major changes have been made to MSM: the Kain-Frisch convective parameterization scheme has been improved to reduce the incidence of false predictions of rainfall areas along coastlines during the warm season, a spectral nudging method has been introduced to avoid phase-gap between the inner model (NHM-5km) and the outer model, and a Simple Biosphere model has been applied for sophisticated representation of land surface processes. This article presents details of the first two of these modifications.A present-day climate simulation is performed using NHM-5km by nesting within the results of a 20-kmmesh atmospheric global climate model (MRI-AGCM3.2S). Taylor’s skill score is used to compare the performances of NHM-5km and MRI-AGCM3.2S in terms of reproducing the spatial pattern of precipitation-based extreme indices over the Japanese Islands. The comparison shows that NHM-5km yields a significant improvement in reproducing the present-day climatology (e.g., the maximum number of consecutive dry days and the simple daily precipitation intensity index), suggesting that NHM-5km is a reliable tool for accurately predicting future changes in extreme weather at a fine spatial resolution.