著者

水野 量

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.70, no.1, pp.115-121, 1992 (Released:2007-10-19)

参考文献数

37

被引用文献数

13 13

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日本列島の150地点における地上気象観測データを用いて、あられ降水の統計的特徴を調べた。1971-1986年の全国150地点の地上気象観測によると、あられ日数は冬期の東北•北陸地方の日本海沿岸で卓越している。また、1982-1986年のデータから、この地域の1月のあられによる降水量は少なくとも月降水量の1/4~1/3であると推定された。以上のあられ降水の統計分析から、日本列島におけるシーディングポテンシャルが議論された。

著者

大泉 伝 斉藤 和雄 Le DUC 伊藤 純至

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.6, pp.1163-1182, 2020 (Released:2020-12-17)

参考文献数

34

被引用文献数

5

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数値気象予測モデルの要素が豪雨のシミュレーションに与える影響を調べるため、広い領域を対象とした超高解像度実験を2014年8月の広島の豪雨事例で行った。本研究はPart 1 の2013年10月伊豆大島での研究に続くものであり同様の実験を行った。これらの研究から豪雨のシミュレーションにおいて広い領域で高解像度モデル(解像度500m以下)を用いる有用性を示した。 広島の事例では降水帯の位置や強度はモデルの解像度に影響を受けることがわかった。解像度2kmの実験では降水帯は再現されたがその位置は北東にずれていた。解像度500mと250mの実験ではこの降水帯の位置ずれは軽減された。最も降水帯の位置と強度をよく再現したのは解像度250mの実験であった。降水帯に対する境界層スキームの影響は小さく、この点は伊豆大島の事例と異なっていた。 本研究では対流コア数のモデル解像度依存性についても調査した。モデルの解像度に対する対流コア数の変化率は解像度500mで小さくなる事がわかった。この結果は、対流コア数は解像度500mより高解像度になると収束する可能性を示す。

著者

NAYAK Sridhara TAKEMI Tetsuya

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.2019-003, (Released:2018-10-29)

被引用文献数

13 27

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Typhoons are considered as one of the most powerful disaster-spawning weather phenomena. Recent studies have revealed that typhoons will be stronger and more powerful in a future warmer climate and be a threat to lives and properties. In this study, we conduct downscaling experiments of an extreme rain-producing typhoon, Typhoon Lionrock (2016) in order to assess the impacts of climate change on resulting hazards by assuming pseudo global warming (PGW) conditions. The downscaled precipitations over the landfall region in the present climate condition agree well with the Radar- Automated Meteorological Data Acquisition System (Radar-AMeDAS) observations. A typhoon track in the future climate similar to that in the present climate is successfully reproduced, with a stronger wind speed (by ~20 knots) and lower central pressure (by ~20 hPa) under the PGW condition. The changes in precipitation amounts associated with the typhoon under PGW condition are analyzed over 7 individual prefectures in the northern part of Japan. The typhoon in the warming climate produces more precipitation over all prefectures. Iwate, Aomori, Akita, Miyagi and Hokkaido are projected to have relatively more precipitation associated with the typhoon in the warming climate. The overall analysis suggests that Typhoon Lionrock under PGW may increase the risk of flooding, damages to infrastructures, and lives staying along the typhoon track.

著者

Sridhara NAYAK 竹見 哲也

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.98, no.6, pp.1147-1162, 2020 (Released:2020-12-12)

参考文献数

59

被引用文献数

12

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極端降水の振る舞いを説明する上でのクラウジウス-クラペイロン(CC)スケーリングの有用性について、現在気候および疑似地球温暖化(PGW)条件で調べた。日本で発生した最近の2つの極端降水イベント、すなわち2017年7月5~6日の九州北部での豪雨および2018年7月5~8日の四国での豪雨を対象として、格子解像度1 kmでの領域気象シミュレーションにより解析した。数値シミュレーションにはWeather Research and Forecasting(WRF)モデルを用い、モデルデータは1時間間隔で格子点毎の値として出力し、解析に用いた。極端に強い降水の発生頻度とその強度は、時間雨量強度で評価すると、2つのイベントともに、PGW条件下で増大する。極端に強い降水(> 50 mm h-1)は、現在気候条件では気温22℃に上がるまでCCスケーリングにしたがい、PGW条件では24℃の気温に上がるまでCCスケーリングにしたがう。降水と気温の関係において、極端降水のピーク強度は、現在気候条件では25℃で約140 mm h-1であり、一方、PGW条件では 27℃で約160 mm h-1となる。極端降水の気温に対する増加率は、現在気候条件では約3% ℃-1であり、PGW条件では約3.5% ℃-1であることが分かった。将来の温暖化気候におけるピーク降水強度の増加と気温に対する降水量の増加率は、気温減率の減少にもかかわらず、大気中の水蒸気および不安定エネルギーが増加することに起因する。著者の知る限りでは、本研究の結果は、事例解析ではあるものの、極端降水に対するCCスケーリングについて定量的に調べた最初の取り組みであると言える。

著者

HARADA Yayoi ENDO Hirokazu TAKEMURA Kazuto

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.2020-062, (Released:2020-08-12)

被引用文献数

5

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To explore large-scale atmospheric factors causing heavy rainfall events that occurred widely in western Japan, a composite analysis of atmospheric fields during the past heavy rainfall events in the region is performed using the Japanese 55-year Reanalysis. During heavy rainfall events, atmospheric fields are characterized by an upper-tropospheric trough over the Korean Peninsula (KP), an upper-tropospheric ridge to the east of Japan, a surface high-pressure system to the southeast of Japan, and southwesterly moisture flux. The composite analysis indicates that a clear wave train due to quasi-stationary Rossby wave-packet propagation (RWPP) along the polar front jet (PFJ) over Siberia tends to occur just before extreme events. Further analysis considering various time-scale variabilities in the atmosphere reveals that surface high-pressure anomalies to the southeast of Japan are dominated by variability with a 25–90-day period, whereas variability with an 8–25-day period dominates lower-pressure anomalies over the East China Sea (ECS) in relation to the development of the upper-tropospheric trough around the KP. We also investigate atmospheric fields during an extreme heavy rainfall event that occurred in early July 2018 (HR18). Atmospheric features during HR18 are generally similar to those of the other heavy rainfall events. However, a remarkable RWPP occurred along the sub-tropical jet (STJ) in late June 2018 and intensified a surface high-pressure system to the southeast of Japan. In addition, a low-pressure system with an 8–25-day period to the south of Japan developed in association with wave breaking induced by the remarkable RWPP along the STJ and propagated northwestward toward the ECS and then to Japan. The simultaneous development of high- and low-pressure systems contributed to the extreme southerly moisture flux into western Japan. HR18 is also characterized by a sharp upper-tropospheric trough over the KP that is dominated by high-frequency variability with a period < 8 days.

著者

SUZUKI Kento IWASAKI Toshiki YAMAZAKI Takeshi

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.2021-002, (Released:2020-10-21)

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Local fronts formed near the coast of the Kanto Plain mainly in a cold season, so-called “coastal fronts”, tend to be forecast on the inland side of their actual positions by the operational mesoscale Numerical Weather Prediction (NWP with a horizontal grid spacing of 5 km) model at Japan Meteorological Agency (JMA). In this study, we confirm a systematic NWP error through statistical validations of coastal fronts that occurred with southerly onshore winds during 2015-2018. Using a nonhydrostatic numerical model (JMA-NHM), we explore the relevant physical mechanisms through sensitivity experiments involving different horizontal resolution, envelope orography, and physics parameterization schemes for three cases with typical errors. The operational NWP model is shown to have a systematic error, with local fronts being consistently shifted to the inland side of their actual positions when the forecast period exceeds 5 hours, regardless of precipitation. The sensitivity experiments suggest that the systematic error associated with coastal fronts may be primarily caused by an underestimation of the mountain barrier surrounding the Kanto Plain in the model. The northwestward distance error of coastal fronts, averaged over the three illustrative cases, can be reduced by 27 % and 37 % by increasing the horizontal resolution from 5 km to 2 km and 1 km, respectively, and can be almost entirely eliminated by using the envelope orography. Moreover, the evaporative cooling of precipitation shifts coastal fronts to the seaward. Most coastal fronts are thought to take the form of cold air trapped on the southeastern slope of the mountains surrounding the Kanto Plain, where the elevation angle of the frontal surface is roughly controlled dynamically. The local front shifts to the seaward when the ridgelines of the mountains become higher, and shifts to the seaward through the reduction of the elevation angle when the trapped air becomes colder.

著者

西井 和晃 田口 文明 中村 尚

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.4, pp.801-820, 2020 (Released:2020-08-26)

参考文献数

32

被引用文献数

8

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2018年7月に日本において2つの極端現象が発生した。本研究では大気大循環モデル(AGCM)のアンサンブル実験にもとづき、これらをもたらした大気大循環偏差に対する海面水温偏差の潜在的影響を評価した。一つ目の極端現象は、7月上旬での西日本を中心とする豪雨であり、日本の南西にあった低気圧性偏差と日本の東にあった高気圧性偏差による顕著な水蒸気輸送がこの主要因である。全球で観測された海面水温を与えたAGCM実験は日本の東の高気圧性偏差を再現できず、このため水蒸気輸送と豪雨を再現できなかった。もう一つの極端現象は7月中下旬に日本で全国的に観測された猛暑であり、これは日本を覆う顕著な高気圧性偏差によるものである。この高気圧性偏差はAGCM実験によって高温偏差とともによく再現された。さらなる実験により、熱帯と中緯度北太平洋のそれぞれの海面水温偏差が、猛暑をもたらした北西太平洋上の大気循環の主要モードを強制していた可能性が示された。また、6月から7月にかけて持続した北西太平洋での亜熱帯ジェットの北偏傾向、及び、北半球中緯度対流圏での高温偏差傾向も、これらの海面水温偏差がそれぞれ強制していた可能性を示した。

著者

KAWANO Tetsuya KAWAMURA Ryuichi

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.2020-033, (Released:2020-05-12)

被引用文献数

21

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A quasi-stationary convective band that persisted for approximately ten hours caused precipitation in the northern part of Kyushu Island, Japan on 5 July 2017. The extreme amount of rainfall produced by this convective band caused a number of landslides and flash floods and resulted in a severe disaster. The Weather and Research and Forecasting (WRF) model was used to perform numerical simulations and to clarify the genesis and maintenance processes of the convective band. A full-physics WRF simulation successfully reproduced the observed features of the convective band and extreme precipitation. It is shown that a quasi-stationary convergence zone in the low level played a crucial role in generating and maintaining the convective band. Trajectory and frontogenesis analyses showed that low-level confluent flows due to the blocking effects of a high pressure system located over the Sea of Japan were responsible for the formation, intensification, and sustenance of the convergence zone. Furthermore, the frontal structure of the convergence zone was intensified due to the land-sea thermal contrast between Kyushu Island and the Tsushima Strait. Two additional experiments, namely a simulation with flattened topography of Kyushu Island and a simulation without considering raindrop evaporation also reproduced the observed band well. These results indicate that topography and a cold pool due to raindrop evaporation played only minor roles in the genesis and maintenance of the convective band.

著者

TAKAMURA Nao WADA Akiyoshi

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.2020-035, (Released:2020-05-26)

被引用文献数

3

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In August 2016, a total of eight typhoons formed in the western North Pacific, and four of which landed on northern and eastern Japan. These typhoons were associated with heavy rainfall and strong winds and caused massive damages in the Japanese archipelago. Moreover, five of the eight typhoons underwent extratropical transition (ET), which was more frequent than an average of 2.1 typhoons per year during August. To clarify the characteristics of the typhoon tracks that caused such unusual landfall and frequent ET in August 2016, we conducted k-means cluster and cyclone phase space (CPS) analyses for typhoons that occurred in August and September. Composite analysis and case study were also conducted to clarify the synoptic environments around the typhoons. To examine the unusual characteristics in August 2016, we compared the results of the analyses for this period with those in August from 2001 to 2015 and those in September 2016. The k-means cluster analysis showed that the direction of the typhoon tracks in August 2016 were more northward than that of the typhoons in August from 2001 to 2015 and those in September 2016. Moreover, the CPS analysis revealed that ET in August 2016 was characterized by a more indistinct structural change from a warm-core structure to a cold-core structure with a shorter duration than ET in August from 2001 to 2015. The synoptic environments around the typhoons in August 2016 were characterized by enhanced undulations of the upper-tropospheric jet stream, increased amplitudes of the mid-tropospheric trough, and relatively warm air around the typhoons in the lower troposphere. These synoptic environments explained the unusual landfall of typhoons with a more northward track and the more frequent ET and more indistinct structural evolution of ET in August 2016.

著者

YAMAJI Moeka TAKAHASHI Hiroshi G. KUBOTA Takuji OKI Riko HAMADA Atsushi TAKAYABU Yukari N.

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.2020-038, (Released:2020-05-27)

被引用文献数

18

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This study investigates the global drop size distribution (DSD) of rainfall and its relationship to large-scale precipitation characteristics using the Dual-frequency Precipitation Radar (DPR) onboard the Global Precipitation Measurement (GPM) Core Observatory. This study focuses on seasonal variations in the dominant precipitation systems regarding variations in DSD. A mass-weighted mean diameter (Dm), which is estimated based on the dual-frequency information derived from the GPM/DPR, is statistically analyzed as a typical parameter of the DSD. Values of the annual mean Dm, in general, are larger over land than over the oceans, and the relationship between Dm and precipitation rate (R) is not a simple one-to-one relationship. Furthermore, Dm exhibits statistically significant seasonal variations, specifically over the northwest Pacific Ocean, whereas R shows insignificant variations, indicating the variations in R cannot explain the distinct seasonal changes in Dm. Focusing on the seasonal variation in Dm over the northwest Pacific Ocean, the results indicate that the variation in Dm is related to the seasonal change in the dominant precipitation systems. In the summer over the northwest Pacific Ocean, Dm is related to the organized precipitation systems associated with the Baiu front over the mid-latitudes and tropical disturbances over the subtropical region, with relatively higher precipitation top heights, composed of both stratiform and convective precipitations. Contrary to the summer, larger Dm over the mid-latitudes in winter is related to extratropical frontal systems with ice particles in the upper layers, which consists of more stratiform precipitation in the storm track region. The smaller Dm over the subtropical northwest Pacific Ocean in winter is associated with shallow convective precipitation systems with trade-wind cumulus clouds and cumulus congestus under the subtropical high.

著者

SHIBATA Kiyotaka LEHMANN Ralph

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.2020-032, (Released:2020-04-02)

被引用文献数

2

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Ozone loss pathways and their rates in the ozone quasi-biennial oscillation (QBO) simulated by a chemistry-climate model of the Meteorological Research Institute of Japan are evaluated by using an objective pathway analysis program (PAP). The analyzed chemical system contains catalytic cycles due to NOx, HOx, ClOx, Ox, and BrOx. PAP quantified the rates of all significant catalytic ozone loss cycles, and evaluated the partitioning among these cycles. The QBO amplitude of the sum of all cycles amounts to about 4 and 14 % of the annual mean of the total ozone loss rate at 10 and 20 hPa, respectively. The contribution of catalytic cycles to the QBO of the ozone loss rate is found to be as follows: NOx cycles contribute the largest fraction (50-85 %) of the QBO amplitude of the total ozone loss rate; HOx cycles are the second-largest (20-30 %) below 30 hPa and the third-largest (about 10 %) above 20 hPa; Ox cycles rank third (5-20 %) below 30 hPa and second (about 20 %) above 20 hPa; ClOx cycles rank fourth (5-10 %); and BrOx cycles are almost negligible. The relative contribution of the NOx and Ox cycles to the QBO amplitude of ozone loss differs by up to 10 and 20 %, respectively, from their contribution to the annual-mean ozone loss rate. The ozone QBO at 20 hPa is mainly driven by ozone transport, which then affects the ozone loss rate. In contrast, the ozone QBO at 10 hPa is driven chemically mainly by NOx and the temperature dependence of [O]/[O3], which results from the temperature dependence of the reaction O + O2 + M → O3 + M. In addition, the ozone QBO at 10 hPa is influenced by the overhead ozone column, which affects [O]/[O3] (through ozone photolysis) and the ozone production rate (through oxygen photolysis).

著者

GENG Biao 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.2020-031, (Released:2020-03-17)

被引用文献数

5

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In this study, an algorithm is developed to detect the spurious differential phase ΦDP and specific differential phase KDP in the rain for application following the removal of gate-to-gate ΦDP fluctuations. The algorithm is a threshold filter that is designed based on the empirical relationship between the KDP and radar reflectivity factor at horizontal polarization ZH for raindrops. The construction and validation of the algorithm was conducted using the data observed by the C-band polarimetric radar on board the research vessel Mirai near Sumatra from 23 November to 17 December 2015, when a pilot field campaign of the Years of the Maritime Continent (YMC) project was conducted. Perturbations exist in the ΦDP and associated spurious values of KDP on a 10-km scale in the range direction, which are mainly induced by second-trip echoes and nonuniform beam filling. These perturbed ΦDP values and the positively and negatively biased KDP values can be efficiently detected by this new algorithm. The standard deviation of the KDP in areas with relatively low ZH is also significantly reduced by applying the algorithm. Simultaneously, the rain rate estimation from the filtered KDP has been greatly improved. The results indicate that the algorithm developed in this study can efficiently manage the quality of the data observed not only in the open ocean but also in coastal areas of the Maritime Continent.

著者

DUC Le SAITO Kazuo HOTTA Daisuke

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.2020-022, (Released:2020-01-16)

被引用文献数

1

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In the ensemble transform Kalman filter (ETKF), an ensemble transform matrix (ETM) is a matrix that maps background perturbations to analysis perturbations. All valid ETMs are shown to be the square roots of the analysis error covariance in ensemble space that preserve the analysis ensemble mean. ETKF chooses the positive symmetric square root Ts as its ETM, which is justified by the fact that Ts is the closest matrix to the identity I in the sense of the Frobenius norm. Besides this minimum norm property, Ts are observed to have the diagonally predominant property (DPP), i.e. the diagonal terms are at least an order of magnitude larger than the off-diagonal terms. To explain the DPP, firstly the minimum norm property has been proved. Although ETKF relies on this property to choose its ETM, this property has never been proved in the data assimilation literature. The extension of this proof to the scalar multiple of I reveals that Ts is a sum of a diagonal matrix D and a full matrix P whose Frobenius norms are proportional, respectively, to the mean and the standard deviation of the spectrum of Ts. In general cases, these norms are not much different but the fact that the number of non-zero elements of P is the square of ensemble size while that of D is the ensemble size causes the large difference in the orders of elements of P and D. However, the DPP is only an empirical fact and not an inherently mathematical property of Ts. There exist certain spectra of Ts that break the DPP but such spectra are rarely observed in practice since their occurrences require an unrealistic situation where background errors are larger than observation errors by at least two orders of magnitude in all modes in observation space.

著者

LI Zhenghui LUO Yali DU Yu CHAN Johnny C. 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.2020-012, (Released:2019-11-30)

被引用文献数

36

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Climatological characteristics of pre-summer (April-to-June) rainfall over Southern China (SC) and associated synoptic conditions are examined using 1980-2017 hourly rainfall observations and reanalysis data. The rainfall amount, frequency, and intensity show pronounced regional variations and substantial changes between pre- and post-monsoon-onset periods. Owing to more favorable thermodynamic conditions after monsoon onset over South China Sea (SCS), rainfall intensifies generally over entire SC irrespective of the rainfall-event durations. Increased magnitudes of rainfall amount in longer-duration (> 6 h) events are found over a designated west-inland region (west of 111°E), which are partially attributed to enhanced dynamic instability. In addition, rainfall events occur more frequently over the west-inland region, as well as coastal regions west side of 118°E, but less over a designated east-inland region. The inland-region rainfall is closely linked to dynamic lifting driven by subtropical synoptic systems (low pressure and an associated front or shearline). The westward extension of the western North Pacific high and the eastward extension/movement of the front or shearline, interacting with the intra-period intensification of the southwesterly monsoonal flows, play important roles in providing high-θe (equivalent potential temperature) air to the west- and east-inland regions, respectively. The warm-sector, coastal rainfall is closely related to the deceleration of the southerly boundary layer (BL) jet (BLJ) over the northern SCS and associated convergence of BL high-θe air near the coast. Meanwhile the southwesterly synoptic-system-related low-level jet in the lower-to-middle troposphere to the south of the inland cold front can contribute to the coastal rainfall occurrence by providing divergence above the BL convergence near the coast. The BLJ often simultaneously strengthens with the lower-troposphere horizontal winds, suggesting a close association between the BLJ and the synoptic systems. The quantitative statistics provided in this study complement previous case studies or qualitative results and thus advance understanding about pre-summer rainfall over SC.

著者

LUO Yali XIA Rudi CHAN Johnny C. 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.2020-002, (Released:2019-10-16)

被引用文献数

44

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Pre-summer rainy season (April to mid-June) over South China (SC) is characterized by high intensity and frequent occurrence of heavy rainfall in the East Asian monsoon region. This review describes recent progress in the research related to such a phenomenon. The mechanisms responsible for pre-summer rainfall consist of multi-scale processes. Sea surface temperatures over tropical Pacific and Indian Ocean are shown to have a great influence on the interannual variations of pre-summer rainfall over SC. Synoptic disturbances associated with regional extreme rainfall over SC are mainly related to cyclone- and trough-type anomalies. Formation and intensification of such anomalies can be contributed by surface sensible heating and mechanical forcing from the Tibetan Plateau. On a sub-daily scale, double rain belts often co-exist over SC. The northern rain belt is closely linked to dynamic lifting by a subtropical low pressure and its associated front/shear line, while the westward extension of the western North Pacific high and the intensification of the southwesterly monsoonal flows play important roles in providing high-equivalent potential temperature air to the west- and east-inland regions, respectively. The southern rain belt with a smaller horizontal span is in the warm sector over either inland or coastal SC. The warm-sector rainfall over inland SC results from surface heating, local topographic lifting, and urban heat island effect interacting with the sea breeze. The warm-sector rainfall over coastal SC is closely associated with double low-level jets, land-sea-breeze fronts, and coastal mountains. A close relationship is found between convectively-generated quasi-stationary mesoscale outflow boundaries and continuous convective initiation in extreme rainfall events. Active warm-rain microphysical processes can play an important role in some extreme rainfall events, although the relative contributions by warm-rain, riming and ice-phase microphysical processes remain unclear. Moreover, to improve the rainfall prediction, efforts have been made in convection-permitting modeling studies.

著者

WANG Jingyu HOUZE Jr. Robert. A. FAN Jiwen BRODZIK Stacy. R. FENG Zhe HARDIN Joseph C.

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.2019-058, (Released:2019-08-06)

被引用文献数

17

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The Global Precipitation Measurement (GPM) core observatory satellite launched in 2014 features more extended latitudinal coverage (65°S-65°N) than its predecessor Tropical Rainfall Measuring Mission (TRMM, 35°S-35°N). The Ku-band radar onboard of the GPM is known to be capable of characterizing the 3D structure of deep convection globally. In this study, GPM’s capability for detecting mesoscale convective systems (MCSs) is evaluated. Extreme convective echoes seen by GPM are compared against an MCS database that tracks convective entities over the contiguous US. The tracking is based on geostationary satellite and ground-based Next Generation Radar (NEXRAD) network data obtained during the 2014-2016 warm seasons. Results show that more than 70 % of the GPM-detected Deep-Wide Convective Core (DWC) and Wide Convective Core (WCC) objects are part of NEXRAD identified MCSs, indicating that GPM-classified DWCs and WCCs correlate well with typical MCSs containing large convective features. By applying this method to the rest of the world, a global view of MCS distribution is obtained. This work reveals GPM’s potential in MCS detection at the global scale, particularly over remote regions without dense observation network.

著者

Kazuyoshi OOUCHI Jun YOSHIMURA Hiromasa YOSHIMURA Ryo MIZUTA Shoji KUSUNOKI Akira NODA

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.84, no.2, pp.259-276, 2006 (Released:2006-05-19)

参考文献数

41

被引用文献数

293 443

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Possible changes in the tropical cyclones in a future, greenhouse-warmed climate are investigated using a 20 km-mesh, high-resolution, global atmospheric model of MRI/JMA, with the analyses focused on the evaluation of the frequency and wind intensity. Two types of 10-year climate experiments are conducted. One is a present-day climate experiment, and the other is a greenhouse-warmed climate experiment, with a forcing of higher sea surface temperature and increased greenhouse-gas concentration. A comparison of the experiments suggests that the tropical cyclone frequency in the warm-climate experiment is globally reduced by about 30% (but increased in the North Atlantic) compared to the present-day-climate experiment. Furthermore, the number of intense tropical cyclones increases. The maximum surface wind speed for the most intense tropical cyclone generally increases under the greenhouse-warmed condition (by 7.3 m s−1 in the Northern Hemisphere and by 3.3 m s−1 in the Southern Hemisphere). On average, these findings suggest the possibility of higher risks of more devastating tropical cyclones across the globe in a future greenhouse-warmed climate.

著者

TSUYUKI Tadashi

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.2019-067, (Released:2019-09-24)

被引用文献数

2

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A multi-scale data assimilation method for the ensemble Kalman filter (EnKF) is proposed for atmospheric models in cases with insufficient observations of fast variables. This method is based on the conservation and invertibility of potential vorticity (PV). The dynamical state variables in the free atmosphere of forecast ensemble members are decomposed into balanced and unbalanced parts by applying PV inversion to the PV anomalies computed from spatially smoothed state variables. The mass variables of the two parts are adjusted to remove additional sampling errors introduced by this decomposition. The forecast error covariances between those parts are ignored in the Kalman gain to suppress spurious error correlations. This approximation makes it possible to apply different covariance localizations to each part. The Kalman gain thus obtained is used to assimilate observations. The performance of the proposed method is demonstrated with a shallow water model through twin experiments in a perfect model scenario. Results using the same localization radius for the two parts show that the proposed EnKF is superior in the accuracy of the analysis to a conventional EnKF unless the ensemble size is sufficiently large. It is found that the adjustment of mass variables is necessary to outperform the conventional EnKF. The benefits of the PV inversion using the Bolin-Charney balance over the quasi-geostrophic inversion are marginal in the experiments.

著者

GAO Meiling CHEN Fei SHEN Huanfeng BARLAGE Michael LI Huifang TAN Zhenyu ZHANG Liangpei

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.2019-060, (Released:2019-08-18)

被引用文献数

10

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Summer heat waves pose a great threat to public health in China. This paper took Wuhan (one of the four hottest furnaces cities in China) as an example to explore several strategies for mitigating the surface urban heat island (UHI) measured by the land surface temperature, including the use of green roofs, cool roofs, bright pavements, and alternations in urban building patterns. The offline urbanized High-Resolution Land Data Assimilation System (u-HRLDAS) was employed to conduct 1-km resolution numerical simulations, which also accounts for the effects of abundant lakes in Wuhan on UHI evolution with a dynamic lake model. The diurnal cycle and spatial distribution of simulated UHI were analyzed under different mitigation strategies. Results show that considering lake effects reduces the daytime (nighttime) UHI intensity by about 1.0 K (0.5 K). Employing green roofs and cool roofs are more effective in mitigating daytime UHI than the use of bright pavements. The maximum UHI reduction is about 2.1 K at 13:00 local time by replacing 80% of conventional roofs with green roofs. The UHI mitigation efficiency increases with larger fractions of green roofs, and increased albedo of roofs and roads. In contrast to the green roofs, cool roofs and bright pavements which are ineffective in nighttime, changing urban building pattern to mitigate the UHI is effective throughout the day. “Height-driven building structure changing” (raising the building height, and meanwhile changing the fraction of impervious surface in each grid to keep the total building volume intact) can reduce the surface UHI intensity by 0.4-0.9 K, and “density-driven building structure changing” (distributing building density uniformly and the building height are modified to make the total building volume unchanged) reduces UHI by 1.2-2.6 K. These results showed new insights in mitigating the urban heat islands for a mega city like Wuhan and provides a practical guideline for policymakers to offer a more habitable city.

著者

Liangtao XU Yijun ZHANG Fei WANG Xi CAO

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.97, no.6, pp.1119-1135, 2019 (Released:2019-12-05)

参考文献数

56

被引用文献数

3

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The charge structure evolution of a mesoscale convective system with an anomalous or inverted charge structure, observed in the Severe Thunderstorm Electrification and Precipitation Study, a field project on the Colorado–Kansas border in summer 2000, is simulated using the Weather Research and Forecasting (WRF) model coupled with electrification and discharge processes. Two noninductive electrification schemes are used, based on the liquid water content (LWC) and the graupel rime accretion rate (RAR). The simulation with the LWC-based electrification scheme cannot reproduce the inverted charge structure with a positive charge region sandwiched by two negative charge layers, while the RAR-based electrification scheme produces the evolution process of a normal–inverted–normal charge structure in the convective region, which is consistent with the observations. In the low RAR (< 2 g m−2 s−1) region, graupel is mainly negatively charged when it bounces off ice crystals, while the ice crystals take up positive charge. However, in the zone where the inverted charge structure forms, a strong updraft (> 16 m s−1), high LWC (> 2 g m−3), and high RAR (> 4.5 g m−2 s−1) region appears above the height of the −20°C layer, so that a positive graupel charging region is generated above the −20°C layer of the convective region, resulting in a negative dipole charge structure with negatively charged ice crystals above the positively charged graupel. The negative dipole is superposed on the positive dipole (positive above negative) charge structure at the lower position to form an inverted tripole charge structure.