著者

Minda LE V. CHANDRASEKAR

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.49-65, 2021 (Released:2021-02-28)

参考文献数

18

被引用文献数

10

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Precipitation consists of many types of hydrometeors, such as raindrops, ice crystals, graupel, and hail. Due to their impacts, graupel and hail (GH) have received particular attention in the literature. Global Precipitation Measurement (GPM) dual-frequency radar (DPR) has proved to be a very reliable system for global precipitation retrievals. This paper aims to develop a GH identification algorithm for GPM DPR. This algorithm is constructed using a precipitation type index (PTI) defined for DPR. The PTI is effective in separating hydrometeor types and is calculated using measurements of reflectivity, dual-frequency ratio, and storm top height data. The output of the algorithm is a Boolean product representing the existence of graupel or hail along with the vertical profile for each Ku- and Ka-band matched footprint. Cross validation is performed with the Weather Service Radar (WSR-88D) network over continental United States as well as during the Remote sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) experiment. Evaluation of the GH identification algorithm is performed on a global basis, which illustrates promising comparisons with the global lightning and hail precipitation maps generated using radar and radiometer.

著者

鈴木 健斗 岩崎 俊樹 山崎 剛

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.27-47, 2021 (Released:2021-02-28)

参考文献数

30

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気象庁のメソスケール数値予報モデル(5kmメッシュ)は、寒候期を主に関東平野の沿岸付近に形成される局地前線(いわゆる沿岸前線)を実況より内陸側に予報する傾向がある。本研究では2015-2018年に海からの南寄りの風を伴って発生した沿岸前線に対する統計解析から前線位置の系統的な数値予報誤差を確かめ、その要因を調べるため、典型的な予報誤差を伴った3事例に対し非静力学モデル(JMA-NHM)による数値感度実験(水平解像度、地形、物理スキーム)を行った。その結果、気象庁メソスケールモデルは予報時間が5時間程度より経過すると降水の有無にかかわらず前線位置を一貫して内陸側へシフトさせる系統的誤差が発生することが明らかになった。数値感度実験からは、沿岸前線の系統的予報誤差は主に数値モデルの山岳が実際より低いことに起因することが分かった。解像度を2キロ、1キロにすることで沿岸前線の北西方向への誤差距離は3事例を平均して27%、37%減少した。また、モデル地形にEnvelope Orographyを導入すると、誤差はほぼ解消した。さらに降水の蒸発冷却は前線を海側にシフトさせることも確認された。 沿岸前線の多くは関東平野北西側の山岳の南東斜面において捕捉された寒気により形成されるものと考える。特に、前線の傾斜角は力学的バランスでおよそ決まる。山の稜線が高くなれば前線は海側にシフトし、冷却により捕捉された寒気が強くなれば、傾斜角が小さくなり海側にシフトする。

著者

青木 俊輔 重 尚一

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.5-25, 2021 (Released:2021-02-28)

参考文献数

48

被引用文献数

5

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本研究は、空間変動の大きい中高緯度大陸西岸の降水に焦点を当て、全球降水観測計画(GPM)主衛星搭載二周波降水レーダ(DPR)Ku帯降水レーダ(KuPR)およびCloudSat衛星搭載雲レーダ(CPR)を用いてアラスカ南岸の気候学的な降水分布や降水メカニズムについて調査した。高緯度では地表へ落下する降水粒子の相を判別することが降水を評価するうえで不可欠である。海岸線からの距離によって衛星降水プロダクトを分類することで、海岸線を挟んだ海側と陸側で降水特性が大きく異なっていることを示した。沿岸の海上では、地形効果で強化された乱層雲からのCPR反射強度7dBZ以上の比較的強い降水が頻繁にとらえられており、KuPRでもとらえられている。一方、海岸山脈上では、CPR反射強度11dBZ以下の弱~中程度の降雪が頻繁に発生していることが、CPRでとらえられているがKuPRではほとんどとらえられていない。この雪は主に海岸域より移流してきた乱層雲や地形効果を受けて強まった浅い対流雲によってもたらされている。夏季を除いて顕著な降水の日周期変動はなく、さらに夏季の日周期変動の振幅も総降水量と比べると特に海上で小さく、総観規模の水蒸気輸送が年間を通して多くの降水をもたらしていることを示唆している。事例解析と季節解析により、アラスカ湾から到来する温帯低気圧に伴う前線システム及び水蒸気の流れが、海岸沿いで地形によりブロックされて停滞し、沿岸に長く持続した降水をもたらしていることが示された。本研究の結果は、降雨・降雪の両方が発生する地域の降水気候値を評価するには、これら2つのレーダの相補的な情報を用いることが重要であることを示している。

著者

孫野 長治 中村 勉

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.43, no.3, pp.139-147, 1965 (Released:2008-05-27)

参考文献数

7

被引用文献数

90 110

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1958年から62年にかけて札幌で落下中の雪片の大きさ,質量及び落下速度の同時観測が行なわれた。その結果,雪片の落下速度はその大きさと密度に左右されるが質量だけの函数として表わすことが不可能であり,もしーつの函数で表わすとすれば,次のように雪片の密度の函数として考えた方がよいようである。u=300(σ-ρ)1/4 C.G.S.ここでuは落下速度,ρは雪片の密度,ρは空気の密度を示す。この理論式は広い範囲にわたつて観測値をよく示す。

著者

津田 敏隆 深尾 昌一郎 山本 衛 中村 卓司 山中 大学 足立 樹泰 橋口 浩之 藤岡 直人 堤 雅基 加藤 進 Harijono Sri Woro B. Sribimawati Tien Sitorus Baginda P. Yahya Rino B. Karmini Mimin Renggono Findy Parapat Bona L. Djojonegoro Wardiman Mardio Pramono Adikusumah Nurzaman Endi Hariadi Tatang Wiryosumarto Harsono

出版者

社団法人日本気象学会

雑誌

Journal of the Meteorological Society of Japan. Ser. II (ISSN:00261165)

巻号頁・発行日

vol.73, no.2, pp.393-406, 1995-06-15

被引用文献数

20

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日本とインドネシアの協力により1992年11月にジャカルタ近郊に赤道大気の観測所(6.4°S、106.7゜E)が開設され、流星レーダー(MWR)と境界層レーダー(BLR)が設置された。MWRにより高度75-100kmにおける水平風と温度変動が1時間と4kmの分解能で測定された。一方、BLRを用いて高度0.3-5kmの大気層の風速三成分を毎分100mの分解能で観測した。さらにBLRに音響発信器を併用したRASS(電波音響探査システム)技術により温度変動の微細構造をも測定した。これらのレーダーの運用は1992年11月のTOGA/COAREの強化観測期間に開始され、その後2年以上にわたって連続観測が続けられている。また、レーダー観測所から約100km東に位置するバンドン市のLAPAN(国立航空宇宙局、6.9°S、107.6゜E)において、1992年11月から1993年4月にかけて、ラジオゾンデを一日に4回放球し、高度約35kmまでの風速・温度変動を150mの高度分解能で測定した。その後、1993年10月から一日一回の定時観測(0GMT)も継続されている。この論文では観測所における研究活動の概要を紹介するとともに、観測結果の初期的な解析で分かった、TOGA/COARE期間中の熱帯惑星境界層の構造、対流圏内の積雲対流、ならびに赤道域中層大気における各種の大気波動の振る舞いについて速報する。

著者

TAKEMURA Kazuto MUKOUGAWA Hitoshi

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.2021-023, (Released:2021-01-13)

被引用文献数

1

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This study assesses predictability of an enhanced monsoon trough south of Japan in late August 2016, which is accompanied by Rossby wave propagation over Eurasia and a consequent anticyclonic Rossby wave breaking east of Japan, with a relaxation technique using an atmospheric general circulation model. Three types of the relaxation experiments are conducted, with nudging the model forecast in the upper troposphere toward reanalysis, for regions of the Rossby wave breaking east of Japan, the Rossby wave propagation over Eurasia, and both the regions from Eurasia to the east of Japan. All types of the relaxation experiments show improved reproducibility of the enhanced monsoon trough, which the operational one-month ensemble prediction in Japan Meteorological Agency failed to predict. Compared to a result of control experiment, the relaxation experiments show the more amplified Rossby wave propagation over Eurasia and Rossby wave breaking east of Japan, as seen in the reanalysis. The upper-level wave amplification contributes to the improved reproducibility of the enhanced monsoon trough, through that of southwestward intrusion of upper-level high potential vorticity airmass toward the southeast of Japan. The results of relaxation experiments indicate primary and secondary contributions from corrected forecast errors of the Rossby wave breaking east of Japan and the Rossby wave propagation over Eurasia to the predictability of the monsoon trough, respectively. Their relative contributions to the enhanced monsoon trough are consistent with a result of ensemble-based simple sensitivity analysis shown in a related previous study.

著者

寺田 寅彦

出版者

公益社団法人 日本気象学会

雑誌

氣象集誌. 第1輯 (ISSN:00261165)

巻号頁・発行日

vol.41, no.10, pp.452-457, 1922-10-10 (Released:2009-02-05)

著者

ZOU Shan ABUDUWAILI Jilili DING Jianli DUAN Weili DE MAEYER Philippe VAN DE VOORDE Tim

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.2020-070, (Released:2020-10-05)

被引用文献数

6

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It is speculated that floods in many areas of the world have become more severe with global warming. This study describes the 2017 spring floods in Kazakhstan, which, with about six people dead or missing, prompted the government to call for more than 7,000 people to leave their homes. Then, based on the Climatic Research Unit (CRU), the NCEP/NCAR Reanalysis 1, and the Coupled Model Intercomparison Project 5 (CMIP5) simulations, the seasonal trends of temperature were calculated using the linear least-squares regression and the Mann–Kendall trend test. The correlation between the surface air temperature and atmospheric circulation was explored, and the attributable risk of the 2017 spring floods was evaluated using the conventional fraction of the attributable risk (FAR) method. The results indicate that the north plains of Kazakhstan had a higher (March–April) mean temperature anomaly compared to the south plains, up to 3°C, relative to the 1901-2017 average temperature. This was the primary cause of flooding in Kazakhstan. March and April were the other months with a higher increasing trend in temperature from 1901 to 2017 compared with other months. In addition, a positive anomaly of the geopotential height and air temperature for the March–April 2017 period (based on the reference period 1961-1990) was the reason for a warmer abnormal temperature in the northwest region of Kazakhstan. Finally, the FAR value was approximately equal to 1, which supported the claim of a strong anthropogenic influence on the risk of the 2017 March–April floods in Kazakhstan. The results presented provide essential information for a comprehensive understanding of the 2017 spring floods in Kazakhstan and will help government officials identify flooding situations and mitigate damage in future.

著者

Qijun HUANG Xuyang GE Melinda PENG

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.1335-1352, 2020 (Released:2020-12-18)

参考文献数

46

被引用文献数

1

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In this study, the Advanced Weather Research and Forecasting (WRF-ARW) model is used to investigate possible influences of a predominantly upper-level easterly wave (EW) on Typhoon Megi's (2010) sharp northward turn on 20 October, 2010 after passing over the Philippines. Observational analysis indicates that an upper-level EW with a cold-cored structure was located to the east of Megi. This EW moved westward along with Megi and modified the large-scale environmental flow around the typhoon, thus affecting its movement. In a control experiment, the sharp northward turn that was observed was captured well by a simulation. The retreat of the subtropical high contributed directly to the poleward steering flow for Megi. Sensitivity experiments were conducted by filtering out the synoptic-scale (3–8-day) signals associated with EWs. In the absence of the upper-level EW, the simulation showed that Megi would not have made a sharp northward turn. Two mechanisms are proposed regarding the impact of the easterly wave on Megi. First, an upper-level EW may have impacted the environmental flows, allowing Megi to move at a slower westward speed so that it entered the eastern semicircle of the nearby monsoon gyre where an enhanced southerly steering flow then led to the typhoon making a sharp northward turn. Second, the diabatic heating and associated cyclonic vorticity induced by the middle-level (around 400 hPa) convergence may have eroded the western flank of the subtropical high in the western North Pacific, causing an eastward retreat of the high-pressure system. The present modeling approach provides a reasonable assessment of the contribution of upper-level wave disturbances to sudden changes in tropical cyclones.

著者

Nathan P. ARNOLD William M. PUTMAN Saulo R. FREITAS

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.1279-1304, 2020 (Released:2020-12-17)

参考文献数

60

被引用文献数

14

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A series of 40-day non-hydrostatic global simulations was run with the NASA Goddard Earth Observing System (GEOS) model with horizontal grid spacing ranging from 50 km to 3.5 km. Here we evaluate the diurnal cycle of precipitation and organized convection as a function of resolution. For validation we use the TRMM 3B42 and IMERG precipitation products and 4 km merged infrared brightness temperature, focusing on three regions: the contiguous United States (CONUS), the Maritime Continent, and Amazonia. We find that higher resolution has mixed impacts on the diurnal phase. Regions dominated by non-local propagating convection show the greatest improvement, with better representation of organized convective systems. Precipitation in regions dominated by local thermodynamic forcing tends to peak too early at high resolution. Diurnal amplitudes in all regions develop unrealistic small-scale variability at high resolution, while amplitudes tend to be underestimated at low resolution. The GEOS model uses the Grell-Freitas scale-aware convection scheme, which smoothly reduces parameterized deep convection with increasing resolution. We find that some parameterized convection is beneficial for the diurnal amplitude and phase even with a 3.5 km model grid, but only when throttled with the scale-aware approach. An additional 3.5 km experiment employing the GFDL microphysics scheme and higher vertical resolution shows further improvement in propagating convection, but an earlier rainfall peak in locally forced regions.

著者

TAMURA Kenta SATO Tomonori

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.2020-065, (Released:2020-08-28)

被引用文献数

2

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Polar mesocyclones (PMCs) occur frequently over the northern Sea of Japan. In this study, topographic effects on PMC genesis in this region were examined using long-term numerical simulations extending over 36 winter seasons. Sensitivity experiments showed that PMC genesis decreases in the part of the northern Sea of Japan when the mountain region at the eastern end of the Eurasian continent is removed. For example, the generation of PMCs over offshore west of Hokkaido decreases significantly when the mountain range is removed, whereas the generation of PMCs over the Strait of Tartary remains unchanged. According to composite analysis, this result can be attributed to the different responses of subregional oceanic surface wind to the removal of the mountains. In the experiment without mountains, cold air outbreaks from the continent blow directly over the Sea of Japan causing strong westerly winds over the offshore west of Hokkaido. Consequently, PMCs tend to make landfall earlier and before reaching maturity. The uniformly distributed westerly wind also has negative impact on PMC genesis because of weakened horizontal wind shear and meridional temperature gradient. In contrast, the low-level wind over the Strait of Tartary prior to PMC genesis is unaffected by the mountains and thus topographic effects are not required for PMC genesis in this region. These results indicate that the responses of PMCs to topographic forcing has a regional variability.

著者

ZHOU Xingyang WU Liguang LIU Qingyuan ZHENG Yan

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.2020-063, (Released:2020-08-28)

被引用文献数

3

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Previous studies suggested that the entrainment of the low-level, high-entropy eye air can provide additional energy for tropical cyclone (TC) intensification, but the previous trajectory analysis only indicated that considerable air parcels below the eye inversion can be entrained into the eyewall. In this study, the one-minute output data from a semi-idealized experiment are used to quantitatively evaluate the relative importance of the entrainment of the high-entropy eye air by enhancing the eyewall convection. It is confirmed that considerable amount of high-entropy eye air below the eye inversion can be entrained into the eyewall. The entrainment occurs favorably on the quandrants of enhanced eyewall convection and is enhanced in the presence of small-scale disturbances in the inner edge of the eyewall. However, the eyewall air parcels below 3 km experience a fast cycling. There are 84.4 % and 7.7 % eyewall air from the low-level boundary inflow and the middle-level dry environment, respectively. The low-level, high-entropy eye air only accounts for 1.7 % of the eyewall air, while 6.2 % eyewall air remains in the eyewall below 3 km during the 90-minute period. The eye air from the low-level, high-entropy reservoir accounts for 5.8 % of the equivalent potential temperature change below 3 km and 4.5 % of the total mass transport at 3 km in the TC eyewall. This study suggests that the low-level, high-entropy air from the eye has little direct influence on TC intensity through enhancing the eyewall convection by providing relatively small mass and thermodynamic contributions.

著者

Liang LIAO Robert MENEGHINI Ali TOKAY Hyokyung KIM

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.1129-1146, 2020 (Released:2020-12-12)

参考文献数

35

被引用文献数

9

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Dual-frequency Ku/Ka-band radar retrievals of snow parameters such as liquid-equivalent snowfall rate (R) and mass-weighted diameter (Dm) have two principal errors, namely, the differences between the assumed particle size distribution (PSD) model from the actual PSD and inadequacies in characterizing the single-scattering properties of snowflakes. Regarding the first issue, this study, based on radar simulations from a large amount of observed PSD data, shows that there exist relatively high correlations between the estimated snow parameters and their true values derived directly from the measured PSD. For PSD data with R greater than 0.1 mm h−1, a gamma PSD model with a fixed shape factor (µ) equal to 0 (or exponential distribution) provides the best estimates of R and Dm. This is despite negative biases of up to −15 % in R and underestimates and overestimates in Dm for small and large Dm, respectively. The µ = 0 assumption, however, produces relatively poor estimates of normalized intercepts of a gamma PSD (Nw), whereas the best estimates are obtained when µ is considered either 3 or 6. However, the use of an inappropriate scattering table increases the errors in snow retrieval. Simple evaluations are made for cases where the scattering databases used for the algorithm input differ from that used for retrieval. The mismatched scattering databases alone could cause at least 30–50 % changes in the estimates of snow water content (SWC) and R and could affect the retrievals of Dm and Nw and their dependence on µ.

著者

KRZYŚCIN Janusz

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.2020-055, (Released:2020-08-25)

被引用文献数

4

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A method is proposed to gain insight into ozone recovery over Antarctica. The following metrics relating to the ozone hole are considered: minimum total column ozone (TCO3) within the hole, TCO3 at the South Pole, area of the ozone hole, mass of ozone loss within the hole, and density of loss per unit area. The daily metric values, based on the Royal Netherlands Meteorological Institute archives of the ozone hole, are averaged for each year over the period 1979-2019 for the following intervals: 1 Sep.–30 Sep., 15 Sep.–15 Oct., 1 Oct.–31 Oct., 15 Oct.–15 Nov., and 1 Nov.–30 Nov. The following indicators of the ozone hole recovery are examined: the metric recovery rate by 2019 (i.e., the change between its extreme and its 2019 level divided by the change between the extreme year and 1980) and the year of metric recovery. The recovery year is derived by forward-in-time extrapolation of the metric linear trend found for the period 2000-2019. The uncertainties in these indicators are obtained using a bootstrap approach analyzing statistics of the synthetic time series of the metrics. A comparison of the proposed ozone hole healing indicators with the indicators inferred from the equivalent effective stratospheric chlorine (EESC) loading over Antarctica (22.1 % and year 2076) shows to what extent recovery of the ozone layer is associated with EESC effects. For the mass and density of ozone loss in the periods 1 Sep.–30 Sep. and 15 Sep.–15 Oct., the metric recovery rate by 2019 is ∼ 2 times larger and the recovery year is at least 20-30 years earlier than the corresponding indicators of the EESC changes. Therefore, the ozone hole is recovering faster during these periods than expected based on the stratospheric halogen loading alone.

著者

WANG Ke CHEN Guanghua BI Xinxin SHI Donglei CHEN Kexin

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.2020-056, (Released:2020-07-13)

被引用文献数

2

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The tropical oceans spawn hundreds of tropical disturbances during the tropical cyclone (TC) peak season every year, but only a small fraction eventually develop into TCs. In this study, using observations from Global Precipitation Measurement (GPM) satellite, tropical disturbances over the western North Pacific (WNP) from July to October during 2014-2016 are categorized into developing and nondeveloping groups to investigate the differences between satellite-retrieved convective and stratiform precipitation properties in both the inner- (within 200 km of the disturbance center) and outer-core (within 200-400 km of the disturbance center) regions. The developing disturbances experience a remarkably more oscillatory process in the inner-core region than in the outer-core region. The large areal coverage of strong rainfall in the inner-core region of the disturbance breaks into scattered remnants, and then reorganizes and strengthens near the disturbance center again. In contrast, the precipitation characteristics in the nondeveloping group evolve more smoothly. It can be summarized that disturbances prone to develop into a TC over the WNP satisfy two essential preconditions in terms of precipitation characteristics. First, a large fraction of stratiform precipitation covers the region that is within 400 km from the disturbance center. The mean vertically-integrated unconditional latent heating rate of stratiform and convective precipitation in the developing group above 5.5 km is 6.6 K h−1 and 2.4 K h−1, respectively; thus, the stratiform rainfall makes a major contribution to warming the upper troposphere. Second, strong convective precipitation occurs within the inner-core region. Compared with stratiform precipitation, which has a critical role in warming the mid-to-upper levels, the most striking feature of convective precipitation is that it heats the mid-to-lower troposphere. Overall, tropical cyclone formations evolving from parent disturbances can be regarded as an outcome of the joint contribution from the two distinct types (convective and stratiform) of precipitation clouds.

著者

HERMOSO Alejandro HOMAR Victor GREYBUSH Steven J. STENSRUD David J.

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.2020-053, (Released:2020-07-09)

被引用文献数

4

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Uncertainty in numerical weather forecasts arising from an imperfect knowledge of the initial condition of the atmospheric system and the discrete modelling of physical processes is addressed with ensemble prediction systems. The breeding method allows the creation of initial condition perturbations in a simple and computationally inexpensive way. This technique uses the full nonlinear dynamics of the system to identify fast-growing modes in the analysis fields, obtained from the difference between control and perturbed runs rescaled at regular time intervals. This procedure is more suitable for the high resolution ensemble forecasts required to reproduce small scale high impact weather events, as the complete nonlinear model is applied to generate the perturbations. The underdispersion commonly found in ensemble forecasts emphasizes the need to develop methods that increase ensemble spread and diversity at no cost to forecast skill. In this sense, we investigate the benefits of different breeding techniques in terms of ensemble diversity and forecast skill for a mesoscale ensemble over the Western Mediterranean region. In addition, we propose a new method, Bred Vectors Tailored Ensemble Perturbations designed to control the scale of the perturbations and indirectly the ensemble spread. The combination of this method with orthogonal bred vectors shows significant improvements in terms of ensemble diversity and forecast skill with respect to the current arithmetic methods.

著者

CAO Xi WU Renguang DAI Yifeng XU Jing

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.2020-052, (Released:2020-07-09)

被引用文献数

1

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The effects of an upper-level anticyclonic circulation and a lower-level cyclonic circulation on tropical cyclone (TC) genesis are examined by idealized simulations using the Advanced Research Weather Research and Forecasting (WRF-ARW) model. The simulation results show that the upper-level anticyclonic circulation makes a negative contribution to TC genesis, whereas the lower-level cyclonic circulation makes a positive contribution. The upper-level anticyclonic circulation results in slower TC genesis due to a large vertical zonal wind shear that shifts the upper-level vortex eastward from its initial position, which is unfavorable for the vertical alignment and warm core maintenance of the vortex. This large vertical zonal wind shear is associated with the asymmetries of the vertical motion and associated diabatic heating induced by the lower-level beta gyre. The upper-level anticyclonic circulation increases the westerly wind to the north of the vortex, resulting in a large vertical westerly wind shear. Thus, the initial upper-level anticyclonic circulation is not necessary for TC genesis, and the strong upper-level anticyclonic circulation generally observed with a strong TC should be regarded as a result of deep convection. In contrast, strong lower-level winds due to the superposition of the large-scale lower-level cyclonic circulation and vortex induce large surface heat fluxes and vorticity, leading to strengthened convection and diabatic heating and a quick build-up of positive vorticity, resulting in rapid TC genesis.

著者

CHEN Xiuhong HUANG Xianglei CAI Yifan SHEN Haoming LU Jiayue

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.2020-048, (Released:2020-06-12)

被引用文献数

1

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Accurate forecast of ground horizontal irradiance (GHI) is one of the key issues for power grid managements with large penetration of solar energy. A challenge for solar forecasting is to forecast the solar irradiance with a lead time of 1-8 hours, here termed as intra-day forecast. This study investigated an algorithm using a long short-term memory (LSTM) model to predict the GHI in 1-8 hours. The LSTM model has been applied before for inter-day (> 24 hours) solar forecast but never for the intra-day forecast. Four years (2010-2013) of observations by the National Renewable Energy Laboratory (NREL) at Golden, Colorado were used to train the model. Observations in 2014 at the same site were used to test the model performance. The results show that, for a 1-4 hour lead time, the LSTM-based model can make predictions of GHIs with root-mean-square-errors (RMSE) ranging from 77 to 143 W m−2, and normalized RMSEs around 18.4 ∼ 33.0 %. With 5-minute inputs, the forecast skill of LSTM with respect to smart persistence model is 0.34 ∼ 0.42, better than random forest forecast (0.27) and the numerical weather forecast (−0.40) made by the Weather Research and Forecasting (WRF) model. The performance levels off beyond 4-hour lead time. The model performs better in fall and winter than in spring and summer, and better under clear-sky conditions than under cloudy conditions. Using adjacent information from the reanalysis as extra inputs can further improve the forecast performance.

著者

OSE Tomoaki TAKAYA Yuhei MAEDA Shuhei NAKAEGAWA Toshiyuki

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.2020-047, (Released:2020-07-01)

被引用文献数

6

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The southerly surface wind index over the summertime East Asia (SWI) is strengthened in the future in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). However, the differences among the models are much larger than the ensemble average. The empirical orthogonal function (EOF) analysis is applied to the future changes in the East Asian surface pressure pattern responsible for the SWI. The ensemble average and five EOF modes for the pressure patterns and the associated precipitation changes are identified, and their possible sources are examined. The CMIP5 ensemble mean change in the summertime Asia Pacific surface pressure pattern possesses the characteristics of the first to third modes. The first and second mode components contribute to the positive SWI in the future, but are cancelled mostly by the third mode component. The first mode is high surface pressure anomalies over low Asia Pacific sea surface temperature. The second mode is related to warm temperature anomalies over the Northern Hemisphere continents and the increased equatorial Pacific precipitation. The large model dependence of the SWI is created by the third mode, which represents the weak Pacific High in northern East Asia and is characterized with suppressed vertical motions over the northern Indian and Pacific oceans. The fourth mode is the Okhotsk High. The fifth mode represents the east–west contrast of the southern East Asian surface pressure anomalies and is associated with the Northern Hemisphere ocean temperatures. The fourth and fifth modes feature the mean projection using the 10 models reproducing an accurate present-day summertime East Asian climatology.  The mode-related suppressed vertical motions in global warming reflect the present-day vertical motion (i.e., precipitation) climatology; hence, the future increase/decrease in the SWI tends to be projected by models simulating the relatively small/large Asia Pacific monsoon precipitation over the tropical oceans, except near the mountains, in the present-day model climatology.

著者

山口 宗彦 前田 修平

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.775-786, 2020 (Released:2020-08-25)

参考文献数

34

被引用文献数

13

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観測に基づくと、東京を含む日本の南海岸に接近する熱帯低気圧の数が過去40年間で増加しており、また接近時の強度が強まっている。海面水温の上昇、風の鉛直シアの弱化、さらに大気中の水蒸気量の増加により、熱帯低気圧の発達により好条件な環境場となっている。加えて、熱帯低気圧の移動速度が遅くなっており、これは熱帯低気圧による影響時間が長くなっていることを意味する。前半の20年(1980~1999、P1期間と呼ぶ)と後半20年(2000~2019年、P2期間と呼ぶ)の7~10月の環境場を比較すると、P2期間はP1期間と比べて亜熱帯高気圧の勢力が強く、西および北への張り出しが強まっている。また、対流圏中~上層において、日本の南および上空で偏西風が弱まっている。これらの環境場の変化が、東京に接近する台風を増加させ、および発達に都合の良い条件を作り出していると考えられる。地球温暖化とこれら過去40年間の熱帯低気圧の特徴の変化との関係は不明である。ただし、P1期間は太平洋十年規模振動が正の期間で、P2期間の多くは負の期間であることから、十年規模振動が接近数 の増加や環境場の変化に影響をもたらした可能性がある。