著者

Hiroaki Kawase Munehiko Yamaguchi Yukiko Imada Syugo Hayashi Akihiko Murata Tosiyuki Nakaegawa Takafumi Miyasaka Izuru Takayabu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.17A-002, (Released:2020-12-24)

被引用文献数

20

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Impacts of historical warming on extremely heavy rainfall induced by Typhoon Hagibis (2019) are investigated using a storyline event attribution approach with the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM). Control experiments based on JMA mesoscale analysis data well reproduce the typhoon's track, intensity, and heavy precipitation. First, two non-warming experiments are conducted: One excludes both 40-year atmospheric and oceanic temperature trends from 1980 to 2019, and the other excludes the oceanic trend only. A comparison between control and non-warming experiments indicates that historical warming strengthens typhoons and increases the amount of total precipitation by 10.9% over central Japan. The difference between CTL and non-warming experiments without both atmospheric and oceanic temperature trends is larger than that without just the oceanic trend (7.3%). Additional sensitivity experiments without Japan's topography indicate that topography enhances not only total precipitation but also the changes in total precipitation due to historical warming. Through the storyline event attribution approach, it is concluded that historical warming intensifies strength of Typhoon Hagibis (2019) and enhances the extremely heavy precipitation induced by the typhoon.

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

Ryuichi Kawamura Takuya Ogasawara

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.2, pp.37-40, 2006 (Released:2006-03-21)

参考文献数

14

被引用文献数

30 47

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The extratropical response to typhoon-related convective forcing over the western North Pacific in late summer is examined based on ECMWF global reanalysis (ERA-40) data during the 1958-2001 period. Typhoon activity is intimately associated with most of the major events in which an extratropical wavetrain structure prevails from the north of the Philippines through the central North Pacific. The vertical structure of the wavetrain pattern changes from baroclinic to a barotropic along the great circle. The analysis of the wave activity flux indicates that the extratropical wavetrain is stimulated by stationary Rossby waves. It was found that one or two typhoons, which are a synoptic-scale convective heat source over the western North Pacific, can induce the barotropic Rossby wavetrain and significantly influence the summer weather in the vicinity of Japan as remote forcing.

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。

著者

Francis X. Crum Timothy J. Dunkerton

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.72, no.1, pp.11-18, 1994-02-25 (Released:2009-09-15)

参考文献数

23

被引用文献数

6 6

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赤道ベータ面の多層モデルを用いて、CISKと蒸発-風フィードバックによって発現する不安定なケルビン波への条件付き加熱の影響を調べた。今までの解析的な結果と同様に、(条件付きでない)線型的な加熱の場合に(無限小のスケールが卓越する)スケール選択が破綻する問題は、条件付き加熱によって緩和されるものの解消はされない。条件付き加熱の上昇流域は一つであり、その水平スケールは粘性やモデルの解像度によって決まる最小のスケールになる。この傾向はCISKによる不安定な場合にもっとも顕著である。蒸発-風フィードバックによってケルビン波の不安定はCISKと無関係に起こる。この場合、増幅率は粘性が小さくなるにつれゆるやかに大きくなるが、水平スケールはやはり小さくなる。今までは東風が必要と考えられていた東進する蒸発-風フィードバック不安定モードが、一般風のない場合にもあらわれるのが示された。スケール選択に関しては蒸発-風フィードバックの方がCISKよりも良い。しかし、(1)水蒸気収束フィードバックの強さを決めるパラメータqがCISK中立点に近い値を持ち、(2)蒸発-風フィードバックの強さを決めるパラメータAが小さく、(3)加熱分布は鉛直流に比例する場合以外には、東西方向の位相速度は熱帯季節内振動やスーパークラスダーのものに比べて非常に大きい。こうした三つの条件を満たす場合には、2層モデルで小さな正の位相速度が得られる。

著者

井上 豊志郎

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.75, no.1, pp.59-66, 1997-02-25 (Released:2009-09-15)

参考文献数

14

被引用文献数

11 13

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極軌道衛星NOAAに搭載されているSplit Wiondowを用いて、西太平洋における昼と夜での雲型別雲量のちがいについて調査した。Split Windowでは氷晶で構成されている光学的に薄い巻雲型の雲と光学的に厚い積雲型の雲を分類することができる。この研究では光学的に薄い巻雲型の雲はさらに輝度温度で温かい巻雲型と冷たい巻雲型の2つに、また光学的に厚い積雲型の雲も輝度温度で積乱雲型と下層の積雲/層積雲型の2つに分類した。ISCCPの解析結果との比較から温かい巻雲型、冷たい巻雲型、下層の積雲/層積雲型と積乱雲型の光学的厚さの平均値はそれぞれ2.2,7.4,15.3および33.7であることが分かった。Split Windowで分類される雲型別雲量の昼と夜のちがいを、個々の対流システムとしての台風についてと、熱帯海洋域での緯・経度20°×30°の広い領域について調査した。積乱雲型、温かい巻雲型および下層の積雲/層積雲型の雲量は地方時2:30頃の夜間に多い傾向を示した。それに対し、冷たい巻雲型の雲量は地方時14:30頃の昼間に多い傾向を示すことが分かった。

著者

小倉 義光 浅井 冨雄 土肥 啓介

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.63, no.5, pp.883-900, 1985 (Released:2007-10-19)

参考文献数

44

被引用文献数

39 55

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1982年7月23日,長崎市を中心とする北九州地域をおそった集中豪雨の解析を行った。この豪雨は梅雨前線に沿って発達した中間規模低気圧に伴ったもので,長崎市における5時間の降雨量は412mm に達した。豪雨が発達する前の大気は,対流圏のほぼ全層にわたって非常に湿潤であり,また条件付不安定な成層をしていた。しかしその不安定度は春季米国中西部における巨大雷雨発生前のそれよりはずっと弱く,むしろ熱帯大気の状況に近い。長崎に豪雨が始まる前には,強い降雨バンドが毎時40km の速さで九州北西部を東南東の方向に進行していた。このバンドはそり進行前面にはっきりした先端部を持たず,最も強い降雨域はバンドの中央部にあったという点で,典型的な熱帯性スコールラインとは異った構造をもっていた。このバンドの南西の端が長崎地域に達した頃,バンドに顕著な変化が起った。すなわち,バンドは進行をやめ,長崎地域にその後約5時間停滞し,その結果として豪雨をもたらした。線状をしていた構造も団塊状の構造に変化した。また豪雨が発達した時刻は,南西風の下層ジェット気流に伴って非常に湿潤な空気が流入してきた時刻に一致する。もう一つ重要な事実としては,長崎地域が豪雨におそわれている間に,長崎の西方約300km の海上に新たに雲のクラスターが発生した。このクラスターは発達しながら毎時60km の速さで東方に進行し,やがて長崎地域に豪雨を降らせているクラスターと合併する。これらの事実は長崎地域の豪雨が地形の影響で,ほぼ同じ場所に停滞していたことを示唆する。同じように,梅雨前線に沿って発達した中間規模低気圧に伴って,下層ジェット気流の風上側の沿岸地域で豪雨が起った過去の三,四の例を示した。

著者

CAO Xi WU Renguang WEI Na DAI Yifeng

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.2020-034, (Released:2020-04-02)

被引用文献数

3

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We examined the processes of tropical cyclogenesis in strong monsoon trough pattern over the western North Pacific (WNP) using reanalysis data and numerical experiments. Composite analysis showed that more tropical cyclones are likely to form in the central WNP (130°E-165°E) and that fewer tropical cyclones appear in the western (120°E-130°E) and eastern (165°E-180°E) WNP when monsoon trough extends southeastward. Numerical experiments with the same weak artificial vortices inserted into eight different regions of the monsoon trough showed that weak tropical disturbances tend to develop more rapidly in the central WNP near 140°E-160°E, particularly near 150°E-155°E when the monsoon trough extends eastward, whereas weak tropical disturbances tend to develop more slowly in the eastern WNP near 165°E-170°E and do not form in the western WNP near 120°E-137.5°E. Our modeling results are consistent with the observational analyses. The failure of tropical cyclogenesis in the western WNP is due to the decrease of the moisture and heat (including the sensible and latent heat) from the underlying ocean, whereas large vertical wind shear and dry conditions in the upper level of the vortex reduce the gradient of intensification of tropical disturbances in the eastern WNP when the vortices have a similar initial intensity.

著者

RADHAKRISHNA Basivi SAIKRANTHI Kadiri RAO Thota Narayana

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.2020-030, (Released:2020-03-26)

被引用文献数

15

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Variations in raindrop size distribution (DSD) during the southwest monsoon (SWM) season over different climatic regions in the Indian subcontinent and adjoining seas are studied in this paper using five years (2014-2018) of global precipitation measurement dual-frequency precipitation radar derived DSDs. The rain rate (R) stratified DSD measurements show clearly that land, sea, and orography differ in their mass-weighted mean diameter (Dm) values. Irrespective of R, Dm values of deep rain were found to be larger in continental rain than in maritime and orographic rain. However, for shallow storms, the Dm values were smaller for continental rain than for orographic and maritime rain. Based on the Dm values and their variations with R of the deep systems, the regions could be categorized into four groups, within which the Dm values were nearly equal: (1) the northwest India (NWI) and the southeast peninsular India (SEPI); (2) the foothills of the Himalayas (FHH) and the central India (CI); (3) the northeast India (NEI) and the Bay of Bengal (BOB); and (4) the Arabian Sea (AS), the Western Ghats (WG), and the Myanmar coast (MC). Compared to other geographical regions of the Indian subcontinent, the Dm values of the deep systems were the largest over NWI and SEPI and the smallest over the WG, MC, and AS; while for shallow systems, the Dm values were the largest over the BOB and AS and the smallest over the SEPI and NWI regions. Though the cloud drops were smaller over the continental regions, the raindrops were larger than in the maritime and orographic rain regions. The microphysical and dynamical processes that occur during precipitation play a vital role in altering the DSDs of continental rain.