著者

TSUJI Hiroki YOKOYAMA Chie 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.2020-045, (Released:2020-06-02)

被引用文献数

35

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Precipitation characteristics and environment are compared between two rainfall events in Japan: the July 2018 heavy rainfall event (2018 case) and the 2017 Northern Kyushu rainfall event (2017 case). Both events occurred in the later stage of the Baiu season, after the passage of a tropical cyclone, south of a subtropical jet and to the front side of an upper tropospheric trough. However, contrasting precipitation properties and environments are observed between these cases. In the 2018 case, long-lasting heavy precipitation was observed over a large area with moderately tall precipitation systems. Environment was stable and moist compared with the climatology. A deep trough over the Korean Peninsula played a role to prepare the environment favorable for organizing precipitation systems through moistening of mid-troposphere by quasi-geostrophic dynamically forced ascent. In contrast, in the 2017 case, a short-term intense precipitation was observed over a small area with exceptionally tall precipitation systems. The environment was unstable and moist compared with the climatology but was dryer than the 2018 case. In this case, a shallow trough over the Korean Peninsula destabilized the atmosphere via associated high-altitude cold air.  The observed contrast of characteristics between the 2018 and 2017 cases is like that found between composites of extreme rainfall events and extremely tall convection events included in the previous statistical study by Hamada and Takayabu (2018, doi:10.1175/JCLI-D-17-0632.1). Temperature anomalies and specific humidity anomalies from climatological values in the 2018 and 2017 cases are several times as large as those in the composites of the extreme events although the previous study analyzed the uppermost 0.1 % of extreme events. This result means that the 2018 case is an extreme among the extreme rainfall events and the 2017 case corresponds to an extreme event of the extremely tall convection events.

著者

松川 哲美

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.3, no.6, pp.160-162, 1925-07-30 (Released:2009-02-05)

著者

SUI Chung-Hsiung SATOH Masaki SUZUKI Kentaroh

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-024, (Released:2020-03-01)

被引用文献数

21

---

Precipitation efficiency (PE) is a useful concept for estimating precipitation under a given environmental condition. PE is used in various situations in meteorology: to evaluate severe precipitation associated with a single storm event; as a parameter of cumulus convective parameterization; and to separate clouds and precipitation in climate projection studies. PE has been defined in several ways. In this review, we start with definitions of PE from microscopic and macroscopic perspectives, and provide estimates of PE based on observational and modeling approaches. Then, we review PE in shallow and organized deep convective systems that provide either a conceptual framework or physical constraints on representations of convection in models. Specifically, we focus on the roles of PE in cloud-radiative feedbacks to climate variability. Finally, we argue the usefulness of PE for investigating cloud and precipitation changes in climate projection studies.

著者

SEO Jaemyeong Mango LEE Hyunho MOON Sungju BAIK Jong-Jin

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.2020-003, (Released:2019-10-20)

被引用文献数

3

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This study examines how upslope geometry controls aerosol effects on orographic precipitation through two-dimensional idealized simulations of orographic precipitation from shallow warm convective clouds over a bell-shaped mountain with 1-km height. A total of nine cases are simulated by considering three different prescribed aerosol number concentrations and three different windward-widths of the mountain. For a detailed representation of drop size distributions, the Weather Research and Forecasting (WRF) model that includes a bin microphysics scheme is used with a horizontal grid size of 250 m and 401 terrain-following vertical levels. A higher aerosol number concentration leads to production of more cloud droplets, inhibiting the growth of cloud droplets into raindrops in the cases with the symmetric mountain (the windward-side half-width a1 = 10 km). As a result, the total and maximum surface precipitation amounts decrease and the location of the maximum surface precipitation amount shifts downstream. The aerosol effects on orographic precipitation are more clearly seen in the cases with the narrow windward-width (a1 = 5 km) compared to the cases with the symmetric mountain and the wide windward-width (a1 = 20 km). In the cases with the narrow windward-width, the steep upslope generates strong convection with a short advection timescale (∼ 600 s), resulting in more precipitation being concentrated over a narrow area of the mountain downslope compared to the cases with the symmetric mountain and the wide windward-width. On the other hand, in the cases with the wide windward-width, the gentle upslope generates weak convection with a sufficiently long advection timescale (∼ 2400 s), so that a large portion of liquid drops precipitates out on the wide mountain upslope before reaching the peak.

著者

YUKIMOTO Seiji KAWAI Hideaki KOSHIRO Tsuyoshi OSHIMA Naga YOSHIDA Kohei URAKAWA Shogo TSUJINO Hiroyuki DEUSHI Makoto TANAKA Taichu HOSAKA Masahiro YABU Shokichi YOSHIMURA Hiromasa SHINDO Eiki MIZUTA Ryo OBATA Atsushi ADACHI Yukimasa ISHII Masayoshi

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.2019-051, (Released:2019-06-18)

被引用文献数

434

---

The new Meteorological Research Institute Earth System Model version 2.0 (MRI-ESM2.0) has been developed based on previous models, MRI-CGCM3 and MRI-ESM1, which participated in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). These models underwent numerous improvements meant for highly accurate climate reproducibility. This paper describes model formulation updates and evaluates basic performance of its physical components. The new model has nominal horizontal resolutions of 100 km for atmosphere and ocean components, similar to the previous models. The atmospheric vertical resolution is 80 layers which is enhanced from 48 layers of its predecessor. Accumulation of various improvements concerning clouds, such as a new stratocumulus cloud scheme, led to remarkable reduction in errors in shortwave, longwave, and net radiation at the top of the atmosphere. The resulting errors are sufficiently small compared with those in the CMIP5 models. The improved radiation distribution brings the accurate meridional heat transport required for the ocean and contributes to a reduced surface air temperature (SAT) bias. MRI-ESM2.0 displays realistic reproduction of both mean climate and interannual variability. For instance, the stratospheric quasi-biennial oscillation can now be realistically expressed through the enhanced vertical resolution and introduction of non-orographic gravity wave drag parameterization. For the historical experiment, MRI-ESM2.0 reasonably reproduces global SAT change for recent decades; however, cooling in the 1950s through the 1960s and warming afterward are overestimated compared with observations. MRI-ESM2.0 has been improved in many aspects over the previous models, MRI-CGCM3/MRI-ESM1, and is expected to demonstrate superior performance in many experiments planned for CMIP6.

著者

YOSHIDA Mayumi KIKUCHI Maki NAGAO Takashi M. MURAKAMI Hiroshi NOMAKI Tomoyuki HIGURASHI Akiko

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2018-039, (Released:2018-04-15)

被引用文献数

117

---

We develop a common retrieval algorithm of aerosol properties such as aerosol optical thickness, single-scattering albedo, and Ångström exponent for various satellite sensors over both land and ocean. The three main features of this algorithm are as follows: (1) automatic selection of the optimum channels for aerosol retrieval by introducing a weight for each channel to the object function, (2) setting common candidate aerosol models over land and ocean, and (3) preparation of lookup tables for every 1 nm in the range from 300 to 2500 nm of wavelength and weighting the radiance using the response function for each sensor. This method was applied to the Advanced Himawari Imager (AHI) on board the Japan Meteorological Agency’s geostationary satellite Himawari-8, and the results depicted an approximately continuous estimate of aerosol optical thickness over land and ocean. Further, the aerosol optical thickness estimated using our algorithm was generally consistent with the products from Moderate Resolution Imaging Spectroradiometer (MODIS) and Aerosol Robotic Network (AERONET). Additionally, we applied our algorithm to MODIS on board the Aqua satellite and then compared the retrieval results to those that were obtained using AHI. The comparisons of the aerosol optical thickness retrieved from different sensors with different viewing angles on board the geostationary and polar-orbiting satellites suggest an underestimation of aerosol optical thickness at the backscattering direction (or overestimated in other directions). The retrieval of aerosol properties using a common algorithm allows us to identify a weakness in the algorithm, which includes the assumptions in the aerosol model (e.g. sphericity or size distiribution).

著者

川端 康弘 山口 宗彦

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.821-833, 2020 (Released:2020-08-25)

参考文献数

30

被引用文献数

2 3

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台風進路予報における予報楕円の有効性を、マルチセンターアンサンブル手法を用いて調査した。使用した台風進路予報データは、2016~2018年の気象庁、欧州中期予報センター、米国環境予測センター、英国気象局の数値予報センターの全球アンサンブル予報である。これら4センターの全球アンサンブル予報によるマルチセンターアンサンブルは、初期値ごとに異なる予報の不確実性を、台風の進行方向に沿った成分とそれに直交する成分において、より適切に表現できることがわかった。予報円は進路予報誤差が等方的な分布であることを仮定しているが、予報楕円を導入することにより台風の移動方向あるいは移動速度のどちらに予報の不確実性が大きいか把握することができる。予報円と予報楕円の面積を比較したところ、予報楕円の面積は平均して3日先予報で16%、4日先で15%、5日先で24%減少することがわかった。予報楕円は台風の警戒領域を絞り込むことができ、防災対応・緩和策をより強化できる可能性がある。

著者

HIROCKAWA Yasutaka KATO Teruyuki TSUGUTI Hiroshige SEINO Naoko

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.2020-043, (Released:2020-05-18)

被引用文献数

25

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We propose a new procedure for the objective identification and classification of heavy rainfall areas (HRAs) to advance the understanding of mesoscale convective systems (MCSs) in Japan. The distributions of accumulated precipitation amounts are evaluated from the radar/raingauge-analyzed precipitation amounts and characteristic features of HRAs are examined. The HRAs extracted during the warm season (April–November) in 2009-2018 are classified into four types (e.g., linear-stationary, linear, stationary, and others) from their morphological features and temporal variations. HRAs are frequently distributed on the Pacific sides of eastern and western Japan; 80 % of HRAs appeared from June to September and 60 % of the HRAs were observed in association with stationary fronts and tropical cyclones. Approximately 80 % of those HRAs of the linear-stationary type corresponded to typical elongated and stagnated MCSs, as has been suggested in previous studies.

著者

ISHIDA Junichi ARANAMI Kohei KAWANO Kohei MATSUBAYASHI Kengo KITAMURA Yuji MUROI Chiashi

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2022-043, (Released:2022-07-07)

被引用文献数

11

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The non-hydrostatic numerical weather prediction (NWP) model ASUCA developed by the Japan Meteorological Agency (JMA) was launched into operation as 2 and 5 km-resolution regional models in 2015 and 2017, respectively. This paper outlines specifications of ASUCA with focus on the dynamical core and its configuration/accuracy as an operational model. ASUCA is designed for high computational stability and efficiency, mass conservation and forecast accuracy. High computational stability is achieved via a time-split integration scheme to compute acoustic terms and an advection scheme with a flux-limiter function to avoid numerical oscillation. In addition, vertical advection and sedimentation are calculated together with another exclusive time-splitting technique. ASUCA adopts hybrid parallelization using Message Passing Interface (MPI) and Open Multi Processing (OpenMP) for high computational efficiency on massive parallel scalar computers. The three-dimensional arrays are allocated such that the vertical direction is the stride-one innermost dimension to make effective use of cache and multi-thread parallelization. This is particularly advantageous for physical processes evaluated in a vertical column. To ensure mass conservation, density rather than pressure is integrated as a prognostic variable in flux-form fully compressible governing equations. ASUCA exhibited better performance than the previous operational model in idealized and NWP tests.

著者

KODAMA Shinichi SATOH Masaki

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2022-046, (Released:2022-08-03)

被引用文献数

6

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During the autumn rainy season, typhoons located far from Japan sometimes cause significant precipitation in Japan. In this study, we characterized remote precipitation events in September for 40 years from 1980 to 2019. We also analyzed cases in which remote precipitation did not occur despite approaching typhoons, as well as cases in which heavy precipitation was not affected by typhoons. We characterized the environmental fields of the remote precipitation cases by comparing them with these other two types of cases. Statistical analysis showed that remote precipitation tended to occur when the typhoons were located over the southern or southwestern oceans of mainland Japan and when the tracks of the typhoons were northward or changing to the northeast. The composite analysis of the remote precipitation cases showed that the subtropical high was retreating to the east for the two days before the remote precipitation. By contrast, the cases in which remote precipitation did not occur showed the opposite pattern: the subtropical high was strengthening to the west when typhoons were approaching over the southern or southwestern oceans of the Japanese archipelago. Furthermore, the remote precipitation occurred to the equatorward jet streak entrance of the 200 hPa jet, whereas the 200 hPa jet streak was shifted to the west in the cases where remote precipitation did not occur. The vertical cross-section of the northward water vapor flux showed that the northward water vapor inflow from the middle troposphere was larger in cases of remote precipitation than in cases in which heavy precipitation was not caused by typhoons. In addition, dynamical analysis showed that the area of remote precipitation corresponded to the region of 800-600 hPa mean quasi-geostrophic forcing for ascent and 925 hPa frontogenesis.

著者

MOGI Atsushi WATANABE Masahiro

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.2022-025, (Released:2022-02-03)

---

Extremely hot days in Japan are known to persist for a week or more, and they are measured by the temperature anomaly at 850 hPa averaged over Japan derived from the JRA-55 reanalysis data, denoted as T850JP. Severe high-temperature anomalies are often accompanied by multiple teleconnection patterns that affect the weather in Japan, but their relative contribution to individual heat wave events has not yet been quantified. In this study, we examined the effects of three major teleconnection patterns, namely, the Pacific-Japan (PJ), circumglobal teleconnection (CGT), and Siberian patterns, on T850JP in July and August from 1958-2019 using daily low-pass filtered anomalies with 8 days cutoff time-scale derived from the reanalysis. A linear regression analysis demonstrated that T850JP tended to show a large positive anomaly one or two days after the peak of these patterns. Based on this relationship, we reconstructed a daily T850JP time series using a multivariate statistical model wherein the parameters were estimated using regression analyses between T850JP and indices of the three teleconnection patterns. The reconstructed T850JP showed that the three teleconnection patterns together accounted for 50 % of the total variance of T850JP for extremely hot summers, to which each of the three teleconnection patterns were found to have a similar degree of contribution. The statistical model reproduces the interannual variability along with the long-term T850JP trend. The PJ pattern has the largest effect on the interannual variability of T850JP, probably due to the PJ teleconnection occurring over a longer timescale compared with the other two patterns. The reconstructed T850JP also displays a warming trend associated with an increasing trend in the CGT index, which may be a factor, along with the direct thermodynamic effects due to global warming, to explain the long-term increase in the heat wave frequency in Japan.

著者

IKEDA Takashi KUSAKA Hiroyuki

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.2021-067, (Released:2021-08-20)

被引用文献数

8

---

We developed fifty-five models for predicting the number of ambulance transport due to heatstroke (hereafter referred to as the number of patients with heatstroke) on the next day in Tokyo, using different combinations of eleven explanatory variables sets and five methods (three statistical models and two machine learning) for 10 years (2010-2019). The root mean square error (RMSE) for the number of heatstroke patients was minimal when the best model was developed by combining six explanatory variables (temperature, relative humidity, wind speed, solar radiation, number of days since June 1, and the number of patients with heatstroke on the previous day) and the generalized additive model. The best model remarkably improved prediction by 52.1 % compared to a widely used model, which primarily utilizes temperature as an explanatory variable and the generalized linear model as a method. Further analysis investigating the contribution of the explanatory variables and method to the prediction showed that RMSE was reduced by 49.7 % using the above six explanatory variables compared to using the only temperature and by 14.6 % using the generalized additive model compared to using the generalized linear model.

著者

TOCHIMOTO Eigo YOKOTA Sho NIINO Hiroshi YANASE Wataru

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.2022-007, (Released:2021-10-06)

被引用文献数

1

---

Ensemble forecasts with 101 members (including one ensemble mean) using ensemble Kalman filter analysis were performed to understand the atmospheric conditions favorable for the development of a meso-β-scale vortex (MBV) that caused shipwrecks as a result of sudden gusty winds in the southwestern part of the Sea of Japan on 1 September 2015. A composite analysis was performed to reveal differences in the structure of the MBV and atmospheric conditions around the MBV between the strongest eight (STRG) and weakest ten (WEAK) ensemble members, where two of the strongest ten members that developed the MBV much earlier than the other members were excluded from the analysis. The analysis shows that near-surface cyclonic horizontal shear to the northeast and the south of the MBV was stronger for STRG than for WEAK. In addition, larger low-level water vapor and its horizontal flux for STRG contribute to greater convective available potential energy to the southeast of the MBV, resulting in stronger convection around the MBV. The results of the composite analysis are also statistically supported by an ensemble-based sensitivity analysis. Differences in near-surface horizontal shear were closely related to the structure of the extratropical cyclone in which the MBV was embedded. Although the strength of the extratropical cyclone for STRG was comparable with that for WEAK, the cyclonic horizontal shear of winds in the northeastern quadrant of the extratropical cyclone was greater for STRG than for WEAK.

著者

De MEYER Victorien ROCA Rémy

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.2021-020, (Released:2021-01-14)

被引用文献数

5

---

Extreme precipitation theory has been matured over the last decade and stipulates that the intensity of the extreme precipitation scales with the surface humidity. Surface humidity changes can further be approximated by the surface temperature changes. The analytically derived scaling coefficient based on the Clausius-Clapeyron derivative is ∼ 6 %K−1 in the tropics. While frequently confronted with observations over land, the theory has so far only been marginally evaluated against precipitation data over the ocean. Using an ensemble of satellite-based precipitation products and a suite of satellite-based SST analysis all at the 1°-1day resolution, the extreme scaling is investigated for the tropical ocean (30°S-30°N). The focus is set on the robust features common to all precipitation and SST products. It is shown that microwave constellation-based precipitation products are characterized by a very robust positive scaling over the 300 to 302.5 K range of 2-day lagged SST. This SST range corresponds to roughly 60 % of the tropical precipitation amount. The ensemble mean scaling varies between 5.67 %K−1 ± 0.89 %K−1 to 6.33 %K−1 ± 0.81 %K−1 depending on the considered period and is found very close to the theoretical expectation. The robustness of the results confirms the fitness of the current generation of constellation-based precipitation products for extreme precipitation analysis. Our result further confirms the extreme theory for the whole tropical ocean. Yet, significant differences in the magnitude of the extreme intensity across the products prompts the urging necessity of dedicated validation efforts.

著者

YAMASHITA Yousuke TAKIGAWA Masayuki GOTO Daisuke YASHIRO Hisashi SATOH Masaki KANAYA Yugo TAKETANI Fumikazu MIYAKAWA Takuma

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.2021-014, (Released:2020-12-02)

被引用文献数

3

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Atmospheric transport of aerosols such as black carbon (BC) affects the absorption/scattering of solar radiation, precipitation, and snow/ice cover, especially in areas of low human activity such as the Arctic. The resolution dependency of simulated BC transport from Siberia to the Arctic, related to the well-developed low-pressure systems in September, was evaluated using the Nonhydrostatic Icosahedral Atmospheric Model–Spectral Radiation Transport Model for Aerosol Species (NICAM-SPRINTARS) with fine (∼ 56 km) and coarse (∼ 220 km) horizontal resolutions. These low-pressure systems have a large horizontal scale (∼ 2000 km) with the well-developed central pressure located on the transport pathway from East Asia to the Arctic through Siberia. The events analysis of the most developed low-pressure system in recent years indicated that the high-BC area in the Bering Sea observed by the Japanese Research Vessel Mirai in September 26-27th, 2016 moved to the Arctic with a filamental structure from the low's center to the behind of the cold front and ahead of the warm front in relation to its ascending motion on September 27-28th, 2016. The composite analysis for the developed low-pressure events in September from 2015-2018 indicated that the high-BC area was located eastwards of the low's center in relation to the ascending motion over the low's center and northward/eastward area. Since the area of the maximum ascending motion has a small horizontal scale, this was not well simulated by the 220-km experiment. The study identified the transport of BC to the Arctic in September is enhanced by the well-developed low-pressure systems. The results of transport model indicate that the material transport processes to the Arctic by the well-developed low-pressure systems are enhanced in the fine horizontal resolution (∼ 56 km) models relative to the coarse horizontal resolution (∼ 220 km) models.

著者

Masamichi OHBA Hiroaki UEDA

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.85, no.3, pp.335-348, 2007 (Released:2007-08-09)

参考文献数

46

被引用文献数

59 77

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One possible impact of sea surface temperature (SST) anomalies in the Indian Ocean (IO) on the ongoing El Niño is investigated using an air-sea coupled general circulation model (CGCM). A suite of CGCM experiments by imposing the IO basin-wide warming (BW) and IO dipole/zonal mode (IODZM) are conducted to assess the feedback effects of the El Niño-related SST anomalies on the Pacific. While the IODZM during boreal fall does not have a significant impact on the Pacific sector, the BW during boreal winter enhances the surface easterlies over the equatorial Western Pacific (WP) during the maturedecay phase of El Niño. The strengthened easterlies act to enhance the SST cooling over the WP, thereby the zonal gradient of SST between the IO and WP is greater than the climatology. These enhanced WP easterlies induce an advanced transition to the La Niña phase, which is caused by the upwelling ocean Kelvin waves. These results imply that the BW in the IO, to some extent, can be hastening the El Niño to La Niña transition.

著者

NAKAMURA Yuhi MIYAKAWA Tomoki SATOH 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.2020-046, (Released:2020-06-02)

---

From 9 to 11 September 2015, the Kanto and Tohoku regions of Japan experienced an extremely heavy rainfall event. The synoptic-scale field was characterized by two typhoons, Etau (T1518) and Kilo (T1517). After Etau made landfall in the Tokai region and transformed into an extra-tropical cyclone over the Sea of Japan, meridionally oriented rain bands persisted over the Kanto region for about 12 hours and caused heavy rainfall, particularly over the Tochigi prefecture. During this time, Kilo approached the eastern ocean of the Kanto region. In this study, we examine the role of Kilo in this event by conducting numerical experiments using a stretched version of the Nonhydrostatic Icosahedral Atmospheric Model configured with a minimum grid interval of about 5.6 km. The control experiment reproduced intense rain bands around the same period and place as the observed event, although they were not reproduced in an experiment with a longer lead time. Sensitivity experiments were conducted in which Kilo was weakened by removing moisture in its central region with a longer lead time. In contrast to the expectation that reduced moisture would lead to a weaker typhoon and hence weaker rain, the sensitivity experiment reproduced the rain band with realistic location but 5 % less precipitation than the control experiment. Furthermore, this experiment indicated that precipitation over the outer band of Etau, which covers the Kanto region, increased by 10 % compared to the control experiment. We found that a southeasterly wind induced by a high-pressure ridge between Kilo and the Kanto region played a greater role in supplying moisture to the Kanto region than the strong easterly wind produced by the pressure gradient between Kilo and the Okhotsk high. In this case, weaker Kilo resulted in enhanced northwestward moisture flux associated with the ridge, thereby inducing heavier rainfall over the Kanto region.

著者

伊藤 耕介 Chun-Chieh Wu Kelvin T. F. Chan Ralf Toumi Chris Davis

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.1, pp.5-17, 2020 (Released:2020-03-26)

参考文献数

46

被引用文献数

1 13

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台風の移動の基礎的な理解はかなり成熟しているが、注目に値する研究の進展が近年も見られる。本論文では、単純化された順圧モデル・精緻な物理モデル・データ解析によって、主に2014年以降に得られた台風の移動に関する新しい概念や既存の概念に関する新たな知見を集約する。これには、台風の移動に関する環境場と台風の相互作用、および、予測可能性の研究を含んでいる。指向流・βジャイア・非断熱加熱といった従来の概念は依然として重要であるが、台風の進路を説明するメカニズムをより正確に理解することは、さらなる進路予報の精度向上に向けて、重要な基礎をなすであろう。

著者

AONO Kenji IWASAKI Toshiki SASAI Takahiro

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.2020-017, (Released:2019-12-24)

被引用文献数

1

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This study examined the roles of wind-evaporation feedback in the tropical cyclone (TC) intensification, with special attention devoted to the feedback in weak wind areas (domains where the 10-m wind speed is smaller than 5, 10 and 15 m s−1). This was done by setting lower limits of the 10-m wind speed in the calculation of water vapor exchange between the atmosphere and the underlying ocean in a nonhydrostatic cloud-resolving model. As a result, the surface evaporation is enhanced in outer regions of a TC where the actual wind speed is smaller than the prescribed lower limit(s). Results show that increasing the lower limit reduces the radial water vapor contrast in the lower troposphere (below 100 m) and suppresses the TC size and intensity at the mature stage by 30-33 % and 5-14 %, respectively, compared to the control run with all standard model settings. The increased evaporation enhances the outer convective activity and reduces the radial pressure gradient in the lower troposphere. As a result, the inflow and thus the inward advection of angular momentum were reduced and the enhanced convection in the outer region suppressed eyewall updraft, and thus reduced the secondary circulation and finally the TC intensity. Moreover, the outer region convection suppresses the rainband activity (within a radius of 300 km from the TC center). The contribution of the wind-evaporation feedback to the enhancement of the radial contrast of water vapor in the lower troposphere is a fundamentally important element for TC intensification, suggesting that the TC development process can be revealed more accurately by elucidating the role of the weak wind area.

著者

GENG Biao KATSUMATA Masaki TANIGUCHI Kyoko

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.2020-026, (Released:2020-02-06)

被引用文献数

4

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This study investigated the impact of mixed Rossby-gravity waves (MRGWs) on the diurnal cycle of precipitation over the southwestern coastal area of Sumatra using data captured during a pilot field campaign of the Years of the Maritime Continent (YMC) Project. The study focused on a 19-day period from 24 November to 12 December 2015, using data from intensive surface observations, radiosondes, a C-band polarimetric radar collected onboard the research vessel Mirai at 4.067°S, 101.900°E, and data from global objective analysis. The results indicated a relationship between oscillations with periods of several days in the intensity of diurnal precipitation and the wind field. Wind oscillations were attributed to several westward-propagating MRGWs traversing the study site. Diurnal convection and precipitation over the land and ocean were enhanced (suppressed) when MRGW-induced offshore (onshore) wind perturbations dominated. Large-scale low-level convergence and upper-level divergence, stronger sea-breeze flow, and colder land-breeze flow were also observed with the intensification of MRGW-induced offshore wind perturbations. However, diurnal precipitation displayed a similar well-defined phase and propagation pattern over the land and ocean, coherent with the regular evolution of sea- and land-breeze circulations, regardless of wind perturbations induced by MRGWs. The results suggest that local convergence induced by the land-sea contrast is mainly responsible for driving the diurnal cycle. Notwithstanding, MRGWs exert a significant impact on the amplitude of diurnal convection and precipitation by modulating the large-scale dynamic structure of the atmosphere and the intensity of local sea- and land-breeze circulations.