著者

SHIBATA Kiyotaka LEHMANN Ralph

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

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

被引用文献数

2

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

著者

GENG Biao KATSUMATA Masaki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-031, (Released:2020-03-17)

被引用文献数

5

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

著者

DUC Le SAITO Kazuo HOTTA Daisuke

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

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

被引用文献数

1

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

著者

LI Zhenghui LUO Yali DU Yu CHAN Johnny C. L.

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-012, (Released:2019-11-30)

被引用文献数

38

---

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

著者

LUO Yali XIA Rudi CHAN Johnny C. L.

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-002, (Released:2019-10-16)

被引用文献数

44

---

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

著者

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

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

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

被引用文献数

17

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

著者

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

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

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

参考文献数

41

被引用文献数

293 447

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

著者

TSUYUKI Tadashi

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

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

被引用文献数

2

---

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

著者

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

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

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

被引用文献数

10

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

著者

Liangtao XU Yijun ZHANG Fei WANG Xi CAO

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

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

参考文献数

56

被引用文献数

3

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

著者

菊地 勝弘

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.65, no.2, pp.309-311, 1987 (Released:2007-10-19)

参考文献数

4

被引用文献数

2 2

著者

樋口 敬二

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.40, no.3, pp.170-180, 1962-12-28 (Released:2007-10-19)

参考文献数

6

被引用文献数

2 4

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雪の結晶や雪片が降つてくる径路を研究するために,Fig.1に示したような小紙片(「紙の雪」)を飛行機から散布し,その流れ方と拡散の模様を調べた。地上に落ちた「紙の雪」は,札幌市の一般市民に拾つてもらい,小中学校を通じて回収された。実験は,1961年2月1日,2月28日,3月16日に行なわれた。Fig.10は,2月28日に450mの高度から散布した紙の分布であり,Fig.11は,3月16日に1800mの高度からの紙の分布である。これらの実験によつて,2000m程度の高度から散布した場合,「紙の雪」の流れる距離は,風の鉛直分布から推定したものと一致することがわかつた。1000m以下の高度から散布すると,風からの推定とは異なつた流れ方をする。坂上による瞬間点源の拡散式によつて,水平方向の拡散係数を求めると,105cm2⁄sec程度の値を得た。この値と,分布の標準偏差を比較して,この実験の場合も,Richardsonの関係式がほぼなりたつことがわかつた。

著者

CHIEN Fang-Ching CHIU Yen-Chao

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.2019-057, (Released:2019-07-24)

被引用文献数

4

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This paper examines southwesterly flows and their relationship with rainfall in Taiwan during the warm seasons: spring, Mei-yu, and summer. We found that the percentage of southwesterly flow events in the lower troposphere was the highest in the Mei-yu season, followed by summer. When southwesterly flows occurred, chance of rain greatly rose in Mei-yu and summer and mean rain intensity increased for all three seasons. In northern Taiwan, the percentage of southwesterly flow appearance was the highest in spring and decreased over warm seasons, while the trend reversed in southern Taiwan. Southwesterly flows formed in spring primarily due to a deepening mid-latitude trough over eastern China. Rain in Taiwan increased during southwesterly flow events when the Pacific subtropical high retreated eastward and the trough moved closer to Taiwan. In the Mei-yu season, there was greater moisture and the formation of southwesterly flows was more equally contributed to by the mid-latitude trough and the southwestward extending Pacific high than in spring. The southwesterly flow axis was located roughly over Taiwan. This flow axis shifted southeastward as the Pacific subtropical high weakened. At the same time, the high moisture zone covered the northern South China Sea and the entire island of Taiwan. As a result, moisture-laden air was transported to the Taiwan area by the strong southwesterly flow, providing favorable conditions for continuous rain in Taiwan. In summer, southwesterly flows formed when the Pacific high extended southwest and a low/tropical cyclone moved over southeastern China. Rain tended to be more intense when the low was stronger and closer to Taiwan.

著者

XUE Feng FAN Fangxing

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.2019-054, (Released:2019-07-05)

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Based on the monthly outgoing longwave radiation (OLR) data from 1979 to 2013, a significant correlation of convective activity over the western Pacific warm pool between June and August is detected while there are no significant correlations between June and July and between July and August. The analysis results indicate that consistent anomalies in June and August usually occur during the years with strong warm pool convection. Moreover, two prerequisites are necessary for this consistent anomaly, i.e., a higher sea surface temperature (SST) over the warm pool during the preceding spring and a relatively weak El Niño and Southern Oscillation (ENSO). An analysis based on the selected typical years indicates that convection in June tends to enhance when the warm pool SST is higher in the spring. The enhanced convection, in turn, reduces the solar insolation and local SST and consequently suppresses convection in July. In contrast to June, the local SST tends to increase due to the suppressed convection in July. Accordingly, the warm pool convection in August is subsequently enhanced again. In this process, the local air-sea interaction plays a major role in regulating SST anomalies from June to August and forming the consistent warm pool convection anomalies in June and August. There are additional complications in understanding intraseasonal variation in the warm pool convection from June to August as related to the ENSO forcing. During strong El Niño decaying years (e.g., 1998), the warm pool convection is suppressed with consistent positive OLR anomalies from June to August, implying that the El Niño forcing contributes to the significant positive correlation of convective activity between June and August. During moderate El Niño decaying years (e.g., 2007), however, the convection anomaly in June is opposite to that in August. In general, the local air-sea interaction effect plays an essential role in the significant correlation of convective activity between June and August, though this correlation also depends on the intensity of the El Niño forcing.

著者

MA Libin PETERS Karsten WANG Bin LI Juan

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.2019-053, (Released:2019-06-28)

被引用文献数

11

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Based on the preceding work, the influence of the Stochastic Multicloud Model (SMCM) on the Madden-Julian Oscillation (MJO) in the state-of-the-art ECHAM6.3 at-mosphere general circulation model (AGCM) is further evaluated. The evaluation present-ed here is based on six recently proposed dynamics-oriented diagnostic metrics. Lag-longitude correlation maps of surface precipitation in the East Indian and West Pacific Oceans confirm the previously found improved representation of the MJO in the modi-fied ECHAM6.3 model compared to the standard configuration. In fact, the modified ECHAM6.3 outperforms the default ECHAM6.3 in five of the six MJO-related diagnos-tics evaluated here. In detail, the modified ECHAM6.3 (1) successfully models the east-ward propagation of boundary layer moisture convergence (BLMC); (2) captures the rearward tilted structure of equivalent potential temperature (EPT) in the lower tropo-sphere and forward tilted structure of EPT in the upper troposphere; (3) exhibits the rear-ward tilted structure of equatorial diabatic heating in the lower troposphere; (4) adequate-ly simulates the MJO-related horizontal circulation at 850 and 200 hPa as well as the 300 hPa diabatic heating structure. These evaluations confirm the crucial role of convective-parameterization formulation on GCM-simulated MJO dynamics and support the further application and exploration of the SMCM-concept in full-complexity GCMs.

著者

NISHI Akifumi 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.2019-044, (Released:2019-04-19)

被引用文献数

3

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This study numerically examined how the locally strong “Karakkaze” wind in the Kanto Plain of Japan is affected by terrain shape, particularly by a convex feature in the mountain range. Our method involved running idealized numerical simulations with the Weather Research and Forecast model with a horizontal grid spacing of 3 km. The results revealed that a strong-wind region formed in the lee area of the convex feature, hereafter the semi-basin, and leeward of the semi-basin. In contrast, weak-wind areas formed adjacent to the strong-wind region. These results were consistent with the basic features of the observed surface wind pattern of the Karakkaze during the winter monsoon. However, such a flow pattern did not appear in the numerical simulation with a mountain range that lacked a convex feature. Sensitivity experiments were also conducted to evaluate the detailed effects of a mountain range with convexity. Sensitivity experiments with different convex shapes revealed that strong winds appeared within and leeward of the semi-basin when the aspect ratio of convexity (ratio of the wave amplitude to the wavelength of the convexity) exceeded about 0.5. Sensitivity experiments on terrain shape suggested that saddles in the mountain range were not essential to the formation of the Karakkaze, but they could affect its strength. Sensitivity experiments on the mountain Froude number, Frm, showed that locally strong winds within and leeward of the semi-basin appeared only when the Frm was in the range 0.42–1.04. Sensitivity experiments with surface heat fluxes (SHFs) showed that the basic structure of the strong-wind region in the leeward plain of the convex feature did not depend strongly on SHFs. However, the addition of SHFs reduced the surface wind speed but increased the size of the strong-wind region.

著者

WATANABE Shun-ichi I. MURATA Akihiko SASAKI Hidetaka KAWASE Hiroaki NOSAKA Masaya

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.2019-045, (Released:2019-04-15)

被引用文献数

9

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This study evaluates possible changes in tropical cyclone (TC) precipitation over Japan under a future warmer climate using an ensemble projection generated by a non-hydrostatic regional climate model with a resolution of 5 km (NHRCM05) under the RCP8.5 scenario. NHRCM05 reproduces TC precipitation and TC intensity more accurately than does a general circulation model with a resolution of 20 km. The number of TCs approaching Japan is projected to decrease under the future climate, while the TC precipitation rate increases. As these two effects cancel each other out, total TC precipitation, and the frequency of the moderate TC precipitation that is usual under the present climate, show no significant change. On the other hand, the frequency of extreme TC precipitation increases significantly because the intensification in the TC precipitation rate outweighs the reduction in TC frequency. The increase in the TC precipitation rate is caused primarily by the increase in water vapor around the TCs, which in turn results from the change in environmental water vapor. The intensification and structural changes to TCs also contribute to the enhanced TC precipitation.

著者

MIYAKAWA Tomoki MIURA Hiroaki

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.2019-034, (Released:2019-02-11)

被引用文献数

7

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The properties of tropical convection are evaluated using one-month long simulation datasets produced by the non-hydrostatic icosahedral atmospheric model (NICAM) using 3.5-, 7-, and 14-km horizontal meshes with identical cloud-microphysics configurations. The simulations are targeted on the 2nd Madden-Julian oscillation (MJO) event observed in the CINDY2011/DYNAMO field campaign. An increase of high cloud fraction at 200 hPa level and a reduction of surface precipitation occur as the horizontal resolution increases, corresponding to the reduction of precipitation efficiency due to the shorter residence time inside stronger updrafts that occur at the higher resolution. The increase of high cloud fraction is followed by the warming of the troposphere, which results in an increase in the column water vapor and an elevation of the freezing level. The total water condensation is decreased at higher resolutions, which is likely due to a balance with the decreased outgoing longwave radiation (OLR). The reproduced MJOs, which accounted for a large portion of the tropical convections, were similar in the 3.5-km and 14-km simulations in terms of eastward propagation speeds and structures, including the characteristic westward tilt of the moisture anomaly with height. However, the amplitude of the anomalous MJO circulation was considerably smaller in the 3.5-km simulation. The robust resolution dependence and the interpretations presented in this study underline the necessity for a resolution-aware cloud-microphysics optimization method that will have value in the coming era of global cloud-resolving simulations.

著者

WATANABE Shingo FUJITA Mikiko KAWAZOE Sho SUGIMOTO Shiori OKADA Yasuko MIZUTA Ryo 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.2019-038, (Released:2019-03-13)

被引用文献数

4

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Future changes in the climatological distribution of clear air turbulence (CAT) and its seasonality over the North Pacific are estimated based on an ensemble of climate projections under warming for the globally averaged surface air temperature of 2 K relative to pre-industrial levels, which includes over 3000 years of ensembles using a 60-km atmospheric general circulation model (AGCM). The AGCM outputs are interpolated to a 1.25° horizontal resolution, and the climatological CAT frequency is computed. The CAT broadly decreases in the mid-latitude central to western North Pacific along with the anticyclonic (south) side of its present-day high-frequency band extending from Japan to the eastern North Pacific. Meanwhile, large relative increases are found outside the band, implying an increased risk of CAT encounters. Uncertainty in future CAT changes due to uncertainties in the spatial pattern of sea surface temperature change is addressed for the first time using six selected Climate Model Intercomparison Project Phase-5 (CMIP5) climate models. The uncertainty is greatest in the boreal winter and spring over the central North Pacific, and is associated with uncertainty in future changes in the jet stream and upper-level synoptic-scale disturbances.

著者

IQBAL Waheed HANNACHI Abdel HIROOKA Toshihiko CHAFIK Léon HARADA Yayoi

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.2019-037, (Released:2019-02-15)

被引用文献数

1

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The interaction between the troposphere and the stratosphere has attracted the attention of climate scientists for several decades not least for the benefit it has on understanding dynamical processes and predictability. This interaction has been revived recently in regard to downward disturbance propagation effects on tropospheric circulations. The current study investigates such interactions over the North Atlantic region in relation to the eddy-driven jet stream. The atmospheric low-frequency variability in the winter over the North Atlantic sector is mainly associated with variations in the latitudinal positions of the North Atlantic eddy-driven jet stream. The Japanese Reanalysis JRA-55 data has been used to analyse the jet latitude statistics. The results reveal robust trimodality of the North Atlantic jet reflecting the latitudinal (i.e., northern, central and southern) positions in agreement with other reanalysis products. Thirty major sudden stratospheric warming events were analysed in relation to the three modes or regimes of the eddy-driven jet. The frequency of occurrence of the eddy-driven jet to be in a specific latitudinal position is largely related to the wave amplitude. The stratospheric polar vortex experiences significant changes via upward wave propagation associated with the jet positions. It is found that when the jet is close to its central mode the wave propagation of zonal wave number 2 from the troposphere to the stratosphere is significantly high. Eliassen-Palm fluxes from all waves and zonal wave number 1 depict deceleration of the stratospheric polar vortex for the eddy-driven jet with latitudinal position close to the northern mode. Plumb wave activity variations originate mainly in the Atlantic sector depending on the North Atlantic eddy-driven jet states. These significant associations between preferred latitudinal positions of the North Atlantic eddy-driven jet and the stratospheric dynamics may be a source of predictability.