著者

SEIKI Ayako YOKOI Satoru 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.2021-007, (Released:2020-11-12)

被引用文献数

7

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The impact of diurnal precipitation over Sumatra Island, the Indonesian Maritime Continent (MC), on synoptic disturbances over the eastern Indian Ocean is examined using high-resolution rainfall data by the Global Satellite Mapping of Precipitation project and the Japanese 55-year Reanalysis data during the rainy season from September to April for the period 2000-2014. When the diurnal cycle is strong, the high precipitation area observed over Sumatra in the afternoon migrates offshore during night-time and reaches 500 km off the coast on average. The strong diurnal events are followed by the development of synoptic disturbances over the eastern Indian Ocean for several days, and apparent twin synoptic disturbances straddling the equator develop only when the convective center of the Madden-Julian Oscillation (MJO) lies over the Indian Ocean (MJO-IO). Without the MJO, the synoptic disturbances develop mainly south of the equator. The differences in the locations and behaviors of active synoptic disturbances are related to the strength of mean horizontal winds in the lower troposphere. During the MJO-IO, the intensification of mean northeasterly winds in the northern hemisphere blowing into the organized MJO convection in addition to mean southeasterly winds in the southern hemisphere facilitate the formation of the twin disturbances. These results suggest that seed disturbances arising from the diurnal offshore migration of precipitation from Sumatra develop differently depending on the mean states over the eastern Indian Ocean. Furthermore, it is shown that the MJO events with the strong diurnal cycle tend to have longer duration and continuing eastward propagation of active convection across the MC whereas the convective activities of the other MJO events weaken considerably over the MC and develop again over the western Pacific. These results suggest that the strong diurnal cycle over Sumatra facilitates the smooth eastward propagation of the intraseasonal convection across the MC.

著者

大東 忠保 前坂 剛 鈴木 真一 出世 ゆかり 櫻井 南海子 岩波 越

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.99, no.1, pp.101-112, 2021 (Released:2021-02-28)

参考文献数

50

被引用文献数

2

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本研究では、非降水雲を検出することのできるKaバンド(波長8.6mm)偏波雲レーダーを用い、2016年5月21日に日本の首都圏に出現した晴天エコーの偏波パラメータを調べた。Kaバンド偏波雲レーダー観測において、晴天エコーと雲形成初期における雲・降水エコーを識別する可能性を確立することが目的である。対象とした日には晴天エコーは明瞭な日変化を示した。日の出前には晴天エコーは見られなかった。日の出以降、等価レーダー反射因子(Ze)は時間とともに増大し、現地時間の正午過ぎにはレーダー観測範囲内において水平方向に広範囲に広がったエコー(最大で>−15dBZ)が生じた。日没以降夜の早い時間帯に、Zeは急激に減少した。RHI(距離高度断面)観測によると晴天エコーは高度1.5kmより下層に限定されていた。晴天エコーのレーダー反射因子差(ZDR)は、現地時間18:00には大きな正の値(1.8dB)を示し標準偏差も大きかった。これは同時に観測された雲や弱い降水のエコーのZDR(0.4dB)と比較するとかなり大きい。雲・降水エコーと比べると偏波間相関係数(ρhv)は小さく(< 0.9)、合計の偏波間位相差(ΨDP)の距離方向の変動は大きかった。Zeの上限値、およびZDRとρhvの分布は、先行研究におけるSバンド(波長10cm)レーダーによって観測されたブラッグ散乱の特徴と矛盾していた。一方で、水平方向に広範囲に広がったエコー、大きなZDRと小さなρhvの値、ψDPの距離方向の大きな変動は昆虫エコーの特徴と一致する。ZDRとρhvを用いて定義される偏波抑圧比は、この種の晴天エコーと雲・降水エコーの識別に有効であると思われる。Kaバンド偏波雲レーダーによって取得される偏波パラメータは、晴天エコーと雲・降水エコーの識別に有用である。

著者

Hironobu Ueki Hisahiro Takashima Martina Michaela Friedrich

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-011, (Released:2021-03-03)

被引用文献数

1

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To clarify three-dimensional (3-D) spatiotemporal variations and horizontal–vertical transport processes in nitrogen dioxide (NO2) over urban areas, combined NO2 profile observations by multiple Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) and direct wind observations by 3-D coherent Doppler lidar were made over an urban area in Japan. MAX-DOAS measurements were conducted at Yakuin and Fukuoka University in Fukuoka urban area with high temporal resolution of four minutes.Enhanced NO2 concentrations were often observed over the city center. We conducted a case study on 29 November 2018 under clear sky conditions and NO2 profiles were well retrieved. Using MAX-DOAS at two locations, high NO2 concentrations were observed near the surface of the city center in the morning. Higher NO2 concentrations appearing gradually at higher altitudes over the city center and disappearing in the afternoon are explained using direct evidence of a 3-D wind field: an airmass with a high NO2 concentration was transported upward over the city center. Then, the airmass was advected landward by a sea breeze. Multiple MAX-DOAS combined with 3-D Doppler lidar constitutes a powerful tool for elucidating horizontal–vertical transport processes. It can contribute to the improvement of data retrieval by satellites for urban areas.

著者

Koichi Shiraishi Takashi Shibata

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.30-34, 2021 (Released:2021-02-23)

参考文献数

18

被引用文献数

2

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Stratospheric aerosols over the high Arctic at Ny Ålesund, Svalbard (79°N, 12°E) were observed continuously for four years from March 2014 by a lidar system using the second harmonic wavelength (532 nm) of the Nd:YAG laser. Our observations reveal the seasonal features of stratospheric aerosols and the arrival of the smoke at the high Arctic from Canadian forest-fire in August 2017. We estimated the seasonal variation for three years before the Canadian forest-fire when there was no apparent volcanic effect. In the estimation, we removed polar stratospheric clouds by the threshold temperature of their formation. The seasonal variation for the three years is that the vertical profiles of the backscattering ratio take a maximum value of about 1.05-1.06 at altitudes between 13 and 16 km from December to March, and about 1.02-1.04 at altitudes between 17 and 20 km from April to November. These results are compared with the results observed at the low Arctic, northern Norway. We also present the increases in the backscattering ratio and the volume depolarization ratio from September to December 2017 caused by the smoke from the Canadian forest-fire.

著者

Kuniyasu Sugawara Masaru Inatsu Seiji Shimoda Keach Murakami Tomoyoshi Hirota

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.24-29, 2021 (Released:2021-02-18)

参考文献数

31

被引用文献数

4

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While global warming may expand suitable places for potato cultivation in cold regions, it may reduce the yield due to the increase of hot days during the tuber growth period. This study evaluated the effects of global warming on potato cultivation over Hokkaido by dynamically-downscaled ensemble experiments called d4PDF and assessed applicability of possible adaptive measures. In this study, we define the suitable area based on the accumulated temperature and deduced a relationship between the potato yield per unit area and the number of hot days (maximum temperature > 28°C) from crop statistic data. In a warming environment with 2K or 4K increase in global-mean temperature relative to the present climate (1981-2010), the accumulated temperatures likely satisfied the criterion on potato production almost over Hokkaido. The risk of growth delay due to cold weather was projected to reduce. However, hot days in the tuber growth period would increase, reducing potato yield by 7% in a plus 2-K climate and 16% in a plus 4-K climate. This risk of yield loss would not be avoidable by moving up planting by 30 days, and the development of varieties that are tolerant to 31-33°C would be a possible way to adaptation.

著者

Tomoe Nasuno

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.16-23, 2021 (Released:2021-02-18)

参考文献数

46

被引用文献数

1

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Relationship between diurnal convection and the intraseasonal oscillation (ISO) over the western Maritime Continent (MC) was investigated by a case study of an ISO event that occurred during the Years of the Maritime Continent (YMC)-Sumatra 2017 campaign. Two sets of global cloud-permitting simulations using cloud microphysics settings for ISO prediction (CTL) and for climate simulation (MOD) were performed to clarify their impacts. CTL had biases of weaker diurnal variation and smaller precipitation amounts over land than in observations; these were reduced in MOD by higher probabilities of local intense convection in the middle troposphere and higher precipitation efficiency. The enhanced convection over land coincided with suppressed convection over the surrounding ocean, especially at the diurnal peak time of land convection. Exception is the onset period of the ISO convection, when upward moisture advection and precipitation increased also over ocean in MOD than in CTL at the diurnal peak time of oceanic convection. These results suggest that the enhancement of local convection over the MC by the cloud microphysical processes basically hinders the ISO convection by the activation of land convection, but it also favors the ISO convection development over ocean during the onset period.

著者

Hideo Shiogama Noriko N. Ishizaki Naota Hanasaki Kiyoshi Takahashi Seita Emori Rui Ito Toshiyuki Nakaegawa Izuru Takayabu Yasuaki Hijioka Yukari N. Takayabu Ryosuke Shibuya

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-009, (Released:2021-02-16)

被引用文献数

18

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Climate change impact assessment studies often use future projections of only a few global climate models (GCMs) due to limited research resources. Here we develop a novel method to select a small subset of GCMs that widely capture the uncertainty range of large ensemble. By applying this method, we select a subset of five GCM projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) ensemble for impact and adaptation studies in Japan. At first, we omit GCMs whose global warming projections have been evaluated to be overestimated in the recent literature. Then, we select a subset of five GCMs that widely captures the uncertainty ranges for 8 climate variables and have good performances in present-climate simulations. These selected GCM simulations will be used to provide better climate scenarios for impact and adaptation studies than those in the previous impact assessment project.

著者

James Taylor Arata Amemiya Takumi Honda Yasumitsu Maejima Takemasa Miyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-008, (Released:2021-02-09)

被引用文献数

6

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The predictability of the July 2020 heavy rainfall event that saw record-breaking rainfall over Western Japan in July 2020 is examined with the near real-time SCALE-LETKF numerical modelling system in a low resolution 18-km configuration setting. Ensemble-mean 5-day rainfall total forecasts showed close agreement with Japanese Meteorological Agency 1-km precipitation analyses in relation to the large-scale distribution of rainfall and to location of heaviest rainfall over Kyushu. Onset and duration of rainfall at specific sites across Kyushu were also well predicted by the forecasts. However, the precise prediction of heavy rainfall, including over the worst-hit Kumamoto and Kagoshima prefectures, was severely underestimated. Examination of the atmospheric conditions at the time of the heavy rainfall from reanalysis datasets and ensemble member forecasts showed very high humidity over central Kyushu with strong transport of moisture from the southwest to central regions. In addition, strong low-level convergence was observed to the west of Kyushu in both reanalysis and best performing member forecasts during the time of heavy rainfall, suggesting a potential contributing factor to the record-breaking rainfall.

著者

Sachie Kanada Hidenori Aiki Kazuhisa Tsuboki Izuru Takayabu

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17A, no.Special_Edition, pp.14-20, 2021 (Released:2021-01-28)

参考文献数

37

被引用文献数

8

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Numerical experiments on Typhoon Trami (2018) using a regional 1-km-mesh three-dimensional atmosphere–ocean coupled model in current and pseudo-global warming (PGW) climates were conducted to investigate future changes of a slow-moving intense typhoon under the warming climate. Over the warmer sea in the PGW climate, the maximum near-surface wind speed rapidly increased around the large eye of the simulated Trami. The stronger winds in the PGW simulation versus the current simulation caused a 1.5-fold larger decrease of sea surface temperature (SST) in the storm core-region. In the PGW climate, near-surface air temperature increased by 3.1°C. A large SST decrease due to ocean upwelling caused downward heat fluxes from the atmosphere to the ocean. The magnitude of the SST decrease depended strongly on initial ocean conditions. Consideration of the SST decrease induced by an intense typhoon, and a slow-moving storm in particular, indicated that such a typhoon would not always become more intense under the warmer climate conditions. An atmosphere–ocean coupled model should facilitate making more reliable projections of typhoon intensities in a warming climate.

著者

Le Duc Takuya Kawabata Kazuo Saito Tsutao Oizumi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-007, (Released:2021-01-29)

被引用文献数

15

---

Forecast performances of the July 2020 Kyushu heavy rain have been revisited with the aim of improving the forecasts for this event. While the Japan Meteorological Agency's (JMA) deterministic forecasts were relatively good, the JMA's ensemble forecasts somehow missed this event. Our approach is to introduce flow-dependence into assimilation by running a 1000-member local ensemble transform Kalman filter (LETKF1000) to extract more information from observations and to better quantify forecast uncertainties. To save computational costs, vertical localization is removed in running LETKF1000. Qualitative and quantitative verifications show that the LETKF1000 forecasts outperform the operational forecasts both in deterministic and probabilistic forecasts.Rather than a trick to save computational costs, removal of vertical localization is shown to be the main contribution to the outperformance of LETKF1000. If vertical localization is removed, forecasts with similar performances can be obtained with 100 ensemble members. We hypothesize that running ensemble Kalman filters with around 1000 ensemble members is more effective if vertical localization is removed at the same time. Since this study examines only one case, to assess benefit of removing vertical localization rigorously when the number of ensemble members is around 1000, a larger set of cases needs to be considered in future.

著者

Hiroaki Kawase Akihiko Murata Ken Yamada Tosiyuki Nakaegawa Rui Ito Ryo Mizuta Masaya Nosaka Shunichi Watanabe Hidetaka Sasaki

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.1-7, 2021 (Released:2021-01-27)

参考文献数

29

被引用文献数

12

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We investigate regional characteristics of future changes in snowfall in Japan under two emission scenarios—RCP2.6 and RCP8.5—using a high-resolution regional climate model with 5km grid spacing and discuss the influence of changes in atmospheric circulation. The high-resolution model can simulate details of changes in distributions of total snowfall in Japan. Under RCP2.6, the annual total snowfall decreases in most parts of Japan except for Japan's northern island, Hokkaido. In Hokkaido, the winter snowfall increases even under RCP8.5, especially in January and February. The snowfall peak is delayed from early December to late January in Hokkaido. Along the Sea of Japan in eastern Japan, the winter-total snowfall decreases even if the winter mean temperature is below 0°C in the future climate. The different snowfall changes in Hokkaido and on the Sea of Japan side of eastern Japan are caused by precipitation changes in each region. Future changes in atmospheric circulation related to the Aleutian low cause the enhancement and the inhibition of winter precipitation in Hokkaido and the Sea of Japan side of eastern Japan, respectively, contributing to changes in the regional characteristics of snowfall and snow cover in addition to moistening due to atmospheric and ocean warming.

著者

Bjorn STEVENS Claudia ACQUISTAPACE Akio HANSEN Rieke HEINZE Carolin KLINGER Daniel KLOCKE Harald RYBKA Wiebke SCHUBOTZ Julia WINDMILLER Panagiotis ADAMIDIS Ioanna ARKA Vasileios BARLAKAS Joachim BIERCAMP Matthias BRUECK Sebastian BRUNE Stefan A. BUEHLER Ulrike BURKHARDT Guido CIONI Montserrat COSTA-SURÓS Susanne CREWELL Traute CRÜGER Hartwig DENEKE Petra FRIEDERICHS Cintia Carbajal HENKEN CATHY Hohenegger Marek JACOB Fabian JAKUB Norbert KALTHOFF Martin KÖHLER Thirza W. van LAAR Puxi LI Ulrich LÖHNERT Andreas MACKE Nils MADENACH Bernhard MAYER Christine NAM Ann Kristin NAUMANN Karsten PETERS Stefan POLL Johannes QUAAS Niklas RÖBER Nicolas ROCHETIN Leonhard SCHECK Vera SCHEMANN Sabrina SCHNITT Axel SEIFERT Fabian SENF Metodija SHAPKALIJEVSKI Clemens SIMMER Shweta SINGH Odran SOURDEVAL Dela SPICKERMANN Johan STRANDGREN Octave TESSIOT Nikki VERCAUTEREN Jessica VIAL Aiko VOIGT Günter ZÄNGL

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.2, pp.395-435, 2020 (Released:2020-05-08)

参考文献数

131

被引用文献数

12 85

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More than one hundred days were simulated over very large domains with fine (0.156 km to 2.5 km) grid spacing for realistic conditions to test the hypothesis that storm (kilometer) and large-eddy (hectometer) resolving simulations would provide an improved representation of clouds and precipitation in atmospheric simulations. At scales that resolve convective storms (storm-resolving for short), the vertical velocity variance becomes resolved and a better physical basis is achieved for representing clouds and precipitation. Similarly to past studies we found an improved representation of precipitation at kilometer scales, as compared to models with parameterized convection. The main precipitation features (location, diurnal cycle and spatial propagation) are well captured already at kilometer scales, and refining resolution to hectometer scales does not substantially change the simulations in these respects. It does, however, lead to a reduction in the precipitation on the time-scales considered – most notably over the ocean in the tropics. Changes in the distribution of precipitation, with less frequent extremes are also found in simulations incorporating hectometer scales. Hectometer scales appear to be more important for the representation of clouds, and make it possible to capture many important aspects of the cloud field, from the vertical distribution of cloud cover, to the distribution of cloud sizes, and to the diel (daily) cycle. Qualitative improvements, particularly in the ability to differentiate cumulus from stratiform clouds, are seen when one reduces the grid spacing from kilometer to hectometer scales. At the hectometer scale new challenges arise, but the similarity of observed and simulated scales, and the more direct connection between the circulation and the unconstrained degrees of freedom make these challenges less daunting. This quality, combined with already improved simulation as compared to more parameterized models, underpins our conviction that the use and further development of storm-resolving models offers exciting opportunities for advancing understanding of climate and climate change.

著者

MAEJIMA Yasumitsu MIYOSHI Takemasa KUNII Masaru SEKO Hiromu SATO Kae

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.2019-014, (Released:2018-11-16)

被引用文献数

7

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This study aims to investigate the potential impact of surface observations with a high spatial and temporal density on a local heavy rainstorm prediction. A series of Observing System Simulation Experiments (OSSEs) are performed using the Local Ensemble Transform Kalman Filter with the Japan Meteorological Agency non-hydrostatic model at 1-km resolution and with 1-minute update cycles. For the nature run of the OSSEs, a 100-m-resolution simulation is performed for the heavy rainstorm case that caused 5 fatalities in Kobe, Japan on July 28, 2008. Synthetic radar observation data, both reflectivity and Doppler velocity, are generated at 1-km resolution every minute from the 100-m-resolution nature run within a 60-km range, simulating the phased array weather radar (PAWR) at Osaka University. The control experiment assimilates only the radar data, and two sensitivity experiments are performed to investigate the impact of additional surface observations obtained every minute at 8 and 167 stations in Kobe. The results show that the dense and frequent surface observations have a significant positive impact on the analyses and forecasts of the local heavy rainstorm, although the number of assimilated observations is three orders of magnitude less than the PAWR data. Equivalent potential temperature and convergence at the low levels are improved, contributing to intensified convective cells and local heavy rainfalls.

著者

Katsuya Yamashita Satoru Yamaguchi Takayuki Saito Yuya Yamakura Eiichiro Kanda Sento Nakai Hiroki Motoyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.271-276, 2020 (Released:2020-12-26)

参考文献数

16

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A system with existing snowfall sensors, which is used to control the operation of the sprinkler snow removal system, was developed to acquire data that can be used to generate snowfall distribution with high spatiotemporal resolution. This had advantages such as low installation and management costs, as well as flexibility with respect to the configuration of its observation points. The results confirmed that this system, developed for experimental purposes in Nagaoka City (Niigata Prefecture), made it possible to generate the snowfall amount distribution as well as the precipitation rate within a 25 km × 30 km area at 10-min intervals based on in-situ measurements conducted at 16 ground-based points. A comparison of the system with other observation systems confirmed that it could detect detailed spatial snowfall variations, which could not be achieved using existing the ground-based observation networks, and provide sufficient observation accuracy for winter road management. Since many snowfall sensors are installed on the Sea of Japan side of mainland of Japan, this system has the potential for extensive application in the snowy areas of Japan characterized by heavy snowfall at temperatures of approximately 0°C.

著者

Kentaroh Suzuki Toshihiko Takemura

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.240-245, 2020 (Released:2020-12-12)

参考文献数

25

被引用文献数

2

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The apparent hydrological sensitivity, defined as the global-mean precipitation change per increase of the global-mean temperature, is investigated for scenarios induced by different forcing agents. Simulations with a climate model driven individually by four different climate forcers, i.e. sulfate, black carbon, solar insolation and carbon dioxide (CO2), are analyzed in the context of energy balance controls on global precipitation to explore how different forcing agents perturb different energy components grouped into fast and slow responses. Similarities and differences among the forcing agents are found in ingredients of the tendency contributing to the hydrological sensitivity from various energy budget components. Specifically, the sulfate and solar forcings induce the hydrological sensitivity of ∼2.5%K−1 due to the slow response of radiative cooling whereas the black carbon induces a significantly negative hydrological sensitivity (∼−6.0%K−1) due to the strong atmospheric heating. The CO2-induced hydrological sensitivity is found in between (∼1.2%K−1) as a result from the slow response of radiative cooling and its partial compensation by the atmospheric heating. The findings provide a quantitative basis for interpreting climatic changes of global precipitation driven by a mixture of various natural and anthropogenic forcings.

著者

Sho Kawazoe Masaru Inatsu Tomohito J. Yamada Tsuyoshi Hoshino

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.233-239, 2020 (Released:2020-12-05)

参考文献数

30

被引用文献数

11

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Synoptic circulation patterns associated with heavy snowfall events in Sapporo are examined using large ensemble simulation with 60-km global climate experiments. For snowfall, a 5-km dynamically downscaled model from the 20-km regional simulation is utilized. To identify synoptic circulation patterns, self-organizing maps (SOMs) are applied, and their response to a warming climate is examined. The authors find that heavy snow events predominantly occur due to low pressure anomalies to the north/east of Hokkaido or over central Japan, and by high pressure anomalies over the Siberian continent. The 4 K warming climate shows robust decreases in heavy snowfall amounts associated with low pressure anomalies over central Japan and increases in heavy snowfall amounts under patterns with high pressure anomalies over Siberia. This is attributed to surface air temperature characteristics in future climates, as precipitation in the former with surface winds transporting warm, moist air from the south and east, develops predominantly above 0°C in the +4 K climate, while the latter, often resulting in intense snow band events, continues to be dominated by temperatures near or below zero.

著者

KAWAZOE Sho FUJITA Mikiko SUGIMOTO Shiori OKADA Yasuko WATANABE Shingo

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.2020-067, (Released:2020-08-28)

被引用文献数

2

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This study investigates future changes to extremely cool days (ECDs) during the summer (June-August) season in northeastern Japan by applying self-organizing map (SOM) technique to large ensemble simulations from the “database for Policy Decision making for Future climate change” (d4PDF). Two separate SOMs, one trained on mean sea level pressure using a combination of JRA-55 reanalysis and d4PDF to evaluate model performance, and a “master” SOM, which trained the SOMs using historical, +2K, and +4K simulations, were created to investigate possible climate change impacts to future ECDs. For model evaluation, summer climatology and ECDs were confirmed to occur with similar frequencies between circulation patterns in the JRA-55 and d4PDF. Surface temperature anomalies and horizontal wind composite from several high frequency ECD nodes exhibit similar spatial patterns for all days and ECD occurring in the node, with ECD composites depicting particularly strong northeasterly winds, commonly referred to as Yamase, blowing from high latitudes toward northeast Japan. Future changes using “master” SOMs suggest a gradual shift (from +2K to +4K) in preferred circulation patterns that result in ECDs, with the greatest increase in frequency associated to those with a strong low pressure system off eastern Japan and a moderate intensity Okhotsk Sea high, and decreased ECDs to those with either a strong Okhotsk Sea high or westward extension of the North Pacific high. Lastly, changes to the intensity of future ECDs are investigated by examining low level thermal advection. Results suggest that circulation patterns associated with increased ECD frequency coincide with those with very strong cold air advection for all climates, though the magnitude differs based on circulation patterns. Future changes show a weakening cold air advection and decreasing ECDs, due in large part to weakening meridional temperature gradient east of Japan.

著者

TAKEMURA Kazuto MUKOUGAWA Hitoshi

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-010, (Released:2019-12-01)

被引用文献数

22

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This study investigates a new possible process linking the quasi-stationary Rossby wave propagation (SWP) over Eurasia along the Asian jet and the Pacific-Japan (PJ) pattern through the Rossby wave breaking (RWB) near the jet exit region during boreal summer using a reanalysis dataset. To assess the statistical significance of the process, we conduct a lag composite analysis of the past 44 RWB events east of Japan. The result of the lag composite analysis shows that the SWP along the Asian jet induces the RWB accompanied by an amplified anomalous anticyclone east of Japan. The associated “inverse-S” shaped overturning of the upper-level potential vorticity (PV) distribution causes the southwestward intrusion of the high PV toward the subtropical western North Pacific (WNP). The Q-vector diagnosis and vorticity budget analysis indicate that the upper-level positive vorticity advection associated with the RWB is an important factor dynamically inducing ascent and reinforcing convection over the subtropical WNP, which in turn excites the subsequent PJ pattern. Classification of the cases by RWB strength indicates that the stronger RWB is significantly related to the stronger preceding SWP and subsequent enhanced PJ pattern, and vice versa. A partial correlation analysis of all the cases quantitatively shows the greater contribution of the upper-level positive vorticity advection over the subtropical WNP to the enhanced convection in this area and the formation of the PJ pattern, compared to that of the anomalous warm sea surface temperature condition. These results show that the SWP along the Asian jet can excite the PJ pattern, through the RWB east of Japan and the consequent intrusion of the high PV toward the subtropical WNP.

著者

Takashi Sekiya Yugo Kanaya Kengo Sudo Fumikazu Taketani Yoko Iwamoto Maki N. Aita Akitomo Yamamoto Katsuhiro Kawamoto

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.220-227, 2020 (Released:2020-11-25)

参考文献数

52

被引用文献数

6

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We quantified the global bromine- and iodine-mediated tropospheric ozone loss using global chemical transport model simulations. We tested three datasets of very short-lived substances (VSLS) emissions, three datasets of sea surface iodide concentrations, and an explicit representation of the effects of multi-phase reactions at the air-sea boundary on dry deposition. We then determined optimal model settings based on the evaluation using the ship-borne and aircraft-campaign observations over the ocean. Our evaluation suggested that the explicit representation of multi-phase reaction effects substantially reduced model biases of ozone in the lower troposphere (up to 11%). Moreover, the impacts of using different datasets of VSLS emissions and sea-surface iodide concentrations were relatively small. The global bromine- and iodine-mediated chemical ozone losses were estimated to account for 4% and 17% of the total chemical loss, respectively, while the global iodine-mediated dry deposition loss of ozone was estimated to account for 22% of the global total dry deposition. These bromine- and iodine-mediated ozone losses decreased surface ozone concentrations over the ocean by 10% and 23%, respectively. The observational constraint on model simulations made by this study supports that bromine and iodine substantially impact global tropospheric ozone through atmospheric chemical reactions and dry deposition processes.

著者

Asami Komatsu Kouichi Nishimura

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2020-041, (Released:2020-11-16)

被引用文献数

1

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This paper describes a simple snow-cover model (SSCM) that was developed primarily to evaluate the hazard to traffic posed by snow avalanches. The SSCM requires only air temperature and precipitation or snow depth as input data, and we simplified the physical processes that affect the snowpack in the model. Snow pit observations and the calculation for avalanche cases were carried out to verify the SSCM output. The SSCM was able to reproduce the change in the snowpack properties fairly well. Further, the snow stability index, which shows the ratio of shear strength to shear stress in the snow, indicated that the SSCM can be used to provide a reliable estimate of avalanche hazard.