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.2020-061, (Released:2020-08-03)

被引用文献数

5

---

To reveal a maintenance mechanism for Rossby wave breaking (RWB) east of Japan and Pacific-Japan (PJ) pattern, which are triggered due to quasi-stationary Rossby wave propagation along the Asian jet, the past 44 RWB cases east of Japan is analyzed using a reanalysis dataset. A comparison between the composites of 7 persistent and 7 non-persistent cases, which are classified based on duration of the RWB and the PJ pattern, indicates that the persistent case shows the stronger and longer-lived quasi-stationary Rossby wave propagation along the Asian jet. The subsequent stronger RWB in the persistent case causes the consequential formation of the more enhanced PJ pattern, through the stronger high potential vorticity intrusion toward the subtropical western North Pacific. The persistent case further shows a persistent northward tilting vertical structure of the anomalous anticyclone east of Japan, accompanied by the enhanced anomalous warm air advection in the lower to middle troposphere north of the anomalously extended North Pacific Subtropical High associated with the PJ pattern. The Q-vector diagnosis and partial correlation analysis indicate that the anomalous warm air advection in the middle troposphere is closely associated with dynamically induced anomalous ascent from Japan to the east by an adiabatic process. Enhanced anomalous moisture flux convergence from Japan to the east, which is due to moisture inflow along the fringe of North Pacific Subtropical High from the subtropical western North Pacific, also causes the anomalous ascent over the region by a diabatic process. A simple correlation analysis indicates nearly equivalent associations of the adiabatic and diabatic factors with the anomalous ascent. The anomalous ascent contributes to the enhanced and persistent RWB, through negative vorticity tendency due to vortex squashing in the upper troposphere, which further contributes to the enhanced and persistent PJ pattern in the persistent case.

著者

Koji Terasaki Takemasa Miyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18A, no.Special_Edition, pp.8-14, 2022 (Released:2022-04-02)

参考文献数

22

被引用文献数

5

---

This study investigated the predictability and causes of the heavy rainfall event that brought severe disasters in Kyushu in July 2020 with a global numerical weather prediction system composed of the NICAM (non-hydrostatic icosahedral atmospheric model) and the LETKF (local ensemble transform Kalman filter). We performed ensemble data assimilation and forecast experiments using the NICAM-LETKF system with 1,024 members and 56-km horizontal resolution on the supercomputer Fugaku. The results showed that 1,024-member ensemble forecasts captured the probability of heavy rainfall in Kyushu about five days before it happens, although a 10-day-lead forecast is difficult. Ensemble-based lag-correlation analyses with the 1024-member ensemble showed very small sampling errors in the correlation patterns and showed that the moist air inflow in the lower troposphere associated with a low-pressure anomaly over the Baiu front was related to this heavy rainfall in Kyushu.

著者

Shinta Seto

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.53-57, 2022 (Released:2022-03-23)

参考文献数

14

被引用文献数

1

---

For over 20 years, precipitation measurement has continued with spaceborne radars including the Precipitation Radar (PR) operating at 13.8 GHz on the Tropical Rainfall Measuring Mission and the Ku-band Precipitation Radar (KuPR) operating at 13.6 GHz on the Global Precipitation Measurement mission core satellite. PR and KuPR have essentially the same hardware designs and the same algorithm to make standard products (PRV8 and KuPRV06, respectively). The surface precipitation rate estimates (R) and related variables are statistically compared between PR and KuPR for a common observation area (within 35°N and 35°S) and period (April to September 2014). Due to the difference in sensitivity, the total precipitation amount recorded by KuPR is larger than recorded by PR by approximately 1.3%. For heavy precipitation, PR shows a smaller measured radar reflectivity factor (Zm) and a larger R than KuPR. Zm is affected by the attenuation and it is smaller for PR than KuPR, as the frequency is slightly higher. The attenuation corrected radar reflectivity factor is almost the same for PR and KuPR. However, the adjustment factor is larger for PR, which results in a larger R. Direct comparison between PR and KuPR during matchup cases demonstrates similar results.

著者

KUDO Atsushi

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.2022-011, (Released:2021-11-02)

被引用文献数

2

---

The Japan Meteorological Agency (JMA) operates gridded temperature guidance to predict two-dimensional (2D) snowfall amounts and precipitation types e.g., rain and snow because surface temperature is one of the key elements to predict them. Operational temperature guidance is based on the Kalman filter, which uses temperature observation and numerical weather prediction (NWP) outputs only around observation sites. Correcting a temperature field when NWP models incorrectly predict a front's location or when observed temperatures are extremely cold or hot has been challenging.  In this study, an encoder–decoder-based convolutional neural network (CNN) has been proposed to predict gridded temperatures at the surface around the Kanto region in Japan. Verification results showed that the proposed model greatly improves the operational guidance and can correct NWP model biases, such as a positional error of fronts and extreme temperatures.

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.2022-012, (Released:2022-03-08)

被引用文献数

1

---

We introduce a new procedure to evaluate the snowdrift distribution over complex topography and improve the accuracy of snow avalanche warning systems. We select the Niseko region, Japan, as the target area, and first obtain the wind distribution map at a 50-m grid spacing for 16 wind directions. We then employ these maps to calculate the amount of snow erosion and deposition. We present a case study to demonstrate that the model output agrees fairly well with measurements of local wind speed and observed snowdrift distribution. While improvements can be made to improve the accuracy of the model results, including more comprehensive calculation procedures and quantitative comparisons of snowdrift formation and evolution, it appears that the presented snowdrift analysis is an effective tool that can be incorporated into a snow avalanche warning system that employs a simple snow-cover model.

著者

Asami Komatsu Kouichi Nishimura

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.246-251, 2020 (Released:2020-12-17)

参考文献数

28

被引用文献数

1

---

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.

著者

Koji Terasaki Takemasa Miyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.18A-002, (Released:2022-02-08)

被引用文献数

5

---

This study investigated the predictability and causes of the heavy rainfall event that brought severe disasters in Kyushu in July 2020 with a global numerical weather prediction system composed of the NICAM (non-hydrostatic icosahedral atmospheric model) and the LETKF (local ensemble transform Kalman filter). We performed ensemble data assimilation and forecast experiments using the NICAM-LETKF system with 1,024 members and 56-km horizontal resolution on the supercomputer Fugaku. The results showed that 1,024-member ensemble forecasts captured the probability of heavy rainfall in Kyushu about five days before it happens, although a 10-day-lead forecast is difficult. Ensemble-based lag-correlation analyses with the 1024-member ensemble showed very small sampling errors in the correlation patterns and showed that the moist air inflow in the lower troposphere associated with a low-pressure anomaly over the Baiu front was related to this heavy rainfall in Kyushu.

著者

Yusuke Goto Naoki Sato

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.18, pp.8-12, 2022 (Released:2022-02-02)

参考文献数

18

---

The horizontal movement vectors of the maximum rainfall area associated with local heavy rainfall around Tokyo in the afternoon of high-temperature summer days were analyzed using a numerical algorithm in order to investigate their relationship to the wind vectors in the free atmosphere. First, the movement vectors were objectively identified every 10 minutes from radar echo intensity data, and their time average from the onset to the termination of a heavy rainfall event was calculated. The results show that the maximum areas of localized heavy rainfall around Tokyo most frequently move to the east-southeast and southeast. Moreover, the direction of movement is shifted to the right relative to the mean direction of the free atmospheric winds in most cases. It is also implied that water vapor supply from the south in the boundary layer plays a role in the rightward movement.

著者

Ryosuke Shibuya Yukari Takayabu Chie Yokoyama

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.251-256, 2021 (Released:2021-12-28)

参考文献数

26

---

Atmospheric patterns associated with wide-spread extreme precipitation events during the Baiu season over western Japan have a diversity in the record. Using an objective approach based on the empirical orthogonal function (EOF) analysis, this study introduces a classification of atmospheric parameters related to the wide-spread extreme precipitation events which are not directly caused by tropical cyclones. The number of a rain gauge observation stations that record extreme precipitation during the Baiu season over western Japan is equivalently proportional to the scores of the first two Principal Components, implying that there are two orthogonal controlling factors for the occurrence of wide-spread extreme precipitation. The first Principal Component is well correlated with a typical frontal dynamical structure as the enhanced westerly jet, the large gradient of the equivalent potential temperature, and the upper-level Rossby wave train injecting into a cyclonic anomaly at the north of the precipitation area. On the other hand, the second Principal Component is dominated by moisture fields with a low-level cyclone and no upper-level signal. This finding could provide a physical understanding of the diversity of atmospheric patterns causing wide-spread extreme precipitation over western Japan and physical insight into how it will change in the future climate.

著者

Kazuya Yamazaki

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-039, (Released:2021-10-20)

---

A novel lightweight and high-accuracy variant of the image pan-sharpening technique is designed for Himawari-8 multispectral images. This method, named Additive Template Sharpening, injects higher-wavenumber components of the highest-resolution Band 3 images into lower-resolution visible or shortwave infrared images, thereby providing multispectral high-resolution images. This injection is realized by adding inter-band differential field to the high-resolution band, making use of the specific pixel arrangement of the Himawari-8 imager for simple and accurate coordinate transformations. Both subjective inspection of RGB composite images and objective evaluation of the upsampling indicate that Additive Template Sharpening exhibits higher accuracy than existing methods for Bands 1-6 of Himawari-8. This technique not only enables operational forecasters to diagnose atmospheric conditions in more details using higher-resolution RGB composites, but also provides higher-quality true-color imagery for the public.

著者

Thomas Birner John R. Albers

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.13A, no.Special_Edition, pp.8-12, 2017 (Released:2017-07-25)

参考文献数

34

被引用文献数

64

---

Abrupt breakdowns of the polar winter stratospheric circulation such as sudden stratospheric warmings (SSWs) are a manifestation of strong two-way interactions between upward propagating planetary waves and the mean flow. The importance of sufficient upward wave activity fluxes from the troposphere and the preceding state of the stratospheric circulation in forcing SSW-like events have long been recognized. Past research based on idealized numerical simulations has suggested that the state of the stratosphere may be more important in generating extreme stratospheric events than anomalous upward wave fluxes from the troposphere. Other studies have emphasized the role of tropospheric precursor events. Here reanalysis data are used to define events of extreme stratospheric mean flow deceleration (SSWs being a subset) and events of extreme lower tropospheric upward planetary wave activity flux. While the wave fluxes leading to SSW-like events ultimately originate near the surface, the anomalous upward wave activity fluxes associated with these events primarily occur within the stratosphere. The crucial dynamics for forcing SSW-like events appear to take place in the communication layer just above the tropopause. Anomalous upward wave fluxes from the lower troposphere may play a role for some events, but seem less important for the majority of them.

著者

Ryosuke Shibuya Yukari Takayabu Chie Yokoyama

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-044, (Released:2021-11-16)

---

Atmospheric patterns associated with wide-spread extreme precipitation events during the Baiu season over western Japan have a diversity in the record. Using an objective approach based on the empirical orthogonal function (EOF) analysis, this study introduces a classification of atmospheric parameters related to the wide-spread extreme precipitation events which are not directly caused by tropical cyclones. The number of a rain gauge observation stations that record extreme precipitation during the Baiu season over western Japan is equivalently proportional to the scores of the first two Principal Components, implying that there are two orthogonal controlling factors for the occurrence of wide-spread extreme precipitation. The first Principal Component is well correlated with a typical frontal dynamical structure as the enhanced westerly jet, the large gradient of the equivalent potential temperature, and the upper-level Rossby wave train injecting into a cyclonic anomaly at the north of the precipitation area. On the other hand, the second Principal Component is dominated by moisture fields with a low-level cyclone and no upper-level signal. This finding could provide a physical understanding of the diversity of atmospheric patterns causing wide-spread extreme precipitation over western Japan and physical insight into how it will change in the future climate.

著者

Ayako Seiki Yu Kosaka Satoru Yokoi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.17, pp.177-183, 2021 (Released:2021-10-10)

参考文献数

25

被引用文献数

3

---

The relationship between the boreal summer intraseasonal oscillation (BSISO) in the tropics and the summertime tropical-extratropical teleconnection called the Pacific-Japan (PJ) pattern is investigated. The positive correlation between the BSISO and intraseasonal PJ pattern peaks during BSISO phase 8 when the convective center of the BSISO reaches the vicinity of the Philippines. A composite analysis based on the BSISO events shows that intraseasonal responses to the migration of the BSISO extend to the midlatitudes and form circulation anomalies reminiscent of the PJ pattern. During phases 7-8, cyclonic wind anomalies with low-pressure signals drastically intensify north of the Philippines and southeasterly wind anomalies blow into midlatitude East Asia, influencing the summer climate. Other apparent intraseasonal signals in pressure and surface air temperature are found over the midlatitude central Pacific and eastern Eurasia, respectively. The intraseasonal variability in the PJ pattern associated with the BSISO undergoes strong interannual modulations, with enhanced intraseasonal signals in summers of the positive seasonal-mean PJ pattern and suppressed signals in those of the negative PJ pattern. This asymmetry between the positive and negative PJ summers highlights the importance of cross-scale interactions for a better understanding of summer climate in East Asia.

著者

Shin Fukui Akihiko Murata

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-036, (Released:2021-10-11)

---

This study statistically investigated sensitivities of simulated precipitation to horizontal resolution of a regional climate model, instead of focusing on particular cases. We performed long-term integrations of models with horizontal grid spacings of 20, 5, 2, 1 and 0.5 km over Kyushu in the Baiu seasons of 2009-2020. The 2-km grid model improves simulated precipitation to the 5-km grid models with and without cumulus parameterization. Further decreasing the gird spacing from 2 km to 1 and 0.5 km reduces the dependency of the frequency biases on intensities of hourly precipitation and mitigates the excessive concentration of heavy precipitation in small scale, approaching that of the radar/raingauge analysis. The features of individual deep moist convections, specifically the horizontal scale of updrafts, the representation of downdrafts and the number of convections, start to converge when the grid spacing is reduced from 1 to 0.5 km. The results suggest models with grid spacing of 1 km or less are needed to resolve deep moist convections and represent the resulting precipitations. The 2-km grid models can partly resolve the deep moist convections, but their effective resolution is still insufficient, requiring some parameterizations to simulate convective precipitations appropriately.

著者

Syukuro MANABE Ronald J. STOUFFER

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.85B, pp.385-403, 2007 (Released:2007-10-26)

参考文献数

54

被引用文献数

12 16

---

Based upon the results obtained from coupled ocean-atmosphere models of various complexities, this review explores the role of ocean in global warming. It shows that ocean can play a major role in delaying global warming and shaping its geographical distribution. It is very encouraging that many features of simulated change of the climate system have begun to agree with observation. However, it has been difficult to confirm the apparent agreement because the density and frequency of the observation are insufficient in many oceanic region of the world, in particular, in the Circumpolar Ocean of the Southern Hemisphere. It is therefore essential to intensify our effort to monitor not only at the surface but also in the subsurface layers of oceans.

著者

Akihito Umehara Toru Adachi Wataru Mahiko Hiroshi Yamauchi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-034, (Released:2021-10-04)

被引用文献数

2

---

The tornadic debris signatures (TDSs) of the Ichihara Tornado associated with Typhoon Hagibis (2019) were observed using two operational C-band dual-polarimetric weather radars and an X-band phased-array weather radar (PAWR). This TDS observation was the first to be made over Japan in a typhoon environment. The TDS bins spread over time, and the maximum vertical and aerial extents reached 2.4 km and 9.41 km2, respectively. The estimated rise velocity of the TDS was 8 m s−1. The first TDS was detected ∼1 min before damage reporting began. The TDSs became clearer along with the rotational velocity of the near-surface vortex detected by PAWR. The copolar correlation coefficient reached a minimum (0.27) ∼1 min after the tornado passed the most severely damaged area and increased gradually over 4 min. This suggests that heavy and/or dense debris was lofted and immediately fell out and/or diffused, whereas light debris remained aloft for ≥ 4 min. By comparing the PAWR-detected vortex signatures with aerial photographs, we inferred that the first TDS comprised vegetated debris, the clearest TDS mainly comprised destroyed manmade structures. These results indicate that TDS detection is effective both for investigating damage and for recognizing tornado's occurrence even in a typhoon environment.

著者

Hiroaki Ueda Mikihiro Yokoi Masaya Kuramochi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.17B-002, (Released:2021-08-04)

被引用文献数

7

---

During the early summer of 2020, a stagnation of the Meiyu-Baiu front brought torrential rainfall over East Asia. Meanwhile, the anticyclone was much enhanced over the subtropical western Pacific (SWP), which contributed abundant moisture to the Meiyu-Baiu rainband along the western rim of the anticyclone. Based on the sensitivity experiments of the linear baroclinic model by prescribing the observed diabatic heating anomalies, a combination of anomalous convection over the Indian Ocean and reduced rainfall over the western Pacific can account for the maintenance of zonally elongated SWP anticyclone. Interestingly, this period corresponded to the developing stage of La Niña, while the convective activities were notably suppressed over the warmed western Pacific. The sensitivity experiments to SST anomalies using the atmospheric general circulation model shows that the attenuated convection over the western Pacific can be ascribed to the warmed Indian Ocean associated with an atmospheric Kelvin wave wedge from the Indian Ocean. Overall, the suppressant SST effect of the Indian Ocean opposes and is greater than that of tropical Pacific. We issue a caveat regarding the additivity of the remote influence across the maritime continent. These results have important implications for the predictability of early summer rainfall over East Asia.

著者

Ryota Ishiyama Hiroshi L. Tanaka

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2021-020, (Released:2021-05-03)

被引用文献数

1

---

In this study, we conducted a domain-integrated vorticity budget analysis to quantitatively understand the developing mechanism of the Arctic Cyclone (AC) in August 2016 (AC16). The results showed that the vorticity enhancement of the AC16 was dominated by the horizontal flux convergence of vorticity at all layers with a maximum near the tropopause. The enhancement near the tropopause was characterized not only by the horizontal supply but also by the vertical transport of vorticity. In the boundary layer within the AC16, the convergence of horizontal winds and the corresponding divergence of vertical winds occurred. In addition, during the merging process, updrafts were dominant in the troposphere due to the structure of the mid-latitude cyclone. These structures caused the upward transport of vorticity to the tropopause, which is considered as an important internal process of the AC16. However, time-averaged vorticity budget during the developing stage indicated that the vertical flux term and the divergence term compensate with each other. As a result, it was concluded that the AC is excited and maintained by the merging of the vortices associated with the migrating mid-latitude cyclone and polar vortex.

著者

Wei-Ting CHEN Chien-Ming WU Wei-Ming TSAI Peng-Jen CHEN Po-Yen CHEN

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.1155-1171, 2019 (Released:2019-11-29)

参考文献数

61

被引用文献数

3

---

In this study, the climatological characteristics of object-based precipitation systems (OPSs) and moisture development are analyzed over the South China Sea (SCS) during the sharp transition of the summer monsoon onset. The satellite-observed statistics of the OPSs showed that over the 20-day pre-onset period, OPSs of small (< 100 km) to medium size (100-300 km) are active over the lands surrounding the SCS. The pre-onset composite mean shows a basin-scale (∼ 1000 km) local circulation with anomalous subsidence over the ocean, and ocean convection is mostly suppressed. Over the 20-day post-onset period, large (> 300 km) OPSs develop over the coastal ocean and contribute to over 60 % of the total precipitation. The number of large OPSs observed significantly increases along with the sharp moisture buildup within 10 days after the onset. The moisture budget suggests that the local contribution from convective vertical mixing is the major moisture source during the first pentad after the onset. The relationship between moisture buildup and convection organization is then examined using a set of idealized cloud-resolving model (CRM) experiments, with a land–ocean configuration approximating the SCS basin. The CRM appropriately represents the observed development of coastal convection. In the no-shear environment, a strong basin-scale circulation is formed, which suppresses the ocean moisture development. When large-scale vertical wind shear is imposed to represent the changes of large-scale circulation during the onset pentad, organized convection systems are increased over the coastal ocean and propagate toward the open ocean, accompanied by fast ocean moistening within 5-10 days.

著者

Saori Nakashita Takeshi Enomoto

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.17A-006, (Released:2021-03-23)

被引用文献数

2

---

The predictability of Typhoon Hagibis in October 2019 is examined with ensemble forecasts from four major operational numerical weather prediction centers. From six to four days before the landfall, the forecast from the Japan Meteorological Agency was the best among the four centers. However, the error increased sharply three days before the landfall. Consistent with the westward track error, a northwestward bias is found in the environmental winds. The ensemble sensitivity analysis for the landing region indicates a large sensitivity to a ridge located to the southeast of the typhoon. The member with the largest track error has perturbations that act to weaken the ridge. A low-pressure disturbance to the southeast of the ridge is found to migrate westward faster than the member with the smallest track error. Therefore, the typhoon is advected westward by the easterlies associated with the low. These results indicate a significant influence of the tropical disturbance on the predictability of Hagibis.