文献一覧: 13496476 (ISSN) - Ceek.jp Altmetrics

3 0 0 0 OA Calculation of Snowdrift Distribution over Complex Topography to Improve the Accuracy of Snow Avalanche Warning Systems

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.18, pp.71-75, 2022 (Released:2022-04-22)
参考文献数: 20

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.

2022-04-29 07:14:51
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3 0 0 0 OA Effect of Upper-Air Moistening by Northward Ageostrophic Winds Associated with a Tropical Cyclone on the PRE Enhancement

著者: Kazuo Saito Takumi Matsunobu Tsutao Oizumi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18, pp.81-87, 2022 (Released:2022-04-25)
参考文献数: 26
被引用文献数: 2

As a complement work to the authors' previous studies, we examined the pre-typhoon rainfalls (PRE) ahead of typhoon T0918 (Melor) in October 2009. The influence of moistening in the upper atmosphere induced by the northward ageostrophic winds on PRE precipitation was examined by a sensitivity experiment using a cloud resolving model with a horizontal resolution of 2 km. The cloud resolving simulation showed a large impact of the water vapor in the upper atmosphere on the precipitation over western Japan. In the sensitivity experiment where the moisture in the middle and upper layers was reduced over the area off the south coast of western Japan, the water vapor reduction area was advected northward, and the snow in the middle and upper layers and the cloud ice in the upper layer decreased, reducing the rain below the melting level. The intrusion of drying air into the upper atmosphere reduced the thickness of the moist absolutely unstable layer (MAUL), and the maximum intensity of convective updrafts decreased by about 10% in the test experiment. In this case, the increase of rain in PRE was primarily caused by the deep northward water vapor transport which yielded a large amount of condensation in the middle and upper layers, and change of moist instability in the upper atmosphere subsidiarily enhanced the convective updrafts.

2022-04-29 07:14:38
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3 0 0 0 OA Continuous Measurements of Microbial Particles in Central Japan Using a Real Time Viable Particle Counter

著者: Koichi Watanabe Hirohito Satoh Teruya Maki
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.2022-017, (Released:2022-04-12)
被引用文献数: 1

The number concentrations of microbial (counted as viable) particles and size-separated particles were measured continuously in Imizu City, Toyama, in the coastal region of the Sea of Japan, in 2015 using a commercial real time viable particle counter. From February to June, large increases in the number concentrations of coarse particles with rapid increases of viable particles were observed during Asian dust events. In mid-July, a phenomenon was observed in which the number concentrations of viable particles decreased, although coarse particles significantly increased. From the results of the backward trajectory analysis, the phenomenon was considered to be due to the transport of volcanic ash from Nishinoshima. The monthly average number concentrations of the viable particles were highest in September, whereas the average concentrations of coarse particles were at a maximum in April.

2022-04-19 17:06:31
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3 0 0 0 OA Effect of Upper-Air Moistening by Northward Ageostrophic Winds Associated with a Tropical Cyclone on the PRE Enhancement

著者: Kazuo Saito Takumi Matsunobu Tsutao Oizumi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.2022-014, (Released:2022-04-06)
被引用文献数: 2

2022-04-19 17:06:23
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3 0 0 0 OA Accelerated Increase in Tropical Cyclone Heat Potential in the Typhoon Rapidly Intensifying Zone during 1955-2020

著者: Haruka Sasaki Tatsuo Motoi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18, pp.65-70, 2022 (Released:2022-04-08)
参考文献数: 31
被引用文献数: 3

Previous studies suggested that increases in ocean heat content result in strengthening of tropical cyclone (TC) and causing the associated disasters. In the western North Pacific (WNP), acceleration of increasing rates of tropical cyclone heat potential (TCHP: ocean heat content above 26°C from the surface) in the TC rapidly intensifying (RI: a 24-h intensity change of ≥ 30 kt) zone may have contributed to increases in TC intensity. However, there is no research on the relation of the acceleration of increasing rates to the variations in TCHP in a climatological view, differently from the relation to decadal variations such as Pacific Decadal Oscillation (PDO). This study focused on the relation of the variations in TCHP anomalies (TCHPA) to RITCs over the past six decades. Although the annual mean TCHPA in the global ocean was not accelerated, the TCHPA accelerated recently in the late 1990s over the RI zone particularly in fall (October-December) in the WNP. The acceleration of the increase in TCHPA was possibly explained by the intensification of trade wind-driven ocean general circulation and the combination of the linear trend of TCHPA with PDO phase change.

2022-04-18 22:18:18
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3 0 0 0 OA Impacts of midlatitude western North Pacific sea surface temperature anomaly on the subseasonal to seasonal tropical cyclone activity: case study of the 2018 boreal summer

著者: Tomoe Nasuno Masuo Nakano Hiroyuki Murakami Kazuyoshi Kikuchi Yohei Yamada
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.2022-015, (Released:2022-04-01)
被引用文献数: 3

In this study, we explored the impacts of midlatitude western North Pacific (WNP) sea surface temperature (SST) on tropical cyclone (TC) activity at intraseasonal to seasonal time scales during the 2018 boreal summer. During this period, a positive SST anomaly occurred in the midlatitude WNP and subtropical central Pacific; TC activity was abnormally high under the influence of the strong Asian summer monsoon. We performed sensitivity experiments using a global cloud system-resolving model for global SST (control, CTL) and SST that were regionally restored according to midlatitude WNP climatology (MWNPCLM). TC track density in the eastern WNP was higher in CTL than in MWNPCLM, in association with large-scale atmospheric responses; enhanced monsoon westerlies in the subtropical WNP, moist rising (dry subsiding) tendencies, and reduced vertical wind shear in the eastern (western) WNP. Enhanced TC activity in the eastern WNP was more distinct for intense TCs and during the active phase of intraseasonal oscillation (ISO). These results suggest that the impacts of midlatitude SST anomalies can reach lower latitudes to affect TC activity via large-scale atmospheric responses and ISO, which are usually overwhelmed by the impacts of SST anomalies in the tropics and subtropics.

2022-04-09 22:27:07
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3 0 0 0 OA A Regional Hybrid Gain Data Assimilation System and Preliminary Evaluation Based on Radio Occultation Reflectivity Assimilation

著者: Chih-Chien Chang Shu-Chih Yang Stephen G. Penny
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18, pp.33-40, 2022 (Released:2022-03-18)
参考文献数: 32
被引用文献数: 2

A regional hybrid gain data assimilation (HGDA) system is newly developed using Weather Research and Forecasting model (WRF). The WRF-HGDA augments an ensemble-based Kalman filter (WRF-LETKF) with information from the variational analysis system (WRF-3DVAR) by combining their gain matrices. The performance of WRF-HGDA is evaluated by assimilating the GNSS radio occultation (RO) observations from the FORMOSAT-3/COSMIC (FS3/C) and the FORMOSAT-7/COSMIC2 (FS7/C2) under an Observing System Simulation Experiment (OSSE) framework. The results demonstrate that the variational correction improves the WRF-LETKF, with the equal-weighted WRF-HGDA outperforming its component DA systems in the moisture and wind fields when only conventional observations are assimilated. Assimilating additional RO data from FS7/C2 further improves the WRF-LETKF and WRF-HGDA systems. Although the variational correction for the mid-level temperature causes degradation in the WRF-HGDA analysis, this can be alleviated by adjusting the combination weight to include more flow-dependent information in WRF-HGDA at these levels. Further tuning of the static background error covariance used in WRF-3DVAR also brings some improvement in the WRF-HGDA wind analysis. Our results imply that a well-tuned variational system is critical for the accuracy of the regional HGDA analysis.

2022-04-09 22:26:46
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3 0 0 0 OA Determining Multiple Thresholds for Thermal Health Risk Levels Using the Segmented Poisson Regression Model

著者: Ju-Young Shin Kyu Rang Kim Yong Hee Lee
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18, pp.41-46, 2022 (Released:2022-03-18)
参考文献数: 28

Determining the thresholds for risk assessment is critical for the successful implementation of thermal health warning systems. A risk assessment methodology with multiple thresholds must be developed to provide detailed warning information to the public and decision makers. This study developed a new methodology to identify multiple thresholds for different risk levels for heat or cold wave events by considering simultaneously impact on public health. A new objective function was designed to optimize segmented Poisson regression, which relates public health to temperature indicators. Thresholds were identified based on the values of the objective functions for all threshold candidates. A case study in identifying thresholds for cold and heat wave events in Seoul, South Korea, from 2014 to 2018, was conducted to evaluate the appropriateness of the proposed methodology. Daily minimum or maximum air temperature, mortality, and morbidity data were used for threshold identification and evaluation. The proposed methodology can successfully identify multiple thresholds to simultaneously represent different risk levels. These thresholds show comparable performance to those using the relative frequency approach.

2022-04-09 22:26:43
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3 0 0 0 OA Energy dispersion of westward propagating Rossby waves in tropical easterlies

著者: Yaokun Li Yanyan Kang
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.2022-013, (Released:2022-03-17)
被引用文献数: 2

The energy dispersion process of westward propagating Rossby waves in tropical easterlies are investigated in the linear nondivergent barotropic atmosphere. The variations in wave energy and amplitude along energy dispersion paths are calculated by solving the wave action conservation equation. The results suggest that a westward marching ray can form a cycle-like path near the turning latitude that is located in easterlies. Waves with shorter periods propagate between two turning latitudes, which are located in either the easterlies or westerlies and have the largest meridional propagation range. Waves with longer periods propagate between a turning latitude in westerlies and a critical latitude in easterlies. Both wave energy and amplitude can simultaneously increase to their maximum values at the turning latitudes that are located in easterlies. This implies that waves may develop significantly. Wave energy and amplitude do not always have an in-phase variation when the ray moves toward the turning latitude that is located in westerlies. The oscillating ranges of wave energy and amplitude are also limited. In this case, waves may not develop significantly.

2022-03-30 12:12:45
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3 0 0 0 OA Influence of Stratospheric Variability on the Winter-Mean Polar Tropospheric Climate

著者: Yuhji Kuroda Miho Toryu Hiroaki Naoe
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18, pp.47-52, 2022 (Released:2022-03-18)
参考文献数: 21

This study examined the influence of stratospheric variability on the polar winter tropospheric climate. The winter-mean tropospheric condition can be well represented by a winter-mean stratospheric index (the Polar-night Jet Oscillation (PJO) index) defined from profiles of monthly polar temperature anomalies. In winters with a positive (negative) index, the winter-mean surface pressure anomaly tends to acquire a positive (negative) pattern resembling the Arctic Oscillation (AO). This tropospheric condition tends to become a persistent polarity of the AO index throughout the winter. This tendency is also found when the PJO index for each month is used. Although the PJO index in January shows the best results, those in early winter can be used as predictors for the entire winter troposphere. Use of the PJO index for the stratospheric effect on winter troposphere is compared with that associated with the occurrence of the major stratospheric sudden warmings. The origin of the decadal variability of the index is also discussed.

2022-03-30 12:12:39
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3 0 0 0 OA Accelerated Increase in Tropical Cyclone Heat Potential in the Typhoon Rapidly Intensifying Zone during 1955-2020

著者: Haruka Sasaki Tatsuo Motoi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.2022-011, (Released:2022-03-03)
被引用文献数: 3

Previous studies suggested that increases in ocean heat content result in strengthening of tropical cyclone (TC) and causing the associated disasters. In the western North Pacific (WNP), acceleration of increasing rates of tropical cyclone heat potential (TCHP: ocean heat content above 26°C from the surface) in the TC rapidly intensifying (RI: a 24-h intensity change of ≥ 30 kt) zone may have contributed to increases in TC intensity. However, there is no research on the relation of the acceleration of increasing rates to the variations in TCHP in a climatological view, differently from the relation to decadal variations such as Pacific Decadal Oscillation (PDO). This study focused on the relation of the variations in TCHP anomalies (TCHPA) to RITCs over the past six decades. Although the annual mean TCHPA in the global ocean was not accelerated, the TCHPA accelerated recently in the late 1990s over the RI zone particularly in fall (October–December) in the WNP. The acceleration of the increase in TCHPA was possibly explained by the intensification of trade wind-driven ocean general circulation and the combination of the linear trend of TCHPA with PDO phase change.

2022-03-10 23:18:05
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3 0 0 0 OA Observing System Simulation Experiments of a Rich Phased Array Weather Radar Network Covering Kyushu for the July 2020 Heavy Rainfall Event

著者: Yasumitsu Maejima Takuya Kawabata Hiromu Seko Takemasa Miyoshi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18, pp.25-32, 2022 (Released:2022-03-07)
参考文献数: 35
被引用文献数: 6

This study investigates a potential impact of a rich phased array weather radar (PAWR) network covering Kyushu, Japan on numerical weather prediction (NWP) of the historic heavy rainfall event which caused a catastrophic disaster in southern Kumamoto on 4 July 2020. Perfect-model, identical-twin observing system simulation experiments (OSSEs) with 17 PAWRs are performed by the local ensemble transform Kalman filter (LETKF) with a regional NWP model known as the Scalable Computing for Advanced Library and Environment-Regional Model (SCALE-RM) at 1-km resolution. The nature run is generated by running the SCALE-RM initialized by the Japan Meteorological Agency (JMA) mesoscale model (MSM) analysis at 1800 JST 3 July 2020, showing sustained heavy rainfalls in southern Kumamoto on 4 July. Every 30-second synthetic reflectivity and radial winds are generated from the nature run at every model grid point below 20-km elevation within 60-km ranges from the 17 PAWRs. Two different control runs are generated, both failing to predict the heavy rainfalls in southern Kumamoto. In both cases, assimilating the PAWR data improves the heavy rainfall prediction mainly up to 1-hour lead time. The improvement decays gradually and is lost in about 3-hour lead time likely because the large-scale Baiu front dominates.

2022-03-10 23:17:39
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3 0 0 0 OA Future changes in extreme precipitation and their association with tropical cyclone activity over the western North Pacific and East Asia in 20 km AGCM simulations

著者: Hirokazu Endo Akio Kitoh Ryo Mizuta
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: pp.2022-010, (Released:2022-03-01)
被引用文献数: 1

Future changes in extreme precipitation over the western North Pacific and East Asia (WNP-EA) are investigated using a 20 km mesh atmospheric general circulation model (AGCM). Time-slice simulations are performed under low- and high-emission scenarios using different spatial patterns of changes in sea surface temperature. In the WNP-EA region, future changes in the climatological mean of the annual maximum 1 day precipitation total (Rx1d) are characterized by a large meridional variation, where the higher the latitude, the greater the rate of increase in Rx1d, although this pattern is not so clear under the low emission scenario. This feature probably results from a combination of two factors: a greater warming in high latitudes and a decrease in tropical cyclone (TC) frequency in the subtropics. The future changes in Rx1d climatology for the 20 km AGCM show a marked difference in comparison with those of the lower-resolution AGCM and conventional climate models. Part of this discrepancy may come from differences in model resolution through representation of TCs, suggesting that coarse-resolution models may have some systematic bias in future projections of extreme precipitation in the WNP-EA region.

2022-03-04 20:59:33
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3 0 0 0 OA Influence of an Upper-level Trough on the Formation of a Baiu Frontal Depression that Caused a Torrential Rainfall Event in Southern Kyushu, Japan on July 4, 2020

著者: Eigo Tochimoto Satoshi Iizuka Tadayasu Ohigashi
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18A, no.Special_Edition, pp.1-7, 2022 (Released:2022-02-11)
参考文献数: 24
被引用文献数: 5

The influence of an upper-level trough on a Baiu frontal depression (BFD) that caused a heavy rainfall event in southern Kyushu, Japan, on July 4, 2020, was examined using numerical simulations with and without the upper-level trough. The numerical simulation with the upper-level trough (CNTL) reproduced a reasonable well-developed BFD and heavy rainfall in southern Kyushu. Conversely, the numerical simulation without the upper-level trough (NOUT) produced a weaker BFD and notable southward rainfall shift compared with the situation in the CNTL. The weaker BFD for the NOUT was due to weaker convection than that of the CNTL over mainland China. Thus, strong convection over mainland China was essential for the formation and development of the BFD that caused heavy rainfall in southern Kyushu. Additional sensitivity experiments, in which the strength of the upper-level potential vorticity anomalies was reduced to 75, 50, and 25% of the CNTL, showed that the spatial rainfall distribution shifted southward and resulted in a change in precipitation amounts in southern Kyushu because of the weakening of the BFD.

2022-02-25 21:42:18
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3 0 0 0 OA Seasonal Predictability of Summertime Asian Jet Deceleration near Japan in JMA/MRI-CPS2

著者: Kazuto Takemura Hitoshi Mukougawa Yuhei Takaya Shuhei Maeda
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18, pp.19-24, 2022 (Released:2022-02-11)
参考文献数: 18

Seasonal predictability of summertime Asian jet deceleration near Japan is examined using monthly mean data of hindcasts based on an operational seasonal prediction system of the Japan Meteorological Agency. Interannual variabilities of the Asian jet deceleration averaged during July–August are generally well predicted with moderate to high forecast skill starting from initial months from January to June. The seasonal predictability of the Asian jet deceleration in specific years is, by contrast, limited with large forecast errors. An inter-member regression analysis for the forecast errors of the Asian jet deceleration using ensembles shows that the forecast errors of the Asian jet are associated with those of the Asian jet deceleration near Japan. Furthermore, the forecast errors of El Niño Southern Oscillation (ENSO)-related excessive upper-tropospheric divergence near Southeast Asia can account for the errors of the northward shifted Asian jet. The above-mentioned results indicate that more accurate seasonal prediction of ENSO can further improve the seasonal prediction skill of the Asian jet deceleration and summer climate near Japan.

2022-02-25 21:42:12
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3 0 0 0 OA Extremely Weak Cold-Air Mass Flux and Extratropical Direct Meridional Circulation Linked to the Record-Warm Winter 2019/2020 over East Asia

著者: Chiaki Kobayashi Shuhei Maeda Yuki Kanno Toshiki Iwasaki
出版者: Meteorological Society of Japan
雑誌: SOLA (ISSN:13496476)
巻号頁・発行日: vol.18, pp.1-7, 2022 (Released:2022-01-29)
参考文献数: 18
被引用文献数: 1

We examine the relationship between the record-warm winter (DJF) 2019/2020 over East Asia and the extremely weak hemispheric circulation anomaly. During this period, the polar cold-air mass (PCAM) flux over East Asia was the weakest on record since the DJF 1958/1959 due to the weak Siberian High. The zonal averaged surface temperature over the Northern Hemisphere mid-latitudes in DJF 2019/2020 was the highest since DJF 1958/1959 and was linked to the weakest PCAM flux at the mid-latitudes. The zonal mean field during this period was characterized by weak stationary waves, weak wave activity as diagnosed by Eliassen-Palm flux, and, to balance with this, record-weak extratropical direct meridional circulation (EDC). The weak EDC corresponded to weaker-than-normal meridional heat exchange and was consistent with warm anomalies in the Northern Hemisphere mid-latitudes, since the lower branch of EDC corresponds to zonally averaged cold air outflow. In addition, the statistical relationship also indicates the EDC intensity is negatively correlated with the surface temperature anomaly over East Asia.