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

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

20

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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

THUNDATHIL Rohith SCHWITALLA Thomas BEHRENDT Andreas MUPPA Shravan Kumar ADAM Stephan WULFMEYER Volker

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.2020-049, (Released:2020-07-14)

被引用文献数

7

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The impact of assimilating thermodynamic profiles measured with lidars into the Weather Research and Forecasting (WRF)-Noah-Multiparameterization model system on a 2.5-km convection-permitting scale was investigated. We implemented a new forward operator for direct assimilation of the water vapor mixing ratio (WVMR). Data from two lidar systems of the University of Hohenheim were used: the water vapor differential absorption lidar (UHOH WVDIAL) and the temperature rotational Raman lidar (UHOH TRL). Six experiments were conducted with 1-hour assimilation cycles over a 10-hour period by applying a 3DVAR rapid update cycle (RUC): 1) no data assimilation 2) assimilation of conventional observations (control run), 3) lidar–temperature added, 4) lidar–moisture added with relative humidity (RH) operator, 5) same as 4) but with the WVMR operator, 6) both lidar–temperature and moisture profiles assimilated (impact run). The root-mean-square-error (RMSE) of the temperature with respect to the lidar observations was reduced from 1.1 K in the control run to 0.4 K in the lidar–temperature assimilation run. The RMSE of the WVMR with respect to the lidar observations was reduced from 0.87 g kg−1 in the control run to 0.53 g kg−1 in the lidar–moisture assimilation run with the WVMR operator, while no improvement was found with the RH operator; it was reduced further to 0.51 g kg−1 in the impact run. However, the RMSE of the temperature in the impact run did not show further improvement. Compared to independent radiosonde measurements, the temperature assimilation showed a slight improvement of 0.71 K in the RMSE to 0.63 K, while there was no conclusive improvement in the moisture impact. The correlation between the temperature and WVMR variables in the static-background error-covariance matrix affected the improvement in the analysis of both fields simultaneously. In the future, we expect better results with a flow-dependent error covariance matrix. In any case, the initial attempt to develop an exclusive thermodynamic lidar operator gave promising results for assimilating humidity observations directly into the WRF data assimilation system.

著者

MESINGER Fedor VELJOVIC Katarina

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.2020-050, (Released:2020-06-23)

被引用文献数

6

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While the terrain-following (sigma) system of representing topography in atmospheric models has been dominant for about the last 60 years, already half a century ago problems using the system were reported in areas of steep topography. A number of schemes had been proposed to address these problems. However, when topography steepness exceeds a given limit all these schemes except the vertical interpolation of the pressure gradient begin to use model information that for physical reasons they should not use. A radical departure from the system was that of the step-topography eta; but its attractiveness was reduced by the discovery of the corner separation problem. The shaved-cell scheme, nowadays referred to as cut-cell, was free of that problem, and was tested subsequently in idealized as well as real case experiments with encouraging results. The eta discretization has lately been refined to make it also a cut-cell scheme. Another method referred to usually as Immersed Boundary Method enabling treatment of terrain as complex as urban landscape came from computational fluid dynamics. It was made available coupled to the atmospheric Weather Research and Forecasting model.  Results of recent experiments of the cut-cell Eta driven by European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble members are analyzed. In these experiments, all cut-cell Eta members achieved better verification scores with respect to 250 hPa wind speed than their ECMWF driver members. This occurred when an upper tropospheric trough was crossing the Rocky Mountains barrier. These results are considerably less favorable for the Eta when switched to use sigma, i.e., Eta/sigma, pointing to the benefits of using topography intersecting as opposed to terrain-following systems. But even so the Eta/sigma shows an advantage over its driver members, suggesting that its other features deserve attention.

著者

JIN Kai WANG Fei ZONG Quanli QIN Peng LIU Chunxia

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.2020-040, (Released:2020-05-09)

被引用文献数

4

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Observed surface air temperature (SAT) warming at urban stations often contains both the signal of global warming and that of local urban heat island (UHI) effects which are difficult to be separated. In this study, an urban impact indicator (Uii) developed by the authors was modified to represent the extent to which the observed temperature from a station was influenced by UHI effects. While Uii was calculated through simplifying the city's shape to a circle, the modified Uii (MUii) was calculated considering the realistic horizontal distribution of the urban lands. We selected 45 urban stations in mainland China, and then selected an adjacent station for each urban station to constitute a station pair for which the background climate changes are nearly homogeneous. Thus, difference in the trends of annual averaged daily mean SAT (Trendmean), maximum SAT (Trendmax), and minimum SAT (Trendmin) between urban and adjacent stations (ΔTrend) could be mainly attributed to the difference in MUii changes between urban and adjacent stations (ΔMUii). Several linear regressions between ΔTrend and ΔMUii of 45 station pairs were calculated to estimate the UHI effects on Trendmean (UTmean), Trendmax (UTmax), and Trendmin (UTmin) of the 45 urban stations. The results showed that the mean MUii of the 45 urban stations has increased from 0.06 to 0.35 during 1992-2013. The positive correlations between ΔMUii and ΔTrend of the selected 45 station pairs were significant at the 0.001 significance level except for Trendmax. The average UTmean and UTmin of the 45 urban stations during 1954-2013 were approximately 0.05 and 0.11°C decade−1, respectively, accounting for 18 % and 31 % of the overall warming trends, respectively. The UTmin estimated in this study is about twice that of the previous result based on the regression equations between Uii and SAT trends.

著者

FENG Tao YANG Xiu-Qun WU Liang HUANG Ronghui YANG Dejian

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.2020-037, (Released:2020-04-09)

被引用文献数

5

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Using the Climate Forecast System Reanalysis, Joint Typhoon Warning Center best track, and Tropical Rainfall Measuring Mission precipitation data, two long-lasting synoptic-scale wave trains in 2004 and 2006 are selected to investigate the atmospheric factors controlling the structures of westward-propagating synoptic-scale disturbances over the tropical western North Pacific. The essential difference between these two wave trains is found in their vertical structures, such that the maximum perturbations occurred from the middle to lower troposphere with an equivalent barotropic structure in 2004 but primarily occurred in the upper troposphere with a prominent tilt with height in 2006. Distinct configurations of the monsoon troughs, the tropical upper-tropospheric troughs (TUTT), and associated vertical wind shear caused such structural differences. In 2004, the TUTT shifted eastward, creating an easterly sheared environment to confine synoptic-scale waves in the lower troposphere. Then, the monsoon trough enhanced the wave activity through barotropic energy conversion in the lower troposphere. In contrast, while the TUTT shifted westward in 2006, synoptic-scale waves prevailed in the upper troposphere by the environmental westerly shear. Meanwhile, the disturbances developed in the upper troposphere through to the conversion of kinetic energy from the TUTT, exhibiting a top-heavy vertical structure. The coherent movement of the monsoon trough and the TUTT modulate the vertical structure and the development of the synoptic-scale waves.

著者

YOSHINO Katsumi

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.2019-023, (Released:2018-12-13)

被引用文献数

12

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Aircrafts making landing and takeoff at Narita International Airport (Narita Airport) in Japan report frequently low-level wind shear (LLWS), a local variation of wind vector, with turbulence when the prevailing wind is southwesterly, which is crosswind to the runway direction. On 20 June 2012, an arrival aircraft at Narita Airport encountered a LLWS, which consisted of a sudden change of the wind vector from head wind component of 5 knots (2.6 m s-1) to tail wind component of 10 knots (5.1 m s-1), just before the touchdown and made a hard landing. None of cumulonimbus clouds, a front or a wind shear line was observed around the airport during her approaching and landing. Analyses of the data measured by the landing aircraft and the observations by the Doppler lidar at the airport revealed that the LLWS was caused by horizontal roll vortices, which developed in the atmospheric boundary layer (ABL) over the Shimofusa Tableland around the airport. The horizontal roll vortices had their axes nearly parallel to the mean wind direction, and their horizontal and vertical scales were approximately 800 m and 500 m, respectively. The present study demonstrated that existence of the horizontal roll vortices causing LLWS can be effectively detected by a single-Doppler lidar which utilizes backscattering from aerosols. Although the LLWS associated with the horizontal roll vortices has smaller magnitude than those caused by a microburst, a gust front and a front, a landing aircraft just before touchdown encounters the horizontal roll vortices with much higher probability than the other phenomena mentioned here since the horizontal roll vortices occurs at a horizontal spacing of approximately 800 m over a wide area during daytime of a clear day.

著者

CUI Ye RUAN Zheng WEI Ming LI Feng GE Runsheng

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.2020-028, (Released:2020-02-24)

被引用文献数

3

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Data from the continuous observations of 4 shallow snow events (echo top < 8 km) and 2 deep events (> 10 km) were obtained by the C-band vertically pointing radar with frequency modulation continuous wave technology (VPR-CFMCW) with extremely high resolution during the winter of 2015-2016 in middle latitudes of China. Generating cells (GCs) were found near the cloud top in each event. Reflectivity (Z), radial velocity (Vr), the vertical gradient of Z (dZ/dh, h is the vertical distance) and Vr (dVr/dh) showed different vertical distribution characteristics between the upper GC and lower stratiform (St) regions. The fall streaks (FSs) associated with GCs were embedded in the St regions. In the deep events, the proportions of GC regions were slightly larger, but the average contributions to the growth of Z (33 %) were lower than those in the shallow events (42 %). The average dZ/dh were usually 2-3 times larger inside GCs and FSs compared to outside. Bimodal Doppler spectra were used to establish the relationships between the Z and the reflectivity-weighted particle fall speed (Vz) for the 2 regions. The vertical air velocity (Wa) and Vz were then retrieved. The results show that both updraft and downdraft were alternately observed in GC regions. GC locations usually accompanied strong upward air motions, with average speeds mostly distributed around 1.2 m s−1, while downward air motions often appeared between GCs. In the St regions, the speeds of Wa were mainly within 0.5 m s−1. The upper areas of the St regions consisted primarily of weak upward motions, while weak downward motions dominated the lower areas. There was no apparent difference in Wa inside and outside the FSs. The average Vz was slightly larger inside GCs and FSs compared to outside, with the differences of 0.1-0.3 m s−1 and 0.2-0.4 m s−1 respectively.

著者

MA Yingzhao CHANDRASEKAR V. BISWAS Sounak K.

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.2020-025, (Released:2020-02-12)

被引用文献数

7

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The accurate estimation of precipitation is an important objective for the Dual-frequency Precipitation Radar (DPR), which is located on board the Global Precipitation Measurement (GPM) satellite core observatory. In this study, a Bayesian correction (BC) approach is proposed to improve the DPR's instantaneous rainfall rate product. Ground dual-polarization radar (GR) observations are used as references, and a log-transformed Gaussian distribution is assumed as the instantaneous rainfall process. Additionally, a generalized regression model is adopted in the BC algorithm. Rainfall intensities such as light, moderate, and heavy rain and their variable influences on the model's performance are considered. The BC approach quantifies the predictive uncertainties associated with the Bayesian-corrected DPR (DPR_BC) rainfall rate estimates. To demonstrate the concepts developed in this study, data from the GPM overpasses of the Weather Service Surveillance Radar (WSR-88D), KHGX, in Houston, Texas, between April 2014 and June 2018 are used. Observation errors in the DPR instantaneous rainfall rate estimates are analyzed as a function of rainfall intensity. Moreover, the best-performing BC model is implemented in three GPM-overpass cases with heavy rainfall records across the southeastern United States. The results show that the DPR_BC rainfall rate estimates have superior skill scores and are in better agreement with the GR references than with the DPR estimates. This study demonstrates the potential of the proposed BC algorithm for enhancing the instantaneous rainfall rate product from spaceborne radar equipment.

著者

JANAPATI Jayalakshmi SEELA Balaji Kumar LIN Pay-Liam WANG Pao. K. TSENG Chie-Huei REDDY K. Krishna HASHIGUCHI Hiroyuki FENG Lei DAS Subrata Kumar UNNIKRISHNAN C. K.

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.2020-015, (Released:2020-02-01)

被引用文献数

30

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We made an effort to inspect the raindrop size distribution (RSD) characteristics of Indian Ocean and Pacific Ocean tropical cyclones (TCs) using ground-based disdrometer measurements from observational sites in India and Taiwan. Five TCs (2010-2013) from the Indian Ocean and six TCs (2014-2016) from the Pacific Ocean were measured using particle size and velocity disdrometers installed in south India and south Taiwan, respectively. Significant differences between the RSDs of Indian Ocean and Pacific Ocean TCs are noticed. For example, a higher number of small drops is observed in Indian Ocean TCs, whereas Pacific Ocean TCs have more mid-size and large drops. RSDs of Pacific Ocean TCs have higher mass-weighted mean diameter and lower normalized intercept parameter than Indian Ocean TCs. RSD values quantified based on rainfall rate and precipitation types also showed similar characteristics between Indian Ocean and Pacific Ocean TCs. The radar reflectivity and rainfall rate (Z-R) relations and shape and slope (μ-Λ) relations of both oceanic (Indian and Pacific) TCs are found to be distinctly different. Possible causes for the dissimilarities in RSD features between Indian Ocean and Pacific Ocean TCs are due to relative differences in water vapor availability and convective activity between TCs in these two oceanic basins.

著者

NISHII Kazuaki TAGUCHI Bunmei NAKAMURA Hisashi

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.2020-041, (Released:2020-05-08)

被引用文献数

8

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Through a set of ensemble experiments with an atmospheric general circulation model (AGCM), potential influence of sea-surface temperature (SST) anomalies is assessed on large-scale atmospheric circulation anomalies that induced two extreme events observed over Japan in July 2018. One is a heavy rain event in early July mainly over western Japan, which was primarily due to extreme moisture inflow associated with a cyclonic anomaly to the southwest of Japan and an anticyclonic anomaly to the east of Japan. An AGCM experiment with global SST anomalies prescribed cannot reproduce the anticyclonic anomaly, which leads to the failure to simulate the enhancement of the moisture inflow and thereby precipitation over western Japan. The other extreme event is a heat wave in mid- and late July almost over entire Japan, which was due to a strong anticyclonic anomaly around Japan. The AGCM experiment with global SST anomalies can well reproduce the warm anticyclonic anomalies. The additional experiments have confirmed that SST anomalies in both the Tropics and midlatitude North Pacific have potential for forcing the leading mode of the atmospheric variability over the western North Pacific that brought the heat wave. Both the tropical and extratropical SST anomalies are also found to force poleward shift of the subtropical jet axis over the western Pacific and anomalous tropospheric warming in the midlatitude Northern Hemisphere both of which persisted in June and July.

著者

YANG Huadong WU Liguang XIE Tong

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.2020-020, (Released:2020-01-22)

被引用文献数

15

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The tropical cyclone (TC) center position is often needed in the study of the inner-core processes although there is currently no consensus on the definition of the TC center. While previous studies evaluated center-detecting methods in terms of the center position, vertical tilt and decomposed symmetric and asymmetric circulations, this study used the 1-km resolution output of the predicted Hurricane Wilma (2005) at 5-minute intervals to evaluate the four TC centers that are frequently used in the diagnostic analysis of the inner-core dynamics processes: the pressure centroid center (PCC), the potential vorticity (PV) centroid center (PVC), the maximum tangential wind center (MTC) and the minimum pressure variance center (MVC) by focusing on the evolution of the small-scale track oscillation and vortex tilt. The differences in the detected center position and vertical tilt are generally small during the course of rapid intensification and eyewall replacement. The four methods all lead to similar small-scale track oscillations that rotate cyclonically around the mean track. While the MVC and PVC lead to a relatively smooth rotation, abrupt changes exist in the track oscillation of the MTC; the track oscillation of the PCC contains amplified embedded rotations that are associated with the PV mixing in the eye region. The tracks of the MVC and PVC relative to the lower-level center (vertical tilt) are generally smooth, while the relative tracks of the MTC and PCC contain abrupt changes. The MVC also leads to the strongest symmetric structure in the tangential wind, PV, and radial PV gradient in the eyewall region. This study suggests that the MVC should be selected in the study of inner-core processes.

著者

TOMITA Tomohiko SHIRAI Taiga YAMAURA Tsuyoshi

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.2020-011, (Released:2019-11-30)

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In general, La Niña (LN) events are longer than El Niño (EN) events. Using objective analysis data, we herein investigated the effects of the Australian winter monsoon (AWM) on prolonging LN events. Conventionally, EN events are terminated through the eastward shift of the anomalous Walker circulation in the equatorial Pacific during March–August. In contrast, the stronger-than-usual AWM induced by the LN anchors the upflow branch of anomalous Walker circulation in the Indonesian maritime continent (IMC). The strength of the AWM is controlled by the surface temperature difference between the IMC and the northern Australian continent (NAC). The LN has a large impact on the decrease in surface temperature on the NAC through decrease of the downward surface short-wave radiation flux and increase in surface soil moisture on the NAC. In LN events, the strength of the AWM and the anomalous Walker circulation reinforce each other through the common convective ascending in and around the IMC, which may be termed LN–AWM feedback, prolonging the duration of LN events. During EN events, such feedback is weak so that EN events generally end in the period of March–August.

著者

UMEZAWA Taku ANDREWS Stephen J. SAITO Takuya

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.2020-007, (Released:2019-11-10)

被引用文献数

1

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Although methane plays an important role in climate change and atmospheric chemistry, its global budget remains quantitatively uncertain due mainly to a wide variety of source types. The stable carbon isotope ratio of atmospheric methane (δ13C-CH4) is useful for separating contributions of different source categories, but due to the complex and laborious analysis, limited measurement data exists. We present a new system for δ13C-CH4 measurement, optimized for the automated analysis of air samples. Although the system is designed in principle similarly to those in previous studies, we successfully set up the system with no use of cryogens (e.g. liquid nitrogen) and attained reproducibility sufficient to analyze atmospheric variations (∼ 0.1 ‰). We performed automated continuous measurements of ambient air outside our laboratory at about hourly intervals for 2 months, which characterized imprint of local methane sources well. Future measurement operation for flask air samples from existing atmospheric monitoring programs will provide a large number of atmospheric δ13C-CH4 data.

著者

HA Kyung-Ja YEO Ji-Hye SEO Ye-Won CHUNG Eui-Seok MOON Ja-Yeon FENG Xuelei LEE Yang-Won HO Chang-Hoi

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.2020-009, (Released:2019-11-16)

被引用文献数

15

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In 2018, heatwaves (HWs), which are defined as period of abnormally hot weather with the daily maximum temperature (T_Max) exceeding its 95th percentile threshold for at least three consecutive days, were prevalent during June to August, and temperature records were broken in many countries over East Asia (EA) including China (CH), Japan (JP), and the Korean Peninsula (KP). In particular, extreme HWs through July to August lasted for the longest duration with 21.3 days with T_Max reaching 36.9°C. The highest T_Max, recorded since 1907, exceeded to 41°C in Hongcheon, located east of Seoul in the KP. Here, we examine the factors that influenced the 2018 HW, and how these relate to the 1994 HW, which was second longest HW recorded in the KP. The results show that abnormally strong and northwestward extended anticyclone features observed in July 2018 lasted as a persistent North Pacific anticyclone anomaly until August 2018 centered at the northern KP. These anticyclone features subsequently formed as a modon-like blocking with a cyclonic anomaly in the East China Sea. Meanwhile, in August 1994, the North Pacific High (NPH) extended to eastern EA, which broked the meridional dipole structure and HWs do not persist. The NPH, which persisted till August 2018, was accompanied by a sinking motion, suppression of precipitation, anomalous maximum temperature, weakening of the westerly jet stream, and increased insolation due to clear sky. We find that the prolonged and northwestward-shifted NPH including the KP drove the extraordinarily hot 2018 summer in Korea. In addition, low precipitation and massive evapotranspiration with the persistent insolation in July 2018 influenced the dry condition at the surface. We suggest that the predictions for the location and duration of the NPH associated with the HWs are required to reduce heat-related mortality and the impact on agriculture due to excessive evapotranspiration.

著者

LIN Yu-Feng WU Chun-Chieh YEN Tzu-Hsiung HUANG Yi-Hsuan LIEN Guo-Yuan

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.2020-006, (Released:2019-11-10)

被引用文献数

3

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Using special data from the field program of “Impact of Typhoons on the Ocean in the Pacific” (2010) and an ensemble Kalman filter-based vortex initialization method, this study explores the impact of the Taiwan terrain on the uncertainty in forecasting track, intensity and rainfall of Typhoon Fanapi (2010) based on ensemble simulations. The results show that the presence of Taiwan topography leads to rapid growths of the simulation uncertainty in track and intensity during the landfall period, in particular at the earlier landfall period. The fast moving ensemble members show an earlier southward track deflection as well as the weakening of intensity, resulting in a sudden increase of standard deviation in track and intensity. During the period of offshore departure from Taiwan, our analysis suggests that the latitudinal location of the long-lasting and elongated rainband to the south of tropical cyclone (TC) center has a strong dependence on the latitude of the TC center. In addition, the rainfall uncertainty in southern Taiwan is dominated by the uncertainty of simulated TC rainband, and the latitude of TC track can be regarded as a good predictor of the rainband's location at departure time. It is also found that the rainband develop farther to the south as the topography is elevated. Considering the fact that the rainband impinging the high mountains in the southern Central Mountain Range generates the greatest accumulated rainfall, positions where the rainband associated circulation and its interaction with topography appear to offer an explanation on the uncertainty of the simulated rainfall.

著者

Bing CHEN Li DONG Guangyu SHI Li-Juan LI Liang-Fu 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.92A, pp.157-165, 2014 (Released:2014-11-05)

参考文献数

32

被引用文献数

10 31

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The estimation of the distribution of global anthropogenic heat release (AHR) from 1992 to 2009 was obtained by applying Defense Meteorological Satellite Program (DMSP)/Operational Linescan System (OLS) satellite data. The results indicate that global AHR was geographically concentrated, essentially correlating to economic activities. The anthropogenic heat flux concentrated in the economically developed areas, such as East Asia, Europe, and Eastern North America, reached a level high enough to influence regional climate. In contrast, the anthropogenic heat flux in vast areas, such as Africa, Central and North Asia, and South America, is very small. With the increases in global population and economic development, an increase in AHR was easily found. The model results show that AHR has a significant impact on surface temperature and that it is able to affect global atmospheric circulation, leading to a 1-2 K increase in the high-latitude areas of Eurasia and North America. The results show that AHR is able to affect global climate despite being limited to a region. Although the influence to global warming by AHR is not as large as greenhouse gases, such as carbon dioxide, on a global scale, AHR is an important factor in global climate change that should not be ignored.

著者

QIN Zhengkun ZOU Xiaolei

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.2019-064, (Released:2019-09-13)

被引用文献数

10

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The Tibetan Plateau (TP) and the atmospheric conditions over it strongly affect downstream regional weather. Advanced Microwave Sounding Unit-A (AMSU-A) brightness temperature observations provide temperature sounding information and have been long assimilated successfully for numerical weather prediction. AMSU-A brightness temperatures observed from the polar-orbiting NOAA-15 and -18 satellites in July and August 2016 were collected. During these months, the equator crossing time of these particular satellites was around 0600 local time. Observations collected within the three-hour periods centered at 0000 UTC and 1200 UTC, covering the TP, were assimilated. The weighting coefficients for mid-tropospheric AMSU-A channels 6 and 7 were significantly reduced over areas with terrain heights greater than 2 km and 4 km, respectively, in the National Centers for Environmental Prediction Gridpoint Statistical Interpolation system. The assimilation of AMSU-A observations was improved to better exploit the role of AMSU-A channels 6 and 7 over the TP. This was achieved by not decreasing the weighting coefficients of the two channels over the grassy surface of the TP’s high terrain so that they were consistent with the inverse error variances. This modification produced larger positive impacts of satellite data assimilation on the 48-h forecasts of the mid-tropospheric trough, water vapor, and quantitative precipitation forecasts downstream of the TP. This study also suggests the importance of having AMSU-A observations from early-morning satellite orbits for numerical weather prediction downstream of the TP.

著者

KIM Eun-Hee LEE Eunhee LEE Seung-Woo LEE Yong Hee

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.2019-056, (Released:2019-07-24)

被引用文献数

3

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In this study, we evaluated the impacts of revised observation error on ground-based global navigation satellite system (GNSS) zenith total delay (ZTD) data in the data assimilation system of the Korea Meteorological Administration 1.5 km convective-scale model. Out of 100 total stations on the Korean Peninsula, 40 ground-based GNSS data stations were assimilated using three-dimensional variational (3D-Var) data assimilation. The ZTD observation errors were diagnosed for each station using a posteriori methods, giving errors with a variety of spatial and temporal characteristics. These station-specific error data were then implemented using the data assimilation system, and their impacts were evaluated for a one-month period in July 2016. The root-mean-square error (RMSE) of the relative humidity in the lower troposphere was found to be improved for the period from T+0 to T+36 hours when using GNSS data. Replacing the errors used in the previous model with the average diagnosed errors also provided better results, but they were not as good as the results obtained using station-specific errors. We found that observation error is closely related to precipitable water vapor (PWV); therefore, correction values reflecting seasonal characteristics should be applied. In addition, the quantitative precipitation forecasts were improved in all experiments using GNSS data, although the effects were small.