著者
LEE Meng-Tze LIN Pay-Liam CHANG Wei-Yu SEELA Balaji Kumar JANAPATI Jayalakshmi
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.2019-048, (Released:2019-05-10)
被引用文献数
15

In the present work, long-term (10 years) raindrop size distribution (RSD) measurements from Joss-Waldvogel Disdrometer (JWD) installed at National Central University (NCU, 24&deg58′6″N 121&deg11′27″E), Taiwan and vertical profile of radar reflectivity were used to analyze the variations in gamma parameters of six seasons (winter, spring, mei-yu, summer, typhoon, and autumn) and types of precipitation. The normalized gamma distribution of RSD revealed that the highest mean Dm (Mass-weighted average diameter) values occurred in summer, whereas the highest mean log10Nw (normalized intercept parameter) values were found in winter. Furthermore, most of the rainfall rate falling at less than 20 mm h-1 occurs in Northern Taiwan. In this study, we used radar reflectivity to differentiate between convective and stratiform systems. It was revealed that the mean Dm values are higher in convective systems, whereas the mean log10Nw values are higher in stratiform systems. The structure of RSD in stratiform systems remains constant in all seasons; however, convection is similar to maritime type. The microphysical characteristics that are responsible for different RSD features in different seasons and types of precipitation are illustrated with the help of contoured frequency by altitude diagrams of radar reflectivity.
著者
SONG Bin ZHI Xiefei PAN Mengting HOU Meiyi HE Chengfei FRAEDRICH Klaus
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.2019-050, (Released:2019-05-24)
被引用文献数
4

The turbulent heat flux is the main passageway for air–sea interactions. However, due to lack of long-term observations for the turbulent heat flux, it is difficult to investigate the mechanisms of coupled ocean-atmosphere variabilities, such as the Pacific Decadal Oscillation. We here reconstructed the long-term turbulent heat flux in the North Pacific for the period 1921–2014 based on observations in the International Comprehensive Ocean-Atmosphere Data Set–International Maritime Meteorological Archive. The sea surface temperature, air temperature, wind and humidity were used to reconstruct the turbulent heat flux using the Coupled Ocean–Atmosphere Response Experiment (COARE3.5) algorithm. The modified Fisher–Tippett distribution was employed to calculate the turbulent heat flux at each grid square, and then the missing values were further derived based on data interpolating empirical orthogonal functions (DINEOF). The reconstructed turbulent heat flux was shown to be in accordance with the commonly used short-term heat flux datasets. This reconstruction is further examined by comparison with the long-term data of twentieth century reanalysis from European Center for Medium-range Weather Forecasts twentieth century reanalysis (ERA-20C) and the 20th Century Reanalysis (20CR) dataset from National Oceanic and Atmospheric Administration. It displays a good agreement with the ERA-20C both in spatial and temporal scales, but some differences from the 20CR. By these examinations, the reconstructed turbulent heat flux can well reproduce the main features of the air-sea interaction in the North Pacific, which can be used in studies of the air-sea interaction in the North Pacific on multidecadal timescales.
著者
Suranjith Bandara KORALEGEDARA Chuan-Yao LIN Yang-Fan SHENG
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.4, pp.821-839, 2019 (Released:2019-08-02)
参考文献数
52
被引用文献数
2

In this present study, we analyzed the synoptic and mesoscale dynamics and underlying mechanism of an extreme rainfall and flood event that occurred in Sri Lanka between 14-17 May 2016, using the Weather Research and Forecasting Model simulations with a horizontal grid size of 3 km and observational data. This extreme rainfall event was associated with a low-pressure system (LPS) that originated over the Bay of Bengal in the Indian Ocean and passed over Sri Lanka. The observed maximum accumulation of rainfall during the event exceeded 300 mm at several weather stations on 15-16 May and it resulted in severe flooding and landslides, particularly in the western part of the island. The model closely simulated the timing of the initiation of the LPS and its development along the east coast of Sri Lanka. The model could capture the overall rainfall tendency and pattern of this event. Synoptic and mesoscale analyses indicated that this extreme rainfall event occurred as the cumulative effect of a sustained low-level convergence zone, generated by an enhanced westerly monsoon flow and the circulation of the LPS, alongside a continuous supply of high-magnitude moisture, strong vertical motion, and orographic effects of the Central Mountains of Sri Lanka. Model sensitivity experiments indicated that the rainfall over the western slope area of the mountains was enhanced by mountain lifting, whereas western coastal rainfall was reduced because the mountains blocked the northeasterly flow of the LPS.
著者
浅井 富雄
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.48, no.1, pp.18-29, 1970 (Released:2008-05-27)
参考文献数
18
被引用文献数
66 85

Boussinesq近似にもとづく摂動方程式を差分近似法により数値的に解いて,不安定成層の平面Couette流中で発現する熱対流の性状を調べた.まつ゜流れの安定性を擾乱の水平波長,Richardson数等について示す.一様なシヤーをもつ流れは一般に擾乱の発達を抑制する効果をもち,その効果は波長の短いほど,又流れに直角な方向の波長が平行な方向の波長に比して長い-transverseモード-ほど著しい。一方流れに平行な方向の波長が直角な方向の波長に比して長く-longitudinalモード-なるにつれシヤー流の抑制作用は減じ,,流れに完全に平行なroll状の対流はシヤーの抑制作用を全く受けず増幅率の最も大きい所謂preferredモードとなる.Rayleigh数が大きくなると,基本流の平均速度で伝播する不安定波の他に波長のより短い前者と違った伝播速度をもつ不安定波が現れるが,その増幅率は前者に比して小さい.これらは異る解法により得られたKuo(1963)その他の結論と一致する.以上の予備的調査にもとついて,平均流で移動する波長の長い不安定波(熱対流にとって主要なモード)の構造やそれに伴うエネルギー変換について考察する.対流による熱の鉛直輸送に伴う位置エネルギーから運動エネルギーへの転換の他に,水平運動量の鉛直輸送に伴い基本流と擾乱の間に運動エネルギーの変換が生ずる.特に運動量の鉛直輸送は擾乱の3次元構造に強く依存する.擾乱がtransverseモードの場合,水平運動量は基本流のシヤーに抗して輸送-counter gradient transfer-され,従って擾乱の運動エネルギーから基本流のそれに転換される.この極端な場合が基本流に平行な鉛直面内の2次元対流で,著者(1964)の数値実験はこの結果を裏づけている.他方3次元運動を伴うlongitudinalモードの擾乱はtransverseモードのそれとは逆に運動量を輸送する.即ち基本流から擾乱へ運動エルギーを転換する.そしてシヤー流中ではこのlongitudinalの3次元対流がpreferredモードである.
著者
SEGUCHI Takafumi IWASAKI Suginori KAMOGAWA Masashi USHIYAMA Tomoki OKAMOTO Hajime
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.2019-033, (Released:2019-02-04)
被引用文献数
1

In the summer of 2016, 14 cases of jumping cirrus (JC) were observed around the Kanto region in Japan by ground-based, visible-light cameras. The cameras were set at the summit of Mt. Fuji and National Defense Academy (Kanagawa, Japan), and 15-second time-lapse photography was continually taken for the period. The location and spatial scale of the JC were calculated by measurements using the photometry of background stars in the nighttime and the geostationary meteorological satellite Himawari-8 infrared imagery. The environmental conditions of the JC were also investigated using radiosonde and Himawari-8 visible and infrared measurements. Comparing our cases to the JC in the United States of America (USA) reproduced by a three-dimensional, non-hydrostatic cloud model from previous studies, their motions, morphology, spatial and temporal scales showed similarities, although the horizontal scale of the JC and the magnitude of the underlying convection was relatively smaller in our cases. The sounding by the radiosonde in the vicinity of the storms showed that 3 of the 14 cases reached the stratosphere. However, the hydration of the lower stratosphere was not supported by an analysis of the brightness temperature difference (BTD) between 6.2 and 10.4 µm measured by Himawari-8. The averaged wind shear across the range of the jumping heights above the anvil was -1.1 ms-1 km-1. The maximum value of the convective available potential energy (CAPE) of the 14 cases was 1384 Jkg-1, which is several times smaller than those of the thunderstorm cases observed in the USA in previous numerical JC studies. This indicates that JC occurs from the cumulonimbus anvil top even if the convection is relatively weak. The motion of JC observed by visible-light cameras shows that it can transport moisture above the tops of the anvils of convective clouds regardless of its altitude as cloud ice appears to be sublimated.
著者
ZHAO Haikun WU Liguang WANG Chao KLOTZBACH Philip J.
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.2019-039, (Released:2019-03-11)
被引用文献数
8

Most studies have focused on variations of tropical cyclone (TC) frequency, intensity, and track over the western North Pacific (WNP), while variability of WNP TC season onset date (TCSO) has been less studied. Recent research has indicated a close association between WNP TCSO and sea surface temperature (SST) over the tropical Indian Ocean and the tropical central-eastern Pacific. This study finds the relationship between TCSO and SST underwent an interdecadal change in the late 1990s, likely due to a climate shift that occurred around that time. An observed significant correlation between TCSO and SST before the late 1990s and has been insignificant since that time. It was confrimed by the fact that ENSO positively correlates at 0.46 with TCSO from 1965-1999 (significant at the 95 % level), while the correlation becomes insignificant (0.16) during 1998-2016. Further analysis suggests that the close association between TCSO and SST is robust only for major El Niño events, with consistently extreme late TCSO following major El Niños during the satellite era. Accompanying the decay of major El Niños, tropical equatorial easterly anomalies in the WNP are driven by a Matsuno-Gill-type response to the specific SST anomaly pattern over the tropical Indo-Pacific sector. This in turn induces an anomalous anticyclone, anomalous westerly vertical wind shear, reduced mid-level moisture and suppressed convection over the WNP basin – all of which are unfavorable for WNP TCs, resulting in delayed TCSO following major El Niño events. These inter-decadal changes in the inter-annual correlation between TCSO and ENSO are largely due to the changing influence of moderate El Niño events on TCSO before and after the late 1990s. This study improves understanding of the ENSO-TC relationship, which should aid seasonal outlooks of WNP TC activity.
著者
FUJITA Mikiko SATO Tomonori YAMADA Tomohito J. KAWAZOE Sho NAKANO Masuo ITO Kosuke
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.2019-022, (Released:2018-12-17)
被引用文献数
4

We investigated extremely heavy precipitation that occurred around the Kinugawa River, Japan, in September 2015, and the probability of extreme precipitation occurrence, using data from a large ensemble forecast more than 1,000 members that were dynamically downscaled to 1.6 km horizontal grid spacing. The observed event was statistically rare among simulated cases and 3-day accumulated precipitation around the target area was equivalent to the 95th percentile among all simulated ensemble members. Our results show that this extreme precipitation event occurred under specific conditions: two coexisting typhoons at close proximity that produces a high atmospheric instability, and water vapor transport from the Pacific Ocean. We also assessed the probability of extreme precipitation in mountainous areas other than the Kinugawa River case. Heavy precipitation also occurred southwest of the Kinugawa River region due to two typhoons, similar to the Kinugawa River case. The tracks of these typhoons shifted marginally; however, there was a difference in the water vapor supplied to the area, causing heavy precipitation. The large-ensemble downscaled data used in this study hence enable us to evaluate the occurrence probability of a torrential rainfall event that was rarely observed, which may contribute to updating a disaster mitigating plan for possible similar disasters in future.
著者
OSE Tomoaki
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.2019-018, (Released:2018-12-07)
被引用文献数
8

Global warming experiments using three different 60 km-mesh atmospheric global circulation models are studied to characterize ensemble mean future changes in monthly East Asian precipitation for June to August. During the summer, wetting and drying effects due to changes in mean vertical motion play a key role in future precipitation changes, as does the “wet-get-wetter” effect due to increased moisture. The former processes are related adiabatically to the projected modification of 500 hPa horizontal atmospheric circulation, which is characterized by two cyclonic circulation anomalies extending over the eastern Eurasian Continent (C1) and the western North Pacific Ocean (C2) for each month. Over Japan, the western edge of C2 shifts from a region south of the Japanese Islands to northern Japan during June–August, representing a delayed northward movement or southward shift of the westerly jet over the western North Pacific in the future compared with the present-day climatology. Most regions of Japan lie within the northeasterly wind and associated downward motion zones of C2, leading to significant uncertainties in the future precipitation over Japan by the offset against the “wet-get-wetter” effect and possibly even a future decrease in precipitation. A wetter future climate is anticipated under weak subsidence or the upward vertical motion zone of C2, such as western Japan in August away from C2, and the Southwest Islands of Japan in June in the C2 southwesterly wind zone. Over the eastern Eurasian Continent, C1 is distributed mainly over northeastern China in June, central and southern China in July and August respectively. During these months, most of the eastern regions are located within the southwesterly-to-southeasterly wind zone of C1, indicating wet future conditions due to enhanced upward motion. This tendency drives a further increase in precipitation in future wetter East Asian climate via the “wet-get-wetter” effect and the increased evaporation.
著者
YAMAGUCHI Junpei KANNO Yuki CHEN Guixing IWASAKI Toshiki
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.2019-015, (Released:2018-11-24)
被引用文献数
31

An extreme cold surge event caused record-breaking low temperatures in the East Asia during 20–25 January 2016. The planetary- and synoptic-scale feature of the event is investigated quantitatively using the isentropic cold air mass analysis with the threshold potential temperature of 280 K. Because cold air mass is adiabatically conservative quantity, it is suitable for tracing and examining the extreme cold surges. We further introduce a metric named mean wind of cold air mass, which divides the factor of cold air mass evolution into convergence and advection parts. The new metric allowed us to trace the evolution of the cold air mass with dynamic consistency for a period of more than a week. A thick cold air mass built up over southern Sakha by a convergent cold air mass flow during 16–18 January. It migrated westward and reached Lake Baikal. On 20 January, an intense Siberian High developed with an eastward-moving mid-upper-level ridge, producing a strong surface pressure gradient over coastal regions of the Asian continent. This ridge and a cutoff low to the adjacent east formed a northerly flow in the mid-upper troposphere. The resultant southward flow through the troposphere blew the cold air mass over 480 hPa in thickness to the subtropical region of East Asia, causing strong cold surges there on 24 and 25 January. The abnormality of the event is further quantified using extreme value theory. The cold air mass gradually became rare along the path of the cold air mass from Lake Baikal to eastern China, which experienced as thick a cold air mass as once in 200 years. The cold air mass itself shows little change in thickness. Therefore, the migration of a cold air mass over 540 hPa in thickness from northern Siberia is the major cause of this cold surge extreme.
著者
ZHANG Siqi REN Guoyu REN Yuyu SUN Xiubao
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.2019-004, (Released:2018-10-29)
被引用文献数
5

This study aimed to improve understanding of the differences in surface air temperature data between observations and reanalysis since the beginning of the 20th century and to address the reanalysis data error. The anomaly correlation, standard deviation, and linear trend of temperature during 1909–2010 in eastern China was analyzed based on homogenized observation data from 16 stations and two sets of 20th century monthly mean surface air temperature reanalysis data (20CR and ERA20C). The results show that the inter-annual and decadal variability were consistent between reanalysis and observations in eastern China after 1979. The reanalysis data exhibited a large fluctuation during the 1960s. The average 20CR temperature was lower than the observations during 1920–1950. The inter-annual and decadal variability for winter and spring were consistent with the observations. The correlation and standard deviation ratio between the reanalysis and observations demonstrated a high consistency of their inter-annual variability and dispersion. The ERA20C data were generally closer to the observations than the 20CR data for the period 1979–2010. The linear trends of surface air temperature showed clear warming in both reanalysis datasets and the observations, but the reanalysis trends were significantly smaller than the observational trends for annual mean temperature and most of the seasonal mean temperatures after the 1950s. Overall, ERA20C was generally closer to the observational temperatures than 20CR during 1909–2010, but this consistency does not necessarily indicate ERA20C’s suitability for climate change research because of the systematic bias referenced to the observational data.
著者
KAJINO Mizuo DEUSHI Makoto SEKIYAMA Tsuyoshi Thomas OSHIMA Naga YUMIMOTO Keiya TANAKA Taichu Yasumichi CHING Joseph HASHIMOTO Akihiro YAMAMOTO Tetsuya IKEGAMI Masaaki KAMADA Akane MIYASHITA Makoto INOMATA Yayoi SHIMA Shin-ichiro TAKAMI Akinori SHIMIZU Atsushi HATAKEYAMA Shiro SADANAGA Yasuhiro IRIE Hitoshi ADACHI Kouji ZAIZEN Yuji IGARASHI Yasuhito UEDA Hiromasa MAKI Takashi MIKAMI Masao
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.2019-020, (Released:2018-12-09)
被引用文献数
36

Model performance of a regional-scale meteorology – chemistry model (NHM-Chem) has been evaluated for the consistent predictions of the chemical, physical, and optical properties of aerosols. These properties are essentially important for the accurate assessment of air quality and health hazards, contamination of land and ocean ecosystems, and regional climate changes due to aerosol-cloud-radiation interaction processes. Currently, three optional methods are available: the 5-category non-equilibrium, 3-category non-equilibrium, and bulk equilibrium methods. These three methods are suitable for the predictions of regional climate, air quality, and operational forecasts, respectively. In this paper, the simulated aerosol chemical, physical, and optical properties and their consistency were evaluated by using various observation data in East Asia. The simulated mass, size, and deposition of SO42- and NH4+ agreed well with the observations, whereas those of NO3-, sea-salt, and dust needed improvement. The simulated surface mass concentration (PM10 and PM2.5) and spherical extinction coefficient agreed well with the observations. The simulated aerosol optical thickness and dust extinction coefficient were significantly underestimated.
著者
Kazuaki NISHII Takafumi MIYASAKA Yu KOSAKA Hisashi NAKAMURA
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.87, no.3, pp.581-588, 2009 (Released:2009-07-08)
参考文献数
17
被引用文献数
10 11

A reanalysis dataset is used to establish the relationship between the year-to-year fluctuations in the midwinter storm-track activity over the Far East measured by poleward heat flux associated with subweekly disturbances and the occurrence of the first spring storm with strong southerly winds over Japan (Haru-Ichiban). Our analysis reveals that its early (delayed) occurrence tends to follow the enhanced (suppressed) winter storm-track activity with less (more) apparent minimum in midwinter in the course of the seasonal march. A metric is defined on the basis of the eddy heat flux to measure the reproducibility of the particular seasonal march of the Far East storm-track activity simulated in each of the Coupled Model Intercomparison Project Phase 3 climate models under the present climate. Under a particular global warming scenario, ensemble projection based only on the several models that show the highest reproducibility of the storm-track activity measured with the particular metric indicates that the future enhancement is likely in the midwinter storm-track activity associated with the weakening of the East Asian winter monsoon, implying that Haru-Ichiban is likely to occur earlier in the late 21st century than in the 20th century.
著者
MURATA Hidehiko SAITOH Kotaro SUMIDA Yasuhiko
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.2018-049, (Released:2018-07-13)
被引用文献数
12

Combination of three visible bands of the Advanced Himawari Imager (AHI) on-board JMA's new-generation Himawari-8 and -9 geostationary meteorological satellites enable production of true color imagery. True color is intuitively understandable to human analysts and beneficial for monitoring surface and atmospheric features. It is especially useful when applied to frequent observation from a geostationary platform. This article reports on an application of a color reproduction approach based on the CIE 1931 XYZ color system to imagery rendering. The approach allows consideration of primary color (RGB) differences among satellite and output devices which in turn cause differences in the colors reproduced. The RGB signals observed by AHI are converted to XYZ tristimulus values, which are independent of devices themselves, and then re-converted to RGB signals for output devices via the application of 3 x 3 conversion matrices. The article also covers an objective technique for the evaluation of XYZ values accuracy. The evaluation indicated that the combination of AHI native RGB bands is sub-optimal for obtaining XYZ values as-is, while a combination in which the green band is replaced by a pseudo band with a central wavelength of around 0.555 µm is optimal. The pseudo band is generated via regression with existing visible and near-infrared bands as predictor variables. The imagery produced using this approach was termed True Color Reproduction (TCR). The approach is applicable to other satellites that have several bands in the visible to near-infrared spectral range, and has the potential for development toward the production of standardized sensor-independent true color imagery.
著者
KAZUMORI Masahiro
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.2018-037, (Released:2018-04-07)
被引用文献数
13

This article reports on the impacts of Himawari-8 Clear Sky Radiance (CSR) data assimilation in the global and mesoscale numerical weather prediction (NWP) systems of the Japan Meteorological Agency (JMA). Adoption of the Advanced Himawari Imager (AHI) on board JMA’s Himawari-8 and -9 satellites has enhanced observational capabilities in terms of spectral, horizontal, and temporal resolution. Improvements brought by the switchover from the Multi-functional Transport Satellite-2 (MTSAT-2) to the new-generation Himawari-8 satellite include an upgrade to the horizontal resolution of CSR data from 64 to 32 km and an increase in the number of available water vapor bands from one to three. CSR products are obtained every hour and distributed to the NWP community. The improved horizontal and spectral resolution of Himawari-8 CSR data provides new information on horizontal water vapor distribution and vertical profiles in data assimilation. In data assimilation experiments using JMA’s global NWP system, the assimilation of Himawari-8’s three water vapor bands significantly improved the tropospheric humidity field in analysis, especially in the lower troposphere, as compared to assimilation of the single MTSAT-2 water vapor channel. First-guess (FG) departure statistics for microwave humidity sounders indicated an improvement in the water vapor field, especially over Himawari-8 observation areas. Improved forecasting of tropospheric temperature, humidity, and wind fields for Himawari-8 observation areas was also seen. In data assimilation experiments using JMA’s mesoscale NWP system, a disastrous heavy precipitation event that took place in Japan’s Kanto-Tohoku region in 2015 was investigated. A single water vapor band of Himawari-8 CSR corresponding to MTSAT-2 was assimilated, resulting in enhanced contrast of the water vapor field between moist and dry areas, as well as a realistic representation of moist air flows from the ocean in analysis. The changes also improved mesoscale model heavy precipitation forecasts.
著者
KANG Yunhee JEONG Jong-Hoon YOU Cheol-Hwan LEE Dong-In
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.2018-050, (Released:2018-07-13)
被引用文献数
2

On July 13, 2012, the bow echo was observed over the lee side of the Mt. Halla (1950 m above sea level) on Jeju Island, Korea. Three-dimensional wind-field and surface observation analyses were carried out to understand the structure and evolution of convective system with bow echo on the bell-shaped terrain. The northeastward-moving convective system passed over the approximately bell-shaped, isolated mountain with a mean speed of 17 m s-1. On the windward side of the mountain, the convective system developed by the inflow of unstable warm air from the ocean and terrain-induced upward motion, even with a low CAPE value of 511 J kg-1. When passing the lee side of the mountain, the bow echo was formed in the convective system by the strongest winds behind the bow echo. Behind the leading edge of the bow echo, the strengthened rear-inflow jet (RIJ) descended with relatively dry air along the surface, resulted in enhancing evaporative cooling. The precipitation-induced downdrafts generated a cold pool on the lee side of mountain. The development of an RIJ and cold pool formation both contributed to the evolution of the bow echo. In addition, the isolated bell-shaped terrain had a major indirect influence on the evolution of convective system with bow echo in this event.
著者
CHAN Kelvin T. F. CHAN Johnny C. L.
出版者
Meteorological Society of Japan
雑誌
気象集誌. 第2輯 (ISSN:00261165)
巻号頁・発行日
pp.2018-042, (Released:2018-04-27)
被引用文献数
14

This paper presents a summary of some of the observational and numerical studies on the climatology and possible change mechanisms of the outer-core wind structure of a tropical cyclone (TC), which has been generally referred to as size, a term also to be used in this review although various definitions have been given in the literature. In all the ocean basins where TCs exist, TC size has been found to vary with season, year, decade, latitude and longitude. Such variations are related to those in the synoptic flow patterns in which the TCs are embedded. Several factors have been identified to be responsible for changes in TC size, which include environmental humidity, vortex structure, sea surface temperature and planetary vorticity. Each of these factors can modify the transport of lower tropospheric angular momentum into the TC and hence cause changes in its size. The paper ends with a discussion of outstanding issues in the study of the outer-core wind structure of a TC.
著者
WANG Yafei XU Xiaoyu
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.2018-032, (Released:2018-04-07)
被引用文献数
13

The proposed study aims to examine the relation between the Tibetan Plateau (TP) thermal condition and El Niño and Southern Oscillation (ENSO). There were significantly positive correlations between the snow water equivalent (SWE) over the TP from November to next April and sea surface temperature (SST) in the Eastern Equatorial Pacific (EEP) in Novmber from 1987 to 2005. SST in EEP in November is most significantly correlated with the TP-SWE in next April, which suggests an accumulative effect of the ENSO on the TP snow cover. Although El Niño conditions could bring anomalous snowfall over the TP by generating a wave train entering the North African-Asian jet, it is questionable if this impact could change the thermal condition over the TP. There was almost no significant negative correlation between the SWE and TP surface temperature (representing the TP thermal condition) in winter. This suggests that the TP thermal condition hardly varies with the anomalous snowfall caused by this ENSO impact, despite some cooling effect of snowfall during the El Niño phase. On the contrary, preceding El Niño conditions tended to be associated with increasing TP surface temperature in May and there were significant positive correlations between SWE in April and TP surface temperature in May and June. ENSO might play a part in affecting TP thermal condition in a way that is quite different from the previous research. A plausible mechanism based on the relation of ENSO-TP thermal condition has been proposed. The mechanism explained the direct and indirect effects of ENSO on the TP thermal condition and role that the seasonal progress can play in this relation. The issues about snow cover aging and the impact of global warming, among others, were also included in the mechanism.
著者
KAWAI Kei KAI Kenji JIN Yoshitaka SUGIMOTO Nobuo BATDORJ Dashdondog
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.2018-023, (Released:2018-01-26)
被引用文献数
12

The Gobi Desert is one of the major sources of Asian dust, which influences the climate system both directly and indirectly through its long-range transport by the westerlies. In this desert, three ground-based lidars are operated in Dalanzadgad, Sainshand, and Zamyn-Uud, Mongolia. This study firstly combined these lidars into a lidar network and shows the spatial development of a dust layer over the desert and the long-range transport of the dust during 22–23 May 2013 via the lidar network. During this dust event, a cold front accompanying an extratropical cyclone moved southeastward across the desert and sequentially passed through Dalanzadgad, Sainshand, and Zamyn-Uud. In Dalanzadgad, in the central part of the desert, a dust storm occurred owing to the strong wind (6–10 m s -1) associated with the cold front and reached a top height of 1.6 km. Some of the dust floated at a height of 0.9–1.6 km along the cold frontal surface. In Sainshand and Zamyn-Uud, in the eastern part of the desert, the dust layer extended from the atmospheric boundary layer (ABL) to the free troposphere in the updraft region of warm air in the cold frontal system. Overall, while the dust layer was moving across the desert with the cold frontal system, it was developing up to the free troposphere. The mechanism of this development can be explained by the combination of two processes as follows: (1) continuous emission of dust from the desert surface to the ABL by the strong wind around the cold front and (2) continuous transport of the dust from the ABL to the free troposphere by the updraft of the warm air in the cold frontal system. This mechanism can contribute to the long-range transport of dust by the westerlies in the free troposphere.
著者
SEINO Naoko ODA Ryoko SUGAWARA Hirofumi AOYAGI Toshinori
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.2018-029, (Released:2018-02-17)
被引用文献数
6

During the Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS) intensive observation period (IOP) in 2011-2013 summers, atmospheric environment of several heavy rainfalls was observed by means of radiosonde soundings in the Tokyo metropolitan area. We investigated formation and development processes of an extremely developed thunderstorm (Case 1 on 26 August 2011) and a moderately developed thunderstorm (Case 2 on 18 July 2013) observed in the TOMACS IOP, utilizing the radiosonde sounding data. Compared to Case 2, the mesoscale environment of the severe storm in Case 1 featured a lower level of free convection and a deeper layer of easterly flow. We carried out numerical simulations to investigate the formation processes of the convective systems in the two cases, using the Non-Hydrostatic Model (NHM) of the Japan Meteorological Agency (JMA) incorporating the Square Prism Urban Canopy (SPUC) scheme. Model results fairly represented the spatial distribution and amounts of the rainfall in both cases. In Case 1, the formation of a distinct convergence zone between easterly and southerly flows was the likely trigger of active convective systems around Tokyo. To further examine the urban impact on precipitation, we performed two comparative simulations, one using realistic current urban surface conditions (CRNT experiment) and the other using less urbanized surface conditions (LURB experiment). The CRNT experiment yielded more rainfall than the LURB experiment in the central urban area. It appears that higher temperatures caused by urbanization can lead to increased rainfall in Tokyo by intensifying convergence and ascending motion.