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

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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

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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

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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

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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.

著者

HIRANO Kohin MAKI Masayuki

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.2018-028, (Released:2018-02-24)

被引用文献数

8

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This paper reports the development of a very-short-range nowcast system, VIL Nowcast, which aims to provide precise forecasts of imminent rainfall, and in particular, heavy and localized events. The system is based on the vertically integrated liquid water content (VIL), which is estimated from three-dimensional radar observations as well as the 1-minute-resolution rainfall map obtained from the X-band polarimetric (multi-parameter) RAdar Information Network (XRAIN), to predict rainfall amounts over 10 minutes periods that extend to 10--60 minutes into the future. The spatial resolution of VIL Nowcast was 500 m, and nowcasts were produced at a temporal resolution of 5 minutes. Three precipitation events, of which two were isolated storms and one was a synoptic storm, were used as case studies to verify the model. The performance of VIL Nowcast was evaluated against the XRAIN radar rainfall data and an existing rainfall-rate nowcast system using the same advection scheme. The scope of the evaluation was limited mainly to the first prediction for 10 minutes ahead. It was found that VIL Nowcast showed a small, statistically significant improvement over the entire precipitation event, although its skill decreased at longer lead times and at higher thresholds. The key findings of this study are: (1) VIL Nowcast appears capable of generating skillful forecasts at short lead times, even for very localized heavy rainfall; (2) VIL Nowcast can reduce the time lag in the rainfall-rate nowcast system at initiation and peak precipitation; and (3) this system may improve the accuracy of heavy rainfall alerts provided for public activities and emergency alarms.

著者

KAWASE Hiroaki SASAI Takahiro YAMAZAKI Takeshi ITO Rui DAIRAKU Koji SUGIMOTO Shiori SASAKI Hidetaka MURATA Akihiko NOSAKA Masaya

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.2018-022, (Released:2018-01-30)

被引用文献数

27

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Geographical distributions of heavy snowfall, especially in the Pacific Ocean side of Japan, have not been elucidated due to low occurrence frequency of heavy snowfall and limited number of snow observation points. This study investigates the characteristics of synoptic conditions for heavy daily snowfall from western to northeastern Japan in the present climate, analyzing high-resolution regional climate ensemble experiments with 5-km grid spacing. The Japanese 55-year Reanalysis (JRA-55) and the 10-ensemble members of the database for Policy Decision making for Future climate change (d4PDF) historical experiments are applied to the lateral boundary conditions of the regional climate model. Dynamical downscaling using d4PDF (d4PDF-DS) enables us to evaluate much heavier snowfall events than those simulated by dynamical downscaling using JRA-55 (JRA55-DS). Over the Sea of Japan side, heavy snowfall occurs due to cold air outbreaks, while over the Pacific Ocean side, heavy snowfall is brought by extratropical cyclones passing along the Pacific Ocean coast. A comparison between JRA55-DS and d4PDF-DS indicates that heavier snowfall can occur due to more developed extratropical cyclones and enhanced cold air damming in the Tokyo metropolitan area. The geographical distributions of extremely heavy snowfall are different between two typical synoptic conditions, i.e., cold air outbreaks and extratropical cyclones. The difference is much clearer in the extremely heavy snowfall events than in all snowfall events. Heavy daily snowfall occurs in January and February on the Pacific Ocean side, in December and January on the Sea of Japan side, and in November and March in high mountainous areas. Saturated water vapor pressure is largest around 0 ℃ under the snowing conditions. Synoptic conditions from late fall to winter are closely related to preferable conditions for heavy snowfall over the mountainous areas where the surface air temperature is much less than 0 ℃ in the heavy snowfall events.

著者

Hironori IWAI Shoken ISHII Seiji KAWAMURA Eiichi SATO Kenichi KUSUNOKI

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.96A, pp.3-23, 2018 (Released:2018-02-19)

参考文献数

61

被引用文献数

4

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During the Tokyo Metropolitan Area Convection Study for Extreme Weather Resilient Cities (TOMACS), many isolated convective storms developed in the southern Kanto Plain on August 17, 2012. The aim of this study was to clarify the dynamics leading to the convection initiation of one of them using different remote sensing instruments. Before the convection initiation, a southeasterly flow transported water vapor inland from Tokyo Bay and the well-mixed and a cumulus-cloud-topped convective boundary layer developed. A convergence line in the form of a sea breeze front (SBF) also moved inland from Tokyo Bay. A near-surface air parcel was lifted to its lifting condensation level (LCL) by an updraft in a convergence zone with a 3 km horizontal scale, which formed the west edge of the convergence line. The saturated air parcel at the LCL was then lifted to its level of free convection (LFC) by the updrafts associated with thermals below the cumulus cloud base. A Ku-band radar detected the first echo of hydrometeors about 6 minutes after the air parcel reached its LFC, then the convective cell developed rapidly. When an SBF arriving from Sagami Bay passed under the cell, the updraft over the nose of the SBF triggered a new precipitation cell, but no intensification of the preexisting cell was observed.

著者

Yoshihito SETO Hitoshi YOKOYAMA Tsuyoshi NAKATANI Haruo ANDO Nobumitsu TSUNEMATSU Yoshinori SHOJI Kenichi KUSUNOKI Masaya NAKAYAMA Yuto SAITOH Hideo TAKAHASHI

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.96A, pp.35-49, 2018 (Released:2018-02-19)

参考文献数

16

被引用文献数

4

---

The relationships between the occurrence of intense rainfall and the convergence of surface winds and water vapor concentration for typical heavy-rainfall cases were examined using data from July to August in 2011-2013, obtained from high-density meteorological observations in Tokyo, Japan. Additionally, the temporal variations in wind convergence and water vapor between days with and without heavy rainfall events were compared. Corresponding to heavy-rainfall areas, the convergence of surface winds tended to increase for several tens of minutes prior to the heavy rainfall. The peak of convergence was observed 10-30 min before the heavy-rainfall occurrence, and convergence continued to increase for approximately 30 min until the convergence peak time. Around the heavy-rainfall area, the increase in the water vapor concentration index coincided with the increase in convergence. From these results, by monitoring the temporal variations and distributions of these parameters using a high-density observation network, it should be possible to predict the occurrence of heavy rainfall rapidly and accurately.

著者

Shin-ichi SUZUKI Takeshi MAESAKA Koyuru IWANAMI Shingo SHIMIZU Kaori KIEDA

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.96A, pp.25-33, 2018 (Released:2018-02-19)

参考文献数

20

被引用文献数

4

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X-band dual-polarization (multi-parameter) radars were used to observe a supercell storm that generated an F3 tornado in Ibaraki Prefecture, Japan on 6 May 2012. The observed data collected for this storm clearly exhibited the typical polarimetric features of a supercell storm, such as the ZDR (differential reflectivity) arc, ZDR column, and the KDP (specific differential phase) column, as well as their time evolution. The ZDR arc emerged at 10 to 15 min before the tornadogenesis. The ZDR column appeared approximately 1 h before the formation of the ZDR arc and was intermittent until tornadogenesis. As the ZDR arc appeared, the column became tall and stable and lasted until the dissipation of the tornado. These ZDR signatures of the supercell storm persisted for approximately half an hour.

著者

Shusuke NISHIMOTO Hirotada KANEHISA

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.96, no.1, pp.5-24, 2018 (Released:2018-02-08)

参考文献数

17

被引用文献数

1

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We analytically solve a forced linear problem of vortex Rossby waves (VRWs) associated with the vortex resiliency of tropical cyclones. We consider VRWs on a basic barotropic axisymmetric vortex. VRWs, which are initially absent, are successively forced by a vertically sheared unidirectional environmental flow. The problem is formulated in the quasigeostrophic equations, linearized about the basic vortex. The basic potential vorticity (PV) is assumed to be piecewise constant in the radial direction so that the problem can be analytically solved. The obtained solutions show the following. When the vertical interaction (VI) between the VRWs is weak, a stationary mode (called the pseudo mode) is selectively forced and grows linearly in time, and the vortex is eventually destroyed by the environmental vertical shear. When the VI is moderate, an almost form-preserving quasi-mode (simply called the quasi mode) of the VRWs appears and precesses about a downshear-left tilt equilibrium (DSLTE). The precession does not grow and the vortex maintains vertical coherence. In particular, in the presence of the inward radial gradient of the basic PV at the critical radius, the precession damps and the quasi mode eventually approaches the DSLTE. When the VI is strong, the VRWs are simply advected by the basic angular velocity at each radius to be axisymmetrized to some extent about the DSLTE, and the vortex maintains vertical coherence. To examine the diabatic effect near the eyewall, the solution with the basic buoyancy frequency being small in the central region and large in the outer region is also obtained. The small and large buoyancy frequencies imply strong and weak VIs, respectively. The central VRWs are simply advected by the basic vortex flow. While, the outer VRWs precess about the DSLTE just like a quasi mode, and the vortex maintains vertical coherence.

著者

Philippe BARON Shoken ISHII Kozo OKAMOTO Kyoka GAMO Kohei MIZUTANI Chikako TAKAHASHI Toshikazu ITABE Toshiki IWASAKI Takuji KUBOTA Takashi MAKI Riko OKI Satoshi OCHIAI Daisuke SAKAIZAWA Masaki SATOH Yohei SATOH Taichu Y. TANAKA Motoaki YASUI

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.95, no.5, pp.319-342, 2017 (Released:2017-10-04)

参考文献数

42

被引用文献数

8

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A feasibility study of tropospheric wind measurements using a coherent Doppler lidar aboard a super low altitude satellite is being conducted in Japan. The considered lidar uses a 2.05 μm laser light source of 3.75 W. In order to assess the measurement performances, simulations of wind measurements were conducted. The mission definition is presented in a companion paper (Part 1) while, in this paper, we describe the measurement simulator and characterize the errors on the retrieved line-of-sight (LOS) winds. Winds are retrieved from the Doppler-shift of the noisy backscattered signal with a horizontal resolution of 100 km along the orbit track and a vertical resolution between 0.5 and 2 km. Cloud and wind fields are the pseudo-truth of an Observing System Simulation Experiment while aerosol data are from the Model-of-Aerosol-Species-IN-the-Global-AtmospheRe (MASINGAR) constrained with the pseudo-truth wind. We present the results of the analysis of a full month of data in summer time for a near-polar orbiting satellite and a LOS nadir angle of 35°. Below ≈ 8 km, the ratio of good retrievals is 30-55 % and the median LOS wind error is better than 0.6 m s−1 (1.04 m s−1 for the horizontal wind). In the upper troposphere, the ratio is less than 15 % in the southern hemisphere and high-latitudes. However, the ratio is still 35 % in the northern Tropics and mid-latitudes where ice-clouds frequently occur. The upper-tropospheric median LOS-wind measurement error is between 1-2 m s−1 depending on the latitude (1.74-3.5 m s−1 for the horizontal wind). These errors are dominated by uncertainties induced by spatial atmospheric inhomogeneities.

著者

Shoken ISHII Philippe BARON Makoto AOKI Kohei MIZUTANI Motoaki YASUI Satoshi OCHIAI Atsushi SATO Yohei SATOH Takuji KUBOTA Daisuke SAKAIZAWA Riko OKI Kozo OKAMOTO Toshiyuki ISHIBASHI Taichu Y. TANAKA Tsuyoshi T. SEKIYAMA Takashi MAKI Koji YAMASHITA Tomoaki NISHIZAWA Masaki SATOH Toshiki IWASAKI

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.95, no.5, pp.301-317, 2017 (Released:2017-10-04)

参考文献数

57

被引用文献数

15

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A working group is studying the feasibility of a future Japanese space-borne coherent Doppler wind lidar (CDWL) for global wind profile observation. This study is composed of two companion papers: an instrumental overview of the space-borne CDWL for global wind profile observation (Part 1), and the wind measurement performance (error and bias) investigated using a full-fledged space-borne CDWL simulator (Part 2). This paper aims to describe the future space-borne CDWL in terms of technical points and observation user requirements. The future mission concept is designed to have two looks for vector wind measurement with vertical resolutions of 0.5 (lower troposphere: 0-3 km), 1 (middle troposphere: 3-8 km), and 2 km (upper troposphere: 8-20 km) and horizontal resolution of < 100 km along a satellite. The altitude and orbit of the satellite are discussed from a scientific viewpoint. The candidate altitude and orbit of the satellite are 220 km and an inclination angle of 96.4° (polar orbit) or 35.1° (low-inclination-angle orbit). The technical requirements of the space-borne CDWL are a single-frequency 2-μm pulse laser with an average laser power of 3.75 W, two effective 40-cm-diameter afocal telescopes, a wide-bandwidth (> 3.4 GHz) detector, a high-speed analog-to-digital converter, and a systematic lidar efficiency of 0.08. The space-borne CDWL looks at two locations at a nadir angle of 35° at two azimuth angles of 45° and 135° (225° and 315°) along the satellite track. The future space-borne CDWL wind profile observation will fill the gap of the current global wind observing systems and contribute to the improvement of the initial conditions for numerical weather prediction (NWP), the prediction of typhoons and heavy rain, and various meteorological studies.

著者

IWABUCHI Hironobu PUTRI Nurfiena Sagita SAITO Masanori TOKORO Yuka SEKIGUCHI Miho YANG Ping BAUM Bryan A.

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2018-001, (Released:2017-09-15)

被引用文献数

44

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An algorithm for retrieving the macroscopic, physical and optical properties of clouds from thermal infrared measurements is applied to the Himawari-8 multiband observations. A sensitivity study demonstrates that the addition of the single CO2 band of Himawari-8 is effective for the estimation of cloud top height. For validation, retrieved cloud properties are compared systematically with collocated active remote sensing counterparts with small time lags. While retrievals agree reasonably for single-layer clouds, multilayer cloud systems with optically thin upper clouds overlying lower clouds are the major source of error in the present algorithm. Validation of cloud products is critical for identifying the characteristics, advantages and limitation of each product and should be continued in the future. As an application example, data are analyzed for eight days in the vicinity of the New Guinea to study the diurnal cycle of the cloud system. The present cloud property analysis investigates cloud evolution through separation of different cloud types and reveals typical features of diurnal cycles related to the topography. Over land, middle clouds increase from 0900 to 1200 local solar time (LST), deep convective clouds develop rapidly during 1200–1700 LST with a subsequent increase in cirrus and cirrostratus cloud amounts. Over the ocean near coastlines, a broad peak of convective cloud fraction is seen in the early morning. The present study demonstrates the utility of frequent observations by Himawari-8 for life cycle study of cloud systems, owing to the ability to capture their continuous temporal variations.

著者

Toshihisa ITANO Kiyoshi MARUYAMA

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.87, no.4, pp.747-753, 2009 (Released:2009-09-09)

参考文献数

12

被引用文献数

5 11

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The effect of the horizontal component fH of the planetary vorticity on the symmetric stability of zonal flow is investigated using the linearized Boussinesq equations on the f -plane. It is shown that, as in the case of neglecting fH, the stability under full-component Coriolis force is determined by the sign of the potential vorticity. It is also revealed that even in such a generalized situation, the movement associated with the symmetric instability can be decomposed into two independent motions, i.e., the buoyancy oscillation (or instability) modified by the Coriolis force and the inertial oscillation (or instability) modified by the buoyancy. The squared product of their frequencies remains proportional to the potential vorticity of the zonal flow. Meanwhile, the horizontal component of the planetary vorticity is found to exhibit both stabilizing and destabilizing effects, although there is a wide range of stable regions that are not affected by fH. The existence of fH also causes an asymmetry such that the stability changes depending on the sign of the vertical shear of the zonal flow, even if the Richardson number and the dimensionless relative vorticity are maintained constant.

著者

Masanori OIGAWA Takafumi MATSUDA Toshitaka TSUDA Noersomadi

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.95, no.4, pp.261-281, 2017 (Released:2017-07-20)

参考文献数

34

被引用文献数

13

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Mechanisms related to the diurnal cycle of tropical deep convection over a complex terrain were investigated in the Bandung basin, West Java, Indonesia. Observational data were analyzed from X-band radar, Global Navigation Satellite System (GNSS) receivers, and radiosondes, in conjunction with high-resolution numerical model data. Significant diurnal variation of GNSS-derived precipitable water vapor (PWV), which peaked in the early evening, was observed from 13 to 19 March 2013. During this period, the X-band radar detected convective initiation at approximately 1200 local time over the southern slope of the basin. A 2-km-mesh model successfully simulated the observed diurnal variations of PWV and rainfall from 15 to 17 March 2013. In the model, moist air was present at the bottom of the basin early in the morning, which was transported to the southern slope of the basin by valley wind circulation after sunrise. In contrast, humidity was lower in the northern part of the basin due to a downward circulating valley wind. The valley wind decreased static stability around the southern slope of the basin by transporting moisture. It also caused a low-level wind convergence, resulting in convective initiation on the southern slope of the basin. The GNSS receiver network also recorded this simulated water vapor variability associated with the valley wind. These results suggest that water vapor in the bottom of the basin during mornings and its advection by the valley wind strongly influences convective initiation in Bandung.

著者

Yuhji KURODA Kunihiko KODERA

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.95, no.3, pp.171-180, 2017 (Released:2017-04-28)

参考文献数

14

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This paper proposes a new simple method of multivariable maximum covariance analysis (MMCA) for extracting common variability from multiple (more than two) datasets that expands the singular value decomposition analysis method. The method is based on iteration of a recurrence equation derived by a dual relationship between pattern vectors and time coefficients. Two approaches of the method are proposed, one using the extreme of a summation of covariances (sum MMCA) and the other using the product of covariances (product MMCA). Both approaches are demonstrated by successfully extracting the variability related to the Arctic Oscillation from three monthly-mean meteorological datasets. The method is useful because it is easily programmed and is computationally inexpensive. The method can be applied to an arbitrary number of datasets, although a complete set of the product MMCA method cannot be applied to an even number of datasets.

著者

Yanru ZHAO Wenqian MAO Kequan ZHANG Yining MA Haifei LI Wenyu ZHANG

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.95, no.3, pp.181-197, 2017 (Released:2017-04-28)

参考文献数

35

被引用文献数

7

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Based on the ERA-20C, climatic variations of the boundary layer height (BLH) over arid and semiarid areas in East Asia and North Africa that span 1900-2010 were analyzed. In East Asia, the BLH exhibited a descending trend from arid region centers to the periphery. Over the past 111 years, the BLH has had a rising trend of 14.0 m decade−1. in the representative region (EA1) of the eastern areas with the 111-year average of 725 m and a decreasing trend of −1.6 m decade−1. in the representative region (EA2) of the western areas with the 111-year average of 792 m. From the mid-1960s to 1970s, EA1's BLH had a sharp rise that caused the average to increase by 93 m after the 1980s. In North Africa, the BLH exhibited a high spatial distribution in the western and southern areas and a relatively low spatial distribution in the eastern and northern areas. Over the past 111 years, the BLH has had a rising trend of 9.7 m decade−1. in the representative region (NA1) of the southwestern region with the 111-year average of 915 m and a decreasing trend of −6.3 m decade−1. in the representative region (NA2) of other regions with the 111-year average of 882 m. In the 1940s and the 1970s, NA1's BLH had two obvious increases that caused the average to increase by 51 m and 22 m, respectively, while NA2's BLH had two obvious declines that caused the average to decrease by 48 m and 7 m, respectively. On the spatial distribution, the BLH, sensible heat flux, latent heat flux, and volumetric soil water had a good corresponding relationship. On the temporal change, the BLH in East Asia had a stronger correlation with thermodynamic factors, whereas the BLH in North Africa had a stronger correlation with dynamic factors. Besides, the upper-level stratification also has some influence on the BLH's change.

著者

Jong-Jin Baik Jong-Su Paek

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.78, no.6, pp.857-869, 2000-12-25 (Released:2009-09-15)

参考文献数

30

被引用文献数

1 31

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バックプロパゲーション型ニューラルネットワークを使って、北西太平洋での熱帯低気圧の強度の変化を12,24,36,48,60,72時間について予測するモデルを開発した。用いたデータは、1983-1996の14年間の北西太平洋の熱帯低気圧に対する、低気圧の位置、強度、NCEP/NCARの再解析、それに海面水温である。ニューラルネットワークの予測因子は重線形回帰モデルの予測因子に基づいて選ばれた。回帰分析により、予測因子の一つ風の鉛直シアーが全ての予測時間に渡って一貫して重要であることを示した。予測因子として気候学的、持続的、総観的因子を用いたニューラルネットワークモデルによる平均予測誤差は、同じ予測因子を用いた重線形回帰モデルに比べて7-16さらに、予測因子として気候学的、持続的因子のみを用いたニューラルネットワークモデルの性能でさえも、総観的因子まで含んだ重線形回帰モデルの性能をわずかに上回った。ニューラルネットワークモデルの性能は14年間の全ての年について回帰モデルを上回るわけではないけれども、ニューラルネットワークモデルの方が良い年の方が逆の年よりもずっと多く、その傾向は短い予測時間の方が顕著である。感度実験により、ニューラルネットワークモデルの平均強度予測誤差は、隠れ層や隠れ層のニューロンの数には敏感ではないことを示した。しかし、熱帯低気圧強度予測のために、より良い隠れ層の構造を用いることにより、回帰モデルに比べてニューラルネットワークモデルをさらに改良する余地がいくらかある。この研究は、予測因子として気候学的、持続的、総観的因子を用いたニューラルネットワークモデルが熱帯低気圧の強度予報において有効な道具として使えることを示唆している。

著者

Yan LI Peilong YE Juan FENG Yao LU Jiahe WANG Zhaoxia PU

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.95, no.2, pp.147-165, 2017 (Released:2017-04-08)

参考文献数

51

被引用文献数

7

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It has been argued that the Coupled Model Intercomparison Project phase 5 (CMIP5) models underestimate the frequency of atmospheric blocking, while projecting a decreasing trend of blocking in the 21st century in the Northern Hemisphere. This average trend may not be true for regional blockings. Focusing on three key regions in Eurasia (the Urals, Baikal, and Okhotsk regions) where blocking significantly influences the weather and climate of East Asia, this study first evaluates the performance of the CMIP5 models by comparing historical simulations with National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis (NNR). Possible changes in the first half of the 21st century are then analyzed using the RCP4.5 and RCP8.5 experiments. It is found that instantaneous blocking frequencies are underestimated in the Urals and Baikal regions for the whole year and in the Okhotsk region in summertime but are overestimated in Okhotsk in wintertime. Blocking episode frequency in the Urals and Baikal regions is underestimated by most of the 13 CMIP5 models, especially the short-duration blocking episodes (4–5 days), and the simulations are better in wintertime than in summertime. However, in the Okhotsk region, the modeled frequency of blocking episodes is close to the value from NNR in summertime but is overestimated in wintertime. Model projections of instantaneous blocking frequency for the first half of the 21st century (2016–2065) show that both RCP4.5 and RCP8.5 runs yield an increasing frequency except during June–August in Eurasia. The multimodel ensemble-mean frequency of blocking episodes clearly decreases in the whole year in the Urals and Baikal regions (especially blocking episodes with short duration) and increases a little in summertime in the Okhotsk region in the first half of the 21st century. The model ensemble-mean frequency of blocking episodes with long duration (more than 9 days) decreases by ~40 % in the Urals region but increases by no more than 5 % in Okhotsk region.

著者

Yoshimi KAWAI Qoosaku MOTEKI Akira KUWANO-YOSHIDA Takeshi ENOMOTO Atsuyoshi MANDA Hisashi NAKAMURA

出版者

(公社)日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.95, no.2, pp.71-90, 2017 (Released:2017-03-17)

参考文献数

31

被引用文献数

6

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The present study investigated how impacts of the inclusion of radiosonde observations conducted locally in the early summer of 2012 over the Kuroshio and Kuroshio Extension (KE) can spread over time across the North Pacific basin to influence the predictability of synoptic and large-scale tropospheric circulation. For that purpose, observing system experiments (OSEs) were performed where each of two extra sets of radiosonde data, one obtained over the East China Sea in mid-May and the other over the KE in early July, was added to an atmospheric ensemble data assimilation system for comparison with the corresponding analyses without those data. The experiments show that the impact of the extra data assimilated propagates eastward mainly due to advection by the subtropical jet (STJ) in May and July. The strong STJ in May allows the upper-tropospheric impact to travel across the basin only within two days. Under the weaker STJ, the corresponding impact in July tends to remain within the western Pacific, until it eventually reaches the eastern portion of the basin. Assimilation of the extra radiosonde data over the Kuroshio or KE can lead to a decrease of pressure over the Gulf of Alaska in both May and July.  Additional forecast experiments based on the OSEs for May revealed that the pressure decrease over the Gulf of Alaska can be traced back to the west of the Alaska Peninsula and to the east of Japan over three days. The impacts that originate on different dates via different paths merge over the central North Pacific, reinforcing the cyclone over the Gulf of Alaska. This study presents examples where the impacts of atmospheric observations over the western boundary current can propagate across the ocean basin through the westerlies to influence the forecast skill in distant regions.