著者

AONO Kenji IWASAKI Toshiki SASAI Takahiro

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.2020-017, (Released:2019-12-24)

被引用文献数

1

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This study examined the roles of wind-evaporation feedback in the tropical cyclone (TC) intensification, with special attention devoted to the feedback in weak wind areas (domains where the 10-m wind speed is smaller than 5, 10 and 15 m s−1). This was done by setting lower limits of the 10-m wind speed in the calculation of water vapor exchange between the atmosphere and the underlying ocean in a nonhydrostatic cloud-resolving model. As a result, the surface evaporation is enhanced in outer regions of a TC where the actual wind speed is smaller than the prescribed lower limit(s). Results show that increasing the lower limit reduces the radial water vapor contrast in the lower troposphere (below 100 m) and suppresses the TC size and intensity at the mature stage by 30-33 % and 5-14 %, respectively, compared to the control run with all standard model settings. The increased evaporation enhances the outer convective activity and reduces the radial pressure gradient in the lower troposphere. As a result, the inflow and thus the inward advection of angular momentum were reduced and the enhanced convection in the outer region suppressed eyewall updraft, and thus reduced the secondary circulation and finally the TC intensity. Moreover, the outer region convection suppresses the rainband activity (within a radius of 300 km from the TC center). The contribution of the wind-evaporation feedback to the enhancement of the radial contrast of water vapor in the lower troposphere is a fundamentally important element for TC intensification, suggesting that the TC development process can be revealed more accurately by elucidating the role of the weak wind area.

著者

GENG Biao KATSUMATA Masaki TANIGUCHI Kyoko

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.2020-026, (Released:2020-02-06)

被引用文献数

4

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This study investigated the impact of mixed Rossby-gravity waves (MRGWs) on the diurnal cycle of precipitation over the southwestern coastal area of Sumatra using data captured during a pilot field campaign of the Years of the Maritime Continent (YMC) Project. The study focused on a 19-day period from 24 November to 12 December 2015, using data from intensive surface observations, radiosondes, a C-band polarimetric radar collected onboard the research vessel Mirai at 4.067°S, 101.900°E, and data from global objective analysis. The results indicated a relationship between oscillations with periods of several days in the intensity of diurnal precipitation and the wind field. Wind oscillations were attributed to several westward-propagating MRGWs traversing the study site. Diurnal convection and precipitation over the land and ocean were enhanced (suppressed) when MRGW-induced offshore (onshore) wind perturbations dominated. Large-scale low-level convergence and upper-level divergence, stronger sea-breeze flow, and colder land-breeze flow were also observed with the intensification of MRGW-induced offshore wind perturbations. However, diurnal precipitation displayed a similar well-defined phase and propagation pattern over the land and ocean, coherent with the regular evolution of sea- and land-breeze circulations, regardless of wind perturbations induced by MRGWs. The results suggest that local convergence induced by the land-sea contrast is mainly responsible for driving the diurnal cycle. Notwithstanding, MRGWs exert a significant impact on the amplitude of diurnal convection and precipitation by modulating the large-scale dynamic structure of the atmosphere and the intensity of local sea- and land-breeze circulations.

著者

FUDEYASU Hironori YOSHIDA Ryuji YAMAGUCHI Munehiko EITO Hisaki MUROI Chiashi NISHIMURA Syuji BESSHO Kotaro OIKAWA Yoshinori KOIDE Naohisa

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.2020-004, (Released:2019-10-20)

被引用文献数

5

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This study investigated the characteristics and environmental conditions of tropical cyclones (TCs) over the western North Pacific from 2009 to 2017 that dissipated before reaching tropical storm strength (TDs) under unfavorable environmental conditions; we compared these with TCs that reached tropical storm strength (TSs) in terms of modulations of relevant large-scale flow patterns. The flow patterns were categorized based on five factors: shear line, confluence region, monsoon gyre, easterly waves, and Rossby wave energy dispersion from a preexisting cyclone. Among 476 cases, 263 TDs were detected using best-track data and early stage Dvorak analysis. The TCs in the environments associated with the confluence region or Rossby wave energy dispersion (easterly waves) tended to reach tropical storm strength (remain weak) compared with the other factors. The average locations of TDs at the time of cyclogenesis in the confluence region, monsoon gyre, and easterly waves (Rossby wave energy dispersion) in the summer and autumn were farther to the west (east and north) than those of TSs that exhibited the same factors. The environments around TDs were less favorable for development than those of TSs, as there were significant differences in atmospheric (oceanic) environmental parameters between TDs and TSs in the factors of confluence region, easterly waves, and Rossby wave energy dispersion (shear line, monsoon gyre, and Rossby wave energy dispersion). The environmental conditions for reaching tropical storm strength over their developing stage, using five factors, can be summarized as follows: higher tropical cyclone heat potential in the shear line and monsoon gyre, weak vertical shear in the confluence region, wet conditions in the easterly waves, and higher sea surface temperatures and an intense preexisting cyclone in Rossby wave energy dispersion from a preexisting cyclone.

著者

MIAO Jyong-En YANG Ming-Jen

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.2020-008, (Released:2019-11-16)

被引用文献数

11

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On 14 June 2015, a severe afternoon thunderstorm event developed within the Taipei basin, which produced intense rainfall (with rainfall rate of 131 mm h−1) and urban-scale flooding. Cloud-resolving simulations using the Weather Research and Forecasting (WRF) model were performed to capture reasonably well the onset of sea breeze, the development and evolution of this afternoon thunderstorm system. The WRF model had four nested grids (with the finest grid size of 0.5 km) in the horizontal and 55 layers in the vertical to explicitly resolve the deep convection over complex terrain.  It is found that convection was initiated both by sea breeze at foothill and by upslope wind at mountain peak. Convective available potential energy (CAPE) was increased from 800 to 3200 J kg−1 with abundant moisture transport by the sea breeze from 08 to 12 LST, fueling large thermodynamic instability for the development of afternoon thunderstorm. Strong convergence between sea breeze and cold-air outflow triggered further development of intense convection, resulting in heavy rainfall over Taipei city.  Microphysics sensitivity experiments show that evaporative cooling played a major role in the propagation of cold-air outflow and the production of heavy rainfall within basin plain (terrain height < 100 m), while melting cooling played a minor role. The terrain-removal experiment indicates that the local topography of Mount Datun at coastal region may produce the channel effect through Danshui River Valley, intensify sea-breeze circulation and transport more moisture. This terrain-induced modification of sea breeze circulation made its dynamic and thermodynamic characteristics more favorable for convection development, resulting in stronger afternoon thunderstorm system with heavier rainfall within the Taipei City.

著者

Satoru Yoshida Sho Yokota Hiromu Seko Tetsu Sakai Tomohiro Nagai

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.43-50, 2020 (Released:2020-03-07)

参考文献数

19

被引用文献数

9

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We conducted observation system simulation experiments (OSSE) to investigate the effects of water vapor vertical profiles observed by Raman lidar (RL) on forecasts of heavy precipitation in Hiroshima, Japan, on August 19, 2014 using a local ensemble transform Kalman filter. We employed a simulation result similar to reality as nature-run (NR) and performed two OSSEs. In the first experiment (DaQv), conventional observation data and vertical profiles of water vapor mixing ratio in air (qv) estimated from NR were assimilated. In the second experiment (CNTL), only conventional observation data were assimilated. In DaQv, we assumed that the RL was in the low-level inflow that supplied water vapor to the heavy precipitation in Hiroshima. Assimilating qv for several hours increased qv around the RL observation station, especially at low level. The regions modified by the assimilation of qv moved to Hiroshima by low-level inflow, resulting in 9-hour precipitation being approximately 28% greater than that of CNTL, and was thus closer to that of the NR. The OSSEs suggest that water vapor RL observations on the windward side of the heavy precipitation are a useful approach for improving precipitation forecasts.

著者

Yasumitsu Maejima Takemasa Miyoshi

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.37-42, 2020 (Released:2020-02-23)

参考文献数

19

被引用文献数

4

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This study aims to investigate the tradeoff between the computational time and forecast accuracy with different data assimilation (DA) windows of four-dimensional local ensemble transform Kalman filter (4D-LETKF) for a single-case severe rainfall event. We perform a series of Observing System Simulation Experiments (OSSEs) with 1-, 3-, 5- and 15-minute DA window in a severe rainstorm event in Kobe, Japan, on July 28, 2008, following the prior OSSEs by Maejima et al. (2019). Running 1-minute DA cycles showed the best forecast accuracy but with the highest computational cost. The computational cost could be reduced by taking a long DA window, but the forecast became less accurate even though the same number of observations were used. A significant gap was found between the 3-minute window and 5-minute window. With the 1- and 3-minute windows, the forecasts captured the intense rainfall, while with the 5-minute window or longer, the rainfall intensity was drastically underestimated. This single-case study suggests that 3-minute or shorter DA window be a promising method for a severe rainfall forecast, although more case studies are necessary to draw general conclusion.

著者

Tetsuya Takemi Takashi Unuma

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.30-36, 2020 (Released:2020-02-22)

参考文献数

23

被引用文献数

33

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This study investigated the environmental factors responsible for the development of heavy rainfall in eastern Japan during the passage of Typhoon Hagibis (2019) by using mesoscale gridded analysis data as well as observed data. Environmental indices for diagnosing stability and moisture conditions were examined. It was found that the whole troposphere is almost saturated and the column total water vapor content is extremely large. In the lower troposphere we identified layers of moist absolutely unstable states with the thickness deeper than 2 km. Such deep moist absolutely unstable layers as well as abundant moisture content and almost saturated troposphere set a high potential for convective development. Under these favorable environmental conditions, the fact that the heights of the absolutely unstable layers' bottom are comparable to the mountain elevations is considered to be favorable for topographic lifting of unstable, moist air, which will trigger and activate strong convection and hence heavy rainfall. In spite of a moderate amount of convective available potential energy and a nearly moist-adiabatic lapse rate, moist absolute instability, abundant moisture, and high humidity jointly play a key role to increase the potential for generating the present heavy rainfalls.

著者

Daisuke Hatsuzuka Tomonori Sato Kohei Yoshida Masayoshi Ishii Ryo Mizuta

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.23-29, 2020 (Released:2020-02-14)

参考文献数

28

被引用文献数

11

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This study investigated future changes in extreme precipitation associated with tropical cyclones (TCs) around Japan using large ensemble regional climate simulations for historical and +4 K climates. Under the warmer climate, extreme TC precipitation, defined as the 90th percentile value of the maximum daily precipitation derived from each TC (TCP90), is projected to increase throughout Japan from Kyushu to Kanto. We attributed most of the increase in TCP90 to increased atmospheric moisture due to global warming. Furthermore, it was found that TCP90 is projected to increase for all TC intensity categories. However, the projected increase in intense TCs affects TCP90 in only a limited area. Stronger TCs enhance TCP90 over east- and north-facing slopes of mountainous terrain, while TCP90 in most other areas is insensitive to TC intensity. These results suggest that even relatively weak TCs could have potential to produce extreme precipitation that might cause natural disasters.

著者

Tomomichi Ogata Hidenori Aiki

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.262-267, 2019 (Released:2019-12-27)

参考文献数

45

被引用文献数

4

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This study makes a first attempt to apply the diagnostic scheme of Aiki et al. (2017) to the output of an ocean general circulation model (OGCM), in order to investigate the basin-wide pathway of equatorial and mid-latitude wave energy associated with intraseasonal variability in the Indian Ocean. The vertical mode decomposition shows that 90-day variability of the second baroclinic mode is dominant in a realistic OGCM experiment. For 90-day equatorial Kelvin wave (KW) and Rossby wave (RW), energy input by wind stress appears in the eastern equatorial Indian Ocean that is then transferred eastward by KWs along the eastern equatorial waveguide (while westward as RW off equator). For 30-day Mixed-Rossby Gravity waves (MRG), wave energy is transferred eastward while wave phase propagates westward that is consistent with the dispersion relationship of low-frequency MRG. The new diagnostic scheme is able to show, particularly for 30-day MRG, eastward energy fluxes along the equatorial waveguide, while the other schemes in previous studies (e.g. pressure flux, quasi-geostrophic flux) cannot show the direction of the group velocity of equatorial waves.

著者

SUEKI Kenta KAJIKAWA Yoshiyuki

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.2019-063, (Released:2019-09-06)

被引用文献数

7

---

During the recent catastrophic heavy rainfall event in western Japan in July 2018, both the Hiroshima and Keihanshin areas were subjected to unusual total rainfall amounts in 72 hours from 1200 UTC 4 July onward. However, the number of sediment disasters was significantly larger in the Hiroshima area. Among the possible reasons for the difference in the sediment disaster occurrences between the Hiroshima and Keihanshin areas, here, we focus on the differences in the rainfall characteristics in these two areas during the heavy rainfall event. Based on the radar observations, we investigate the characteristics of precipitation systems striking the Hiroshima and Keihanshin areas and find that significantly large precipitation systems with areas equal to or larger than 104 km2 were dominant in the Hiroshima area, which caused rapid accumulation of the rainfall amount and enhanced the risk of deadly sediment disasters in this area. On the other hand, in the Keihanshin area, rainfall of moderate intensity and relatively small precipitation systems were found to be dominant. We suggest that the difference in the amount of damage between the Hiroshima and Keihanshin areas was mainly caused by the size difference of the precipitation systems striking these two areas. Statistics relating to the background atmospheric conditions for the precipitation systems in the heavy rainfall event reveal that a high vertical wind shear environment provides preferable conditions for the formation of large precipitation systems.

著者

OTSUKA Shigenori KOTSUKI Shunji OHHIGASHI Marimo MIYOSHI Takemasa

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.2019-061, (Released:2019-09-03)

被引用文献数

7

---

Since January 2016, RIKEN has been running an extrapolation-based nowcasting system of global precipitation in real time. Although our previous paper reported its advantage of the use of data assimilation in a limited verification period, long-term stability of its forecast accuracy through different seasons has not been investigated. In addition, the algorithm was updated seven times between January 2016 and March 2018. Therefore, this paper aims to present how motion vectors can be derived more accurately, and how data assimilation can constrain an advection-diffusion model for extrapolation stably for the long-term operation. The Japan Aerospace Exploration Agency's Global Satellite Mapping of Precipitation (GSMaP) Near-Real-Time product is the only input to the nowcasting system. Motion vectors of precipitation areas are computed by a cross-correlation method, and the Local Ensemble Transform Kalman Filter generates a smooth, complete set of motion vectors. Precipitation areas are moved by the motion vectors up to 12 hours, and the product, called “GSMaP RIKEN Nowcast”, is disseminated on a webpage in real time. Most of the algorithmic updates were related to better estimating motion vectors, and the forecast accuracy was gradually and consistently improved by these updates. Particularly, the threat scores increased the most around 40°S and 40°N. A performance drop in the northern hemisphere winter was also reduced by reducing noise in advection. The time series of ensemble spread showed that an increase in the number of available motion vectors by a system update led to a decrease in the ensemble spread, and vice versa.

著者

Bagtasa Gerry

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.2019-052, (Released:2019-06-14)

被引用文献数

17

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The influence of tropical cyclones (TC) on the western North Pacific (WNP) summer monsoon flow and its impact on rainfall in the Philippines during the months of June to September from 1958 to 2017 were investigated. High precipitation event (HPE) days with rainfall in the upper 85th, 95th, and 99th percentile were determined using daily rainfall averaged from eight synoptic stations in northwestern Philippines. More than 90 % of HPE days coincide with TC occurrence in the WNP and landfalling TCs only account for 12.8-15.1 % of HPE days. The present study looks at the non-landfalling TCs coincident with the HPEs. The result shows that these non-landfalling TCs are critical in remotely affecting almost all local HPEs in northwestern Philippines. Analysis of the TC tracks and their influence on the southwesterly of the summer monsoon flow in Southeast Asia during HPE days show that most of the TCs moved along a line segment connecting northern Luzon and Okinawa, Japan. The composite low-level flow of all HPE days is characterized by a zonally-oriented eastward trough of the 1005-1007 hPa sea level isobar along 20°N that extends to at least 135°E longitude over the northern half of the Philippines, and a deepening of the monsoon trough in northern South China Sea. The 1005-1007 hPa trough induces an eastward shift of the southwesterly that increased the mean zonal wind along western Luzon by 1.94-4.69 times and water vapor flux by 2.67-6.92 times by way of the ‘moisture conveyor belt’. In addition, significant increasing trends of 6.0 % per decade in the mean annual number of HPE days per decade and 12.7 % per decade in the annual total HPE precipitation are found for the upper 85th percentile daily rainfall. These are attributed to the recent changes in WNP TC tracks.

著者

Truong Van Thinh Phan Cao Duong Kenlo Nishida Nasahara Takeo Tadono

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.28-31, 2019 (Released:2019-02-11)

参考文献数

23

被引用文献数

12

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A land use/land cover map is an important input for different applications. However, the accuracy of land cover maps remains a great uncertainty and mapping accuracy assessment is not well-documented. The objective of this paper is to examine the relationship between overall accuracy and the number of classification classes by conducting a literature review of land cover/land use studies. The results revealed a weak negative correlation between the map's accuracy and the number of classes. The paper suggests a decrease of 0.77% map's overall accuracy with respect to the increase of 1 land cover class. The average overall accuracy produced by 05 sensor types does not show the big difference. In addition, high spatial resolution sensor such as Airborne might not be always advantageous for producing high overall accuracy map since its accuracy depends on several factors including the number of land cover classes.

著者

Hiroki Teramura Tomonori Sato Kenta Tamura

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.143-148, 2019 (Released:2019-06-27)

参考文献数

24

---

This study investigated the impact of land surface heterogeneity on Mesoscale Convective System (MCS) initiations in East Asia, using geostationary satellite data during June–August from 1996 through 2018. The detected MCSs over land exhibited clear diurnal variation with the lowest existence frequency at 10:00 and highest initiation frequency during 12:00-17:00 local time. To quantify land surface heterogeneity, the spatial standard deviation of equivalent Black-Body Temperature (TBB) within a cloud-free 0.35° × 0.35° box (σLSTBB: Land Surface TBB) was computed for 10:00 each day. A comparison of the σLSTBB and MCS databases revealed that the probability of MCS initiations increased with increasing σLSTBB in East Mongolia while the probability was not sensitive to σLSTBB in East China. This indicated that MCSs tend to form over heterogeneous land surface conditions in the semiarid region. We found that the impact of land surface heterogeneity on MCS initiations was highest over flat terrain in East Mongolia, where the convection trigger due to topographically-induced circulation was absent. These results suggest that the impact of land surface heterogeneity on MCS initiations during the warm season varies with climate zones and terrain complexities in East Asia, with strongest impact in semiarid and flat regions.

著者

Akifumi Nishi Hiroyuki Kusaka

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.160-165, 2019 (Released:2019-08-21)

参考文献数

46

被引用文献数

2

---

In the present study, we conducted dual-sonde observations and a numerical simulation when the “Karakkaze”, a local wind in Japan, blew. The result showed that the basic features of the Karakkaze coincide closely with the characteristics of convexity wind defined as “strong winds in the leeward region of a convex-shaped mountain range”.Firstly, we investigated the horizontal distribution of surface winds during the Karakkaze event on 24 January 2019. The results showed that the Karakkaze blows in the downwind plain of the convexity of the mountain range.Secondly, we compared the vertical distribution of the winds inside and outside the Karakkaze region, using the results of dual-sonde observations and a numerical simulation. Our results showed that strong winds blew from near ground level to a height of 1.8 km above mean sea level (AMSL) in the Karakkaze region. In contrast, weaker winds were observed and simulated outside the Karakkaze region. The reason of the weaker winds is that a hydraulic jump occurs on the slope of the mountain range and that the area outside the Karakkaze region is located in a more leeward direction than the hydraulic jump. These features closely match the characteristics of convexity winds.

著者

Hossain Mohammed Syedul Hoque Hitoshi Irie Alessandro Damiani Prajjwal Rawat Manish Naja

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.14, pp.159-164, 2018 (Released:2018-11-09)

参考文献数

56

被引用文献数

8

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Since January 2017 continuous multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations have been performed for the first time at Pantnagar (29.03°N, 79.47°E), a semi-urban site located in the Indo-Gangetic Plain region in India. Here we report the formaldehyde (HCHO), glyoxal (CHOCHO), and nitrogen dioxide (NO2) concentrations for the lowest layer (0-1 km) of the retrieved vertical profiles. The ratio of CHOCHO to HCHO concentrations (RGF), an important tracer indicative of changes in volatile organic compound emissions was estimated. During spring and autumn enhanced concentrations of HCHO and CHOCHO were observed under the influence of biomass burning. The mean RGF for the whole observation period (January–November) in Pantnagar was estimated to be 0.029 ± 0.006. Comparing with similar MAX-DOAS observations in central Thailand and reported literature values, we found that the RGF tends to be < ∼0.04 under the influence of biomass burning and/or anthropogenic emissions.

著者

JINNO Takuya MIYAKAWA Tomoki SATOH Masaki

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.2019-017, (Released:2018-12-07)

被引用文献数

3

---

In August 2016, a monsoon gyre persisted over the western North Pacific and was associated with the genesis of multiple devastating tropical cyclones. A series of hindcast simulations was performed using the nonhydrostatic icosahedral atmospheric model (NICAM) to reproduce the temporal evolution of this monsoon gyre. The simulations initiated at dates during the mature stage of the monsoon gyre successfully reproduced its termination and the subsequent intensification of the Bonin high, while the simulations initiated before the formation and during the developing stage of the gyre failed to reproduce subsequent gyre evolution even at a short lead time. These experiments further suggest a possibility that the development of the Bonin high is related to the termination of the monsoon gyre. High predictability of the termination is likely due to the predictable mid-latitudinal signals that intensify the Bonin high.

著者

SHUSSE Yukari MAESAKA Takeshi KIEDA Kaori IWANAMI Koyuru

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.2019-021, (Released:2018-12-13)

被引用文献数

4

---

This study describes the spatial distribution of the melting layer (ML) in a winter stratiform precipitation system associated with a south-coast cyclone (SCC) on 30 January 2015 over the Kanto Plain, Japan, using an X-band polarimetric radar at Funabashi operated by the Ministry of Land, Infrastructure, Transport and Tourism. The detailed horizontal distribution of surface precipitation types based on Weather Reports from citizens provided by Weathernews Inc. (WNI reports) was also investigated in relation to the ML structure. Surface precipitation in the Kanto Region started with rain and then changed to snow around Tokyo. According to WNI reports, a large dry snow area had formed around Tokyo by 0900 Japan Standard Time (UTC + 9 hours), while surface rainfall continued in the southeast of the Kanto Plain (most part of Chiba and southern part of Kanagawa). A boundary line between the surface dry snow and rain areas became clear in the eastern part of Kanagawa and the northwestern part of Chiba. This boundary then gradually moved inland. Polarimetric ML signatures suggesting the presence of melting snow were continuously observed above the rainfall area in the southeast of the Kanto Plain. The polarimetric ML signatures, on the other hand, approached the ground near the surface dry snow-rain boundary while the surface snowfall was predominant around Tokyo. During the mature snowfall period around Tokyo, the ML vertically extended below 1 km above sea level near the surface dry snow-rain boundary, which indicates the presence of a local horizontal temperature gradient and a surrounding ~0°C near-isothermal layer. It is suggested that this vertically extending ML coincided with the edge of a cold air mass in the lower atmosphere, which often forms during snowfall associated with SCCs in the Kanto Region.

著者

Van Q. Doan Hiroyuki Kusaka

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.37-40, 2019 (Released:2019-02-19)

参考文献数

27

被引用文献数

3

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This study introduces a new multiple-layer urban canopy model (MUCM) combined with a ray-tracing algorithm. In the model, we parameterize the urban morphology as an infinite array of identical three-dimensional buildings separated by roads. Heat exchanges are solved for each urban surface at each vertical layer. The ray-tracing scheme is used to explicitly calculate the view factors as well as both the sunlit and shadow fractions of the urban surfaces during the daytime. As a test, we show that this combined MUCM accurately models observations at Kugahara, Tokyo. Thus, the combined MUCM is a new tool for urban climate modelers to more realistically represent radiative processes on urban surfaces. In particular, it may contribute to our understanding of urban climate in the mega-cities of Asia, which generally have high-rise buildings that are more difficult to model with simpler radiative schemes.

著者

Akifumi Nishi Hiroyuki Kusaka

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.12-16, 2019 (Released:2019-02-05)

参考文献数

24

被引用文献数

2

---

This study uses a numerical model to examine how a convex feature and a gap feature in a mountain range affect the leeward wind field. In the “convexity case”, the mountain ridge has a convex feature (viewed from above). In the “gap case”, the mountain ridge has a gap. The results show that both cases have local winds at the surface exceeding 8 m s−1, and both have similar spatial flow-patterns. However, the momentum budgets at the strong-wind regions differ between the cases. In the convexity case, the downdrafts are important in the momentum balance, whereas in the gap case, both the downdrafts and the pressure-gradient force are important. Thus, although their spatial patterns of surface wind are similar to each other, their mechanisms for producing a strong local wind differ.Sensitivity experiments of Frm show that strong-wind appears in both the convexity and gap cases when Frm is between 0.42 and 1.04. In contrast, when Frm is 0.21, strong winds only appear in the gap case because the flow can go around the gap. When Frm exceeds 1.25, strong surface winds appear in the entire leeward plain.