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.17-21, 2019 (Released:2019-02-05)

参考文献数

34

被引用文献数

17

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In this study, we use observational data and numerical models to reveal whether foehn wind affects the record-breaking high-temperature event (41.1°C) at Kumagaya on July 23, 2018. On this day, the weather conditions at Kumagaya satisfied the conditions described in Takane et al. (2014) for a likely extreme high temperature (EHT) day: a “whale-tail” pressure pattern, no precipitation for 6 days, a high potential temperature at 850 hPa, and northerly surface winds. Our back-trajectory analysis shows that the air parcels came to Kumagaya from heights up to 3.0 km above sea level over the Sea of Japan. The Lagrangian energy budget analysis shows that adiabatic heating accounts for about 87.5% of the increase of the thermal energy given to the air parcel, with the rest from diabatic heating. The diabatic heating is caused by heating associated with surface sensible heat flux and the mixing by turbulent diffusion. The adiabatic and diabatic heating are calculated to have raised the temperature of air parcel by 14 and 2.0 K, respectively, for this EHT event. We conclude that the dynamic foehn effect and diabatic heating from the surface, together with mixing in the atmospheric boundary layer, affected the formation of this EHT event.

著者

Hiroyuki KUSAKA

出版者

The Association of Japanese Geographers

雑誌

地理学評論 (ISSN:13479555)

巻号頁・発行日

vol.81, no.5, pp.361-374, 2008-05-31 (Released:2010-03-12)

参考文献数

139

被引用文献数

14 18

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A review of urban climate studies in Japan since 1980 is presented. First, we describe recent research on an urban heat island. In this section, we focus on the heat island with a scale larger than a single city, heterogeneous temperature distribution in an urban district, and quantitative analysis of the formation mechanism of the heat island using numerical models. We then summarize the interaction between a sea breeze and a heat island. Cloud formation and precipitation over the urban area are also summarized. Furthermore, recent studies on the estimation of urban surface parameters and anthropogenic heat maps are briefly described. Observational studies on the urban canopy layer are also introduced. Some recent studies on urban planning are introduced, focusing on the cooling effect of parks and rivers on the urban temperature. Finally, we conclude the review by describing ongoing work.

著者

Akifumi Nishi Hiroyuki Kusaka Lidia Lazarova Vitanova Yuma Imai

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.132-136, 2019 (Released:2019-06-20)

参考文献数

27

被引用文献数

5

---

We quantitatively evaluated the contributions of foehn winds and the urban heat island (UHI) effect to an extreme high-temperature nocturnal event at Niigata city on 23-24 August 2018. During this event, southeasterly winds blew continually across the Niigata Plain and temperatures on the plain were higher than those in the windward region of the mountain range. Back-trajectory analysis and numerical simulations with and without topography showed that the southeasterly winds were foehn winds that caused precipitation and latent heating on the windward slope of the mountain range. The foehn winds and UHI contributed about 2.8°C and 1.9°C, respectively, to the extreme high-temperature of 31.0°C at 2100 JST in Niigata city. The combined impact of the foehn winds and the UHI at Niigata was about 4.0°C during the night. The contribution of the foehn winds was greater at around midnight, whereas that of the UHI was greater during the early night.

著者

Asuka Suzuki-Parker Hiroyuki Kusaka Izuru Takayabu Koji Dairaku Noriko N. Ishizaki Suryun Ham

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.14, pp.97-104, 2018 (Released:2018-07-27)

参考文献数

49

被引用文献数

14

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Targeting to East Asian summer monsoon for the first time, this study presents an assessment of projection uncertainty in ensemble dynamical downscaling (DDS) simulations. Based on 12-member DDS simulations comprised of three global climate models (GCMs) and four regional climate models (RCMs), we evaluate contributions of GCM and RCM uncertainty to the total uncertainty of summer-time precipitation projections around Japan. Our results show that contribution of RCM uncertainty can be comparable to that of GCM uncertainty in magnitudes. This finding draws a distinction from the past studies showing the dominance of GCM uncertainty. Most notably, our results show that RCM uncertainty for number of precipitating days appears around and over the land. RCM uncertainty for precipitation amounts also shows a dependence on topography but to a lessor degree. These RCM uncertainty characteristics are potentially linked to the difference in various RCM configurations such as physics schemes and model topography. In contrast, GCM uncertainty mostly appears over the ocean, which can be attributed to the difference in the GCM's future projections of East Asian summer monsoon. Our finding may be of an importance for water disaster and water resource management with DDS.

著者

Takuto Sato Hiroyuki Kusaka Hideitsu Hino

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.16, pp.104-108, 2020 (Released:2020-06-26)

参考文献数

19

被引用文献数

10

---

This study reveals the best combination of meteorological variables for the prediction of the number of emergency transport due to heat stroke over 64 years old in Tokyo metropolis based on a generalized linear model using 2008-2016 data. Temperature, relative humidity, wind speed, and solar radiation were used as candidates of the explanatory variables. The variable selection with Akaike's information criterion (AIC) showed that all the four meteorological elements were selected for the prediction model. Additional analysis showed that the combination of daily mean temperature, maximum relative humidity, maximum wind speed, and total solar radiation as explanatory variables gives the best prediction, with approximately 19% less error than the conventional single-variable model which only uses the daily mean temperature. Finally, we quantitatively estimated the relative contribution of each variable to the prediction of the daily number of heat stroke patients using standardized partial regression coefficients. The result reveals that temperature is the largest contributor. Solar radiation is second, with approximately 20% of the temperature effect. Relative humidity and wind speed make relatively small contributions, each contributing approximately 10% and 9% of the temperature, respectively. This result provides helpful information to propose more sophisticated thermal indices to predict heat stroke risk.

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

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

---

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.

著者

Van Q. Doan Van Nguyen Dinh Hiroyuki Kusaka Thanh Cong Ansar Khan Du Van Toan Nguyen Dinh Duc

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.15, pp.113-118, 2019 (Released:2019-05-30)

参考文献数

32

被引用文献数

5

---

This study revealed great potential and shortcoming of offshore wind energy in Vietnam by numerical simulations with Weather Research and Forecasting (WRF) model at 10-km resolution for 10 years (2006-2015). The greatest energy potential was found in the offshore area of Phu Quy island (Binh Thuan province). The area, alone, can provide the 38.2 GW power generation capacity corresponding to the increasing renewable-energy demand by 2030 planned by the country. There is also a drawback of the wind resource, which is associated with strong multiple-scale temporal variabilities. The seasonal variability associated with monsoon onsets and daily variability associated with the wind diurnal cycles were found ranging 30-50%. Meanwhile, the inter-annual variability could reach up to 10%. These variabilities must be considered when designing wind farms and grids over the region. Additionally, due to the fact that the WRF model performed climatological features of the winds well against the observations, this results indicate that it can be useful tools for wind-power assessment as compared to other reanalysis or QuikSCAT data with coarser spatio-temporal resolutions.

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.149-153, 2019 (Released:2019-07-17)

参考文献数

23

被引用文献数

2

---

This study revealed that the Karakkaze events accompanied by rising temperature are more frequent than those accompanied by dropping temperature. This finding contrasted with the general belief for many years that the Karakkaze is a bora-type local wind. By focusing on the temporal evolution of temperature and wind, we were able to characterize three types of Karakkazes as follows: the surface wind speed and temperature both increase in the morning and then decrease in the afternoon (type Foehn-D); during the night, the temperature increases or stops decreasing, and the surface wind speed increases (type Foehn-N); and in the morning, the temperature decreases or stops increasing, and the surface wind speed increases (type Bora). As a result, we found that among the 238 Karakkazes that we identified, 103 were type Foehn-D events, 56 were type Foehn-N events, and 79 were type Bora events.

著者

Takuto Sato Hiroyuki Kusaka

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.19, pp.165-172, 2023 (Released:2023-08-11)

参考文献数

18

---

In this study, synthetic inflow turbulence generation methods developed in computational fluid dynamics (CFD) and meteorological fields were applied to thermally driven convective boundary layer (CBL) simulations. Methods developed in the CFD field include the Reynolds stress Cholesky decomposition and digital filter-based method (DF method), and the cell perturbation method (CPM) is a method developed in the meteorological field. Intercomparison results show that both methods can reproduce turbulence in thermally driven CBLs when a proper driver region is ensured. The turbulence reproduced using the DF method in a thermally driven CBL has a shorter driver region than that reproduced using CPM. However, CPM can be applied to a simulation without limiting the inflow boundary, although it requires a longer driver region than the DF method. Therefore, it was confirmed that both methods have unique merits that can be useful for downscaling from meteorological mesoscale models to microscale large-eddy simulation models.

著者

Takuto Sato Hiroyuki Kusaka Hideitsu Hino

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2020-018, (Released:2020-05-20)

被引用文献数

10

---

This study reveals the best combination of meteorological variables for the prediction of the number of emergency transport due to heat stroke over 64 years old in Tokyo metropolis based on a generalized linear model using 2008-2016 data. Temperature, relative humidity, wind speed, and solar radiation were used as candidates of the explanatory variables. The variable selection with Akaike's information criterion (AIC) showed that all the four meteorological elements were selected for the prediction model. Additional analysis showed that the combination of daily mean temperature, maximum relative humidity, maximum wind speed, and total solar radiation as explanatory variables gives the best prediction, with approximately 19% less error than the conventional single-variable model which only uses the daily mean temperature. Finally, we quantitatively estimated the relative contribution of each variable to the prediction of the daily number of heat stroke patients using standardized partial regression coefficients. The result reveals that temperature is the largest contributor. Solar radiation is second, with approximately 20% of the temperature effect. Relative humidity and wind speed make relatively small contributions, each contributing approximately 10% and 9% of the temperature, respectively. This result provides helpful information to propose more sophisticated thermal indices to predict heat stroke risk.

著者

Akifumi Nishi Hiroyuki Kusaka Lidia Lazarova Vitanova Yuma Imai

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.2019-024, (Released:2019-05-27)

被引用文献数

5

---

We quantitatively evaluated the contributions of foehn winds and the urban heat island (UHI) effect to an extreme high-temperature nocturnal event at Niigata city on 23-24 August 2018. During this event, southeasterly winds blew continually across the Niigata Plain and temperatures on the plain were higher than those in the windward region of the mountain range. Back-trajectory analysis and numerical simulations with and without topography showed that the southeasterly winds were foehn winds that caused precipitation and latent heating on the windward slope of the mountain range. The foehn winds and UHI contributed about 2.8°C and 1.9°C, respectively, to the extreme high-temperature of 31.0°C at 2100 JST in Niigata city. The combined impact of the foehn winds and the UHI at Niigata was about 4.0°C during the night. The contribution of the foehn winds was greater at around midnight, whereas that of the UHI was greater during the early night.

著者

Hiroyuki Kusaka Haruka Kitahata

出版者

(公社)日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.5, pp.61-64, 2009 (Released:2009-04-29)

参考文献数

16

被引用文献数

1 3

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The synoptic-scale climatology of cold frontal precipitation systems during the passage over central Japan was investigated for 19 years (1988-2006). Cold frontal precipitation events are classified into the following three types: Widespread, Hokuriku, and Jump type. Widespread-type events, which bring precipitation throughout Japan, mainly occur in spring and autumn, and the cyclones tend to move northeastward from the central part of the Sea of Japan. The central pressure of the Widespread-type cyclones is the deepest and this type has the most moisture out of the three types. Hokuriku-type events, which bring precipitation exclusively over the Hokuriku area often appear in winter, and the cyclones move eastward from the northern part of the Sea of Japan. As a result, the isobars form in an east-west orientation over mainland Japan as the cold front arrives in the Hokuriku area. The Hokuriku-type cyclones tend to be relatively weak and there is less moisture during the events. For the Jump-type events, in which the precipitation distribution appears as precipitation bands jumping over the Kanto area, cyclones develop rapidly due to the deep trough at the 500 hPa level, changing the isobars from east-to-west to northeast-to-southwest during the events.