Mountain Meteorology

Fohen Wind

  On 16 August 2007, a surface air temperature of 40.9 oC -the highest ever in Japan- was recorded in the cities of Kumagaya and Tajimi cities.
  In our laboratory, we have been examining these extreme events by numerical simulations using the WRF model and statistical analysis of observation data.

  The results show that the extreme event in Kumagaya on 16 August 2007 was mainly caused by a new type of foehn wind 
  with diabatic heating from the ground surface- which is different from typical thermodynamic (wet) foehn and dynamic (dry) foehn.
  Through our efforts, the actual conditions of the extreme high temperature events in the Tajimi area are now becoming clear.
(Yuya Takane)

  • Takane, Y., H. Kusaka, H. Kondo, M. Okada, M. Takaki, S. Abe, S. Tanaka, K. Miyamoto, Y. Fuji and T. Nagai, 2016: Factors causing climatologically high temperatures in a hottest city in Japan: a multi-scale analysis of Tajimi., International Journal of Climatology., DOI: 10.1002/joc.4790, 2016/06/15(Acknowledgement: CCS, Tajimi City) .
  • Takane, Y., H. Kusaka, and H. Kondo, 2015: Investigation of a recent extreme high-temperature event in the Tokyo metropolitan area using numerical simulations: the potential role of a 'hybrid' foehn wind. Quarterly Journal of the Royal Meteorological Society, 141(690), 1857-1869. 2015/07/01(Acknowledgement: RECCA, S-8, T2K) .
  • Takane, Y., H. Kusaka, H. Kondo, 2014: Climatological study on mesoscale extreme high temperature events in the inland of the Tokyo Metropolitan Area, Japan, during the past 22 years. International Journal of Climatology, DOI:10.1002/joc.3951.2014/02/01(Acknowledgement: S-8, RECCA) .
  • Takane, Y., Y. Ohashi, H. Kusaka, Y. Shigeta, and Y. Kikegawa, 2013: Effects of Synoptic-Scale Wind under the Typical Summer Pressure Pattern on the Mesoscale High-Temperature Events in the Osaka and Kyoto Urban Areas by the WRF Model. J. Appl. Meteor.Climatol., 52, 1764-1778. 2013/08/01 (Acknowledgement: S-8,RECCA,T2K) .
  • Takane, Y., Kusaka, H., 2011: Formation mechanism of the extreme surface air temperature of 40.9 C observed in the Tokyo metropolitan area: Considerations of dynamic foehn and foehn-like wind. J. Appl. Meteor. Clim., 50(9), 1827-1841. 2011/09/01(Acknowledgement: S5, S8, T2K) .
Press Release
  • NHK「NEWS WATCH」(Prof. Kusaka)(8.21,2012)
  • Chubu-Nippon Broadcasting Co.,Ltd.「N suta」(D3 Takane) (8.19,2012)
  • Chubu-Nippon Broadcasting Co.,Ltd.「IPPOU」」(Prof. Kusaka)(6.30,2011、8.16,2010)
  • Tokai Televison Broadcasting Co., Ltd.「PI-KAN TV」」」(Prof. Kusaka)(7.26,2010)
  • Nikkei Inc. (7.21,2011、7.22,2011)
  • The Mainichi Newspapers (7.8,2012、7.22,2011)
  • The Asahi Shimbun Comapany(7.22,2011、7.23,2010)
  • The Chunichi Shimbun(8.22,2012、7.1,2011、5.28,2010、7.31,2010)

  • Other

Local Wind ( Downslop winds, Land and sea breezes, Lake and land breezes, Gap Winds )

 In many locations, there are distinctive wind patterns.
 In most cases, unusual topographic or geographic features are responsible for such local winds. Examples of these include downslope winds, land and sea breezes, and land and lake winds. We study these phenomena using observation data, the WRF model, and own local meteorological model.

(1)Downslope winds
 Downslope wind sometimes causes disaster due to its strong wind speed. Our group has been doing a research about local strong wind by the numerical and statistics approaches.

(2)Land and sea breezes
 Land and sea breezes are winds that develop in coastal areas.Land breezes blow from the land toward the sea; sea breezes blow from the sea toward the land. These breezes result from differences in temperature between the land and water.To better understand the thermal environment of urban areas, actual wind conditions need to be known in detail.
We study these phenomena, using our own numerical models and the WRF model.

(3)Lake and land breezes
 Similarly to the land/sea breeze circulation system, lake breezes are caused by differences in surface temperature between the land and a lake. However, lake wind systems are smaller than sea wind systems, and the circulation in a lake wind system does not persist as long. We use numerical models to investigate the interactions between lake breezes and other local circulation.

(4)Gap Wind
 Gap wind also sometimes causes disaster. However, mechanism of gap wind formation in Japan has not well understood yet because the spatial scale is much smaller than European and American ones and terrain is more complicated. Our group has been examining climatological features and mechanism of gap wind in Japan.

(Takayuki KATO and Yuma IMAI)

Distribution of surface wind on the day of "Karakkaze". (14:00 February 19, 2002) Conceptual diagram of Arakawa gap wind.
Arrows indicate the flow of air. The wind passing canyons, it becomes strong wind around exit in Niigata Prefecture Arakawa.
  • Kusaka, H., H. Fudeyasu, 2017: Review of Downslope Windstorms in Japan. Wind & Structures, 24(6), 637-656, 2017/06/24 (Acknowledgement: SIP) .
  • Kusaka, H.,Akifumi, N.,2012: Local Winds in Japan. Journal of Wind Engineering 37(3), 164-171. 2012/08/01 .
  • Kusaka, H., Miya, Y., Ikeda, R., 2011: Effects of solar radiation amount and synoptic-scale wind on the local wind “Karakkaze” over the Kanto plain in Japan. J. Meteor. Soc. Japan., 89(4), 327-340. 2011/08/01(Acknowledgement: S8, Grant-in-Aid for Scientific Research B) .
  • Kusaka, H., 2011: Numerical simulation of local wind. Study Group for Climate Impact and Application Newsletter, 29, 5-11. 2011/07/31 .
  • Kawaguchi, J., Kusaka, H., Kimura, F., 2010: Analyses of Southerly Winds along the Kitakami Basin when the Yamase Prevails.Geophysical Review of Japan., 83(4), 375-383. 2010/07/01 .
  • Miya, Y., Kusaka, H., 2009: Climatological study of the vrtical structure of the Karakkaze wind over the Kanto plain. Geophysical Review of Japan., 82, 346-355. 2009/07/01 (Acknowledgement: Grant-in-Aid for Scientific Research B) .
  • Kusaka, H., Hayami, H., 2006: Numerical simulation of local weather for a high photochemical Oxidant even using the WRF model. JSME Int. J. Ser. B., 49, 72-77. 2006/02/15 (Citations:5times) .
  • Kusaka, H., Kimura, F., Hirakuchi, H., Mizutori, M., 2000: The effects of land-use alteration on the sea breeze and daytime heat island in the Tokyo metropolitan area. J. Meteor. Soc. Japan, 78, 405-420. 2000/08/25 (Citations:55times) .

Local Front

 Local front means areas of rapid changes in winds and temperatures, which cannot be observed in synoptic, scale.

In Kanto area of Japan, the size of local front is normally several hundred meters lengths and thicknesses. Increasing of precipitation and lower visual range are seen as the formation of the local front.

 How to deciding the position of local front? How to growing cold layer or warm advection that key points at local front.

 In Kusaka.Lab, in order to find out the mechanism of the local front, we do the numerical simulations with WRF modeling and Statistical Analysis by observation data.

(Wataru HIRATA)

  • Kusaka, H., Kitahata, H., 2009: Synoptic-scale climatology of cold frontal precipitation systems during the passage over central Japan. SOLA, 5, 61-64. 2009/05/01 .


A thermal column (or thermal) is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection, specifically atmospheric convection. The Sun warms the ground, which in turn warms the air directly above it. Dark earth, urban areas and roadways are good sources of thermals (from wiki).

Mount Asio, located northeast of Tokyo, is popular among sky sports pilots, who utilize updrafts such as thermals during flight. Our laboratory investigates the formation mechanism of the thermals by the field experiment and numerical simulations.

(Ryouhei TOYOTA)

Catch and observe the Thermals by the GPS installed Hang gliding sports.

With the GPS in hang gliding, we can catch the thermals phenomena as the red lines showed.

Inversion Layer(Thermal Belt on the Slope)

 The height of the warmer part, the thermal belt, of the mountain slopes changes with time from early evening, midnight to early morning and also seasonally and differs according to the velocity of the upper general wind and cloudiness, but is generalized by the height difference between the bottom of the basin and the surrounding mountain ridges.

In our laboratory, we use the thermal camera to do the observation, and analyze the thermal belt with high-resolution simulation.

(Takayuki KATO)

Photo of thermal belt on slope took by thermal camera for the northwest side of Mt.Tsukuba (12.13.2012 21:00 by Kato)

Local Heavy Rainfall

Extreme heavy rainfall is sometimes happening in urban area which may paralyzed the city functions. Especially at noonday in summer season, the cumulonimbus cloud is growing up by the instability air, and the local convection rainfall is happened.

Because of the complex topography in Japan, it is very hard to expound the mechanism so clearly.

In our laboratory, we try to use the statistic way or WRF model to do the numerical simulation to figure out the factor of the phenomena.

Study area:The simulation result of local heavy rainfall used WRF ideal experiment in Kansai region.

Simulated results of 3-hourly accumulated precipitation from the WRF model
Left panel: Control experiment
Center panel: Sensitivity experiment without mountains
Right panel: Sensitivity experiment without ocean.

  • Kuno, Y., H. Kusaka, 2014: Climatological study of the heavy precipitation around the Nobi plain in summer. Tenki, 61(8), 661-667. 2014/08/31(Acknowledgement:RECCA) .
  • Kusaka, H., T. Hanyu, and K. Nawata, 2010: Case study of local heavy rainfall, focusing on GPS precipitable water vapor-rainfall event observed in Tokyo on July 4, 2000-. Geophysical Review of Japan., 83(5), 479-492. 2010/09/01 (Acknowledgement: S5) .


 Some areas in Japan are among the most prone to fog formation in the world. In particular, basin fog and sea fog appearing on the Pacific coast are well known. Fog can cause a serious traffic hazard because of poor visibility. On the other hand, fog creates beautiful and fantastic scenery, which can be a tourism resource.

In our laboratory, we mainly focus on fog appearing around Ibaragi Airport and in the Aizu basin. Currently, we investigate the mechanism of fog formation using live-camera image data, the WRF model and LES model.


(1) Fog in the Aizu basin
The Aizu basin is located in the northwestern part of Fukushima Prefecture where fog frequently appears. We have developed a method for predicting fog in this basin, which has higher accuracy than the previous approach.

(2) Fog around Ibaragi Airport
Ibaragi Airport, located about 85 km north of Tokyo in eastern Japan, opened in 2010, where fog frequently appears. We investigate the horizontal distribution of the fog, using a live-camera image data.

(3) Fog in HAKONE

(4) Developing Fog-models

Fog observation around Lake Ashi by the live cameras
Pictures token by Live cameras (Left), in Sunny day (Center), in Fog day (Right)
  • Akimoto,Y., H.Kusaka, 2015: A climatological study of fog in Japan based on event data. Atmos. Res., 151, 200-211. 2015/01/01(Acknowledgement: SOUSEI, RECCA) .