著者

Hisaki EITO Masataka MURAKAMI Chiashi MUROI Teruyuki KATO Syugo HAYASHI Hiroshi KUROIWA Masanori YOSHIZAKI

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.88, no.4, pp.625-648, 2010 (Released:2010-10-05)

参考文献数

43

被引用文献数

15 17

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During a cold-air outbreak, a broad cloud band is occasionally observed over the Japan-Sea Polar-Airmass Convergence Zone (JPCZ) that forms over the Sea of Japan from the base of the Korean Peninsula to the Japanese Islands. On 14 January 2001, a broad cloud band associated with the JPCZ (JPCZ cloud band) extended in a southeastward direction from the base of the Korean Peninsula to Wakasa Bay, and it stagnated for half a day. The JPCZ cloud band consisted of two cloud regions: one was a long cloud band extending along its southwestern edge (a developed convective cloud band), and the other was the region consisting of cloud bands normal to a wind direction of winter monsoon (transversal cloud bands). The structure and formation mechanism of the transversal cloud bands were examined on the basis of observations (e.g., satellite images, in situ measurement and cloud-pro.ling radar data from an instrumented aircraft and upper-air soundings from observation vessels) and simulation results of a cloud-resolving model with a horizontal resolution of 1 km.The transversal cloud bands had the following characteristic structures; they extended along a northeast-southwest direction, which was parallel to the direction pointed by the vertical shear vector of horizontal wind in the mixed layer, they mainly consisted of convective clouds, which slanted with height toward the down-shear side, and they widened and deepened toward southwest, as the depth of the mixed layer increased. An examination of simulation results presented that the transversal cloud bands were accompanied by roll circulations. The axes of rolls were oriented nearly parallel to the direction of the vertical shear vector in the mixed layer. An analysis of the eddy kinetic energy budget indicated that the roll circulations derived most of its energy from the mean vertical shear and the buoyancy.

著者

Hisaki EITO Teruyuki KATO Masanori YOSHIZAKI Ahoro ADACHI

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.83, no.4, pp.551-576, 2005 (Released:2005-10-07)

参考文献数

32

被引用文献数

23 25

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On 16 January 2001 during the field experiment named WMO-01, a meso-β-scale snowband extending eastward from Toyama Bay was observed in the coastal area of eastern Hokuriku district, middle part of Japan. This snowband stagnated for about half a day and brought a snowfall of about 50 cm in this region.Numerical simulations of this snowband are performed using a nonhydrostatic cloud resolving model (NHM), with a horizontal grid size of 1 km. The NHM well reproduces many characteristics of the observed snowband. The snowband forms over the convergence zone between a cold southerly land breeze and a northwesterly winter monsoon, to which heat and moisture is supplied from relatively warm sea surface. Convective snow cells with the horizontal scale of a few km successively form at the northern part of the snowband and propagate east-southeastward. Meso-γ-scale convective snow systems are organized, consisting of developed snow cells in the snowband. A cold pool forms under the snowband. The diabatic cooling due to the sublimation of snow is responsible for the formation of the cold pool. After the land breeze became weak, the cold pool contributes to the maintenance of the horizontal convergence with the northwesterly winter monsoon at the northern edge of the snowband by compensating for the weakened land breeze. Therefore, the formation of the cold pool is significant for the maintenance of thesnowband.

著者

Hisaki EITO Kazumasa AONASHI

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.87A, pp.425-446, 2009-03-31 (Released:2009-08-07)

参考文献数

34

被引用文献数

7 16

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This paper compares satellite microwave radiometer and ground-based radar observations with the Japan Meteorological Agency nonhydrostatic model (JMA-NHM) simulations, using a bulk microphysical parameterization, for a typical rainfall system associated with the Baiu front around the Okinawa Islands, Japan, on 8 June 2004.  The JMA-NHM correctly replicated the shape, location and intensity of the precipitation associated with the observed rainfall system. Radar reflectivities and microwave brightness temperatures (TBs) were simulated using output from the JMA-NHM simulations. They were then compared with concurrent corresponding observations by the National Institute of Information and Communications Technology (NICT), CRL Okinawa Bistatic Polarimetric Radar (COBRA), and Advanced Microwave Scanning Radiometer for EOS (AMSR-E). Fairly good agreement was obtained between the simulated and observed reflectivities under the melting layer and TBs at low frequency (18.7 GHz), indicating that the JMA-NHM adequately simulated the amount of liquid hydrometeors. However, the intensity of scattering in the simulations was stronger than that in the COBRA observations above the melting layer and the AMSR-E observations at high frequencies (36.5 and 89.0 GHz). This was due to the fact that the JMA-NHM overestimated the amount and size of snow particles as a result of large depositional growth.  The excessive snow contents were reduced by adjusting some of the microphysical processes in the JMANHM: the snowfall speeds were increased and a riming threshold for snow to graupel conversion was changed. These adjustments helped to reduce the amount and size of snow, resulting in further agreement with the COBRA observations. These adjustments also further improved the simulated TBs at high frequencies, especially at 36.5 GHz. However, differences still exist between the simulated and the observed TBs at high frequencies, suggesting that additional adjustment to and improvement of the snow microphysical processes are needed for the application of the model to microwave remote sensing of precipitation.