A Rotor Circulation near the Baiu Front Observed by the MU Radar

Akira Watanabe
Faculty of Education, Fukushima University, Fukushima 960-12, Japan

Shoichiro Fukao, Manabu D. Yamanaka
Radio Atmospheric Science Center, Kyoto University, Uji, Kyoto 611, Japan

Akimasa Sumi
Center for Climate System Research, University of Tokyo, Tokyo 153, Japan

and Hiroshi Uyeda
Department of Geophysics, Hokkaido University, Sapporo 060, Japan


Journal of the Meteorological Society of Japan , Vol. 72 , No.1, pp.91-105.

Extended from a paper presented at the Fifth Workshop on Technical and Scientific Aspects of MST Radar, Aberystwyth, Wales, UK, 6--9 August 1991.
First draft: August 3, 1991; Second draft: November 1, 1992; Third draft: January 16, 1993;
Submitted: March 25, 1993; Received: March 31, 1993; Revised: September 20, 1993; Final manuscript completed: September 27, 1993; Received: September 29, 1993
Published: February, 1994


ABSTRACT , CONTENTS , CORRECTIONS , FIGURES , REFERENCES , CITATIONS


Abstract
A rotor circulation was directly observed near the Baiu front in the lower troposphere by three-dimensional Doppler measurements with the MU radar at Shigaraki, Japan (35\degr N,\ 136\degr E). The temporal and vertical scale of the rotor were $\sim 50$ min and $\sim 2$ km, and the stratification observed by radiosondes was statically stable. The synoptic meteorological analysis suggests that the rotor existed just below and between Baiu-frontal banded precipitation clouds which were organized in a meso-$\alpha$ scale cyclone. Precipitation echoes observed simultaneously by C/Ku-band radars were quite weak in downdraft in front of the rotor, and became significant and tall up to $\sim 9$ km altitude at the back of the rotor circulation. The rotor was identified with a meso-$\beta$ scale depression observed by the routine meteorological network, which had a horizontal scale of $\sim 40$ km in the zonal direction and 150--200 km in the meridional direction, and moved from west to east at $\sim 50$ km/h. Based on brief discussions, we conclude that the rotor circulation was locally developed from an orographic disturbance by shear instability which was occasionally induced in a weak statically-stable layer maintained by (conditional) symmetric instability.


Contents
1. Introduction
2. Synoptic-Scale Situation
3. Observations at MU Radar Observatory
3.1. MU Radar Observations
3.2. Radiosonde Observations
3.3. C/Ku-band Radar Observations
4. Mesoscale Horizontal Structure
5. Discussions on Generation Mechanism
6. Conclusion


Corrections and Additional Remarks
(Nothing)


List of Figures (no tables)


References (Updated after publication)


Citations by Subsequent Papers
(Under construction !!!!!)


  • List of Original Papers by M. D. Yamanaka

  • Bibliography by any authors


    M. D. YAMANAKA homepage (English)


    E-mail : yamanaka@kurasc.kyoto-u.ac.jp
    MUレーダーで観測された梅雨前線近傍のローター循環 \\

    {\bf 渡 辺   明} \\ {\small 福島大学教育学部} \\

    {\bf 深 尾 昌一郎 ・ 山 中 大 学} \\ {\small 京都大学超高層電波研究センター} \\

    {\bf 住   明 正} \\ {\small 東京大学気候システム研究センター} \\

    {\bf 上 田   博} \\ {\small 北海道大学理学部} \\

    MUレーダー(滋賀県信楽町)を用いた下部対流圏3次元風速ベクトルの 連続ドップラー観測から, 梅雨前線近傍に存在するローター循環を検出した. ここで報告するような顕著なものが, 流れの鉛直成分を含めて現実に観測されたのは, 筆者等の知る限りにおいてこれが初めてである. ローターの時間および鉛直スケールは約50分および約2 kmであり, また並行して行われたラジオゾンデ観測によれば, 出現領域は静力学的に安定な成層構造をなしていた. 気象庁高層観測および衛星観測に基く総観場および雲の解析から, ローターが出現した領域は梅雨前線面のすぐ下方であり, かつ中間(メソ$\alpha$)規模低気圧に伴って組織化されたバンド状降水雲の 間に位置することがわかった. MUレーダーと同時に行った2周波(C/Ku帯)気象レーダー観測で得られた 降水粒子エコーは, ローター前面の下降流域では極めて弱く, 後面の上昇流域では極めて顕著で約9 km高度にまで達していた. さらに大阪管区気象台によるレーダー観測およびメソ天気図解析から, このローターは, 東西に約40 km, 南北に約40 kmの大きさを持ち 東方へ時速約50 kmで進む中(メソ$\beta$)規模擾乱と同定された. 成因について現時点で最も有力と考えられるのは, 中間規模(条件付)対称不安定擾乱に伴って維持された弱い静力学的安定層中で, 局所的シア不安定で偶発的に成長した中規模擾乱であるとするものである.