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

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

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

• Fig. 1. (a) Surface synoptic map at 21 JST (12 UT) on July 2, 1990 and (b) GMS IR image at 00 JST on July 3 (15 UT on July 2), 1990 transcribed directly from the routine products of the Japan Meteorological Agency (JMA).
• Fig. 2. Quasi-meridional cross-section at 21 JST (12 UT) on July 2, 1990 of temperature (thicker solid contours, every 10$^{\circ}$C), zonal wind velocity (thinner solid contours, every 5 m/s), relative humidity (dotted contours, every 20\% ) and the tropopause and frontal surface (thick dashed curves), based on observations at the MU radar observatory (34.85\degr N,\ 136.10\degr E) and five JMA stations located along an approximately NNE-SSW line passing through the central Japan (a map was given in Fukao et al.,\ 1988; Larsen et al.,\ 1991): of Sapporo (47412), Akita (47582), Wajima (47600), Shionomisaki (47778) and Minamidaitojima (47945). Pressure is taken as the vertical coordinate (the ordinate), and altitude plotted in the right-hand side axis is correct at Shionomisaki. Total horizontal winds at standard pressure levels over the JMA stations are also indicated by short (5 m/s) and long (10 m/s) barbs.
• Fig. 3. (a) Zonal-vertical (eastward and upward positive) and (b) meridional-vertical (northward and upward positive) air flows observed by the MU radar from 2357 JST on July 2 to 0136 JST on July 3,\ 1990. Time resolution is approximately 2.5 minutes.
• Fig. 4. (a) Zonal-meridional (eastward and northward positive) and (b) vertical (upward positive) air flows observed by the MU radar from 2357 JST on July 2 to 0136 JST on July 3,\ 1990. Time resolution is approximately 2.5 minutes.
• Fig. 5. Vertical profiles of potential temperature (----- 21 JST on July 2; $\cdot \cdot \cdot$ 03 JST on July 3,\ 1990) and equivalent potential temperature (-$\cdot$-$\cdot$- 21 JST on July 2; - - - 03 JST on July 3,\ 1990), observed with radiosondes launched at the MU radar observatory. The data of 03 JST on July 3 are displaced by 5 K.
• Fig. 6. Distribution of the Richardson number (for wet air) calculated based on horizontal wind obtained from 10-min averaged MU radar data and equivalent potential temperature interpolated from the observations by radiosondes launched at $\sim 21$ JST on July 2 and at $\sim 03$ JST on July 3,\ 1990 (with correcting the time lags of balloons passing each altitude). The regions of values less than 1/4 are shaded.
• Fig. 7. Echo power observed by the Ku-band radar at the MU radar site (unit is dBZe) from 1915 JST on July 2 to 0115 JST on July 3,\ 1990.
• Fig. 8. Distribution of echo power observed by a standard meteorological radar ($\odot$) of the Osaka Meteorological Observatory (OMO) of JMA at (a) 00 JST and (b) 01 JST on July 3,\ 1990. The black region indicates rainfall between 1 and 4 mm/h, and the shaded region indicates rainfall less than 1 mm/h. The MU radar site is shown by a star.
• Fig. 9. Surface pressure (solid contours, every 0.2 hPa) and temperature (dashed contours, every 0.2\degr C) changes (a) from 23 JST on July 2 to 00 JST on July 3 and (b) during 00--01 JST on July 3 1990, analyzed from the routine meteorological data collected by OMO. Surface winds are also indicated by barbs (1 m/s) and pennants (5 m/s).
• Fig. 10. Schematic structure of the rotor circulation observed in this study.

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