The multi-scale features of the Meiyu-Baiu front (MBF) and associated precipitation systems are described based on the recent observational studies for the intense rainfalls period in July of 1991.The MBF extends from the Yangtze River basin to the Japan Islands along the northwestern rim of the westward protruding North Pacific subtropical anticyclone. A blocking ridge develops over Primorskiy Kray of Russia, while a cold upper low develops over Mongolia during this period. The low-level jet stream, nearly moist neutral stratification, and a strong gradient of the specific humidity characterize the MBF. The thermal gradient in the Meiyu front is weak, whereas the relatively large thermal gradient in the Baiu front is sustained between the tropical maritime airmass and the polar maritime airmass.The strong meridional convergence of the moisture flux sustains the large precipitation in the MBF. The differential advection of the equivalent potential temperature generates convective instability against the stabilizing effect of the cumulus convection, and sustains moist neutral stratification and intense precipitation. The northward ageostrophic winds from the northwestern rim of the westward protruding subtropical anticyclone causes strong low-level convergence in the MBF.The short-wave trough that propagates along the southern rim of the upper cold low couples with the short-wave trough in the MBF. The coupling of the troughs causes the development of the subsynopticscale depression (SD) and the associated subsynoptic-scale cloud system. Successively with the development of the SD, a series of the meso-a-scale cloud systems are formed along the long trailing portions of the SD. Thus the ''cloud system family'' with a length of @2000 km, which consists of a subsynoptic-scale cloud system and a few meso-a-scale cloud systems aligned along the trailing portion of the SD, is formed along the MBF. Features and the development process of the subsynoptic-and meso-a-scale cloud systems are studied in detail.

[1] Intense gravity wave activities were investigated in the lower stratosphere during the typhoon 9426. Strong vertical winds were observed just a few hours before the arrival of the typhoon-center at the MU radar site. About 30 min to 1 hour after the typhooncenter had passed, a considerable reduction in vertical wind amplitude was detected. Dominant gravity waves showed time period in the range of 7-8 min, 15 min, and 40-60 min in the upper troposphere and lower stratosphere. In the vicinity of the central region of the typhoon, a gravity wave was observed, which was monochromatic in nature with a vertical wavelength $3 km between 1.5 km and 23 km height. In the lower stratosphere, the horizontal wavelength for the prominent period was detected in the range of 10-15 km (for 15 min wave period) and 25-50 km (for 40-60 min wave period). The vertical wavelength of these waves was examined from 2.5 km to 4.0 km. In the horizontal direction, the intrinsic group velocity was estimated between 9 ± 2 and 11 ± 2 m/s. Near the tropopause, the average direction of group velocity was assessed at about 20°± 3°f rom the horizontal. The generation of gravity wave like features, in the lower stratosphere, is believed induced by convection, as the low temperature of the clouds indicates a deep penetration over the radar region as seen in the satellite GMS images.

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An experiment was conducted in the month of June 2000 to study the atmospheric dynamical behavior in the troposphere and lower stratosphere in the presence of a cloudy and moist background environment due to the onset of the summer monsoon over Indian peninsula. The cardinal objective was to observe the gravity wave signatures in the convective environment. We successfully monitored the development, maximizing and weakening of convective phenomena within a time span of 3–4 hours on 21–22 June 2000. The vertical wind in the troposphere during this period was found about 6–8 m/s. Variations of the radar returned signal power for the vertical beam with height and time show the continuous growth of high turbulence in the ambient air, ascending as high as the tropopause. The satellite cloud images exhibited the temporal growth and movement of cloud clusters over the region of the radar site during this period.

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A special tropospheric observation was conducted during 10 April-09 May 2004 as a part of the first campaign of the Coupling Processes in the Equatorial Atmosphere (CPEA-I), using upper soundings at seven stations in/around Sumatera, and weather radar and wind profilers at Kototabang (KT; 100.32 E, 0.20 S, 865 m above mean sea level), West Sumatera. A super cloud cluster (SCC) with a westerly wind burst (WWB) propagated eastward over the Indonesian Maritime Continent during 04-07 May. In the present report, we examine the evolution of that SCC and the associated wind behavior in detail, usingCorresponding author: Yoshiaki Shibagaki, Faculty of Information and Communication Engineering, Osaka Electro-Communication University, 18-8 Hatsu-cho, Neyagawa, Osaka 572-8530, Japan. E-mail: sibagaki@maelab.osakac.ac.jp ( 2006, Meteorological Society of Japan Geostationary Operational Environmental Satellite (GOES-9) Infrared (IR) data and CPEA observations. During the analysis period, the SCC developed over the eastern Indian Ocean, decayed rapidly as it reached Sumatera, and re-developed over Kalimantan. The eastward propagation of SCC resulted from the successive formation of meso-scale cloud clusters (CCs) with westward propagation. The transition of the SCC was related to the evolution of CCs. A CC generated over Sumatera began to diminish as the WWB arrives at a mountain range in western Sumatera, but it dominated in/around the mountain range for @9 hours. From upper sounding data aligned along the equator, it was found that the migration speed of the WWB over Sumatera was approximately half that over the sea region between Sumatera and Kalimantan, due to the orography of the Indonesian Maritime Continent. In western Sumatera, the peak height of the WWB at the mountain range ascended 1.5 km from that on the windward side. This shows that the eastward migration of the WWB was intercepted by the mountain range. The orographic influence on the WWB is considered to persist during the retention of the CC in its vicinity. Further, we reveal features of the orographic precipitation associated with the WWB and the detailed wind structure inside the SCC over the mountain range, from radar observations at KT.

[1] Five years of tropospheric data below 12 km from the Equatorial Atmosphere Radar (EAR) are examined for seasonal and interannual gravity wave activity. Results are compared with data from the Tropical Rainfall Measuring Mission (TRMM) satellite. A semiannual cycle of vertical wind variances inside and above convection is found. Maxima occur at the equinoxes and minima at the solstices. This semiannual cycle is also observed in the TRMM storm height and surface rainfall. Half of the vertical wind variance above convection is due to waves with periods of less than 2 h, with the rest coming from waves with periods of less than 24 h. On average, 78% of the total horizontal wind variance above convection is due to waves with periods of less than 24 h. The TRMM rainfall at 2 km altitude is greater than the EAR surface rainfall, suggesting that the EAR site is not representative of regional rainfall conditions. Momentum fluxes are calculated and shown to be dominated by multiday processes, although standard deviations are greater than the mean values.