Band Structure of Mesoscale Echo Clusters Associated with Low-Level Jet Stream

Abstract

A large echo band, whose length is about 1,000km, developed over the East China Sea adjacent to southwestern Japan on 7 July 1970. The three dimensional structure of the echo band is analyzed by using the data of the Experiment of Severe Rainstorms Research Project.The echo band is associated with strong precipitations and a remarkably developed ageostrophic low-level jet stream. The analyzed moisture field around the jet stream coincides well with the model of the low-level jet's circulation proposed by Matsumoto and Ninomiya (1971). It is inferred about the mechanism of the echo band that the convective mixing of the horizontal momentum in the echo band maintains the ageostrophic low-level jet. The unbalanced solenoidal field caused by the ageostrophic wind field accelerates the vertical circulation and thus maintains the convective activities of the echo band.It is also found that the echo band is not a zone of uniformly distributed echo cells but a row of mesoscale echo clusters whose spacing is about 150km.Two other cases of large-scale echo bands, one over the Pacific coastal area and another over the Midwest of U. S. A., are also presented as similar examples.

Multi-scale Features of Baiu, the Summer Monsoon over Japan and the East Asia

“…Various case studies of Baiu front and the Baiu frontal disturbances associated with intense precipitation have been studied in several papers (e. g., Matsumoto and Akiyama, 1969;Ninomiya, 1978;Ninomiya and Akiyama, 1971, 1972, 1974Ninomiya and Yamazaki, 1979;Ninomiya et al, , 1988a. Although the features of Baiu intense rainfalls varied from case to case, some common characteristics are found in the Baiu frontal heavy rainfall events.…”

“…convective systems in the Baiu front have been studied for the various cases (Matsumoto and Akiyama, 1970;Ninomiya and Akiyama, 1974;Ninomiya and Yamazaki, 1979;Akiyama, 1978Akiyama, , 1979.…”

Subtropical Rainband along the Western Side of a Slow-moving Ridge

“…The fine-mesh model used in the present study (6L-77km model) is the same as that used in Ninomiya andTatsumi (1980 and1981). Brief descriptions of 4L-NHM2 and 6L-77km models are given in Table 1.…”

“…After middle of July, it loses gradually its identity as it advances further north (*45 N), and then the mid-summer comes to the Japan Islands (Yoshino, 1966;Akiyama, 1973). The Baiu front and associated disturbances have been studied in detail (Matsumoto et al, 1971;Akiyama, 1973Akiyama, , 1975Akiyama, , 1978Ninomiya, 1980;Ninomiya andAkiyama, 1971, 1974;Ninomiya and Yamazaki, 1979;Yoshizumi;Yano, 1973). During the mid-summer, hot and fine weather covers the Japan Islands when the Pacific anticyclone protrudes northwestward and the Tibe-K. Ninomiya 2.…”

Hierarchical Structures of Vertical Velocity Variations and Precipitating Clouds near the Baiu Frontal Cyclone Center Observed by the MU and Meteorological Radars

“…For example, Akiyama (1972, 1973) and Akiyama (1973) have reported that the cloud clusters are developed due to warm moist air-mass transport near the medium-scale cyclone and a low-level jet stream is intensified within the cloud zone. Convective activity in the rainfall zone is maintained by upward motion on the northern side of the low-level jet stream axis, in which the unbalanced solenoidal circulation structure around the axis has been estimated from a systematic distribution of moisture (Ninomiya and Akiyama, 1974). Ninomiya and Yamazaki (1979) have shown that an upward motion estimated from the convergence of horizontal wind is accompanied by developing clouds and heavy rainfalls in a neutral region after the appearance of the low-level jet stream, and Ninomiya (1980), Ninomiya and Tatsumi (1981) and Ninomiya and Kurihara (1987) have also explained the enhancement of the low-level jet stream and cyclonic circulation due to cumulus convective activity associated with south-westerly wind by using hemispheric and mesoscale primitive equation models.…”