Diurnal Variation of Cb-Clusters over China and Its Relation to Large-Scale Conditions in the Summer of 1979

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  • Kato Kuranoshin
    Institute for Hydrospheric-Atmospheric Sciences, Nagoya University
  • Matsumoto Jun
    Department of Geography, Graduate School of Science, the University of Tokyo
  • Iwasaki Hiroyuki
    Department of Earth Science, Faculty of Education, Gumma University

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Other Title
  • 中国東部における積乱雲群出現の日変化と総観場の解析(1979年6～8月)
  • 中国東部における積乱雲群出現の日変化と総観場の解析(1979年6～8月)〔英文〕
  • チュウゴク トウブ ニ オケル セキランウングン シュツゲン ノ ニチヘンカ
  • Diurnal variation of Cb‐clusters over China and its relation to large‐scale conditions in the summer of 1979

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Abstract

The appearance frequency of Cb-clusters and its diurnal variation were examined in relation to large-scale conditions based on the observational data from June to August 1979. The analysis was applied to the three stages in the seasonal march in that year, i. e., “Pre-Meiyu” (1-17 June), “Meiyu” (20 June-22 July) and “Mid-summer” (23 July-17 August). The main results are as follows.<br>(1) The Cb-clusters appeared frequently not only in the Baiu frontal zone but also in North to Northeast China (Area N1) in “Meiyu”, and in Central China (Area C2) in “Mid-summer”. A remarkable diurnal variation of appearance frequency of the Cb-clusters with an evening maximum was observed in Area N1 in “Meiyu” and Area C2 in “Mid-summer”. The daily maximum of ground surface temperature in these two cases was very high.<br>(2) In Area N1 in “Meiyu”, the Cb-clusters with diurnal variation were mainly embedded in large-scale cloud systems corresponding to slow-moving upper-level lows or troughs. The specific humidity in the lower layer increased from “Pre-Meiyu” to “Meiyu”. These two factors, as well as the strong surface heating, would provide a favorable condition for the frequent appearance of Cb-clusters due to the increase of convective instability. The large-scale horizontal convergence in the lower layer was stronger at 12 UTC (20 BST) than at 00 UTC (08 BST), which would lead to the development of Cb-clusters in the evening.<br>(3) Area C2 was covered by the subtropical high, and the low-level divergence was generally stronger at 12 UTC than at 00 UTC. In spite of these conditions, the isolated Cb-clusters developed very frequently in the evening. The very strong surface heating in the daytime could contribute to release of the strong convective instability by generating meso-scale upward motion as a trigger.

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