“Moist Tongue” over Japan in the Baiu Season (Preliminary Report)

Abstract

At the time of heavy rainfall, very humid air named “moist tongue” is found in the upper air levels over Japan. This air, extending as a tongue from a moist air to the west or to the southwest, has been repeatedly observed during the rainy periods. In this paper, the moist air area around Japan was analyzed statistically from the vie wpoint of dew-point distribution during the baiu season (June and July). The observed frequency of dew-points above 6°C., 8°C., 10°C., and 12°C. indicates that between the 1st and the 10th of June in the average of three years, 1960-1962 (Figs. 1-4) the axis of the moist area lies in South China and extends to the east; and that between the 1st and the 10th of July (Figs. 5-8) the axis lies in central China and extends to the east. Each group of figures for June and July shows that the core of the moist area exists approximately in SW China with its axis moves toward the north in the early summer when the baiu frontal zone moves toward the north.The observed frequency of high dew-points is shown in Table. Analyzing each observation, the authors conclude that the “moist tongue” appearing over Japan emanates, in many cases, from the above mentioned moist air area.