To clarify the behavior of the standard deviation of vertical velocity σw under various meteorological conditions, many data obtained by tethered balloon, high tower and light airplane were analized. Relations between σw, wind speed U, and many meteorological elements, for example, insolation, local lapse rate, Pasquill's stability categories, classification of cloud and inversion base height, were checked. It has been found from observations at height of 50 m that σw was proportional to U in case of weak insolation while with increasing of insolation, σw tended to show characteristics caused by free convective fluctuations. Temperature gradient at the observation height of σw can not explain variation of the relation between σw and U with stability. Pasquill's stability categories are not explanatory index either for the σw-U relations, except at 50m. Three different relations between σw and U were found from observations taken at various heights. First is the relation for strong convective layer; second, in the layer below inversion base; and third, in the inversion layer. In the case of second group, there is a critical wind speed Ucγ. When U is weaker than Ucγ, free convection is redominant and σw is independent of wind speed. When U is stronger than Ucγ, however, forced convection is predominant and σw/U tends to be constant. The height dependency of Ucγ was observed.
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