Abstract
Momentum budget analysis is made o ver western Japan in the Baiu season in 1968and 1969. Ensemble means of results obtained and other variables are compared between two cases, i. e., with an area-mean precipitation of 5 mm/12 hr or more (Case MH) and one of less than 5 min/12 hr (Case NL). Heat budget analysis shows that convective activity is high throughout the troposphere in Case MH and confined to the lower troposphere in Case NL.
Although some systematic error is contained in the estimated residual terms of the momentum equation, especially in its component normal to the wind, it is shown from comparison between results for Cases MH and NL that in Case MH the convective vertical transport of westerly momentum is downward with a maximum value of 2-4 dyn/cm2in the mid-troposphere. The estimated downward transport of southerly momentum does not exceed 2 dyn/cm2.
Total kine t i c energy dissipation for the layer 1000-100 mb is about 20 w/m2 in Case MH, one order of magnitude greater than in Case NL. Dissipation rate remains low in the layer 800-600 mb even in Case MH in spite of the great total dissipation. These facts suggest that in Case MEI there exist energy transfers from the large- to subgridscale motion, especially in the upper troposphere, and from the upper to the lower troposphere through the downward momentum transport by the subgrid-scale or convective motion. The difference in the interaction between the large- and subgrid-scale motions may be responsible for the difference between the observed wind profiles in Cases MH and NL.
