The statistical technique for analyzing and forecasting the track of tropical storms and typhoons is described. Twenty-five years of data (1951-75) for the western North Pacific were evaluated to determine the track characteristics. The results show that the first two out of possible twenty-four eigenvectors account for 75 per cent of the observed variance. The coefficients of the selected eigenvectors were used as the predictands in the development of the forecasting equations. Climatological parameters and 5-day mean 500 mb heights were employed as the potential predictors. Using these predictands and potential predictors at the formation of a tropical storm, forecasting equations for the whole track were derived by regression technique.
A finite differencing scheme of invariant form for the shallow convection equations, which conserves momentum and total energy, is proposed. The proposed scheme is compared with another energy conserving scheme, i.e. that of flux form, with respect to their finite differencing expressions. It turns out that the scheme of invariant form is identical with that of flux form, if there are no computational errors in the continuity equation on every grid point. The scheme is tested and compared with that of flux form in the simulation of dry thermal, and it is confirmed that the scheme of invariant form conserves momentum and total energy as well as that of flux form.
Atmospheric turbidity is one of the important factors in monitoring climatic change but the accuracy of the present observation by the hand-operated type of sunphotometer may not be sufficient. The design feature of a new sunphotometer that measures atmospheric turbidity at discrete wavelengths is described. This sunphotometer was designed to measure solar intensity at seven wavelengths with less than 1-3% error by using interference filters and Si photodiode. Its specifications satisfy the WMO recommendations. In order to derive accurate atmospheric turbidity, great care in calibration is required. In this paper, errors due to various temporal variations in atmospheric optical thickness are calculated and it is shown that the linear Langley plot in a larger airmass region is not always an index to good conditions for calibration. A method is proposed to estimate atmospheric optical thickness (τ) from the Langley plot when it changes as τ=A+Bm or τ=A+Bm2, where m is the optical airmass and A, B are constant.
The conception of surface moisture availability is introduced and its values are estimated from the meteorological data in the surface boundary layer. By use of this conception, the daily evaporation from the non-saturated surface is very well parameterized with the air temperature at the roughness height and the water content of soil near the surface. The relation between the surface moisture availability and the water content of soil agrees well with the results obtained by methods different from ours. It is suggested that for parameterization effectual to the diurnal variation of evaporation it is necessary to investigate the transport mechanism of soil water content in the skin layer near the surface. Under a certain assumption, it is tried to evaluate the soil water content in the skin layer. Its diurnal variation obtained seems to be reasonable.
Wind structure over water waves is analyzed using the drywell-bubble flow visualization method. Significant variation of the wind structure along a wave profile, especially a strong wind near the crest, is observed. The distribution of vertical wind profile along a wave profile is qualitatively similar to the result by Gent and Taylor (1977), but the distribution of turbulent intensity near the wave surface is different from their result; the maximum turbulent intensity is observed on the slope of the leeward side of the wave and the minimum is on the slope of the windward side in our study. Disturbances induced by waves decrease exponentially with height proportional to exp(-2πη/L), where L and η are the wave length and the height above water waves respectively, and become nearly zero at η/L=0.25.
A warm water region has always been seen south of the Kuroshio, south of Honshu. Focusing our attention on the warm water region, we analysed oceanographic data since 1938. The results suggest that there may be two dominant circulation patterns superposed upon each other, in the western North Pacific, one of which may be a circulation intensely affected by zonal wind stress and elongated in the east-west direction along the Kuroshio, and the other may be constrained by bottom topography and elongated in the north-south direction, when zonal wind stress weakens in the northern hemisphere. In the latter, the oceanic area south of Tokaido becomes a dynamical trough and a cold water region is likely to occur. The warm water region south of Shikoku becomes dominant, too.