With the very high horizontal resolution (T63 and T159), an aqua-planet version of the JMA operational global model was integrated. For both resolutions, the Madden Julian (M-J) oscillation with the period of 40 days has appeared. The structures with the scale of zonal wave number one in two different resolution models are nearly identical, while the amplitude of the M-J oscillation in the T159 model is two times larger than that in the T63 model. To the east of the equatorial convergence in the lower troposphere, moist connective systems are mainly found in the equatorial region, while to the west of the convergence, convective systems are found in the off-equatorial tropics. Moisture budget analysis indicates the importance of frictional convergence near the surface for the maintenance of the M-J structure.In the T159 model, the ensemble of cloud clusters (a super cloud cluster) behaves similarly to that in the nature analyzed by Nakazawa (1988). However, the scale separation between the M-J oscillation and the super cloud cluster is not obtained in our model.We examine the influence of the M-J oscillation upon the generation of tropical cyclones. A large number of tropical cyclones are generated near or near-west of the equatorial lower convergence associated with the oscillation. These cyclones contribute to the formation of a symmetric Rossby wave structure elongated in the zonal direction.

The interannual and annual variations in the intra-seasonal oscillation (ISO) are examined using upper air radiosonde data at Singapore. Spectral analysis of the zonal wind using the maximum entropy method (MEM) was made for each season, starting from the autumn of 1960 through to 1985. It is shown that the strongest signal of the I S 0 occurs during the Northern Hemisphere winter, while the weakest occurs in the Northern Hemisphere summer.The main finding of this study is a quasi-biennial oscillation (QBO) in the intensity of the 1.90. The cross-spectral analyses indicate that the intensity of the I S 0 at 150mbar is well correlated for a time-scale of 2-3 years with the stratospheric QBO as well as with the strength of the zonal wind and the static stability of the upper troposphere.These results suggest that the stratospheric QBO may act as a trigger for the tropospheric QBO. The physical interpretation of this interaction requires further work, especially in the field of numerical modelling.

A physical initialization method for the economical prognostic Arakawa-Schubert scheme (EPAS) is developed to incorporate observed precipitation data into a numerical weather prediction model. The method adopted is a variational approach which minimizes the difference between the first guess and the initialized model variables, subject to strong constraints on precipitation areas and precipitation rates. The physical initialization method is divided into 2 parts:(1) Adjustment of the initial thermodynamic variables such that the model precipitation areas diagnosed from the adjusted variables become consistent with the observed precipitation areas at the initial time.(2) Adjustment of the initial cloud-base mass flux (Mb) in such a way that the model precipitation rates are equal to the observed precipitation rates.In order to examine the impact of the physical initialization method, forecast experiments for a case study of Typhoon WALT (T9407) were performed.The results of the forecast experiments indicate that the physical initialization method eliminated the spin-up error of precipitation forecast for the first one hour, and reduced the positional error of precipitation forecasts for the first few hours.The results suggest that the adjustment of the initial cloud base mass flux was essential for eliminating the spin-up error. It is also found that the adjustment of the initial cloud base mass flux contributed to reduce the positional error by strengthening the model convective precipitation around the observed heavy-rain area, and that the adjustment of the initial thermodynamic variables reduced the positional error by removing extreme moist-convective instability in the observed rain-free areas.

Linear responses of the stationary planetary scale disturbances to subtropical and tropical heat sources are investigated for summer northern hemisphere. The model with high vertical resolution is used. Its top is 80km. Zonal mean flows are assumed using FGGEIIIB data by ECMWF. If there are heat sources at 30*N and 10*N, the solutions agree well with observations. The wave of zonal wave number 1 propagates to 60*N. It has two maxima around 30*N and 60*N and minimum at 40*N. The wave of wave number 5 can propagate to 45*N and has only one maximum there.The results suggest that Indian Monsoon activities and heat sources over the Tibetan Plateau can affect on the stationary patterns in middle and high latitudes through poleward propagation of stationary Rossby waves even in summer. On the other hand, the meridional profiles of zonal flows significantly affect on whether the waves forced by heating at ITCZ can propagate northward or not.