A model which estimates the parameters in the convective boundary layer using routine meteorological observation data is developed. The data required are net radiation, air temperature, wind speed, and a radiosonde sounding. The model includes the estimation schemes of surface heat flux and friction velocity, and a mixed layer height model modified from the jump model. The field observation of the boundary layer was carried out at Tsukuba, Japan. Estimated data by the model fit well with field observation data. Seasonal and diurnal variations of the convective boundary layer are estimated by the model with the data obtained over a period of 3 years at Tsukuba. Results are as follows. Convection is most intensive in spring. There are two peaks on the seasonal variation pattern of the mixed layer height, with a maximum in spring and secondary peak in autumn. Notably, it is not so high in the summer, despite strong solar radiation. It is known that the potential temperature gradient is large in summer and small in winter, with this feature being related to air mass types. The potential temperature gradient of continental air mass is small and that of maritime air mass is large. Together with the surface heat flux, the occurrence frequency of types of air mass is one of the important factors in explaining seasonal variation of the structure of the convective boundary layer.