A numerical model of the atmosphere with a seasonal variation of insolation and sea surface temperature is time integrated for over 3 simulation years on a finite difference grid network having a nearly uniform horizontal resolution of approximately 265 km. There are 11 levels in the model from 80 m to 31 km above the ground. The model has realistic continents with smoothed topography. In addition to wind, temperature, pressure, and water vapor, the model simulates rainfall, snowfall, and evaporation at the surface. The runoff rate and the rates of change of soil moisture and snow depth are determined by a budget of liquid water, snow, and heat at the ground surface. The simulated precipitation and other hydrologic quantities are compared with those derived from observed data. In addition, the correspondence between the distribution of precipitation rate and those of other relevant quantities, such as sea level pressure and kinetic energy of transient disturbances, is examined. To obtain an overall impression of the climate simulation, a map of K¿ppen climate types, which is obtained from simulated temperatures and precipitation rates throughout the year, is compared with a similar map based upon observed climatic data. It is shown that the model locates the major arid regions of the earth, such as the Sahara Desert in northern Africa and the deserts of central Asia and Australia. Furthermore, the tropical rain belt and its seasonal movement are well reproduced. The model approximately simulates the changeover from dry winter to wet summer conditions in southern Asia and the seasonal reversal of the monsoon wind system over Asia. The wet zone in middle and high latitudes, such as in Canada, Europe, and western Siberia, is also simulated by the model. Examination of the distribution of runoff over continents of the model reveals that the watersheds of many important rivers of the world are correctly positioned in the simulation. In general, the quality of the simulation tends to deteriorate in the neighborhood of major mountain ranges. Furthermore, the rate of precipitation and that of runoff over continental regions in the model tropics is much larger than estimates of the actual rates of these quantities. Nevertheless, this study demonstrates that the model is capable of reproducing many of the basic features of the seasonal variation of hydrology and climate on a global scale.