Papers in Meteorology and Geophysics

We estimated an attenuation function of displacement amplitude based on moment magnitude. The function enable us to calculate conventional magnitude that would agree with moment magnitude on the average in all depth ranges. Magnitude calculated with the function is smaller than that calculated with M. Katsumata's formula by about 0.3 for deep-focus earthquakes. The function is applicable to data when the hypocentral distance is from about 30 to 2000 kilometers. The function was estimated based on data from the Japan Meteorological Agency (JMA) between January 1977 and February 1994. Some corrections are provided to apply the function to data from the current JMA seismological network developed in 1994.

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A preliminary result of a new atmospheric general circulation model (MRI/JMA98) in the Meteorological Research Institute is described focusing on the seasonal and monthly mean fields. The model is based on the spectral global model, which is operationally used for weather forecasting in the Japan Meteorological Agency. The horizontal resolution is reduced to that of triangular 42 truncation (T42), but the top level is raised up to the mesopause (0.01hPa) with an increase of layers to 45 (L45) layers. A little lower model is also made, the top of which is at 0.4hPa just above the stratopause, with 30 layers (L30). Some physical process schemes are improved. The radiative scheme is replaced for solar and terrestrial radiation to yield sufficient accuracy in the middle atmosphere. The ground hydrology scheme is also updated. Soil layers for temperature are increased from two to three layers, similar to those for water, leading to a rigorous treatment of melting and freezing of water through the consistency between heat and water budgets.
Four- and three-year simulations are made with T42L45 and T42L30 models, respectively, under a climatological sea surface temperature, and both models reproduce reasonably well the general features of the observed atmosphere. Additional runs are performed to investigate the effects of top level position and enhanced horizontal diffusion, and their results are also described.

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