Numerical Simulation Of Planetary Atmosphere

By using the NCAR'S atmospheric general circulation model (AGCM) CAM2, the features of circulation have been investigated under different rotation rates and obliquities on Earth. Furthermore, the CAM2 was developed to simulate the Titan's circulation. We name it the PGCM. The features of Titan's circulation when assuming the Earth's rotation rate are investigated to search for possible influences of the rotation rate on Titan's circulation. The results of this paper can be summarized in the following aspects:1 The intensity of three-cell circulation turn strong when the rotation rate turn slow either for annual mean or for seasonal mean. The intensity of three-cell circulation turns weak when the rotation rate turns faste. The change of the intensity of three-cell circulation is different in different season. The change is the biggest in autumn.2 Under slow rotation rate, for annual mean temperature field, there exist the negative anomalies in the Northern Hemisphere and positive anomalies in the Southern Hemisphere. The region of negative anomaly and that of positive anomaly are divided by 15°S.3 The annual mean zonal wind field has positive anomaly and negative anomaly when the rotation rate is changed. The positive anomalies and negative anomalies are cross.4 Compared with summer and autumn, in spring, the changes of geopotential height field, temperature field, meridional wind field in the stratosphere and vertical velocity field are opposite under different rotation rates. Compared with annual mean result, the situation of these three fields is reverse.5 The westerly in mid-latitude are all strengthened in four seasons under slow rotation rate. The change trends of the zonal wind in two Hemisphere are opposite in spring and autumn.6 The changes of physical quantities have significant seasonal difference. The change in autumn is the biggest.7 African monsoon and monsoon in temperate zone and Frigid Zone are weakening when the rotation rate turn slow.8 Three-cell circulation turn weak when the obliquity turn large except that the three-cell circulation in Northern Hemisphere in winter, Hadley circulation in Southern Hemisphere in spring and Hadley circulation in Southern Hemisphere in summer turn strong with the obliquity turn large. For annual mean three-cell circulation, its intensity turns weak with the obliquity turn large.9 The extension and the velocity of easterly wind in stratosphere over the equator turn large when the obliquity turns large. While the easterly in the troposphere and westerly in the Northern Hemisphere turn weak when the obliquity turns large.10 The scope of global monsoon turn large with the obliquity turns large. The African monsoon, South American monsoon, monsoon over the north of Pacific Ocean and East Asian monsoon are strengthened with the obliquity turn large.11 The transplantable Planetary General Circulation model (PGCM) based on the earth-representative CAM2 is developed to simulate other planetary atmospheres. In this research we test the basic performance of the PGCM by simulating Titan's atmospheric circulation. The results of the PGCM model are compared with those of the LMD model. Moreover, the features of Titan's circulation when assuming the Earth's rotation rate are investigated to search for possible influences of the rotation rate on Titan's circulation. The PGCM is able to adequately simulate basic circulation structures of Titan, e.g., the equatorial superrotation (～108 m/s) in the Titan's stratosphere, vertical meridional circulations, some vertical profiles, easterly wind near the surface etc. The magnitude of Titan's rotation rate can significantly affect the dynamical structure of the Titan's circulation. The westerly winds of a whole layer are weakened, but the easterly winds are strengthened near the surface, when the rotation rate of Titan is changed to that of the Earth. The effects of the different Titan rotation rates on the meridional circulation mainly pertain to the troposphere. Furthermore, when the Earth's rotation rate is assumed, three cells are present in the troposphere in the two hemispheres, whereas only two cells occur for Titan's rotation rate.12 There are two necessary conditions about existence of the zonal wind sink on Titan. First, the length of solar day on Titan must lie between five times the length of earth's day and fifty times the length of earth's day. Second, the gradient of temperature in upper atmosphere must larger than that in deeper atmosphere, and the gradient of temperature in deeper atmosphere is very small.