【作者】 刘鑫华；

【导师】 李建平；

【作者基本信息】 兰州大学 ， 气象学， 2008， 博士

【摘要】 本文利用NCAR的大气环流模式CAM2,研究了不同地转速度和倾角对地球大气环流的影响。并将CAM2推广到行星大气数值模拟,初步对土卫六大气环流进行了模拟,进而研究了不同自转速度下土卫六大气环流的差异。本文主要结论如下:1三圈环流的变化无论从年平均气候态,还是季节平均气候态来讲,均以慢地转条件下全球范围的环流增强,快地转条件下全球范围的环流减弱为主要特征。强度变化存在季节差异,秋季变化最大。2慢地转条件下,年平均气候态温度场北半球为负异常,南半球为正异常。正负异常大致以15°S为界。3改变地转速度后,年平均气候态纬向风场发生了正负相间的异常变化,且快地转与慢地转反向变化发生的纬度稍有南北移动。4不同地转速度下春季,位势高度场、温度场、平流层经向风场、平流层垂直速度场的变化趋势与夏、秋两个季节以及年平均气候态的结果相反。5慢地转时,中纬度西风加强的现象在四季表现的都很明显,两半球纬向风的变化趋势在春季和秋季基本反向。冬夏两半球纬向风的变化不存在明显的反向变化趋势。慢地转和快地转条件下纬向风的变化趋势是反向的。6不同地转速度条件下,各要素场的变化有明显的季节差异。以秋季的变化最为明显。7非洲季风和温寒带季风大致表现为慢地转条件下减弱,快地转条件下增强的特征。8除了冬季北半球三圈环流、春季南半球Hadley环流和夏季南半球Hadley环流随着地转倾角增大而增强外,其他季节、其他环流均随着地转倾角增大而减弱。对于年平均而言,随着倾角增大,三圈环流强度逐渐减弱。南半球Hadley环流上升支在倾角为60°条件下明显增强。随着倾角增大,南半球Hadley环流范围有所增加,北半球Hadley环流和南半球Ferrel环流的范围有所减小。9随着倾角不同,风速变化有共同点但也存在明显季节差异。相同点为在四季均表现为随着倾角变大赤道东风范围增大,东风风速增强,赤道上空对流层东风减弱,北半球西风减弱,北半球中纬度急流减弱。不同点为,春季南半球中纬度急流增强,其余均为西风减弱,夏季和秋季南半球中纬度(西风增强)和高纬度(西风减弱)西风存在反向变化趋势,冬季全球西风减弱。对于年平均而言,倾角变大时,平流层东风范围增大、风速增强:而南北半球西风范围减小,北半球急流减弱,南半球急流增强;近地面,随着倾角变大,除了10°S-10°N之间东风增强以外,其他地区原有东西风场均减弱。10随着倾角变大,全球季风范围变大。这种变化又有水平和垂直方向的复杂性。850 hPa面上,当倾角增加时,非洲季风、南美季风、北太平洋上的季风和东亚季风都显著增强,全球季风范围有所增加;倾角减小时,非洲季风、南美季风、北太平洋上的季风和东亚季风都显著减弱,全球季风范围有所减小。11基于地球大气环流模式CAM2发展了可移植行星大气环流模式PGCM。通过模拟土卫六大气环流测试了PGCM模式的基本性能。并将PGCM模式结果与LMD模式结果进行比较。进而我们研究了地球转速下土卫六大气环流的特征,来研究旋转速度对土卫六大气环流产生的可能影响。PGCM模式可以充分模拟土卫六大气环流的基本结构,例如赤道上空平流层超级旋转(～108 m/s)、垂直经圈环流、一些垂直廓线及近地面东风等等。土卫六自转速度的大小可以显著影响土卫六大气环流的动力结构。当自转速度变为地球自转速度之后,土卫六大气环流表现为,整层西风减弱,而近地面东风加强。不同旋转速度对于土卫六经向环流的影响主要体现在对流层。在地转速度下,土卫六对流层大气环流表现为,两半球分别为三圈环流;而在土卫六转速下对流层南北半球各仅有两个环流圈。12日长在5倍地球日长到50倍地球日长范围内以及上层大气水平温度梯度要大于下层大气水平温度梯度,且下层大气水平温度梯度要很小,是土卫六存在西风塌陷的两个必要条件。更多还原

【Abstract】 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.更多还原