Simulation And Investigation Of The Greenhouse Climate During The Cooling Of The Eocene

The global temperature has been rising since the20thcentury, which has drawngeneral concern of the community. In order to realize the impact of the global warmingon the human race, a lot of scholars in the geosciences have been conducting extensiveand in-depth researches on the greenhouse climate during the geological history fromdifferent views, yielding an enormous amount of results. Just under this background,the climate of Eocene (40Ma), which is the nearest greenhouse period from now, areinvestigated through the numerical simulation in this dissertation. The main contentsare as follows.I. Based on the existing geological records during the Eocene, the preconditions ofthe numerical simulation, which mainly includes the land-sea distribution, the elevationof the earth’s surface, the vegetation distribution and the concentration of the CO2, areset.II. According to the results of the simulation, the climatology of the Eocene arereproduced, the global sea level pressure and the atmospheric circulation are similar tothat of today. During the Eocene, the surface temperature pattern is symmetricalfranking the equator between45°N and45°S. However, the gradients of the zonalaverages of the temperature are not the same in mid-high latitudes (>45°) of twoHemispheres: In the northern Hemisphere, the temperature gradients is greater, and thetemperature does not decrease along the latitudes until67.5°N; Over the SouthernOcean, the surface temperature gradients are less, so the temperature is higher than thatof the same latitudes in the northern Hemisphere, but the surface temperature declinesrapidly in the An tarctic Continent, and reaches244K （-32℃）at the Antarctic Pole. To understand the circulation of the whole troposphere comprehensively, theclimatology of the different levels in the troposphere are also analyzed in detail in thisdissertation.III. Aiming at the global monsoon during the Eocene, the south Asian monsoonregion and the east Asian region are, respectively, identified utilizing the two proposedmonsoon intensity index. According the results obtained by using the monsoonintensity index, Asia has been the most typical monsoon region during the Eocene. Insummer, there is a low in Asia, while a high over the North Pacific; in winter, there area high in the Northern Asia and a low over the Northwestern Pacific, and the NorthPacific subtropical high moves southward and eastward. The high over the SouthIndian Ocean strengthens and moves westward in the boreal summer, while weakensand moves eastward in the boreal winter. The precipitation in summer is much greaterthan that in winter over the East Asia. Located in the tropics, the precipitation isprominent either in summer or in winter over the southeastern part of the Asia.Consequently the Asian monsoon during the Eocene has been analogous to the presentclimate. During the austral summer, there are two precipitation maxima, respectively,located in the India and the Southern Africa, while they do not exist in the austral winter,which is also a manifestation of the weak monsoonThe final section of this dissertation is devoted to a summary and prospect offurther study of the paleoclimate.