全球变暖背景下热带大气季节内振荡的变化特征及数值模拟

利用欧洲中期数值预报中心的ERA40再分析逐日的200 hPa风场资料,选取1958—1977年和1980—1999年各20年,对比分析了在全球变暖背景下前后两个时段热带大气季节内振荡(ISO)的特征及其变化。研究表明:近20 a来,原来在赤道中太平洋上活跃的ISO减弱,而在中印度洋、孟加拉湾地区ISO变得活跃;全球变暖背景下,ISO的强度变化幅度加大,表明ISO更加活跃,且季节变化明显,冬、春季强,夏、秋季弱;对流层上层的纬向风能量更集中于1—3波,ISO的频率有加大的趋势。还利用中国科学院大气物理研究所LASG发展的耦合气候系统模式FGOALS-1.0g中的控制试验及其二氧化碳浓度加倍试验结果,分别对应实测资料的前后20年进行对比分析。发现模式对ISO的空间结构模拟较好,但低估了ISO的强度;时空谱分析表明模式结果中包含有更多的纬向风的高频成分,由于能量的分散,导致对ISO活动强度的低估。但通过对模式的控制试验和温室气体增加试验结果的对比分析,发现耦合模式还是较好地反映出在全球变暖背景下ISO在中印度洋、孟加拉湾地区变得活跃、频率加大等变化特征。

CHARACTERISTICS AND NUMERICAL SIMULATION OF THE TROPICAL INTRASEASONAL OSCILLATIONS UNDER GLOBAL WARMING

Using the ECMWF reanalysis daily 200 hPa wind data in the two 20-year periods from 1958 to 1977 and 1980 to 1999,the characteristics and changes of Intraseasonal Oscillations(ISO) in the two periods associated with the global warming are analyzed and compared in this study.It is found that during the last 20 years,the ISO has weakened in the central equatorial Pacific Ocean,but become more active in the central Indian Ocean and the Bay of Bengal;under the background of the global warming,increase in the amplitude of ISO intensity suggests that the ISO has become more active than before,with an obvious seasonal cycle,i.e.strong in winter and spring,but weak in summer and autumn;the energy of the upper tropospheric zonal wands has more concentrated in the wave numbers 1-3,and the frequency of ISO tended to increase.Comparison of the results of the control experiment and CO_2 increase(1% per year) experiment of FGOALS-1.0-g(developed at LASG) with the first and second 20-year observations,is also performed,respectively.The comparative results show that the spatial structure of the ISO was well reproduced,but the strength of ISO underestimated.On the basis of space-time spectral analysis,it is found that the simulated ISO contains too much high frequency waves,leading to the underestimation of ISO intensity due to the distraction of ISO energy.However,the FGOALS-1.0-g captured the salient features of ISO under the global warming background by two contrast experiments,such as the vitality and frequency-increasing of ISO in the central Indian Ocean and the Bay of Bengal.