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ZHANG Dongling,ZHU Juan,LU Xu,ZHANG Ming. 2019. Wave packet solutions in a bounded equatorial ocean and its interannual and decadal variabilities. Acta Oceanologica Sinica, 38(3):45-59
Wave packet solutions in a bounded equatorial ocean and its interannual and decadal variabilities
有界赤道大洋波包解及其年际年代际变率
Received:January 25, 2018  
DOI:10.1007/s13131-019-1398-2
Key words:bounded equatorial ocean  wave packet solutions  decadal variability  Kelvin wave  Rossby wave
中文关键词:  有界赤道大洋  波包解  年际年代际变率  Kelvin波  Rossby波
基金项目:The National Major Research High Performance Computing Program of China under contract 2016YFB0200800; the Strategic Priority Research Program of Chinese Academy of Sciences under contract No. XDA20060501.
Author NameAffiliationE-mail
ZHANG Dongling Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China  
ZHU Juan Special Office of Marine Environment, National Marine Environment Forecasting Center, Ministry of Natural Resources, Beijing 100081, China
Atmospheric Circulation and Short-term Climate Prediction Laboratory of Meteorology and Marine Institute, National University of Defense Technology, Nanjing 211101, China 
 
LU Xu Atmospheric Circulation and Short-term Climate Prediction Laboratory of Meteorology and Marine Institute, National University of Defense Technology, Nanjing 211101, China
32021 Troop, People's Liberation Army, Beijing 100094, China 
 
ZHANG Ming Atmospheric Circulation and Short-term Climate Prediction Laboratory of Meteorology and Marine Institute, National University of Defense Technology, Nanjing 211101, China zhangm1945@163.com 
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Abstract:
      Linearized shallow water perturbation equations with approximation in an equatorial β plane are used to obtain the analytical solution of wave packet anomalies in the upper bounded equatorial ocean. The main results are as follows. The wave packet is a superposition of eastward travelling Kelvin waves and westward travelling Rossby waves with the slowest speed, and satisfies the boundary conditions of eastern and western coasts, respectively. The decay coefficient of this solution to the north and south sides of the equator is inversely proportional only to the phase velocity of Kelvin waves in the upper water. The oscillation frequency of the wave packet, which is also the natural frequency of the ocean, is proportional to its mode number and the phase velocity of Kelvin waves and is inversely proportional to the length of the equatorial ocean in the east-west direction. The flow anomalies of the wave packet of Mode 1 most of the time appear as zonal flows with the same direction. They reach the maximum at the center of the equatorial ocean and decay rapidly away from the equator, manifested as equatorially trapped waves. The flow anomalies of the wave packet of Mode 2 appear as the zonal flows with the same direction most of the time in half of the ocean, and are always 0 at the center of the entire ocean which indicates stagnation, while decaying away from the equator with the same speed as that of Mode 1. The spatial structure and oscillation period of the wave packet solution of Mode 1 and Mode 2 are consistent with the changing periods of the surface spatial field and time coefficient of the first and second modes of complex empirical orthogonal function (EOF) analysis of flow anomalies in the actual equatorial ocean. This indicates that the solution does exist in the real ocean, and that El Niño-Southern Oscillation (ENSO) and Indian Ocean dipole (IOD) are both related to Mode 2. After considering the Indonesian throughflow, we can obtain the length of bounded equatorial ocean by taking the sum of that of the tropical Indian Ocean and the tropical Pacific Ocean, thus this wave packet can also explain the decadal variability (about 20 a) of the equatorial Pacific and Indian Oceans.
中文摘要:
      本文采用赤道β平面近似下的线性化浅水方程组,得到了上层有界赤道大洋波包异常的解析解,主要结果如下:该解由向东传播的Kelvin波和向西传播最慢的Rossby波叠加而成,叠加后分别满足东西海岸的边界条件。决定该解向赤道南北两侧衰减程度的系数仅与上层海水中的Kelvin波相速成反比。该解的振荡频率与其模态数及上述Kelvin波的相速成正比,与赤道大洋东西长度成反比,且为此海洋的固有频率。该解模态1的流场异常大多时刻为方向一致的纬向流;该流场异常在赤道大洋中部最大,并向赤道南北两侧迅速衰减,呈现赤道俘获波的形式。模态2的流场异常大多时刻在半个大洋中为方向一致的纬向流,在整个大洋的中间处,其流场异常恒为0,流场异常向赤道南北两侧的衰减情形同模态1。该解模态1、2的空间结构和振荡周期,均与实际赤道大洋流场异常复EOF分析第一、二模态的表层空间场和时间系数周期相吻合,该解在实际大洋中确实存在,而ENSO和IOD都与该解模态2有关。在考虑了印尼穿越流后,可将赤道有界大洋长度取赤道印度洋和赤道太平洋之和,这样该解还能解释赤道太平洋和赤道印度洋中约20年的年代际变率。
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