CAS-ESM 1.0模式对7月份热带太平洋上层流场异常模态的模拟评估

Simulation and Evaluation of the CAS-ESM 1.0 Model Used for Studying Upper Layer Flow-Field Abnormal Modes in the Tropical Pacific Ocean in July

利用CAS-ESM 1.0模式模拟得到的1922~2005年共84年的7月份资料,对流场异常作了复EOF分解,并与该模式模拟的1月份结果以及相应的实况(SODA资料)和理论结果作了对比和分析。结果表明:在表层、近表层、次表层及上层底,该EOF分解的第一、二模态空间场中明显流场异常都分布在10°S~10°N,为赤道所俘获。总体上流场异常以纯纬向流动为主;它们均与赤道流系异常及赤道波动有较好对应。从表层到上层底流场异常随海洋深度明显减弱。第一、二模态都具有3~5年的年际变化周期,并以4年的年际变化最明显,并都落在ENSO的变化范围中。这两个模态都无明显年代际变化。次表层第一模态的海温异常为,西太平洋暖池区以及西、中太平洋赤道附近有负异常,在东太平洋赤道区及南美洲沿岸有正异常,两者随时间呈跷跷板变化;第二模态海温异常为,中西太平洋以负异常为主,中东太平洋则以正异常为主,并也呈跷跷板变化,且该变化包括了第一模态的跷跷板变化。本文第一、二模态的性质分别是ENSO的主、次模态。本文时间系数无明显年代际变化是因模式未能很好反映印尼穿越流所致;模式模拟的赤道两侧的明显流场异常宽度要较实况宽一倍;以上这些都表明模式在近赤道处的分辨率还不够高,须进一步提高;此外该模式的物理过程和海气耦合程序也需继续改进和优化。

Using simulated data from 1922 to 2005 for the month of July obtained from the CAS-ESM 1.0 model,we performed a complex empirical orthogonal function analysis of flow-field anomalies.The results were compared with the corresponding simulated data for January,actual observations(SODA data),and theoretical results.The main conclusions were as follows:In the surface,near-surface,subsurface,and upper bottom layers significant flow-field anomalies were distributed between 10°S and 10°N in the first and second modes,centered around the equator.Overall,the flow-field anomalies were mainly characterized by pure latitudinal flows.They all corresponded well with the anomalies of equatorial flow systems and fluctuations.The flow-field anomalies from the surface to upper bottom layers significantly weakened with increasing ocean depth.Both the first and second modes showed 3–5-year interannual variation,with the most obvious changes observed over a four-year period,and all variations fell within the range of ENSO.There was no significant interdecadal variation in either mode.The SSTA of the first mode in the subsurface layer was characterized by negative anomalies in the western Pacific warm pool and near the equator in the western and central Pacific,as well as positive anomalies in the equatorial region of the eastern Pacific and along the coast of South America.Further,both anomalies exhibited a seesaw pattern over time.The SSTA of the second mode showed negative anomalies dominating the central and western Pacific,while positive anomalies prevailed in the central and eastern Pacific,which also showed a seesaw pattern.This change encompassed the seesaw pattern observed in the first mode.The characteristics of the first and second modes described in this paper correspond to the primary and secondary modes of ENSO,respectively.The absence of significant interdecadal variation in the time coefficient is attributed to the model’s inability to accurately represent the Indonesian Throughflow.The width of the pronounced flow-field anomalies on both sides of the equator,as simulated by the model,is twice that of the actual case.This indicates that the model resolution near the equator is insufficient and needs further improvement.Additionally,the physical processes and coupled air–sea interactions within this model require further refinement and optimization.