ENSO强度模拟差异对全球变暖下热带太平洋大气变化预估结果的影响
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摘要
热带太平洋海洋-大气耦合系统对全球变暖的响应是气候变化的热点问题。前人研究发现,气候模式的模拟偏差对于全球变暖响应结果有重要影响。本文利用美国大气研究中心(National Center for Atmospheric Research, NCAR)的地球系统模式(The Community Earth System Model,CESM)中的大气模式(Community Atmosphere Model version 5, CAM5)设计数值试验,在相同的SST(Sea Surface Temperature)增暖强迫下,通过改变海洋SST的年际变化振幅,来分析热带海洋年际变化强度的模拟对未来热带海区降水和大气环流场未来变化的影响。试验结果表明,随着SST年际变化强度的增加,全球变暖后热带太平洋降水变化的东西不对称性,以及向暖池区域辐合的风场变化等特征都逐渐减弱。进一步的分析发现,不同年际变化信号导致的大气场变化差异主要发生在冬季,是由于热带太平洋SST年际变化主模态ENSO(El Niňo-Southern Oscillation)的不对称性造成的:在厄尔尼诺年,强(弱)的年际变化信号会造成降水在东太平洋产生较大(小)的变化;而在拉尼娜年和正常年份,年际变化信号的强弱对热带降水变化的影响则不大。当热带海温的年际变化较大时,厄尔尼诺年的海温异常更强,造成的降水和风场的变化特征也会更加显著。
The response of the ocean-atmosphere coupled system to global warming in the tropical Pacific is a hot topic in climate change studies. Previous studies found that climate model biases have great impacts on the results of global warming. In this study, we used the atmospheric component(Community Atmosphere Model version 5, CAM5) of Community Earth System Model(CESM) from the National Center for Atmospheric Research(NCAR) to design experiments, and examined the changes of tropical Pacific precipitation and atmospheric circulation with different interannual SST variances forced by an identical SST warming pattern. The results showed that with interannual SST variance increasing, the east-west asymmetry of precipitation change in tropical Pacific and convergent wind change to warm pool both gradually weakens. Further analyses revealed that the differences of these atmospheric changes under different interannual SST variance mainly appear in wintertime, and are mainly related to the asymmetric atmospheric response to El Niňo-Southern Oscillation(ENSO). In the El Niňo events, the large(small) interannual SST anomalies lead to more(less) precipitation anomalies in east Pacific Ocean, while in La Niňa events and neutral years, the precipitation anomalies are similar in different SST anomalies. When the interannual SST variance is larger, the SST anomalies are larger in El Niňo years. Therefore, the precipitation and wind responses to global warming are more remarkable in El Niňo years than La Niňa and neutral years.
The response of the ocean-atmosphere coupled system to global warming in the tropical Pacific is a hot topic in climate change studies. Previous studies found that climate model biases have great impacts on the results of global warming. In this study, we used the atmospheric component(Community Atmosphere Model version 5, CAM5) of Community Earth System Model(CESM) from the National Center for Atmospheric Research(NCAR) to design experiments, and examined the changes of tropical Pacific precipitation and atmospheric circulation with different interannual SST variances forced by an identical SST warming pattern. The results showed that with interannual SST variance increasing, the east-west asymmetry of precipitation change in tropical Pacific and convergent wind change to warm pool both gradually weakens. Further analyses revealed that the differences of these atmospheric changes under different interannual SST variance mainly appear in wintertime, and are mainly related to the asymmetric atmospheric response to El Niňo-Southern Oscillation(ENSO). In the El Niňo events, the large(small) interannual SST anomalies lead to more(less) precipitation anomalies in east Pacific Ocean, while in La Niňa events and neutral years, the precipitation anomalies are similar in different SST anomalies. When the interannual SST variance is larger, the SST anomalies are larger in El Niňo years. Therefore, the precipitation and wind responses to global warming are more remarkable in El Niňo years than La Niňa and neutral years.
引文
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[2] Xie S P,Ma J,Deser C,et al.Global warming pattern formation:Sea surface temperature and rainfall[J].Journal of Climate,2010,23(4):966-986.
[3] Xie S P,Yu K,Du Y,et al.Indo-western Pacific Ocean capacitor and coherent climate anomalies in post-ENSO summer:A review[J].Advances in Atmospheric Sciences,2016,33(4):411-432.
[4] Zheng X T,Xie S P,Lv L H,et al.Intermodel uncertainty in ENSO amplitude change tied to Pacific Ocean warming pattern[J].Journal of Climate,2016,29(20):7265-7279.
[5] Lin J L,Qian T,Shinoda T.Is the tropical atmosphere in convective Quasi-Equilibrium?[J].Journal of Climate,2015,28(11):4357-4372.
[6] Clement A C,Seager R,Cane M A,et al.An ocean dynamical thermostat[J].Journal of Climate,1996,9(9):2190-2196.
[7] Cane M A.A role for the Tropical Pacific[J].Science,1998,282(5386):59-61.
[8] Soden B J and Held I M.An assessment of climate feedbacks in coupled ocean atmosphere models[J].Journal of Climate,2006,19(14):3354-4360.
[9] Vecchi G A and Soden B J.Effect of remote sea surface temperature change on tropical cyclone potential intensity[J].Nature,2007,450(7172):1066-1070.
[10] Vecchi G A,Clement A,Soden B J.Examining the Tropical Pacific’s response to global warming[J].Eos Transactions American Geophysical Union,2008,89(9):81-83.
[11] Deser C,Alexander M A,Xie S P,et al.Sea surface temperature variability:Patterns and mechanisms[J].Annual Review of Marine Science,2010,2(1):115-143.
[12] Huang P,Ying J.A multimodel ensemble pattern regression method to correct the Tropical Pacific SST change patterns under global warming[J].Journal of Climate,2015,28:4706-4723.
[13] Li G,Xie S P,Du Y.A robust but spurious pattern of climate change in model projections over the tropical Indian Ocean[J].Journal of Climate,2016,29(15):5589-5608.
[14] Hoerling M P.El Nino,La Nina and the nonlinearity of their teleconnections[J].Journal of Climate,1997,10(10):1769-1786.
[15] An S I,Jin F F.Nonlinearity and asymmetry of ENSO[J].Journal of Climate,2004,17(11):2033-2038.
[16] An S I,Li J P.A review of interdecadal changes in the nonlinearity of the El Niňo-Southern Oscillation[J].Theoretical Applied Climatology,2009,97(1-2):29-40.
[17] Ogata T,Xie S P,Lan J.Importance of ocean dynamics for the skewness of the Indian Ocean dipole[J].Journal of Climate,2013,26(7):2145-2159.
[18] Tokinaga H,and Xie S P.Weakening of the equatorial Atlantic cold tongue over the past six decades[J].Nature Geoscience,2011,4(4):222-226.
[19] Tokinaga H,Xie S P,Timmermann A,et al.Regional patterns of tropical Indo-Pacific climate change:Evidence of the Walker circulation weakening[J].Journal of Climate,2012a,25(5):1689-1710.
[20] Tokinaga H,Xie S P,Deser C,et al.Slowdown of the walker circulation driven by tropical Indo-Pacific warming[J].Nature,2012b,491(7424):439-443.