# Lagged Responses of the Tropical Pacific to the 11-yr Solar Cycle Forcing and Possible Mechanisms

## 热带太平洋对太阳准11年周期强迫的滞后响应及其可能机制

• Corresponding author: Ziniu XIAO, xiaozn@lasg.iap.ac.cn
• Funds:

Supported by the National Key Basic Research and Development (973) Program of China (2012CB957804); Project from State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences (LTO1916); National Natural Science Foundation of China (42075040); and Science and Technology Project of State Grid Corporation of China (SGCC; NY71-19-013)

• doi: 10.1007/s13351-021-0137-8
• This paper uses two subsets of ensemble historical-Nat simulations and pi-Control simulations from CMIP5 as well as observational/reanalysis datasets to investigate responses of the tropical Pacific to the 11-yr solar cycle. A statistically significant 11-yr solar signal is found in the upper-ocean layers above the thermocline and tropospheric circulations. A warming response initially appears in the upper layers of the central equatorial Pacific in the solar maximum years in observations, then increases and shifts into the eastern Pacific at lagged 1–3 yr. Meanwhile, an anomalous updraft arises over the western equatorial Pacific and shifts eastwards in the following years with anomalous subsidence over the Maritime Continent. These lagged responses are confirmed by the historical-Nat simulations, except that the initial signal is located more to the west and all the responses are weaker than the observed. A simplified mixed-layer heat budget analysis based on the historical-Nat simulations suggests that the atmospheric forcing, especially the shortwave radiation, is the major contributor to the initial warming response, and the ocean heat transport effect is responsible for the eastward displacement of the lagged warming responses. In the solar maximum years, the zonal ocean temperature gradient in the western–central Pacific is reduced by the initial warming, and anomalous westerly winds appear over the western equatorial Pacific and extend into the eastern Pacific during the lagged years. These anomalous westerly winds reduce the wind-driven ocean dynamical transport, resulting in the initial warming in the central equatorial Pacific being amplified and the surface warming shifting eastward during the lagged 1–3 yr.

本文采用来自CMIP5自然强迫历史气候模拟和工业革命前控制实验的两个子集，以及观测和再分析数据集，分析了热带太平洋对太阳准11年周期强迫的响应，为提高年代际气候预测技巧提供参考。本文证实了在热带太平洋海洋温度中存在独立于ENSO循环的准11年太阳周期信号，对太阳最大值的显著增暖响应首先出现在赤道中太平洋，并随滞后时间向东移动。而自然强迫历史气候模拟中的响应强度比观测弱，且初始信号位置偏西。基于简化的混合层热量收支诊断可以发现，增强的太阳短波辐射（在太阳活动最大值年）是赤道太平洋初始增暖响应的主要贡献者，在滞后太阳周期峰值的1–3年里，由于海气耦合过程，增暖响应逐渐增强并引起热带太平洋的海洋次表层和对流层环流出现响应。

• Fig. 1.  The reconstructed TSI (solid gray line at top) used in the CMIP5 historical-Nat simulations and its 3-yr running mean (solid black line at top), as well as the observed annual mean SSN (dotted gray line at bottom) and 3-yr running mean SSN (dotted black line at bottom). The black dots (circles) indicate the solar maximum (minimum) years used for composite analysis in this study.

Fig. 2.  (a–d) Lagged correlation maps between TSI and the observational annual SST anomaly (ERSST; only 1950–2018 is used here). (e–h) As in (a–d), but between TSI and the MME SST anomaly from CMIP5 historical-Nat simulations (1861–2005). The dotted (solid) lines indicate a negative (positive) correlation. Black dots indicate the 95% confidence level (two-tailed Student’s t-test and controlling FDR method).

Fig. 3.  (a) The spatial pattern of the EOF1 of the annual mean MME SST anomaly over the tropical Pacific region in the historical-Nat simulations, (b) the corresponding PC1, and (c) the spectrum of PC1 (black thick solid line). The black thin (dotted) lines represent the 90% (95%) confidence level of the Markov “red noise” spectrum, and the red lines are the same as the black ones but for the spectrum of TSI. (d–f) As in (a–c), but for the pi-Control simulations.

Fig. 4.  Composite differences of the annual mean SST anomaly (ERSST; shaded; only values above the 90% confidence level are shown) and wind anomaly at 850 hPa (NCEP/NCAR Reanalysis 1; vector) between the (a) solar maximum and minimum years and (b–d) lagged 3 yr for 1950–2018. Green vectors indicate that it is above the 90% confidence level for zonal wind (bootstrapping difference).

Fig. 5.  As in Fig. 4, but for the annual mean MME SST anomaly (shaded and only values above the 90% confidence level are shown) and MME wind anomaly at 850 hPa (vector) from the CMIP5 historical-Nat simulations.

Fig. 6.  Composite differences of the annual mean MME vertical velocity anomaly averaged over the equatorial Pacific (5°S–5°N) in the CMIP5 historical-Nat simulations for (a) solar maximum minus minimum years and (b–d) lagged 3 yr. Black dots indicate the 95% confidence level (bootstrapping difference). Downward is positive (solid lines).

Fig. 7.  As in Fig. 6, but for the annual mean subsurface temperature anomaly from the objective analyses EN4 dataset (1950–2018). Black dots indicate the 95% confidence level (bootstrapping difference) and the thick black line represents the 20°C-isotherm depth (m).

Fig. 8.  As in Fig. 7, but for the annual mean MME subsurface temperature anomaly in CMIP5 historical-Nat simulations.

Fig. 9.  Lagged composite solar maximum minus minimum differences for the (a) annual mean SST change and associated (b) atmospheric forcing (${Q_{\rm{a}}}$), and (c) ocean transport effect (${D_{\rm{o}}}$) of the histori-cal-Nat simulations, in which all variables are averaged over 10°S–10°N. Black dots in (a) indicate exceedance of the 95% confidence level (bootstrapping difference test).

Fig. 10.  Lagged composite solar maximum minus minimum differences (W m−2) for the (a–d) surface net shortwave radiation (${Q_{\rm{S}}}$), (e–h) surface net longwave radiation (${Q_{\rm{L}}}$), (e–h) net sensible heat flux (${Q_{\rm{H}}}$), and (m–p) latent heat flux from atmospheric forcing ($Q_{\rm{E}}^{\rm{a}}$) after subtracting the ocean Newtonian cooling response. Downward is positive. Black dots indicate exceedance of the 95% confidence level (bootstrapping difference test).

Fig. 11.  Lagged composite solar maximum minus minimum differences of the annual mean MME total cloud fraction anomaly in historical-Nat simulations (color shading). Black dots indicate exceedance of the 95% confidence level (bootstrapping difference test) and the white contours in (a) are the climatological total cloud fraction averaged over 1861–2005.

###### 通讯作者: 陈斌, bchen63@163.com
• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

## Lagged Responses of the Tropical Pacific to the 11-yr Solar Cycle Forcing and Possible Mechanisms

###### Corresponding author: Ziniu XIAO, xiaozn@lasg.iap.ac.cn;
• 1. State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
• 2. Research Division Ocean Circulation and Climate, GEOMAR Helmholtz Centre for Ocean Research, Kiel 24105, Germany
• 3. State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
• 4. Innovation Academy of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences, Guangzhou 510301, China
• 5. Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
Funds: Supported by the National Key Basic Research and Development (973) Program of China (2012CB957804); Project from State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences (LTO1916); National Natural Science Foundation of China (42075040); and Science and Technology Project of State Grid Corporation of China (SGCC; NY71-19-013)

Abstract:

This paper uses two subsets of ensemble historical-Nat simulations and pi-Control simulations from CMIP5 as well as observational/reanalysis datasets to investigate responses of the tropical Pacific to the 11-yr solar cycle. A statistically significant 11-yr solar signal is found in the upper-ocean layers above the thermocline and tropospheric circulations. A warming response initially appears in the upper layers of the central equatorial Pacific in the solar maximum years in observations, then increases and shifts into the eastern Pacific at lagged 1–3 yr. Meanwhile, an anomalous updraft arises over the western equatorial Pacific and shifts eastwards in the following years with anomalous subsidence over the Maritime Continent. These lagged responses are confirmed by the historical-Nat simulations, except that the initial signal is located more to the west and all the responses are weaker than the observed. A simplified mixed-layer heat budget analysis based on the historical-Nat simulations suggests that the atmospheric forcing, especially the shortwave radiation, is the major contributor to the initial warming response, and the ocean heat transport effect is responsible for the eastward displacement of the lagged warming responses. In the solar maximum years, the zonal ocean temperature gradient in the western–central Pacific is reduced by the initial warming, and anomalous westerly winds appear over the western equatorial Pacific and extend into the eastern Pacific during the lagged years. These anomalous westerly winds reduce the wind-driven ocean dynamical transport, resulting in the initial warming in the central equatorial Pacific being amplified and the surface warming shifting eastward during the lagged 1–3 yr.

Reference (49)

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