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Impact of Surface Sensible Heating over the Tibetan Plateau on the Western Pacific Subtropical High: A Land-Air-Sea Interaction Perspective


doi: 10.1007/s00376-016-6008-z

  • The impact of surface sensible heating over the Tibetan Plateau (SHTP) on the western Pacific subtropical high (WPSH) with and without air-sea interaction was investigated in this study. Data analysis indicated that SHTP acts as a relatively independent factor in modulating the WPSH anomaly compared with ENSO events. Stronger spring SHTP is usually followed by an enhanced and westward extension of the WPSH in summer, and vice versa. Numerical experiments using both an AGCM and a CGCM confirmed that SHTP influences the large-scale circulation anomaly over the Pacific, which features a barotropic anticyclonic response over the northwestern Pacific and a cyclonic response to the south. Owing to different background circulation in spring and summer, such a response facilitates a subdued WPSH in spring but an enhanced WPSH in summer. Moreover, the CGCM results showed that the equatorial low-level westerly at the south edge of the cyclonic anomaly brings about a warm SST anomaly (SSTA) in the equatorial central Pacific via surface warm advection. Subsequently, an atmospheric Rossby wave is stimulated to the northwest of the warm SSTA, which in turn enhances the atmospheric dipole anomalies over the western Pacific. Therefore, the air-sea feedbacks involved tend to reinforce the effect of SHTP on the WPSH anomaly, and the role of SHTP on general circulation needs to be considered in a land-air-sea interaction framework.
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  • Chen L. X., F. Schmidt, and W. Li, 2003: Characteristics of the atmospheric heat source and moisture sink over the Qinghai-Tibetan Plateau during the second TIPEX of summer 1998 and their impact on surrounding monsoon. Meteor. Atmos. Phys., 83( 1-2), 1- 18.http://link.springer.com/article/10.1007/s00703-002-0546-x
    Chen P., M. P. Hoerling, and R. M. Dole, 2001: The origin of the subtropical anticyclones. J. Atmos. Sci., 58, 1827- 1835.http://adsabs.harvard.edu/abs/2001JAtS...58.1827C
    Cui Y. F., A. M. Duan, Y. M. Liu, and G. X. Wu, 2015: Interannual variability of the spring atmospheric heat source over the Tibetan Plateau forced by the North Atlantic SSTA. Climate Dyn., 45, 1617- 1634.http://onlinelibrary.wiley.com/resolve/reference/XREF?id=10.1007/s00382-014-2417-9
    Dee, D. P., Coauthors, 2011: The ERA-interim reanalysis: Configuration and performance of the data assimilation system.Quart. J. Roy. Meteor. Soc., 137, 553- 597.http://onlinelibrary.wiley.com/doi/10.1002/qj.828/full
    Duan A. M., G. X. Wu, 2005: Role of the Tibetan plateau thermal forcing in the summer climate patterns over subtropical Asia. Climate Dyn., 24, 793- 807.http://link.springer.com/10.1007/s00382-004-0488-8
    Duan A. M., G. X. Wu, 2008: Weakening trend in the atmospheric heat source over the Tibetan Plateau during recent decades. Part I: Observations. J.Climate, 21, 3149- 3164.http://nsr.oxfordjournals.org/external-ref?access_num=10.1175/2007JCLI1912.1&link_type=DOI
    Duan A. M., Y. M. Liu, and G. X. Wu, 2005: Heating status of the Tibetan Plateau from April to June and rainfall and atmospheric circulation anomaly over East Asia in midsummer. Science in China Series D: Earth Sciences, 48, 250- 257.http://d.wanfangdata.com.cn/Periodical/zgkx-ed200502012
    Duan A. M., G. X. Wu, and X. Y. Liang, 2008: Influence of the Tibetan Plateau on the summer climate patterns over Asia in the IAP/LASG SAMIL model. Adv. Atmos. Sci.,25, 518-528, doi: 10.1007/s00376-008-0518-2.http://d.wanfangdata.com.cn/Periodical_dqkxjz-e200804002.aspx
    Duan A. M., M. R. Wang, Y. H. Lei, and Y. F. Cui, 2013: Trends in summer rainfall over China associated with the Tibetan Plateau sensible heat source during 1980-2008. J.Climate, 26, 261- 275.http://nsr.oxfordjournals.org/external-ref?access_num=10.1175/JCLI-D-11-00669.1&link_type=DOI
    Flohn H., 1957: Large-scale aspects of the "summer monsoon" in South and East Asia. J. Meteor. Soc.Japan, 75, 180- 186.http://ci.nii.ac.jp/naid/10014595971/
    Gill A. E., 1980: Some simple solutions for heat-induced tropical circulation.Quart. J. Roy. Meteor. Soc., 106, 447- 462.http://onlinelibrary.wiley.com/doi/10.1002/qj.49710644905/full
    He B., S. Yang, and Z. N. Li, 2016: Role of atmospheric heating over the South China Sea and western Pacific regions in modulating Asian summer climate under the global warming background. Climate Dyn.,46, 2897-2908, doi: 10.1007/s00382-015-2739-2.http://link.springer.com/10.1007/s00382-015-2739-2
    Jian M. Q., H. B. Luo, and Y. T. Qiao, 2004: On the relationships between the summer rainfall in China and the atmospheric heat sources over the eastern Tibetan Plateau and the western pacific warm pool. Journal of Tropical Meteorology, 10, 133- 143.http://d.wanfangdata.com.cn/Periodical/rdqxxb-e200402003
    Krishnamurti T. N., S. M. Daggupaty, J. Fein, M. Kanamitsu, and J. D. Lee, 1973: Tibetan High and upper tropospheric tropical circulation during Northern summer. Bull. Amer. Meteor. Soc., 54, 1234- 1249.
    Li J. N., W. G. Meng, A. Y. Wang, L. M. Liu, R. Q. Feng, and E. B. Hou, 2003: Climatic characteristics of the intensity and position of the subtropical high in the western pacific. Tropical Geography, 23( 1), 35- 39. (in Chinese)http://en.cnki.com.cn/article_en/cjfdtotal-rddd200301008.htm
    Liu Y. M., G. X. Wu, 2004: Progress in the study on the formation of the summertime subtropical anticyclone. Adv. Atmos. Sci.,21(3), 322-342, doi: 10.1007/BF02915562.http://d.wanfangdata.com.cn/Periodical_dqkxjz-e200403003.aspx
    Liu Y. M., G. X. Wu, H. Liu, and P. Liu, 2001: Condensation heating of the Asian summer monsoon and the subtropical anticyclone in the Eastern Hemisphere. Climate Dyn., 17, 327- 338.http://link.springer.com/article/10.1007/s003820000117
    Luo H. B., M. Yanai, 1983: The large-scale circulation and heat sources over the Tibetan Plateau and surrounding areas during the early summer of 1979. Part I: Precipitation and kinematic analyses. Mon. Wea. Rev., 111, 922- 944.http://adsabs.harvard.edu/abs/1984MWRv..112..966L
    Peng G., M. Domrös, 1987: Connections of the west Pacific subtropical high and some hydroclimatic regimes in China with Antarctic ice-snow indices. Meteor. Atmos. Phys., 37, 61- 71.http://link.springer.com/article/10.1007/BF01040839
    Rayner N. A., D. E. Parker, E. B. Horton, C. K. Folland , L. V. Alexand er, D. P. Rowell, E. C. Kent, and A. Kaplan, 2003: Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res., 108( D14), 4407.http://onlinelibrary.wiley.com/doi/10.1029/2002JD002670/full
    Rodwell M. J., B. J. Hoskins, 2001: Subtropical anticyclones and summer monsoons. J.Climate, 14, 3192- 3211.http://adsabs.harvard.edu/abs/2001JCli...14.3192R
    Wang B., R. G. Wu, and X. H. Fu, 2000: Pacific-East Asian teleconnection: How does ENSO affect East Asian climate? J.Climate, 13, 1517- 1536.http://xueshu.baidu.com/s?wd=paperuri%3A%28c25afe041658a4f704de554223c4d38e%29&filter=sc_long_sign&tn=SE_xueshusource_2kduw22v&sc_vurl=http%3A%2F%2Fwww.bioone.org%2Fservlet%2Flinkout%3Fsuffix%3Di1551-5036-22-3-625-Wang1%26dbid%3D16%26doi%3D10.2112%252F04-0156.1%26key%3D10.1175%252F1520-0442%282000%290132.0.CO%253B2&ie=utf-8&sc_us=573464951031400502
    Wang C. L., L. Zou, 2004: West pacific subtropical high's interannual variability and relativity to ENSO. Journal of Tropical Meteorology, 20( 2), 137- 144. (in Chinese)http://en.cnki.com.cn/Article_en/CJFDTOTAL-RDQX200402003.htm
    Wang Z. Q., A. M. Duan, and G. X. Wu, 2014: Time-lagged impact of spring sensible heat over the Tibetan Plateau on the summer rainfall anomaly in East China: Case studies using the WRF model. Climate Dyn., 42, 2885- 2898.http://adsabs.harvard.edu/abs/2014AGUFMPP43D1502D
    Wu G. X., Y. S. Zhang, 1998: Tibetan Plateau forcing and the timing of the monsoon onset over South Asia and the South China Sea. Mon. Wea. Rev., 126, 913- 927.http://adsabs.harvard.edu/abs/1998MWRv..126..913W
    Wu G. X., Y. M. Liu, 2003: Summertime quadruplet heating pattern in the subtropics and the associated atmospheric circulation. Geophys. Res. Lett.,30, doi: 10.1029/2002GL016209.http://onlinelibrary.wiley.com/doi/10.1029/2002GL016209/full
    Wu G. X., W. P. Li, and H. Liu, 1997: Sensible heating-driving air pump of the Tibetan Plateau and the Asian summer monsoon. Memorial Volume of Prof, J. Z. Zhao and D. Z. Ye, Eds., Science Press, Beijing, 116- 126. (in Chinese)
    Wu G. X., Y. M. Liu., and P. Liu, 1999: The effect of spatially nonuniform heating on the formation and variation of subtropical high I. Scale analysis. Acta Meteorologica Sinica, 57( 3), 257- 263. (in Chinese)
    Wu B., T. J. Zhou, and T. Li, 2009: Contrast of rainfall-SST relationships in the Western North Pacific between the ENSO-developing and ENSO-decaying summers. J.Climate, 22, 4398- 4405.http://www.cabdirect.org/abstracts/20093252197.html
    Wu B., T. Li, and T. J. Zhou, 2010a: Relative contributions of the Indian Ocean and local SST anomalies to the maintenance of the western North Pacific anomalous anticyclone during the El Niño decaying summer. J.Climate, 23, 2974- 2986.http://www.cabdirect.org/abstracts/20103214989.html
    Wu B., T. Li, and T. J. Zhou, 2010b: Asymmetry of atmospheric circulation anomalies over the Western North Pacific between El Niño and La Niña. J.Climate, 23, 4807- 4822.http://www.cabdirect.org/abstracts/20103330883.html
    Xie S. P., K. M. Hu, J. Hafner, H. Tokinaga, Y. Du, G. Huang, and T. Sampe, 2009: Indian Ocean capacitor effect on Indo-western Pacific climate during the summer following El Niño. J.Climate, 22, 730- 747.http://www.cabdirect.org/abstracts/20093117314.html
    Yang J. L., Q. Y. Liu, S. P. Xie, Z. Y. Liu, and L. X. Wu, 2007: Impact of the Indian Ocean SST basin mode on the Asian summer monsoon. Geophys. Res. Lett.,34, doi: 10.1029/2006GL028571.http://onlinelibrary.wiley.com/doi/10.1029/2006GL028571/full
    Ye D. Z., G. X. Wu, 1998: The role of the heat source of the Tibetan Plateau in the general circulation. Meteor. Atmos. Phys., 67, 181- 198.http://link.springer.com/article/10.1007/BF01277509
    Yeh T. C., Y. X. Gao, 1979: Meteorology of the Qinghai-Xizang (Tibet) Plateau. Science Press, Beijing, 278 pp. (in Chinese)
    Yeh T. C., S. W. Lo, and P. C. Chu, 1957: The wind structure and heat balance in the lower troposphere over Tibetan Plateau and its surrounding. Acta Meteorologica Sinica, 28, 108- 121. (in Chinese)http://en.cnki.com.cn/Article_en/CJFDTotal-QXXB195702002.htm
    Zhang R., H. S. Shi, and S. H. Yu, 1995: A study of non-linear stability of the western-Pacific subtropical high. Scientia Atmospherica Sinica, 19, 687- 700. (in Chinese)
    Zhang R. H., A. Sumi, 2002: Moisture circulation over East Asia during El Niño episode in northern winter, spring and autumn. J. Meteor. Soc.Japan, 80, 213- 227.http://ci.nii.ac.jp/naid/110001807731
    Zhao P., L. X. Chen, 2001: Climatic features of atmospheric heat source/sink over the Qinghai-Xizang Plateau in 35 years and its relation to rainfall in China. Science in China Series D: Earth Sciences, 44, 858- 864.http://d.wanfangdata.com.cn/Periodical_zgkx-ed200109010.aspx
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    [5] Wu Aiming, Ni Yunqi, 1997: The Influence of Tibetan Plateau on the Interannual Variability of Atmospheric Circulation over Tropical Pacific, ADVANCES IN ATMOSPHERIC SCIENCES, 14, 69-80.  doi: 10.1007/s00376-997-0045-6
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    [18] Lihua ZHU, Gang HUANG, Guangzhou FAN, Xia QU, Guijie ZHAO, Wei HUA, 2017: Evolution of Surface Sensible Heat over the Tibetan Plateau Under the Recent Global Warming Hiatus, ADVANCES IN ATMOSPHERIC SCIENCES, 34, 1249-1262.  doi: 10.1007/s00376-017- 6298-9
    [19] WANG Leidi, LÜ Daren, HE Qing, 2015: The Impact of Surface Properties on Downward Surface Shortwave Radiation over the Tibetan Plateau, ADVANCES IN ATMOSPHERIC SCIENCES, 32, 759-771.  doi: 10.1007/s00376-014-4131-2
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Manuscript received: 11 January 2016
Manuscript revised: 06 August 2016
Manuscript accepted: 12 September 2016
通讯作者: 陈斌, bchen63@163.com
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Impact of Surface Sensible Heating over the Tibetan Plateau on the Western Pacific Subtropical High: A Land-Air-Sea Interaction Perspective

  • 1. State Key Laboratory of Numerical Modelling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 2. Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing 210044, China
  • 3. University of Chinese Academy of Sciences, Beijing 100049, China

Abstract: The impact of surface sensible heating over the Tibetan Plateau (SHTP) on the western Pacific subtropical high (WPSH) with and without air-sea interaction was investigated in this study. Data analysis indicated that SHTP acts as a relatively independent factor in modulating the WPSH anomaly compared with ENSO events. Stronger spring SHTP is usually followed by an enhanced and westward extension of the WPSH in summer, and vice versa. Numerical experiments using both an AGCM and a CGCM confirmed that SHTP influences the large-scale circulation anomaly over the Pacific, which features a barotropic anticyclonic response over the northwestern Pacific and a cyclonic response to the south. Owing to different background circulation in spring and summer, such a response facilitates a subdued WPSH in spring but an enhanced WPSH in summer. Moreover, the CGCM results showed that the equatorial low-level westerly at the south edge of the cyclonic anomaly brings about a warm SST anomaly (SSTA) in the equatorial central Pacific via surface warm advection. Subsequently, an atmospheric Rossby wave is stimulated to the northwest of the warm SSTA, which in turn enhances the atmospheric dipole anomalies over the western Pacific. Therefore, the air-sea feedbacks involved tend to reinforce the effect of SHTP on the WPSH anomaly, and the role of SHTP on general circulation needs to be considered in a land-air-sea interaction framework.

1. Introduction
  • The low-level circulation over the subtropical oceans is characterized by vast subtropical anticyclones that exist year-round and occupy about 40% of Earth's surface (Rodwell and Hoskins, 2001). These subtropical anticyclones play an important role in the major teleconnection patterns around the globe, such as the Pacific-North American pattern and the North Atlantic Oscillation. The western Pacific subtropical high (WPSH) is a dominant low-level circulation system of the East Asian monsoon that is closely linked to the onset and withdrawal of the summer monsoon, and its formation and evolution have long been topics of interest in the atmospheric studies (e.g., Krishnamurti et al., 1973; Peng and Domrös, 1987; Zhang et al., 1995; Liu et al., 2001; Rodwell and Hoskins, 2001; Wu and Liu, 2003; Wang et al., 2014). However, due to multiple forcing sources and nonlinear processes, predicting the seasonal and interannual variations of the WPSH remains a challenge.

    In spring (March-April-May), the air column over the Tibetan Plateau (TP) changes from a heat sink to a source for rapidly enhanced sensible heating (e.g., Yeh and Gao, 1979; Luo and Yanai, 1983; Wu et al., 1997; Zhao and Chen, 2001; Duan et al., 2005). Strong elevated surface sensible heating over the TP (SHTP) warms up the air column above at a daily rate of 2°C to 4°C (Yeh and Gao, 1979; Wu and Zhang, 1998; Duan and Wu, 2005). Vigorous ascension of the air column due to SHTP sucks the surrounding air from below and expels it outwards in the upper troposphere, acting as an efficient air pump (Wu et al., 1997). SHTP generates near-surface positive vorticity and upper-level negative vorticity, and regulates the atmospheric circulation over a broad area. SHTP plays an important role in maintaining and modulating the large-scale circulation in upper layers (Flohn, 1957; Yeh et al., 1957; Ye and Wu, 1998; Duan et al., 2008).

    The importance of the thermal forcing associated with both monsoon precipitation and SHTP in modulating the WPSH has been investigated in many studies (e.g., Wu et al., 1999; Chen et al., 2001; Rodwell and Hoskins, 2001; Chen et al., 2003; Jian et al., 2004; Liu and Wu, 2004; Wang et al., 2014). However, most studies have focused on the summertime simultaneous relationship, and hence do not provide useful information for seasonal predictions. But how does the spring SHTP influence the WPSH anomaly? And to what degree is this forcing modulated by the air-sea interaction? In this study, we address these questions from a land-air-sea interaction perspective using data analysis and numerical simulations.

    The remainder of this manuscript is organized as follows: In section 2, the data and model are briefly described. Section 3 presents the interannual linkage among SHTP, the WPSH, and ENSO, determined by data analysis. Section 4 is devoted to demonstrating the processes involved, based on numerical experiments using both an AGCM and a CGCM. Finally, a summary and discussion are presented in section 5.

2. Data and model
  • The data used in this study were from the following sources:

    (1) Regular surface meteorological observations from 73 stations over the TP, provided by the China Meteorology Administration, gathered four times daily (0000, 0600, 1200 and 1800 UTC). Variables included surface air temperature, ground surface temperature, and wind speed at 10 m above the surface. The locations of these stations are shown in Fig. 1a. All these data had undergone quality control procedures to eliminate erroneous data and ensure homogeneity.

    (2) Satellite radiation data from GEWEX-SRB (http://eosweb.larc.nasa.gov/PRODOCS/srb/table_srb.html) at a resolution of 1.0°× 1.0°. Radiation fluxes included the downward and upward shortwave and longwave fluxes at the TOA and at the surface.

    (3) ERA-Interim data (Dee et al., 2011). Variables included monthly mean horizontal and vertical wind speed and geopotential height (resolution: 1.5°× 1.5°; 37 pressure levels).

    (4) Monthly SST data from the Hadley Center (Rayner et al., 2003) at a resolution of 1.0°× 1.0°.

    (5) From the 74 circulation indices provided by the National Climate Center of China, we chose three indices to investigate the intensity, latitudinal position and meridional position of the western Pacific subtropical high (WPSH) (Li et al., 2003), as follows:

    Intensity index: The sum of the differences between grid points at the mean geopotential height is equal or more than 5880 gpm and the geopotential height is 5870 gpm, between 110°E and 180°E (e.g., 5880 to 1, 5890 to 2, 5900 to 3, and so on). The cumulative value is defined as the intensity index.

    Figure 1.  (a) Extent of the TP represented by the height of 2000 m (green line), and the locations of the 73 meteorological stations across the TP (black dots). (b) Annual cycle of the atmospheric heat source and sink and each of its components over the TP during 1984-2007. (c) Time series of the standard anomalies of the spring mean sensible heating flux averaged over the 73 stations (blue line) and the Niño3.4 (5°S-5°N, 170°-120°W) SSTA index during 1980-2008 with the linear trend excluded (red line).

    Westernmost ridge point index: The westernmost longitude of the 5880 gpm contour between 90°E and 180°E is defined as the westernmost ridge point of the subtropical high.

    Ridge position index: The average latitude of the intersection points of the WPSH between 110°E and 150°E with nine meridians (e.g., 110°E, 115°E, 120°E, 125°E, 130°E, 135°E, 140°E, 145°E, 150°E) is defined as the ridge position of the subtropical high.

    The timespan of all the datasets used in this study was 1980-2008, except for GEWEX-SRB, which is only available from 1984 to 2007. Following (Duan and Wu, 2008), the sensible heating flux was calculated using in situ observations from all 73 stations over the TP according to the bulk aerodynamic method, and the latent heating flux was obtained from the same stations' observed precipitation. Statistical significance was evaluated using the t-test, and a partial regression analysis was employed to detect the relationship between SHTP and the WPSH, relative to ENSO.

  • FGOALS-s2 and its atmospheric component, i.e., SAMIL2 (Spectral AGCM of IAP/LASG, version 2), were the CGCM and AGCM employed in this study, and a detailed description of the model configuration can be found in (He et al., 2016).

3. Observed WPSH anomaly associated with SHTP and ENSO
  • Owing to the limited duration of the GEWEX-SRB data, the atmospheric heat source and sink, i.e., the sum of sensible heating, latent heating and radiation cooling over the TP, was calculated based on the station and satellite data from 1984 to 2007. The gridded satellite radiation data had been interpolated onto the station points in advance. Figure 1b shows the annual cycle of the atmospheric heat source and sink and each of its components over the TP. The air column over the TP is a heat source from March to September and a heat sink in the other months. The strongest heat source occurs in July (110 W m-2), contributed primarily by precipitation-induced latent heating. In spring, however, the surface sensible heating reaches its annual peak (70 W m-2 in April and May) and dominates the sum of sensible heating, latent heating, and radiation cooling. Therefore, SHTP is representative of the overall thermal forcing over the TP in spring.

    Figure 1c shows the time series of the standard anomalies of the spring SHTP index averaged over the 73 stations and the Niño3.4 (5°S-5°N, 170°-120°W) SST anomaly (SSTA) index during 1980-2008, with the linear trend excluded, in which the anomalous strong and weak years for both indices are represented by an intensity larger or smaller than 0.6 standard deviations, respectively. ENSO events typically peak in winter, while the spring Niño3.4 SSTA index is highly correlated with its counterpart in the preceding winter, with a correlation coefficient of 0.87 during 1980-2008 (above the 99% confidence level). Therefore, we chose the spring Niño3.4 SSTA index to compare the influence of ENSO on the WPSH with the influence of SHTP in the same season. There are seven strong SHTP years (1980, 1986, 1987, 1989, 1991, 1995, and 2003) and seven weak SHTP years (1981, 1984, 1985, 1997, 2001, 2005, and 2008) during the analysis period, and more than half of the years correspond to normal or weak ENSO conditions. Note that the correlation coefficient between SHTP and ENSO is only 0.21 (below the 90% confidence level), indicating that SHTP is independent of ENSO. In fact, a recent study (Cui et al., 2015) elucidated that the interannual variability of the spring SHTP depends mainly on the intensity of the overlying subtropical westerly jet, which is directly linked with the early spring SSTA over the North Atlantic.

  • Partial regressions were performed to identify the degree to which SHTP connects with the WPSH. The partial regression coefficient fields of the spring wind vectors and geopotential height on the simultaneous circulation field, with ENSO excluded at different tropospheric levels (i.e., 200, 500 and 850 hPa), are shown in Figs. 2a, c and e. The large-scale circulation is characterized by a clear stationary wave pattern. When the spring SHTP is above normal, significantly positive southwest-northeast-oriented geopotential height anomalies extend from the Indochina Peninsula to the North Pacific, and significantly negative geopotential height anomalies occur on both sides, accompanied by two anticyclonic anomaly centers over Southwest China and the North Pacific (30°-60°N, 160°E-150°W) and an anomalous cyclonic center to the equatorial side. Such a circulation pattern exhibits an equivalent vertical barotropic structure, and acts to weaken the spring mean WSPH, as represented by the 5840 gpm contours (thick purple lines in Fig. 2c). The reverse picture is also true when SHTP is below normal. Of note is that the circulation connection with the spring SHTP is by no means limited to East Asia and the western Pacific. Rather, significant circulation anomalies even appear over North America and the southern Pacific, indicating SHTP may have a global-scale effect. Owing to length limitations, however, in this work we focused only on the WPSH anomaly.

    Figure 2.  Partial regression fields of wind vectors (arrows; units: m s-1) and geopotential height (shaded; units: gpm) on SHTP: (a, c, e) spring simultaneous results; (b, d, f) summer lagged circulation response to the spring SHTP; (a, b) 200 hPa; (c, d) 500 hPa; (d, e) 850 hPa. Only the results significant at the 90% level for wind vectors are plotted, and the results for geopotential height at the 90% confidence level are dotted. The green line in Fig. 2 and figures below indicates the TP. The thick purple lines indicate the climate mean 5840 gpm contour in spring and the 5880 gpm contour in summer at 500 hPa, and represent the seasonal mean location of the WPSH.

    Figure 3.  As in Fig. 2, but for regression fields on the spring Niño3.4 SSTA index.

    The background circulation and diabatic heating are very different in spring and summer (June-July-August); hence, it is reasonable that the summer circulation anomalies related to the preceding spring SHTP might change to a certain degree (Figs. 2b, d and f). At 500 hPa, when the spring SHTP is above normal, a significant positive geopotential height anomaly occupies the whole of southeastern East Asia and the tropical western Pacific. Correspondingly, an anomalous anticyclone center occurs over East China and the western Pacific, located to the west side of the summer-mean WPSH, as represented by the 5880 gpm contour at 500 hPa (thick purple lines in Fig. 2d). The circulation anomalies at 850 and 200 hPa are almost identical over East Asia and the western Pacific. Therefore, an above-normal spring SHTP is followed by an enhanced and westward-extended WSPH in summer, and vice versa. A consistent result was obtained using composite analysis based on anomalously strong and weak SHTP years (data not shown). A recent case study (Wang et al., 2014) demonstrated a weak spring SHTP followed by a suppressed summer WPSH as having occurred in 2001, and the reverse situation in 2003; however, the linkage between SHTP and the WPSH in terms of interannual variability was not discussed.

    Previous studies have demonstrated that ENSO events affect the WPSH efficiently in terms of both intensity and location (e.g., Wang and Zou, 2004, Wu et al., 2010b, Zhang and Sumi, 2002). To further illustrate this point, in Fig. 3 we show the partial regression coefficient fields of the wind vectors and geopotential height on the spring ENSO signal with SHTP excluded. At 850 hPa, significantly positive geopotential height anomalies are distributed over a large part of the tropics, extending from the Indian Ocean to the western Pacific, and the circulation anomaly presents as an east-west seesaw pattern over the Pacific, i.e., an anticyclone over the southwestern Pacific and a cyclone over the northeastern Pacific. The situation is similar in the middle and upper troposphere for most regions, except the tropical eastern Pacific where negative geopotential height anomalies are replaced by positive anomalies at 500 and 200 hPa. Owing to ocean thermal inertia, the tropical circulation related to the ENSO signal is comparable in spring and summer. Over the East Asian summer monsoon region and higher latitudes, the circulation anomaly is very different, attributable to the strong latent heating induced by the monsoonal precipitation. ENSO is the dominant signal of the climate system in terms of interannual variability, and thus it is reasonable that the corresponding circulation is stronger and broader than the SHTP. By comparing the circulation anomalies with the climate mean state, we can see that the circulation connecting with El Niño events benefits an enhanced WPSH in both spring and summer. Therefore, the spring SHTP and ENSO play reverse roles in modulating the interannual variability of the spring WPSH, but work cooperatively for the summer WPSH anomaly.

    The relationships among the WPSH, SHTP and ENSO are summarized quantitatively in Table 1, in which the three chosen indices of the summer WPSH (intensity index, westernmost ridge point index, and ridge position index) were utilized to depict the WPSH anomaly. Significant correlation exists between the spring SHTP and the summer WPSH in both the western edge point and intensity. After removing the ENSO signal, the correlation with the intensity index is reduced slightly, but still significant; whereas, the correlation with the western edge point index is no longer robust. Similarly, the spring ENSO signal is significantly correlated with the intensity and western edge point indices of the summer WPSH, even with the SHTP signal excluded, with partial correlation coefficients of 0.61 and -0.51, respectively. This means that an enhanced and westward-extended WPSH appears in El Niño decaying summers. Meanwhile, the partial correlation between the spring ENSO and the summer WPSH ridgeline index is only -0.15, indicating that the meridional movement of the WPSH is less influenced by ENSO. The mechanism by which ENSO affects the WPSH has been widely discussed. Some studies have focused on the atmospheric Rossby wave response to the SSTA-relevant diabatic heating and the wind evaporation-SST positive feedback over the tropical Pacific (e.g., Wang et al., 2000; Xie et al., 2009), while others have emphasized the spring and summer SSTA in the Indian Ocean during El Niño decaying years (e.g., Yang et al., 2007; Wu et al., 2009). However, this topic is beyond the scope of the present study, and we do not attempt to discuss it further. Nevertheless, all these results indicate that the zonal position of the summer WPSH is more related to ENSO, while the spring and summer WPSH intensity is substantially influenced by both SHTP and ENSO in spring. The processes involved are addressed in the following section, based on numerical experiments using both the AGCM and CGCM.

4. Simulation of the SHTP impact on the WPSH
  • Utilizing the AGCM and CGCM introduced in section 2.2, four experiments were carried out under different SHTP and SST conditions, with the aim of explaining the processes involved in the spring SHTP modulation of the summer WPSH and the possible influence of the air-sea interaction. In the AGCM control run, monthly SST and sea-ice-extent data were prescribed according to the 20-year climatology used by AMIP II (see http://www-pcmdi.llnl.gov/ projects/amip/AMIP2EXPDSN/BCS_OBS/amip2_bcs.htm for details). In the idealized AGCM and CGCM sensitivity runs, the surface sensible heating at elevations above 500 m within the area (20°-45°N, 70°-110°E) (Fig. 6b) was not allowed to heat the atmosphere in boreal spring (March-April-May), i.e., the vertical diffusive heating term in the atmospheric thermodynamic equation was set to zero, while the surface energy balance was kept unchanged. The difference between the control and sensitivity runs reflects the atmospheric response to SHTP.

    The two AGCM runs were integrated over 37 years, and the last 30 years were selected for analysis. To identify the role of air-sea interaction, another pair of experiments was carried out using the CGCM. The CGCM control run used the same external forcing as the AGCM, but was integrated over 40 years, and the last 30 years were analyzed when the SST reached a quasi-equilibrium state. The difference between the CGCM and AGCM runs was used to investigate the air-sea feedback.

  • The tropospheric level of 500 hPa is often chosen as the representative level to depict the WPSH. To demonstrate the model performance in reproducing the general circulation, we plotted the observed and simulated 500 hPa horizontal wind vectors and SST and their differences in spring and summer, respectively (Figs. 4 and 5). The large-scale circulation systems in terms of position and intensity simulated by the two control runs bears a general resemblance to observations, including the WPSH, westerlies over the midlatitude, easterlies over the northern Indian Ocean, as well as the anticyclones over North America. The differences between the simulated and the observed are shown (Figs. 4b and d, and Figs. 5b and 5d), noting that the reference vector is smaller. A similar result was also obtained for the lower and upper troposphere (figures not shown here). In addition, the observed SST pattern and magnitude (Figs. 4e and 5e) are reasonably reproduced by the CGCM control run (Figs. 4c and 5c). Some differences are apparent, mainly in the North Pacific and tropical East Pacific (Figs. 4d and 5d). Moreover, the simulated sensible heating was very important in the experiment. We interpolated the simulated sensible heating to the 73 stations (Fig. 1a) and plotted the annual cycle (Fig. 6a). The AGCM and CGCM both simulate the seasonal variabilities. Although the simulated values are smaller than the stations', the magnitude is equivalent. And the tendency of the CGCM's annual cycle is closer to the stations'.

    However, despite these discrepancies, the overall consistency in the large-scale circulation, SST pattern and sensible heating between the models and observations provided confidence for the following sensitivity experiment.

    Figure 4.  The spring mean simulated and observed 500 hPa wind vectors (arrows; units: m s-1) and SST (shading; units: °C) and their difference fields: (a) AGCM control runs; (b) difference between AGCM control runs and observations; (c) CGCM control runs; (d) difference between CGCM control runs and observations; (e) observations; (f) difference between CGCM control runs and AGCM control runs.

    Figure 5.  As in Fig. 4, but for summer.

  • As mentioned earlier, the difference between the control and sensitivity runs can be used to detect the effect of SHTP. The results are presented in Figs. 7 and 8. In the AGCM runs, the spring circulation response to SHTP features a dipole pattern over the Pacific with an equivalent vertical barotropic structure. That is, an anticyclonic response appears over the North Pacific, while a cyclonic center exists over the tropical western Pacific to the southwest side (Figs. 7a, c and e). Compared with the climate mean state (Fig. 4a), we can see that the circulation response to the spring SHTP results in a suppressed spring WPSH. This result is consistent with the data analysis in section 3. Moreover, the same result can be seen in the CGCM runs (Figs. 8a, c and e), indicating the independent impact of SHTP on the WPSH relative to the SST forcing.

    Figure 6.  (a) Annual cycle of the sensible heating averaged over the 73 stations of the TP. The blue line is the same as the red line in Fig. 1b; the red line represents the results of the AGCM runs; the green line represents the results of the CGCM runs. (b) Surface sensible heating at elevations above 500 m within the shaded area (20°-45°N, 70°-110°E), where it was not allowed to heat the atmosphere in the sensitivity runs.

    Figure 7.  Difference in wind vectors (arrows; units: m s-1) and geopotential height (shading; units: gpm) between the AGCM control and sensitivity runs: (a, c, e) spring; (b, d, f) summer; (a, b) 200 hPa; (c, d) 500 hPa; (d, e) 850 hPa. Only the results at the 90% confidence level are plotted for the wind vectors, and the dots indicate the 90% confidence level for the geopotential height results. The thick purple lines indicate the climate mean 5840 gpm contour in spring and the 5880 gpm contour in summer at 500 hPa, and represent the seasonal mean location of the western Pacific subtropical high (WPSH).

    Figure 8.  Difference in wind vectors (all panels; arrows; units: m s-1), geopotential height [(c, d); shading; units: gpm] and SST [(e, f); shading; units: °C] between the CGCM control and sensitivity runs: (a, c, e) spring; (b, d, f) summer; (a, b) 200 hPa; (c, d) 500 hPa; (d, e) 850 hPa. Only the results at the 90% confidence level are plotted for wind vectors, and the dots indicate the 90% confidence level for the geopotential height and SST results. The thick purple lines indicate the climate mean 5840 gpm contour in spring and the 5880 gpm contour in summer at 500 hPa, and represent the seasonal mean location of the western Pacific subtropical high (WPSH).

    In summer, the large-scale circulation response to SHTP in the AGCM runs changes to a certain degree, and the vertical barotropic structure weakens systematically (Figs. 7b, d and f). A positive geopotential height anomaly at 500 hPa occupies almost the whole Pacific, and the anomalous anticyclonic center moves northward by about 10° of latitude from spring to summer. Meanwhile, the anomalous cyclone to the southwest side weakens significantly and appears only in the lower troposphere. Over the Pacific warm pool, an anticyclonic anomaly rather than a cyclonic anomaly appears in the middle and lower troposphere. Unlike the case in spring, an obvious difference between the AGCM and CGCM can be detected in some areas. For example, the near-Equator easterly anomaly at 500 hPa extends from the eastern Pacific to the Indian Ocean in the AGCM, but is replaced by a westerly anomaly over the Indian Ocean and western Pacific in the CGCM. As for the WPSH, the results from both the AGCM and CGCM indicate an enhanced summer WPSH when the SHTP effect is taken into account. Therefore, the observed response of the WPSH anomaly to SHTP is further verified by the numerical simulations.

    Figure 9.  Difference in wind vectors (arrows; units: m s-1) and geopotential height (shading; units: gpm) between the CGCM and AGCM runs, i.e., Fig. 8 minus Fig. 7: (a, c, e) spring; (b, d, f) summer; (a, b) 200 hPa; (c, d) 500 hPa; (d, e) 850 hPa. Only the results at the 90% confidence level are plotted for wind vectors, and the dots indicate the 90% confidence level for the geopotential height results.

    Figure 10.  Difference in zonal and meridional temperature advection (shading; units: K d-1) in the top ocean layer between the CGCM control and sensitivity runs: (a, c) spring; (b, d) summer; (a, b) zonal temperature advection; (c, d) meridional temperature advection. Dotted areas denote the 90% confidence level.

    By comparing the AGCM and CGCM results, one can see a stronger circulation anomaly in the CGCM runs than in the AGCM runs during summer (Figs. 9b, d and f). But why does the air-sea interaction reinforce the circulation response to SHTP over the Pacific? To explain this, we need to look back at the SST difference between the CGCM control and sensitivity runs (Figs. 8e and f; shaded areas). In spring and summer, a warm SSTA belt exists in most parts of the tropical Pacific, with a maximum value of about 2°C. Such a warm SSTA corresponds to a significant in situ surface zonal warm advection anomaly, as shown in Figs. 10a and b, which is directly related to the atmospheric low-level westerly anomalies at the south edge of the anomalous cyclone (Figs. 7e and f; arrows) as a response to SHTP. Meanwhile, the meridional advection anomaly seems to cool the local SST, but its magnitude is insufficient to cancel out the warming effect of the zonal warm advection. Therefore, SHTP modulates the remote SSTA, at least over the tropical Pacific, through large-scale air-sea interaction.

    The seasonal timescale is long enough for atmospheric feedback. As indicated in Figs. 8a, c and e, the near-Equator warm SSTA over the Pacific further stimulates an atmospheric Rossby wave to the northwest side and a Kelvin wave to the east side (Gill, 1980), which in turn reinforces the tropical cyclonic anomaly over the Pacific warm pool and the anticyclonic anomaly over the North Pacific, resulting in a weakened spring WPSH. Such air-sea interaction can still be detected in summer. However, with the seasonal evolution from spring to summer, the anomalous cyclone, together with the warm SSTA center, moves to the central and eastern Pacific (Figs. 8b and d). The southern part of the anomalous anticyclone is located in the same position as the summer mean WPSH, and hence enhances it to a considerable degree. Some discrepancies between the data analysis and numerical simulations do exist. For instance, the response of atmospheric circulation to SHTP in the numerical simulations is clearly stronger than that obtained from data analysis. This can be attributed mainly to the idealized experimental design and model bias. Nevertheless, the overall consistency between the data analysis and the numerical simulations indicates that SHTP exerts a significant impact on the WPSH in both spring and summer. Moreover, the air-sea interaction over the tropical Pacific may further reinforce the atmospheric response to SHTP in some circumstances——a result not previously reported in the literature.

5. Summary and discussion
  • Using station records from 73 meteorological stations over the TP, ERA-Interim data, and SST from the Hadley Center during 1980-2008, we investigated the linkage between SHTP and the WPSH in terms of interannual variability. Furthermore, both AGCM and CGCM experiments, based on FGOALS-s2, were conducted to reveal the processes involved. The main findings can be summarized as follows:

    (1) The spring SHTP exerts a significant impact on the simultaneous and subsequent summer WPSH in terms of interannual variability, i.e., above-normal spring SHTP induces a weak spring WPSH, but a strong summer WPSH, and vice versa. In particular, SHTP acts as an independent factor for the WPSH anomaly relative to ENSO events.

    (2) Results from the AGCM experiments confirmed that the spring SHTP generates a large-scale circulation response in the downstream regions, characterized by a barotropic anticyclonic response over the northwestern Pacific and a cyclonic response to the south. Owing to the different background circulation in spring and summer, such a response tends to weaken the spring WPSH but enhances the summer WPSH.

    (3) By further comparing the CGCM and AGCM results, we found that the low-level westerlies at the south edge of the cyclonic anomaly facilitate a warm SSTA in the equatorial central Pacific via the surface zonal warm advection anomaly. Subsequently, an atmospheric Rossby wave is excited to the northwest of the warm SSTA, which in turn enhances the dipole pattern of the circulation anomaly over the Pacific. Moreover, the air-sea feedbacks involved reinforce the SHTP effect on the WPSH, bringing about an enhanced WPSH. Overall, we reveal two ways in which SHTP influences the WPSH anomaly. The direct way is the atmospheric response to SHTP, and the indirect way comes from the equatorial Pacific air-sea interaction.

    Despite the progress made in this study to demonstrate the influence of SHTP on the WPSH anomaly, some issues still need to be addressed further. For example, in Figs. 8e and f, it is noticeable that SHTP induces a warm SSTA in the Indian Ocean, and previous studies (Wu et al., 2010a) have indicated that a warm Indian Ocean favors an intensified WPSH. Therefore, the WPSH anomaly induced by the remote Indian Ocean SSTA and its relationship to TP thermal forcing needs to be considered in future studies. Also, our recent studies (Duan et al., 2013; Wang et al., 2014) have suggested that intense spring SHTP may lead to an overall stronger in situ atmospheric heat source in summer through a local circulation-diabatic heating positive feedback, which further induces the summertime circulation and climate anomaly over East Asia and the western Pacific. Therefore, the relative contribution to the summer WPSH variability of this process and the air-sea interaction process proposed in this study is still an open question. However, these results remind us that the role of TP thermal forcing on large-scale circulation should be considered in a land-air-sea interaction framework.

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