Prediction of the Western North Pacific Subtropical High in Summer without Strong ENSO Forcing

• Corresponding author: Chaofan LI, lichaofan@mail.iap.ac.cn
• Funds:

Supported by the National Key Research and Development Program of China (2018YFC1506005), National Natural Science Foundation of China (41775083), and the Second Tibetan Plateau Scientific Expedition and Research (STEP) Program (2019QZKK0102). Nick Dunstone was supported by the UK–China Research and Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund

• doi: 10.1007/s13351-021-0113-3
• The western North Pacific subtropical high (WNPSH) is one of the deterministic predictors of the East Asian summer climate, and a better prediction of the WNPSH favors more reasonable forecast of the East Asian summer climate. This study focuses on seasonal prediction of the WNPSH during neutral summers without strong El Niño–Southern Oscillation (ENSO) forcing, and explores the associated predictable sources, using the one-month lead time retrospective forecasts from the Ensembles-Based Predictions of Climate Changes and Their Impacts (ENSEMBLES) project during 1960–2005. The results indicate that the ENSEMBLES atmosphere–ocean–land coupled models exhibit considerable prediction skill for the WNPSH during neutral summers, with successful reproduction of the WNPSH in the majority of neutral summers. The anomalous WNPSH in neutral summers, which corresponds to cyclonic/anticyclonic anomalies in the lower troposphere, is highly correlated with an east–west dipole local sea surface temperature (SST) distribution over the tropical WNP, suggesting an intimate local air–sea coupling. Further diagnosis of the local SST–rainfall relationship and surface heat flux indicates that the anomalous local SST plays an active role in modulating the variation of the WNPSH during neutral summers, rather than passively responding to the atmospheric change. The local SST anomalies and relevant air–sea coupling over the tropical WNP are reasonably well reproduced in the model predictions, and could act as primary predictable sources of the WNPSH in neutral summers. This could aid in forecasting of the East Asian rainband and associated disaster mitigation planning.

• Fig. 1.  Prediction skill (shaded; ${\rm P}\_{\rm Cor}$) of the (a) 850-hPa zonal wind, (b) precipitation, and (c) SST for ENSO-neutral summers. The ENSO-neutral summers include 1960, 1961, 1962, 1967, 1979, 1980, 1981, 1990, 1993, 2001, 2004, and 2005 (after 1979 for precipitation). The contours represent statistical significance of the prediction correlation at the 0.05 and 0.01 confidence levels. The blue boxes indicate the domains of the WNPSH index.

Fig. 2.  (a) The normalized WNPSH index for the observations (OBS; blue bar) and model predictions (MME; red bar) during all neutral summers and (b) associated observed evolution of the Niño 3.4 SST index. The positive (negative) years with an observed WNPSH index larger (less) than 0.8 (–0.8) are marked by grey dashed lines in (a) and green (orange) lines in (b) as the significant neutral summers.

Fig. 3.  Composites of the anomalies of (a, b) 850-hPa wind (vector; m s−1) superimposed with precipitation (shading; mm day−1) and (c, d) SST (°C) during the significant neutral summers for (a, c) observations and (b, d) MME predictions. The purple boxes indicate the domains of the dipole SST over the tropical WNP.

Fig. 4.  The normalized dipole SST index over the WNP for the observations (OBS; blue) and the MME predictions (Model; red) during the significant neutral summers. The index is defined by the east–west SST gradient over the WNP, with the domains indicated in Fig. 3c.

Fig. 5.  Seasonal evolution of the observed SST gradient (°C) over the WNP. The anomaly in 1993 (short dashed line) is multiplied by −1 for ease of comparison with the other positive years. Com. denotes composite.

Fig. 6.  Scatter diagrams of the standardized SST and precipitation anomalies over the (a) eastern and (b) western WNP for the significant neutral summers after 1979. The blue, red, and grey markers indicate the observations, the MME prediction, and the individual ensemble members, respectively. The domains for the eastern and western WNP are shown in Fig. 3c. The anomaly in 1993 is multiplied by –1. The correlation coefficients between the SST and precipitation anomalies for all these dots are 0.28 in (a) and 0.62 in (b).

Fig. 7.  As in Fig. 6, but for the standardized WNPSH index and precipitation anomalies over the (a) eastern and (b) western WNP. The correlation coefficients between the WHPSH index and precipitation anomalies for all these dots are 0.61 in (a) and –0.31 in (b).

Fig. 8.  Composites of the surface fluxes from the observations (left panels) and MME predictions (right panels) during the significant neutral summers, including (a, b) longwave (LW) radiation, (c, d) shortwave (SW) radiation, (e, f) latent heat (LH) flux, and (g, h) sensible heat (SH) flux. The units are W m−2 and positive values indicate downward flux.

Fig. 9.  As in Fig. 8, but for the total surface flux anomalies.

•  [1] Adler, R. F., G. J. Huffman, A. Chang, et al., 2003: The Version-2 Global Precipitation Climatology Project (GPCP) monthly precipitation analysis (1979–present). J. Hydrometeor., 4, 1147–1167.. [2] Chou, C., T. Y. Tu, and Y. J. Yu, 2003: Interannual variability of the western North Pacific summer monsoon: Differences between ENSO and non-ENSO years. J. Climate, 16, 2275–2287. doi: 10.1175/2761.1. [3] Ding, H., R. J. Greatbatch, W. Park, et al., 2014: The variability of the East Asian summer monsoon and its relationship to ENSO in a partially coupled climate model. Climate Dyn., 42, 367–379.. [4] Hong, X. W., and R. Y. Lu, 2016: The meridional displacement of the summer Asian jet, Silk Road pattern, and tropical SST anomalies. J. Climate, 29, 3753–3766.. [5] Huang, B. Y., P. W. Thorne, T. M. Smith, et al., 2016: Further exploring and quantifying uncertainties for extended reconstructed sea surface temperature (ERSST) version 4 (v4). J. Climate, 29, 3119–3142.. [6] Huang, R. H., and F. Y. Sun, 1992: Impacts of the tropical western Pacific on the East Asian summer monsoon. J. Meteor. Soc. Japan, 70, 243–256.. [7] Kalnay, E., M. Kanamitsu, R. Kistler, et al., 1996: The NCEP/NCAR 40-year reanalysis project. Bull. Amer. Meteor. Soc., 77, 437–472.. [8] Kosaka, Y., and H. Nakamura, 2006: Structure and dynamics of the summertime Pacific–Japan teleconnection pattern. Quart. J. Roy. Meteor. Soc., 132, 2009–2030.. [9] Kosaka, Y., J. S. Chowdary, S.-P. Xie, et al., 2012: Limitations of seasonal predictability for summer climate over East Asia and the northwestern Pacific. J. Climate, 25, 7574–7589.. [10] Kosaka, Y., S.-P. Xie, N.-C. Lau, et al., 2013: Origin of seasonal predictability for summer climate over the Northwestern Pacific. Proc. Natl. Acad. Sci. USA, 110, 7574–7579.. [11] Lee, S. S., J. Y. Lee, K. J. Ha, et al., 2011: Deficiencies and possibilities for long-lead coupled climate prediction of the western North Pacific–East Asian summer monsoon. Climate Dyn., 36, 1173–1188.. [12] Li, C. F., R. Y. Lu, and B. W. Dong, 2012: Predictability of the western North Pacific summer climate demonstrated by the coupled models of ENSEMBLES. Climate Dyn., 39, 329–346.. [13] Li, C. F., R. Y. Lu, and B. W. Dong, 2014: Predictability of the western North Pacific summer climate associated with different ENSO phases by ENSEMBLES multi-model seasonal forecasts. Climate Dyn., 43, 1829–1845.. [14] Li, C. F., R. Y. Lu, and B. W. Dong, 2016: Interdecadal changes on the seasonal prediction of the western North Pacific summer climate around the late 1970s and early 1990s. Climate Dyn., 46, 2435–2448.. [15] Li, C. F., W. Chen, X. W. Hong, et al., 2017: Why was the strengthening of rainfall in summer over the Yangtze River valley in 2016 less pronounced than that in 1998 under simi-lar preceding El Niño events?—Role of midlatitude circulation in August. Adv. Atmos. Sci., 34, 1290–1300.. [16] Liu, Y., H.-L. Ren, A. A. Scaife, et al., 2018: Evaluation and statistical downscaling of East Asian summer monsoon forecasting in BCC and MOHC seasonal prediction systems. Quart. J. Roy. Meteor. Soc., 144, 2798–2811. doi: 10.1002/qj.3405. [17] Lu, R. Y., 2004: Associations among the components of the East Asian summer monsoon system in the meridional direction. J. Meteor. Soc. Japan, 82, 155–165.. [18] Lu, R.-Y., and S. Lu, 2014: Local and remote factors affecting the SST–precipitation relationship over the western North Pacific during summer. J. Climate, 27, 5132–5147.. [19] Lu, R.-Y., J.-H. Oh, and B.-J. Kim, 2002: A teleconnection pattern in upper-level meridional wind over the North African and Eurasian continent in summer. Tellus A: Dyn. Meteor. Oceanogr., 54, 44–55.. [20] Lu, R.-Y., C.-F. Li, S. H. Yang, et al., 2012: The coupled model predictability of the western North Pacific summer monsoon with different leading times. Atmos. Ocean. Sci. Lett., 5, 219–224.. [21] MacLachlan, C., A. Arribas, K. A. Peterson, et al., 2015: Global Seasonal forecast system version 5 (GloSea5): A high-resolution seasonal forecast system. Quart. J. Roy. Meteor. Soc., 141, 1072–1084. doi: 10.1002/qj.2396. [22] Miyasaka, T., and H. Nakamura, 2005: Structure and formation mechanisms of the Northern Hemisphere summertime subtropical highs. J. Climate, 18, 5046–5065.. [23] Rodwell, M. J., and B. J. Hoskins, 2001: Subtropical anticyclones and summer monsoons. J. Climate, 14, 3192–3211.. [24] Trenberth, K. E., and D. J. Shea, 2005: Relationships between precipitation and surface temperature. Geophys. Res. Lett., 32, L14703.. [25] Van Der Linden, P., and J. F. B. Mitchell, 2009: ENSEMBLES: Climate Change and Its Impacts: Summary of Research and Results from the ENSEMBLES Project. Met Office Hadley Centre, UK, 160 pp. [26] Wang, B., and Z. Fan, 1999: Choice of South Asian summer monsoon indices. Bull. Amer. Meteor. Soc., 80, 629–638.. [27] Wang, B., and Q. Zhang, 2002: Pacific–East Asian teleconnection. Part Ⅱ: How the Philippine sea anomalous anticyclone is established during El Niño development. J. Climate, 15, 3252–3265.. [28] 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.. [29] Wang, B., Q. H. Ding, X. H. Fu, et al., 2005: Fundamental challenge in simulation and prediction of summer monsoon rainfall. Geophys. Res. Lett., 32, L15711.. [30] Wang, B., J.-Y. Lee, I.-S. Kang, et al., 2008: How accurately do coupled climate models predict the leading modes of Asian-Australian monsoon interannual variability? Climate Dyn., 30, 605–619.. [31] 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.. [32] Wu, B., T. Li, and T. J. Zhou, 2010: 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.. [33] Wu, G. X., and Y. M. Liu, 2003: Summertime quadruplet heating pattern in the subtropics and the associated atmospheric circulation. Geophys. Res. Lett., 30, 1201.. [34] Wu, R. G., and B. P. Kirtman, 2007: Regimes of seasonal air–sea interaction and implications for performance of forced simulations. Climate Dyn., 29, 393–410.. [35] Wu, R. G., J. L. Kinter Ⅲ, and B. P. Kirtman, 2005: Discrepancy of interdecadal changes in the Asian region among the NCEP–NCAR reanalysis, objective analyses, and observations. J. Climate, 18, 3048–3067.. [36] Wu, R. G., B. P. Kirtman, and K. Pegion, 2006: Local air–sea relationship in observations and model simulations. J. Climate, 19, 4914–4932.. [37] Xie, S.-P., K. M. Hu, J. Hafner, et al., 2009: Indian Ocean capaci-tor effect on Indo-western Pacific climate during the summer following El Niño. J. Climate, 22, 730–747.. [38] Xie, S.-P., Y. Kosaka, Y. Du, et al., 2016: Indo-western Pacific ocean capacitor and coherent climate anomalies in post-ENSO summer: A review. Adv. Atmos. Sci., 33, 411–432.. [39] Yu, L. S., and R. A. Weller, 2007: Objectively analyzed air–sea heat fluxes for the global ice-free oceans (1981–2005). Bull. Amer. Meteor. Soc., 88, 527–540..
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

Prediction of the Western North Pacific Subtropical High in Summer without Strong ENSO Forcing

Corresponding author: Chaofan LI, lichaofan@mail.iap.ac.cn;
• 1. Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
• 2. State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
• 3. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
• 4. Met Office Hadley Centre, Exeter EX1 3PB, UK
Funds: Supported by the National Key Research and Development Program of China (2018YFC1506005), National Natural Science Foundation of China (41775083), and the Second Tibetan Plateau Scientific Expedition and Research (STEP) Program (2019QZKK0102). Nick Dunstone was supported by the UK–China Research and Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund

Abstract:

The western North Pacific subtropical high (WNPSH) is one of the deterministic predictors of the East Asian summer climate, and a better prediction of the WNPSH favors more reasonable forecast of the East Asian summer climate. This study focuses on seasonal prediction of the WNPSH during neutral summers without strong El Niño–Southern Oscillation (ENSO) forcing, and explores the associated predictable sources, using the one-month lead time retrospective forecasts from the Ensembles-Based Predictions of Climate Changes and Their Impacts (ENSEMBLES) project during 1960–2005. The results indicate that the ENSEMBLES atmosphere–ocean–land coupled models exhibit considerable prediction skill for the WNPSH during neutral summers, with successful reproduction of the WNPSH in the majority of neutral summers. The anomalous WNPSH in neutral summers, which corresponds to cyclonic/anticyclonic anomalies in the lower troposphere, is highly correlated with an east–west dipole local sea surface temperature (SST) distribution over the tropical WNP, suggesting an intimate local air–sea coupling. Further diagnosis of the local SST–rainfall relationship and surface heat flux indicates that the anomalous local SST plays an active role in modulating the variation of the WNPSH during neutral summers, rather than passively responding to the atmospheric change. The local SST anomalies and relevant air–sea coupling over the tropical WNP are reasonably well reproduced in the model predictions, and could act as primary predictable sources of the WNPSH in neutral summers. This could aid in forecasting of the East Asian rainband and associated disaster mitigation planning.

Reference (39)

/