Covariability between tree-ring-based precipitation reconstructions in Northwest China and the sea-surface temperature of Indian and Pacific Oceans

Abstract

We investigated the coherent variability between precipitation variations in NW China and the sea-surface temperatures of the Indian and Pacific Oceans, using both instrumental data and tree-ring-based precipitation reconstructions. Major coherent hydroclimatic variations in NW China were identified based on the first 2 leading singular value decomposition modes. The modes include the 'southern Xinjiang' pattern, the 'coherent NW-SE' pattern with positive or negative loadings over both the northwestern and southeastern parts and the 'NW-SE dipole' pattern, with inverse correlation patterns between them. The southerly winds near the western boundary of NW China and Lake Balkhash during the early stage of the Indian summer monsoon influence the hydroclimate variability in western NW China (Xinjiang area). The East Asian summer monsoon variability is related to the hydroclimate of eastern NW China, which is modulated by the El Niño Southern Oscillation, geopotential heights in northeastern Asia and over the Philippine Sea, as well as the western Subtropical Pacific High. The strength of the geopotential height in northeastern Asia may be related to the 'coherent NW-SE' pattern, while the inverse relationships between the Pacific Decadal Oscillation and Indian summer monsoon and westerlies may account for the 'NW-SE dipole'.

A reconstruction of the Asia‐Pacific Oscillation Index for the past 1500 years and its association with the Asian summer monsoon

“…During El Niño, warm western tropical Pacific SST can be accompanied by a weak Walker circulation and a suppressed advection in the western tropical Indo‐Pacific oceans (Feng and Hu, ; Lu, ; Fang et al , , ). This leads to a weak Asian summer monsoon and reduced latent heat transport to the northern upper troposphere over East Asia (Hoerling and Kumar, ; Fu et al , ; Seager, ), resulting in a low APO.…”

“…This discrepancy may be because the atmospheric circulations related to the APO‐PDO linkages are largely dependent on the atmospheric circulation that propagates the latent heat from the surface to the upper troposphere, which may not be the case during the dry process (Zhao et al , ). Our study is generally in agreement with the previous studies that highlighted the important roles of the SST on climate change on different timescales (Hoerling and Kumar, ; Lu, ; Fang et al , ).…”

“…; Fang et al , ). The positive phase of the El Niño–Southern Oscillation (ENSO) correlates significantly with pluvial events over western North America and a weakening of Asian summer monsoon via modifications of the Walker circulation, and vice versa (Feng and Hu, ; Seager et al , ; Cook et al , ; Fang et al , ; Li J, Xie SP, Cook E. 2012. pers. comm.).…”

“…comm.). The impacts of ENSO can be strengthened when it is in‐phase with the Pacific Decadal Oscillation (PDO) and the Indian Ocean Dipole (IOD) (Ýsaji et al , ; Ma, ; Fang et al , ; Ummenhofer et al , ). In addition to such tropical ocean‐atmospheric interactions, the Asian‐Pacific Oscillation (APO), defined as the thermal difference at the middle and upper troposphere (500–200 hPa) between East Asia (60°–120°E, 15°–50°N) and the north Central Pacific Ocean (180°–120°W, 15°–50°N), influences the Asian summer monsoon and large‐scale hydroclimate variations between East Asia and North America (Zhao et al , , , ; Nan et al , ; Liu et al , ).…”

“…Although prior studies have investigated the relationships between ocean‐atmospheric patterns and hydroclimate responses in East Asia and North America during the historical era (Seager et al , ; Cook et al , ; Seager, ; Fang et al , , ; Li et al , ; Li J, Xie SP, Cook E. 2012. pers. comm.…”