Reversed impacts of the Arctic oscillation on the precipitation over the South China Sea and its surrounding areas in Oc
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Reversed impacts of the Arctic oscillation on the precipitation over the South China Sea and its surrounding areas in October and November Tianyun Dong1,2 · Wenjie Dong1,2 · Taichen Feng3 · Xian Zhu1,2 Received: 1 March 2020 / Accepted: 12 September 2020 © The Author(s) 2020
Abstract The reversed impacts of the Arctic oscillation (AO) on precipitation over the South China Sea and its surrounding areas (SCSA) in October and November during 1979–2014 are investigated. The correlation coefficients between AO and the precipitation in October and November are 0.44 and − 0.31, which are statistically significant at the 99% and 90% confidence levels, respectively. In October (November), the specific humidity exhibits obvious positive (negative) anomalies in the SCSA, and an upward (downward) airflow moving from ground to the upper troposphere (1000–150 hPa) between 10°N and 30°N (10°N and 20°N) is observed with more (less) cloud cover. Moisture budget diagnosis suggests that the precipitation’s increasing (decreasing) in October (November) mainly contributed by zonal moisture flux convergence (divergence). Furthermore, the Rossby wave guided by westerlies tends to motivate positive geopotential height in the upper troposphere over approximately 20°–30°N, 40°–80°E in October, which is accompanied by a stronger anticyclone in the Arabian Sea region. However, in November, the wave train propagating from the Arabian Sea to the Bay of Bengal is observed in the form of cyclones and anticyclones. Further analysis reveal that the AO in October may increase precipitation through the southern wave train (along the westerly jet stream from North Africa to the Middle East and South China). Moreover, air-sea interactions over the North Pacific might also generate horseshoe-shaped sea surface temperature (SST) anomalies characterized by positive SST in the central subtropical North Pacific surrounded by negative SST, which may affect the precipitation in the SCSA. Ensemble-mean results from CMIP6 historical simulations further confirm these relationships, and the models that can better simulate the observed positive geopotential height in the Arabian Sea present more consistent precipitation’s increasing over the SCSA in October. Keywords Arctic oscillation · Precipitation anomaly · Climate change · CMIP6
1 Introduction Thompson and Wallace (1998) used the empirical orthogonal function (EOF) analysis method to study the SLP poleward of 20°N and found that the first EOF mode shows reversed phase between the mid-latitude and Arctic regions. * Wenjie Dong [email protected] 1
School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China
2
Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai 519082, China
3
College of Atmospheric Sciences, Lanzhou University, Lanzhou, China
This pattern is named the Arctic oscillation (AO). Subsequently, a lot of studies reveal that the AO not only has significant impact on climate change in mid- and high-latitude areas, such as North America (Hurrell
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