Regulation of the intraseasonal oscillation over mid-to-high latitude Eurasia on winter surface air temperature over China
Introduction
Since Madden and Julian (1971, 1972) firstly discovered atmospheric intraseasonal oscillation (ISO) in tropical region (Madden–Julian Oscillation, MJO), a number of studies have shown that ISO exists not only in tropics (Lau and Chan, 1986; Wang and Rui, 1990; Annamalai and Slingo, 2001; Li and Wang, 2005; Wang et al., 2006; Jiang and Waliser, 2009; Wen et al., 2010), but also over mid- and high- latitudes (Jeong et al., 2008; Yang et al., 2010; Kikuchi and Wang, 2009; Yang and Li, 2016, 2017). The ISO has a significant effect on weather and climate, including on precipitation and surface air temperature (SAT) (Jeong et al., 2008; Barlow et al., 2005; Donald et al., 2006). Jeong et al. (2005) demonstrated that most extreme cold surges occur when the MJO convection center is located over the Indian Ocean. Vecchi and Bond (2004) revealed that MJO phase has an important impact on the seasonal variability of SAT over entire Arctic winter. By composite analysis of geopotential height and specific humidity, they found that changes in temperature advection and solar radiation induced by MJO play important roles in regional SAT variation. Yuan and Yang (2010) found that MJO had a significant influence on winter precipitation in southeastern China, that is, precipitation in the first (last) four phases of MJO presents positive (negative) anomaly. They pointed out that water vapor flux anomaly advected by meridional wind anomaly is the main reason for precipitation anomaly. Jia et al. (2011) proposed that MJO influences the precipitation over China by adjusting the subtropical and mid-to-high latitude circulation. In subtropical region, MJO affects the meridional transport of water vapor from the Bay of Bengal and the South China Sea by influencing the trough south of the Bay of Bengal and the western Pacific subtropical high.
Most the above-mentioned studies are on the role of tropical ISO, while the feature and role of mid-to-high latitude ISO have been also studied. Yang et al. (2013a,2013b, 2014) shown that Eurasian ISO is dominated by 10–30-day period during boreal winter and boreal summer. The mid-to-high-latitude ISO presents obviously southwestward propagation in boreal summer (Yang et al., 2013a) and southeastward propagation in boreal winter (Yang et al., 2014, 2016). Yang and Li (2017) revealed that a negative (positive) temperature tendency appears to the southeast of a negative (positive) ISO temperature anomaly center throughout the troposphere. They reported that the advection of the temperature anomaly by the meridional mean flow mainly contributes to the observed southeastward shift. Those point out the important role of the ISO-mean flow interaction in causing the southeastward propagation of mid-to-high-latitude ISO in boreal winter. On the other hand, a wave activity flux analysis indicates that the southeastward propagating wave train over the mid-to-high latitudes is likely a result of Rossby wave energy propagation. The mid-to-high-latitude ISO in summer has a significant effect on the rainfall in the mid-low reaches of the Yangtze River (2013b). While the influence of the mid-to-high-latitude ISO in winter on the temperature in whole China is unclear. This study further investigated the regulation of mid-to-high latitude ISO circulation, during its southeastward propagating journey, on SAT over China. Yang et al. (2014) reported that the zonal wind, meridional wind, and SAT over Eurasian area exhibits significantly 10–30-day periodicity in most years. Thus, in this study we focus on the influence of the 10–30-day oscillation over the mid-to-high latitudes on the SAT in China.
The remaining of the paper is organized as follows. Datasets and methods used in this study are described in Section 2. The modulation of the ISO over the mid-to-high latitude Eurasia on SAT over China is described in Section 3. A conclusion is given in Section 4.
Section snippets
Data and method
Daily SAT data, including daily mean temperature (Tave), daily maximum temperature (Tmax) and daily minimum temperature (Tmin), provided by National Meteorological Information Center of China Meteorological Administration, at 585 ground oberservational stations over China are used in the present study. The geographical position of these stations is shown in Fig. 1. It is seen that the selected stations distribute evenly over the entire China, except the southwestern region with relatively less
Intraseasonal temperature anomaly evolution based on ISO phases
In this section, composite analysis was used to investigate the distribution of intraseasonal SAT (Tave, Tmax and Tmin) over China corresponding to different ISO phases over the mid-to-high latitude Eurasia in boreal winter. Fig. 4 shows Tave anomaly evolution with ISO phases (only stations passing the 0.05 significance level were shown). The number in the brackets represents the sample size (in days) of the corresponding phase during the 32 winters (32 × 90 = 2880 days). Since the rainfall
Summary
In this study, we examined the modulation of the ISO over the mid-to-high latitude Eurasia on winter SAT over China by using NCEP-NCAR reanalysis data and SAT data at 585 gauge stations. The amplitude of the mid-to-high latitude ISO is defined based on the first two principal components of EOF of T-2 m over Eurasia (20°‒80 °N, 0°‒140 °E), and each ISO event is divided into 8 phases. The first two leading modes reflect the same propagating mode in different phases.
The ISO over the mid-to-high
Acknowledgements
This work was supported by the National Key R&D Program of China (Grant No. 2018YFC1505905), the National Natural Science Foundation of China (Grant No. 41605035), the Startup Foundation for Introducing Talent of NUIST (2018R027 and 2018R026), the Natural Science Foundation of the Jiangsu Higher Education Institution of China (18KJB170015) and the Key Laboratory of Meteorological Disaster of Ministry of Education (KLME1504). Zhiwei is supported by Young Elite Scientists Sponsorship Program by
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