The Dynamics Of Eurasian Teleconnection Pattern And Its Influence On Climate Anomalies Over China

It is a well-established fact that Eurasian teleconnection pattern (EU) is one of the most important low frequency mode in Northern Hemisphere winter science it has great influence on climate anomalies over Eurasian region. Based on the monthly mean and daily NCEP/NCAR reanalysis dataset and the surface air temperature and precipitation data form 756 China stations, the interannual and interdecadal variations of EU pattern are investigated. The associated circulation feature over East Asian is analyzed as well as the important influence of EU on East Asian upper-level jet is also revealed. Furthermore, we exhibit the life cycle of EU and dynamic process in the growth and decay period of EU pattern. We also discuss the role configuration of polar front jet and subtropical jet in the relationship between EU and climate anomalies over China. The main results are as follows:1 Interannual and interdecadal variation of Eurasian teleconnection patternThe significant period of EU pattern is 2.6 years,3.5years and 20 years which indicate that EU pattern has obvious interannual and interdecadal variation. The variance in January is largest among the three months in winter. The horizontal structure of EU pattern shows minus-plus-minus wave train in 500 hPa level in positive EU phase. Negative phase is opposite. In vertical direction, the geopotential anomalies show barotropic structure below 300 hPa while the anomalies show a little tile above that level. In positive phase, the East Asian polar front jet reduces and moves more polarward. The East Asian subtropical jet over Pacific accelerates obviously. Positive EU phase is accompanied with deepened East Asuab trough, strong Siberian High and Aleutian Low. The circulation feature is opposite in negative phase.The orientation of East Asian trough is northeast-southwest in positive and north-south in negative. EU pattern shows significant negative correlation with polar front jet zonal wind index but is negative correlated with meridoinal wing in polar front jet. The variation of meridional wind in polar front jet region is important in the climate effect of EU pattern.2 Evolution of Eurasian teleconnection pattern and its relationship to climate anomalies in ChinaThe Eurasian teleconnection pattern (EU) is a major mode of low-frequency variability in the Northern Hemisphere winter, with notable impacts on Eurasia temperature and precipitation. To investigate the structure, life cycle and dynamical mechanisms of EU pattern, diagnostic analyses are conducted to clarify EU pattern evolution, with an emphasis on EU development and decay. In the developing stage, a geopotential height anomaly over North Atlantic emerges 6 days before EU peak phase and other three geopotential height anomalies appear one by one in the following days. During this period, all geopotential height anomalies experience considerable growth and the four-center structure of EU pattern forms two days before peak phase. The obvious wave train structure appears in 300 hPa level. EU pattern growth is driven by both relative vorticity advection and transient eddy fluxes. After the peak phase, the geopotential height anomaly over North Atlantic becomes weak as it decays earlier than other anomaly centers, which leads to the classic three-center structure of EU teleconnection pattern. The complete life cycle of EU pattern experience considerable growth and decay within 10 days. During the decaying stage, the horizontal divergence and the transient eddy fluxes play important roles. Additionally, the relationship of EU pattern to winter climate anomalies in China is also analyzed focusing on the decaying stage. The impact of EU pattern on temperature and precipitation in China are significant in 2 to 4 days after EU peak phase and the distribution of temperature and precipitation anomaly has obvious regional differences.3 Connections between Eurasian teleconnection and concurrent variation of the upper-level jets over East AsiaThe variation of East Asian jet streams (EAJS) associated with Eurasian teleconnection (EU) pattern is investigated with the use of 60-yr (1951-2010) NCEP/NCAR daily reanalysis dataset. The EAJS consists of three parts:polar front jet (PFJ), plateau subtropical jet (PSJ) and ocean subtropical jet (OSJ). Among the three jets over East Asia, the EU pattern exhibits significant influence on PFJ and OSJ. There is a negative correlation between EU pattern and PFJ simultaneously, while a significant positive correlation is found between EU pattern and OSJ, with EU leading OSJ by about 5 days. But there is no obvious correlation between EU pattern and PSJ. Positive EU phase is accompanied by a weaker and more poleward-intruding PFJ which coincides with an intensified OSJ. Meanwhile, the PFJ also moves westward, and OSJ migrates eastward. In negative EU phase, PFJ is unusually strong and moves more southward, resulting in unclear separation between PFJ and SJ. A possible mechanism for the variation of EAJS during different EU phases is also examined through analyzing the effects of 10-day high-and low-frequency eddy forcing. The zonal wind tendency due to high-frequency eddy forcing contributes to the simultaneous negative correlation between EU and PFJ as well as the north-south shift of PFJ. Low-frequency eddy forcing is responsible for the west-east shift of PFJ in company with the evolution of EU. High- and low-frequency eddy forcings are both responsible for the positive correlation between EU and OSJ but only high-frequency eddy contributes to the lag variation of OSJ. The concurrent variation between PFJ and OSJ is important in linking the EU signal to climate anomalies in China. The negative correlation between EU and temperature/precipitation anomalies in north/east China sustains only when PFJ and OSJ is out of phase.4 Relationship between EU pattern and cold surge over ChinaCold surge is defined by the day-to-day variation of surface temperature and the strength of Siberian High. This section analyzes the time and space evolution of the occurrence of cold surge over China. From 1955 to 2010, there are 709 cold surges and 238 strong cold surges. The occurrence frequency of cold surge is large before 1971. An obvious decrease of occurrence frequency appears until 2007 and an increase appears in recent years. More cold surge occurs over Xingjiang, Innor Mogolia and costal of China. When cold surge happens, the Siberian High becomes stronger, surface temperature over East Asian drops, East Asian trough deepens, subtropical jet gets stronger and polar front jet gets weaker. The occurrence frequency of cold is well related to the phase of EU pattern. There are 172 cold surges appears in positive phase and 59 cold surges in negative phase. The comparation of cold surge in positive and negative EU phase indicates that the circulation in positive phase is more convenient for the occurrence of cold surge.