Anomalies And Their Mechanism Of Teleconnection Among Atmospheric Centers Of Action During Boreal Winter

An atmospheric center of action(ACA) is defined as a spatially extensive high-pressure or low-pressure system in the monthly mean sea level pressure (SLP) field, stagnating over a specific geographic area throughout the year and/or season. Seasonal variations of ACA determine the seasonality of the regional climate. The anomaly and teleconnection of ACA are closely related with atmospheric circulation and regional climate anomalies. Therefore, ACA is an important research subject of the atmospheric circulation anomalies and short-term climate prediction. The members and characteristics of ACA over the Northern Hemisphere are identified using Hadley monthly mean SLP dataset (from1850to2009). The circulation indices (area S, the intensity P, the center position) with clear physical meaning of5ACAs are defined and calculated for winter season over the Northern Hemisphere, and their climatic and abnormal features of ACA are preliminarily analyzed. On this basis, the climatic effects of the ACA, teleconnection between ACAs and the relationship between the abnormal teleconnection of ACA and abnormal heat source-sink of atmospheric heat engine are researched, through which more systematic and more in-depth understanding of the ACA for winter over the Northern Hemisphere are obtained. The main conclusions are as follows:1)There are6ACAs over the Northern Hemisphere demonstrated by reliable data, including Icelandic low(LI) and North Atlantic subtropical high (HA) over the North Atlantic, Aleutian Low (LA) and North Pacific subtropical high (HP) over the North Pacific, together with Mongolian high (HM) and India low(LIN) over the Asian continent. Among them, LI, HM, LA at the high latitudes throughout the winter season and LIN at the low latitudes throughout the summer season are semi-permanent ACAs. HA and HP in low-latitude ocean throughout the year are permanent ACAs, or quasi-permanent ACAs (Winter weak).2) The seasonal and monthly Circulation Indices (S、P、λc、φc) of five ACAs (LI, HA, HM, LA, HP) from1850to2009are calculated by uniform definitions and calculation methods, based on reliable data. The climatic and abnormal characteristics of the ACA are quantitatively analyzed and the reasonableness is demonstrated by the three independent Circulation Indices (P、λc、φc). Thus, a set of application value circulation indices are provided for atmospheric circulation anomaly and short-term climate prediction research.3) It is demonstrated that the ACA significantly affects the climate and anomaly at the location and the surrounding area, according with the synoptic dynamics significance. The impact area of ACA on climate is much larger on the ocean than on the continent. The impact on climate from ACA intensity anomalies is greater than from its position anomalies. The impact on temperatures is greater than on precipitation from ACA anomalies. The impacts of LI and HA over the North Atlantic on climate anomalies in both the properties and the distribution areas are very similar, while the impact on properties of climate anomalies is nearly opposite. HM is the main ACA that affects China’s winter climate and anomalies. In winter, the temperature is lower on China (except Southwest Region) and precipitation over Sichuan and some areas of North China is more on the positive phase of HM. LI and HA, which located on the upstream of China, are the secondary ACAs that affects on China’s winter climate and anomalies. When LI and HA are stronger, the temperature is higher over China’s’Three North’parts. The impacts of LA and HP on China climate anomalies are relatively weak.4) It is revealed that there are three significant teleconnections among five ACAs in winter over the Northern Hemisphere, which are LI-HA, LI-HM and LA-HP. LI-HA is the North Atlantic Oscillation (NAO). LI-HM and LA-HP are newly defined teleconnections. The intensity of LI’s (LA’s) and HM’s (HP’s) is negatively correlated. The teleconnections among ACAs in winter over the Northern Hemisphere are divided into two relatively independent systems:(1) the North Atlantic/Eurasia teleconnection system consists of LI-HA and LI-HM, and (2) North Pacific teleconnection system includes only LA-HP. Winter season atmospheric circulation and climate anomalies in China are mainly influenced by the North Atlantic/Eurasia teleconnection system.5) The relationships among climate anomalies, teleconnections of ACAs, and Ocean external forcing can be summarized as follows:(1) Sea ice anomalies at high-latitude mainly affect the North Atlantic/Eurasia teleconnection system. When sea ice is above normal, polar vortex is stronger, HM is weaker, LI is stronger and shifts southward, and NAO is stronger. LA and HP over the North Pacific have no obvious anomalies.(2) SST anomalies over tropical central East Pacific mainly affect teleconnection system over the North Pacific. Positive SST anomalies over tropical central East Pacific cause LA strengthening and HP weakening, and the sinking branch of Hadley circulation associated with HP move southward and become weaker.6) CCSM4can qualitatively simulate the teleconnections of ACA in comparison to observations. However, role of the tropical ocean as external forcing is overemphasized in the simulations for controlling ACA anomoalies and teleconnection. Forcing mechanism due to sea ice at high-latitude and polar vortex is under estimated in model simulations, as compared with observed data.