Statistical Characteristics of Wintertime Extra-Tropical Anticyclone Activity in the Northern Hemisphere

Based on the NCEP/NCAR reanalysis dataset of sea level pressure and winds for the period 1948-2013, temporal and spatial distribution and period and lifespan characteristics of wintertime extra-tropical anticyclone activity in the Northern Hemisphere were presented in this study using objective identification method and tracking algorithm. The results show that the wintertime extra-tropical anticyclones in the Northern Hemisphere are active mainly in the Northeast Pacific, the North Atlantic, the eastern Rocky Mountains and eastern United States, Europe, and Central and East Asia. The genesis regions of anticyclones in the Pacific and the Atlantic are dispersed. Most anticyclones originally form in the western part of the ocean, become mature in the middle and eastern parts of the ocean, and decay in the eastern part of the ocean and western coasts of the continents. The difference in the region of lysis of anticyclone between the Pacific and the Atlantic Ocean is that, the large value area of lysis is a belt extending from the middle of the Atlantic to the western coast of Europe in the Atlantic along the southwest-northeast direction, while in the Pacific Ocean the two large value areas of lysis are distributed separately. Over the continent, anticyclones mostly occur in the high latitudes and polar regions, and move eastward or southeastward. It is found that the frequency and intensity, and the mean latitude and latitudinal range of the moving trajectories of anticyclones have different interannual and interdecadal variabilities in different regions. The occurrence frequency of anticyclones shows a significant period of 2-3 years in most part of the Northern Hemisphere, and a significant period of 16-18 years in Eurasia. As the anticyclone intensity increases, its trajectory becomes further northward in all regions except Eurasia. In North America, the stronger the anticyclone is, the greater the mean latitudinal range will be. On the contrary, the anticyclone intensification is often accompanied with a smaller latitudinal range in Eurasia. The occurrence frequency of anticyclones decreases rapidly with longer lifespan, and less than 10% of the total anticyclones can last for more than one week.