Abstract:
In this study, the dominant modes of winter temperature over eastern China (to the east of 100°E) are analyzed using the monthly temperature data recorded at 160 stations in China, National Centers for Environmental Prediction (NCEP) reanalysis data, National Oceanic and Atmospheric Administration-Cooperative Institute for Research in Environmental Sciences (NOAA-CIRES) 20th century reanalysis data, and NOAA Sea Surface Temperature (SST) data. The formation mechanism and precursory signals for the second (dipole) mode are primarily studied. Moreover, the prediction method for the second mode is explored by using the winter of 2012-2013 as an example. The results indicate that in addition to the unanimously colder or warmer first mode, the dipole mode, which is characterized as a colder (warmer) region over northern China and to the east of 110°E accompanied by a warmer (colder) region over southern China and to the west of 110°E, is also a main mode dominating the region over eastern China. The winter of 2012-2013 belongs to the second mode. The first mode is related mainly to the SST anomalies in the tropical eastern and central Pacific, the snow cover anomalies over the northern Asian continent, and the sea ice concentration anomalies in the Arctic Ocean along northern Asia during the previous autumn. For the second (dipole) mode, the SST anomalies have no clear influence; however the snow cover anomalies over the middle latitudes over East Asia, the sea ice concentration anomalies from the Svalbard archipelago to the Franz Josef Land archipelago of the Arctic Ocean during the previous autumn, and the surface air temperature pattern of the Arctic Ocean-East Asian temperature contrast caused by the aforementioned snow cover and sea ice anomalies seem to be important. The previous autumn Arctic Ocean-East Asian temperature contrast (AE) index, which involves the synthesized signals of snow cover and sea ice concentration, is closely related to the second mode and should be considered as an important predictor. In the autumn of 2012, several previous signals, such as the normal SST state in the equatorial Eastern and central Pacific, the warmer surface air temperature over the Arctic Ocean, and the colder surface air temperature over the middle latitudes of East Asia, are not conducive to the first mode but are favorable for the second (northern-colder-southern-warmer) mode. By using the previous AE index, the anomalous temperature pattern over eastern China in the winter of 2012-2013 can be effectively predicted.