The researchers studied extremely cold months in south China over 45 years. They found that high geopotential in the north and low in the south of the Asian-Pacific region, along with meridional circulation, are common during severely cold months. Anomalies in the geopotential field were observed in the months leading up to the cold periods. Sea surface temperatures showed a continuous pattern leading up to the cold months, with El Niño in January and La Niña in February and December. The researchers concluded that they can predict severely cold winter months by analyzing the geopotential field at 500 hPa and sea surface temperatures in the months before.