Severe Ice Conditions in the Bohai Sea, China, and Mild Ice Conditions in the Great Lakes during the 2009/10 Winter: Links to El Nino and a Strong Negative Arctic Oscillation

This study investigates the causes of severe ice conditions over the Bohai Sea, China, and mild ice cover over the North American Great Lakes under the same hemispheric climate patterns during the 2009/10 winter with a strong negative Arctic Oscillation (AO) and an El Nino event. The main cause of severe ice cover over the Bohai Sea was the strong negative AO. Six of seven winters with severe ice were associated with a strong negative AO during the period 1954-2010. The Siberian high (SH) in the 2009/10 winter was close to normal. The influence of El Nino on the Bohai Sea was not significant. In contrast, the mild ice conditions in the Great Lakes were mainly caused by the strong El Nino event. Although the negative AO generally produces significant colder surface air temperature (SAT) and heavy ice cover over the Great Lakes, when it coincided with a strong El Nino event during the 2009/10 winter the El Nino-induced Pacific-North America (PNA)-like pattern dominated the midlatitudes and was responsible for the flattening of the ridge-trough system over North America, leading to warmer-than-normal temperatures and mild ice conditions over the Great Lakes. This comparative study revealed that interannual variability of SAT in North America, including the Great Lakes, is effectively influenced by El Nino events through a PNA or PNA-like pattern whereas the interannual variability of SAT in northeastern China, including the Bohai Sea area, was mainly controlled by AO and SH.