The researchers studied the timing of summer monsoon rain in South China and its connection to winter atmospheric patterns and sea surface temperatures. They found that the starting date of the rain varies from year to year and over decades. Earlier rain is linked to stronger cold air in the preceding winter, while later rain is associated with warmer sea temperatures near the Okhotsk Sea. This affects the atmospheric circulation over China, with different wind patterns leading to either tropical or cold air dominating South China. The study suggests that winter conditions can influence the timing of summer monsoon rain in South China.