核心问题
（1）Most of North and South China will have a cold wet day.
(2) The Shute family lived in the southern part of the USA.
south 和 southern 都可用作形容词, 它们有无区别呢?
词典解答
有人提出一个大体的使用趋势: 当明确地划定地域范围或政治范围时, 使用 south, north, west, east。例如 South Africa(南非), South America(南美), North America(北美), South China(华南), North Pole(北极); 当对地域不作明确的划分时, 则使用 southern, northern, western, eastern, 例如, Southern Africa(南部非洲), Southern England(英国南部), the northern climate(北方气候), the western United States(美国西部), eastern customs(东方的习俗)。但是, 上述说法并不是绝对严格的使用规则。例如, 北美是 North America, 而北欧却是 Northern Europe。