The weather in the south is different from that in the north

The weather in the south is different from that in the north.南方天气和北方天气不一样.不是定语从句,that在里面是代词,代 the weather.定语从句在句中做定语,修饰一个名词或代词,被修饰的名词,词组或代词即先行词.定语从句通常出现在先行词之后,由关系词（关系代词或关系副词）引出.He is the man that I saw yesterday.他就是我昨天见的那个人.这是个定语从句,that 在从句中做宾语.