CFSR降水量下载

矮油喂

下载CFSR月降水量资料时，有以下6个选项，请问是什么意思，我在计算年降水量的时候需要做怎样的处理呢，谢谢
Monthly Mean (4 per day) of 1-hour Accumulation (initial+Oto initial+1)
Monthly Mean (4 per day) of 2-hour Accumulation (initial+Oto initial+2)
Monthly Mean (4 per day) of 3-hour Accumulation (initial+Oto initial+3)
Monthly Mean (4 per day) of 4-hour Accumulation (initial+Oto initial+4)
Monthly Mean (4 per day) of 5-hour Accumulation (initial+Oto initial+5)
Monthly Mean (4 per day) of 6-hour Accumulation (initial+Oto initial+6)