问嵌套函数中的Javascript变量值

EN

{
  "success":true,
  "days":[
     {
        "date":"2,March 2013",
        "posts":[
           {
              "post_id":"10",
              "post_title":"tgfkyhhj",
              "created_on":"2013-03-02 21:24:17",
              "time":"09:24 PM"
           }
        ]
     } 
  ] 
}

function archivePostMonth(month) {
    var days; 
    $.ajax({
        'type' : 'get',
        'url' : base_url + 'index.php/blog/blogArchiveMonth',
        'data' : {
            'blogId' : blogId,
            'month' : month,
        },
        success : function(response) {
            var res = jQuery.parseJSON(response);
            if (res.success == true) {
                console.log(res.days); //displays the data
                days = res.days;
                console.log(days); // displays the data
            }
        }
    });
    console.log(days); //undefined
    return days; // returns undefined
}