The Nikkei stock index jumped over 2 percent Thursday morning as exporters were bought on a weaker yen against the U.S. dollar and semiconductor-linked shares got a boost from a stronger-than-expected earnings outlook by U.S. chip giant Micron Technology Inc. At 10:30 a.m., the 225-issue Nikkei Stock Average was up 796.17 points, or 2.10 percent, from Wednesday at 38,666.43. The broader Topix index was 43.08 points, or 1.63 percent, higher at 2,693.58.