1. Xiaofeng Shao is Assistant Professor and Xianyang Zhang is Ph.D. Candidate, Department of Statistics, University of Illinois at Urbana–Champaign, Champaign, IL 61820. We are grateful to the two referees and Zhibiao Zhao for detailed comments, which led to substantial improvements. We thank Wei Biao Wu for providing Argentina rainfall data used in this paper. The research is supported in part by NSF grants DMS-0804937 and DMS-0724752.