1. Statistics Department, North Carolina State University (NCSU), Raleigh, NC 27695–8203, USA. E‐mail: .
2. University of Washington, Seattle, WA 98195–4322, USA. E‐mail: .
3. James Rennell Division for Ocean Circulation and Climate, Southampton Oceanography Centre, Southampton, SO14 3ZH, UK. E‐mail: