Lockheed Martin Solar & Astrophysics Lab, 3251 Hanover St., Org. ADBS, B. 252, San Francisco, CA 94304, USA
Space and Atmosphere Research Center Department of Applied Math University of Sheffield, Hounsfield Road Hicks Building, Sheffield, S3 7RH UK United Kingdom
School of Mathematics and Statistics University of St. Andrews, North Haugh, St. Andrews, KY16 9ss United Kingdom
Lockheed Martin Solar & Astrophysics Lab, 3251 Hanover St., Org. ADBS, B. 252, San Francisco, CA 94304, USA