He specializes in stratospheric processes including wave dynamics, ozone depletion and trace gas transport. He has over 228 refereed publications. over 8600 citations in atmospheric science journals (Hirsch Index 51) and one patent. He retired from NASA in 2009. He was previously the Aura and UARS Project Scientist. He is a Fellow of the American Geophysical Union (1996), the American Association for the Advancement of Science (1996), and the American Meteorological Society (1996). He was awarded Goddard’s William Nordberg Memorial Award for Earth Sciences (1998), NASA's Exceptional Scientific Achievement Medal (1991), NASA’s Outstanding Leadership Medal (1996), Distinguished Service Award (2000), the William Pecora Award in 2002 and 2006, and the Presidential Rank Award in 2005.