摘要 : The recent paper by Chepfer and Noel [2009] (here-inafter referred to as CN09), analyzed measurements ofclouds in the tropical tropopause layer (TTL) by the lidaronboard the CALIPSO (Cloud-Aerosol Lidar and InfraredPathfinder Sate... 展开 The recent paper by Chepfer and Noel [2009] (here-inafter referred to as CN09), analyzed measurements ofclouds in the tropical tropopause layer (TTL) by the lidaronboard the CALIPSO (Cloud-Aerosol Lidar and InfraredPathfinder Satellite Observations) spacecraft. CN09 con-cluded that about 20% of the CALIPSO TTL cloud data hadthe optical characteristics of nitric acid trihydrate (NAT),and that NAT-like particles covered the entire tropical belt.Some earlier spaceborne observations of clouds in the TTLwere also interpreted as evidence of NAT, for example,backscatter data from the Lidar-In Space TechnologyExperiment (LITE) [Omar and Gardner, 2001] and extinc-tion data from the Halogen Occultation Experiment(HALOE) [Hervig and McHugh, 2002]. These earlier inter-pretations were challenged by Jensen and Drdla [2002](hereinafter referred to as JD02), whose Mie calculationsindicated there is insufficient HNO_3in the TTL to explainthe observed HALOE optical signature in terms of NATparticles. Furthermore, JD02 suggested that the observedwavelength dependence of LITE TTL cloud data could beexplained by a mixture of liquid aerosols and optically thincirrus, which produces an optical signature that could bemisinterpreted as small NAT particles. 收起