Impact of Pinatubo aerosol extinction on the Halogen Occultation Experiment (HALOE) infrared occultation measurements

Abstract

The use of limb radiation measurements to infer atmospheric parameters continues to be a popular technique. The HALOE (Halogen Occultation Experiment) instrument is a gas correlation radiometer on board the UARS (Upper Atmosphere Research Satellite) that performs solar occultation measurements for inferring vertical profiles of HF, HCl, CH 4 , NO, O 3 , H 2 O, NO 2 , aerosol extinction and temperature. The first four gases and aerosol are inferred from gas correlation measurements. The remainder are inferred from broadband (> 20 cm -1 ) radiometer measurements. The eruption of Mt. Pinatubo before the UARS launch presented a number of challenges for HALOE data processing. Although ideally the gas correlation technique is insensitive to aerosol, in practice the aerosol signature induces optical effects that must be accurately addressed. The inference of extinction profiles for modeling aerosol signature in the radiometer channels was found to require high vertical resolution. The impact due to vertical resolution and other optical effects on the retrieved results is discussed. Simulations and HALOE results are presented to demonstrate and validate the effects. It is found that the Pinatubo layering demands a vertical resolution on the order of 2 km or less to accurately model aerosol effects on broadband limb viewing radiometers.