The Halogen Occultation Experiment

TLDR

HALOE, launched on UARS in September 1991, used solar occultation to obtain 1.6 km‑resolution vertical profiles of O₃, HCl, HF, CH₄, H₂O, NO, NO₂, aerosols, and temperature from ~15 km to 60–130 km across 80°S–80°N over a year. HALOE operations were flawless, meeting all performance criteria, and its data confirmed known atmospheric features while providing the first global distributions of HCl, HF, and NO, revealing dehydration in the Antarctic lower stratosphere, a tropical water‑vapor hygropause, and Antarctic air in the tropics.

Abstract

The Halogen Occultation Experiment (HALOE) was launched on the Upper Atmosphere Research Satellite (UARS) spacecraft September 12, 1991, and after a period of outgassing, it began science observations October 11. The experiment uses solar occultation to measure vertical profiles of O 3 , HCl, HF, CH 4 , H 2 O, NO, NO 2 , aerosol extinction, and temperature versus pressure with an instantaneous vertical field of view of 1.6 km at the Earth limb. Latitudinal coverage is from 80°S to 80°N over the course of 1 year and includes extensive observations of the Antarctic region during spring. The altitude range of the measurements extends from about 15 km to ≈ 60–130 km, depending on channel. Experiment operations have been essentially flawless, and all performance criteria either meet or exceed specifications. Internal data consistency checks, comparisons with correlative measurements, and qualitative comparisons with 1985 atmospheric trace molecule spectroscopy (ATMOS) results are in good agreement. Examples of pressure versus latitude cross sections and a global orthographic projection for the September 21 to October 15, 1992, period show the utility of CH 4 , HF, and H 2 O as tracers, the occurrence of dehydration in the Antarctic lower stratosphere, the presence of the water vapor hygropause in the tropics, evidence of Antarctic air in the tropics, the influence of Hadley tropical upwelling, and the first global distribution of HCl, HF, and NO throughout the stratosphere. Nitric oxide measurements extend through the lower thermosphere.