High-resolution solar absorption spectra obtained from Table Mountain Facility (TMF, 34.3S0N, 1 17.68OW, 2286 m elevation) have been analyzed in the region of the 0 2 A-band. The photon paths of direct sunlight in clear sky cases are retrieved from the 0 2 absorption lines and compared with ray-tracing calculations based on the solar zenith angle and surface pressure. At a given zenith angle, the ratios of retrieved to geometrically derived photon paths are highly precise (-0.2%), but they vary as the zenith angle changes. This is because current models of the spectral lineshape in this band do not properly account for the significant absorption that exists far from the centers of saturated lines. For example, use of a Voigt function with Lorentzian far wings results in an error in the retrieved photon path of as much as 5%, highly correlated with solar zenith angle. Adopting a super-Lorentz function reduces, but does not completely eliminate this problem. New lab measurements of the lineshape are required to make further progress.

A compact, high-resolution Fourier-transform spectrometer for atmospheric near-ultraviolet spectroscopy has been installed at the Jet Propulsion Laboratory's Table Mountain Facility ͑34.4°N, 117.7°W, elevation 2290 m͒. This instrument is designed with an unapodized resolving power near 500,000 at 300 nm to provide high-resolution spectra from 290 to 675 nm for the quantification of column abundances of trace atmospheric species. The measurement technique used is spectral analysis of molecular absorptions of solar radiation. The instrument, accompanying systems designs, and results of the atmospheric hydroxyl column observations are described.

Helium in the Earth's thermosphere traces the dynamical systems that redistribute energy and mass. Measurements of the global helium distribution in the thermosphere, using Atmosphere Explorer satellite C. (A&C), show a gradual seasonal change in the number density of helium for all latitudes. The enhancement in helium over the winter pole (the helium bulge) changes in magnitude slowly as seasons progress. The bulge builds and recedes following the progression of winter North to South and back again. This progression of the winter helium enhancement is presented in this paper using latitudinal profiles of helium number density for each month during the year. The absolute magnitude of the winter helium enhancement in the aurora1 regions is affected by aurora1 heating at low altitudes. The reduction in the winter helium bul~eatlowaItitudesshownin~~-Cdata~an betraced tothisio~ali~edbeating.Thegradua~~ari~ltion in helium concentration measured at many latitudes for all seasons of the year implies that global thermosph~ric wind systems change gradually with the seasons,

The column abundance of OH over Table Mountain Facility, California, (TMF) has been measured regularly since July 1997 using the Fourier‐transform Ultraviolet Spectrometer. The annual average OH column observed for 1998–2000 is 10–20% larger than that observed by another group over Tokyo for 1992–1995; 30–65% smaller than that observed by other groups over Colorado and New Mexico for 1980–1996; and 15–30% smaller than calculated by photochemical models. The Tokyo annual average and model estimates are within the range of geophysical variability for the OH column observed over TMF but the Colorado and New Mexico annual averages are not. This suggests the possibility of systematic errors in one or more of the data sets.

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