Halley Bay (75.5øS, 26.8øW) that has occurred annually since the mid-1970s in September and October. This Antarctic ozone "hole" which is characterized by 50% or more decreases in column ozone has now been extensively studied using satellite, aircraft, and ground-based instruments. In addition, further analyses of satellite and ground-based Dobson data have shown northern hemisphere (30øN to 64øN) The Halogen Occultation Experiment (HALOE) was conceived to provide critical data for study of the ozone distribution and those processes which affect ozone levels. The experiment uses the principle of satellite solar occultation to sound the stratosphere, mesosphere, and lower thermosphere. Using this technique, absorption of solar energy in selected spectral bands is used to infer vertical profiles of temperature, pressure, and mixing ratios of key gases involved in the ozone chemistry. The HALOE instrument includes both broadband and gas filter channels Together, these observations form a minimum but adequate set which can be used to derive, under appropriate conditions, the unmeasured concentrations of several other gases needed to test understanding of the chemistry (see Figure 1). In this regard, HALOE 03, H20, and CH4 measurements, for example, can be used to derive OH levels. In turn, these parameters can be used to derive atomic chlorine and, from that, C10 through reactions with 03. Chlorine monoxide can be used with NO2 observations to derive chlorine nitrate (C1ONO2). Since C10

The HALogen Occultation Experiment (HALOE) instrument on UARS observes vertical profiles of ozone and other gases of interest for atmospheric chemistry using the solar occultation technique. A broadband radiometer in the 9.6-ttm band is used for ozone measurements. Version 17 ozone retrieved by HALOE is intercompared successfully with about 400 profiles of other sounders, including ozonesondes, lidars, balloons, rocketsondes, and other satellites. Usually, the HALOE data are within the error range of the correlative measurements between about 100 and 0.03 mbar atmospheric pressure. Between about 30 and 1 mbar, HALOE agrees typically within 5%, with a tendency to be low. In the first year of data, larger errors sometimes occur in the lower stratosphere due to the necessary correction for Pinatubo aerosol effects, but these differences do not exceed 20%. The data show internal consistency for sunrise and sunset events at the same locations. Some examples of observed ozone distributions, including polar regions, are given.

Global distributions of CH 4 in the mesosphere and stratosphere have been measured continuously since October 11, 1991, by the Halogen Occultation Experiment (HALOE) onboard the UARS. CH 4 mixing ratio is obtained using the gas filter correlation technique operating in the 3.3-grn region. Since measurements are made during solar occultation in the 57 ø inclination orbit, data are collected 15 times daily for both sunrises and sunsets. This provides coverage of one hemisphere in a month period. One complete hemispheric sweep (from equator to -80 ø latitude) is made during the spring and summer seasons of two hemispheres, and a partial sweep (from equator to around 50 ø latitude) is made during the fall and winter seasons of two hemispheres. HALOE CH 4 measurements are validated using direct comparisons with correlative data and internal consistency checks using other HALOE-measured tracers, HF, and aerosols. It is estimated for the 0.3-to 50-mbar region that the total error, including systematic and random components, is less than 15 % and that the precision is better than 7%. The CH4 gas filter channel does not depend significantly on the Pinatubo aerosol extinction. An experimentally accurate measurement of CH 4 is very important because CH 4 is a primary interfering gas in the HALOE HC1 channel and, subsequently, can cause HC1 measurement error. Simultaneous measurements of CH4 and other HALOE species (03, H20, NO, NO2, HC1, HF, and aerosol extinction coefficients) provide important information on atmospheric dynamic and chemical processes, since CH4 can be used as a tracer and an indicator of atmospheric transport processes. Several new pieces of infolsnation on previously unreported HALOE-observed features are also presented. Introduction Atmospheric methane, CH 4, naturally produced and released from the surface, has an important role in the greenhouse effect, causing a global warming, and in atmospheric chemistry, by removing hydroxyl radicals in the troposphere and in the stratosphere by converting reactive chlorine atoms to HC1 and producing hydrogen species to form water vapor by oxidation (see summary [World Meteorological Organization (WMO), 1982]). Methane can be used as a tracer to study atmospheric transport processes when enough measurements are made on a regional or global scale. For example, the features of CH 4 and other species observed by the Halogen Occultation Experiment (HALOE) were reported by Russell et al. [1993a] for the springtime Antarctic and by Park and Russell [1994] for the summertime polar region. Both papers used CH 4 as a tracer, and in the latter paper it was used to separate dynamical effects and to assess the importance of chemical processes for ozone deficiency in the polar regions. Methane measurements in the stratosphere before the Upper Atmosphere Research Satellite (UARS) [Reber, 1993] include the 1979 global measurements by stratospheric and mesospheric sounder (SAMS) on Nimbus 7 [Rodgers et al., 1984] and otherwise sparse individual profiles obtained by in situ sampli...

computational procedure is described to evaluate the Voigt function with a maximum relative error of about one part in IO', for use in line-by-line transmittance calculations and other applications. An efficient Fortran IV subprogram is given in the Appendix. OUTLINE OF COMPUTATIONAL PROCEDURE ATMOSPHERIC transmittance calculations for regions in which both Doppler and Lorentz line broadening are important require the evaluation of the Voigt profile function, viz.

The Halogen Occultation Experiment (HALOE) onboard UARS measures profiles of limb path solar attenuation in eight infrared bands. These measurements are used to infer profiles of temperature, gas mixing ratios of seven species, and aerosol extinction at five wavelengths. The objective of this paper is to validate profiles of temperature retrieved from atmospheric transmission measurements in the 2.80-gm CO2 band. Temperatures are retrieved for levels above where aerosol affects the signals (35 km) to altitudes where the signal-to-noise decreases to unity (--85 km). At altitudes from 45 to 35 km the profile undergoes a gradual transition from retrieved to National Meteorological Center (NMC) temperatures and below 35 km the profile is strictly from the NMC. This validation covers the uncertainty analysis, internal validations, and comparisons with independent measurements. Monte Carlo calculations using all known random and systematic errors determine typical measurement uncertainties of 5 K for altitudes below 80 km. Comparisons of coincident HALOE sunrise and sunset measurements are an indicator of the upper limit of measurement uncertainty. The sunrise-sunset comparisons have random and systematic differences which are less than 10 K for altitudes below 80 km. Comparisons of HALOE to lidar and rocket measurements typically have random differences of •-5 K for altitudes below 65 km. The mean differences for the correlative comparisons indicate that HALOE temperatures have a cold bias (2 to 5 K) in the upper stratosphere and stratopause. 10,277 :.. t. ... jAiNDOM ß DIFFERENCE ß ß ß ß ß ß ,.