The cryogenic limb array etalon spectrometer (CLAES) on UARS: Experiment description and performance

Abstract

The cryogenic limb array etalon spectrometer (CLAES) is one of 10 experiments launched in September 1991 on the NASA Upper Atmosphere Research Satellite (UARS). CLAES measures altitude profiles of temperature, pressure, O3, H2O, CH4, N2O, NO, NO2, N2O5, HNO3, ClONO2, HCl, CFC 11, CFC 12, and aerosol absorption coefficients. These data are obtained between 10 and 60 km with 2.5‐km vertical resolution and 500‐km horizontal grid size and between latitudes 80° north and south. Since CLAES actually measures infrared spectral earthlimb emissions, it can operate continuously throughout the diurnal cycle. The on‐orbit lifetime as dictated by stored cryogens which cool optics and detectors is estimated to be 21 months. The experiment will perform the first global mapping of stratospheric ClONO2, CFC 11, CFC 12, and N2O5, and these data, along with the simultaneous measurement of temperature and the other constituents listed above, should contribute to a significant improvement in our understanding of stratospheric and mesospheric photochemistry, radiative structure, and dynamics. CLAES began viewing the atmosphere in early October 1991, and the first several months of observations will be discussed. Examples of atmospheric spectral emission profiles for a number of constituents are presented as well as responsivity and noise parameters. These data show the instrument performance to be excellent and close to prelaunch predictions. An overview of the experiment and instrumentation is presented, various scientific observational modes are described, and the algorithms and software used to retrieve atmospheric parameters from emission spectra are discussed.

Intra-seasonal Oscillations (ISO) of zonal-mean meridional winds and temperatures as measured by UARS

“…These orbital parameters, combined with the measurement characteristics for the limbviewing atmospheric sensors, yield a measurement pattern that covers much of the globe on a daily basis. The instruments from which we use data here include the High Resolution Doppler Imager (HRDI; Hays et al, 1993), the Microwave Limb Sounder (MLS; Barath et al, 1993), and the Cryogenic Limb Array Etalon Spectrometer (CLAES; Roche et al, 1993). The CLAES and MLS instruments view the atmosphere at 90 • to the spacecraft velocity vector, and they can "see" over one orbit to 80 • latitude in one hemisphere and to 34 • in the other.…”

Cryogenic Limb Array Etalon Spectrometer observations of tropical cirrus

“…The instrument and operation have been described in detail by Roche et al [1993]. In brief, CLAES acquired mediumresolution spectra of infrared thermal emission from the Earth's limb in nine channels ranging from 3.5 to 12.8 /am, corresponding to the altitude range of approximately 10-60 km.…”

“…While the SAGE II data provide a good climatological description of thin cirrus, aerosol data from the Cryogenic Limb Array Etalon Spectrometer (CLAES) instrument on the Upper Atmosphere Research Satellite (UARS) [Roche et al, 1993] obtained in thermal amission provide an opportunity to observe thin cirrus with much more frequent, near-global sampling. Although CLAES was designed to observe the stratosphere, the lower-altitude limit of its observations was frequently below the tropopaus½, particularly in the tropics, where the tropopaus½ is high.…”

High Resolution Dynamics Limb Sounder observations of polar stratospheric clouds and subvisible cirrus

“…Subsequent solar occultation experiments, including the Stratospheric Aerosol and Gas Experiment (SAGE) [McCormick and Veiga, 1992], Polar Ozone and Aerosol Measurement (POAM) [Bevilacqua et al, 2002], and HALOE [Russell et al, 1993] experiments, have measured stratospheric aerosol and PSCs from 1978 through 2005. Emission limb sensors, such as the Cryogenic Limb Array Etalon Spectrometer (CLAES) [Roche et al, 1993] and Improved Stratospheric and Mesospheric Sounder (ISAMS) [Taylor et al, 1993], measured PSCs in the early 1990s, while the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is currently collecting PSC measurements [Spang et al, 2005]. Measurements of cirrus near the tropopause commenced with SAGE [Wang et al, 1996], and continued through 2005 with SAGE III [Kent et al, 2007] and HALOE observations.…”