The seasonal evolution and spatial distribution of upper tropospheric tropical cirrus have been analyzed using a 19-month record of infrared aerosol volume absorption coefficients obtained by the Cryogenic Limb Array Etalon Spectrometer (CLAES) aboard the Upper Atmosphere Research Satellite (UARS). An empirical method of separating clouds from background volcanic aerosol is described. Cloud occurrence frequencies are compared with the Stratospheric Aerosol and Gas Experiment (SAGE) II cloud climatology of Wang et al. [1996]. The seasonal distribution of clouds derived from CLAES agrees well with the SAGE II results that show predominantly subvisual cirrus in this region. This agreement demonstrates that CLAES data contain information describing subvisual cirrus in addition to thicker clouds. Examples of interannual variations in cloud occurrence frequency observable in the CLAES data are discussed. The eastward shift in cloud occurrence frequency over the western Pacific accompanying the 1992 El Nino was observed. Substantially fewer cirrus were seen at the 68-hPa level in the winter of 1991-1992 compared with 1992-1993. This variation could be related to either El Nino or reduced convection during a period when Mount Pinatubo stratospheric aerosol cooled the tropics.

CH4 and N2O are useful as dynamical tracers of stratospheric air transport because of their long photochemical lifetimes over a wide range of altitudes. The cryogenic limb array etalon spectrometer (CLAES) instrument on the NASA UARS provided simultaneous global measurements of the altitude profiles of CH4 and N2O mixing ratios in the stratosphere between October 1, 1991, and May 5, 1993. Data between January 9, 1992, and May 5, 1993 (388 days), have been processed using version 7 data processing software, and this paper is concerned with the assessment of the quality of this data set. CLAES is a limb‐viewing emission instrument, and approximately 1200 profiles were obtained each 24‐hour period for each constituent over a nominal altitude range of 100 to 0.1 mbar (16 to 64 km). Each latitude was sampled 30 times per day between latitudes 34°S and 80°N, or 34°N and 80°S depending on the yaw direction of the UARS, and nearly all local times were sampled in about 36 days. This data set extends the altitude, latitude, and seasonal coverage of previous experiments, particularly in relation to measurements at high winter latitudes. To arrive at estimates of experiment error, we compared CLAES profiles for both gases with a wide variety of correlative data from ground‐based, rocket, aircraft, balloon, and space‐borne sensors, looked at the repeatability of multiple profiles in the same location, and carried out empirical estimates of experiment error based on knowledge of instrument characteristics. These analyses indicate an average single‐profile CH4 systematic error of about 15% between 46 and 0.46 mbar, with CLAES biased high. The CH4 random error over this range is 0.08 to 0.05 parts per million, which translates to about 7% in the midstratosphere. For N2O the indicated systematic error is less than 15% at all altitudes between 68 and 2 mbar, with CLAES tending to be high below 6.8 mbar and low above. The N2O random error is 20 to 5 ppb between 46 and 2 mbar, which also translates to 7% in the low to midstratosphere. Both tracers have useful profile information to as low as 68 mbar, excluding the tropics, and as high as 0.2 mbar (CH4) and 1 mbar (N2O). The global fields show generally good spatial correlation and exhibit the major morphological and seasonal features seen in previous global field data. Several morphological features are pointed out for regions and conditions for which there have been essentially no previous data. These include the differential behavior of the tracer isopleths near and inside the Antarctic winter vortex, and local maxima in the tropics in 1992, probably associated with the Mount Pinatubo sulfate aerosol layer. Overall, the results of this validation exercise indicate that the version 7 CH4 and N2O data sets can be used with good confidence for quantitative and qualitative studies of stratospheric and lower‐mesospheric atmospheric structure and dynamics.

The cryogenic limb array etalon spectrometer (CLAES) aboard UARS made near‐global measurements of HNO 3 and 388 days from January 9, 1992, to April 25, 1993, have been processed to data version 7 (V7). Results from UARS instruments, including CLAES, the improved stratospheric and mesospheric sounder, and the microwave limb sounder, provide the first near‐global documentation of the evolution of denitrification in the Antarctic 1992 winter and spring vortex. We provide a description of the CLAES HNO 3 V7 quality that includes comparisons with correlative measurements to assess overall quality, accuracy, and precision. Correlative profiles of volume mixing ratio (vmr) included those obtained by the space shuttle deployed ATMOS in two missions, March–April 1992 and April 1993, data from a variety of balloon‐borne instruments at midlatitude (11 profiles), and in high‐latitude northern winter (six profiles), and LIMS data. In general, the CLAES V7 HNO 3 maximum values of vmr were of the order of 6–15% less than correlative for CLAES values ≤8 parts per billion by volume (ppbv). However, when CLAES peak vmr values were 10 to 13 ppbv, then CLAES values exceeded correlative by 0–7%. The comparisons were within the combined instrumental error estimates, or observed measurement variability, for the large majority of comparisons. As discussed, the retrieval of future versions will utilize updated spectral parameters and will also correct for a small uncompensated drift in radiometric calibration that occurred in the latter part of the mission. This is expected to improve the comparisons in the ≤8 ppbv range, perhaps at the expense of those in the ≥8 ppbv range. The data obtained January 9 to April 15, 1992, in comparison with data obtained January 9 to April 15, 1993, reveal strikingly evident 1‐year period deseasonalized trends on a global basis. These trends agree quantitatively with available correlative data suitable for trend analysis. These include ATMOS in the southern midlatitudes and published long‐term time series of HNO 3 column obtained at 45°S and 20°N. These trends reveal a large decrease in the southern hemisphere and small increases in the northern hemisphere, such that the global average is toward a decrease. The global average decrease we attribute to the diminishing influence of heterogeneous conversion of N 2 O 5 to HNO 3 as the Pinatubo aerosol settles out during this time period, and the HNO 3 recovers toward pre‐Pinatubo conditions. We establish plausibility that the small increases in the north are due to hemispherically asymmetric QBO‐like effects that are strong in the northern hemisphere and weak in the southern hemisphere and are phased to produce an increase in HNO 3 over the 1‐year time period of just the right magnitude to more than offset decrease due to settling out of the Pinatubo aerosol. Based on this study, our range of confidence in the CLAES HNO 3 V7 product is from 70 to 3 mbar, in comparison with correlative data, and the precision on this range is of the order of 0.3–1.0 ppbv. This precision was derived from data repeatability and agrees within a factor of 2 or better with estimates based on instrument characterization and with error estimates embedded within the V7 data.

CH 4 and N20 are useful as dynamical tracers of stratospheric air transport because of their long photochemical lifetimes over a wide range of altitudes. The cryogenic limb array etalon spectrometer (CLAES) instrument on the NASA UARS provided simultaneous global measurements of the altitude profiles of CH 4 and N20 mixing ratios in the stratosphere between October 1, 1991, and May 5, 1993. Data between January 9, 1992, and May 5, 1993 (388 days), have been processed using version 7 data processing software, and this paper is concerned with the assessment of the quality of this data set. CLAES is a limb-viewing emission instrument, and approximately 1200 profiles were obtained each 24-hour period for each constituent over a nominal altitude range of 100 to 0.1 mbar (16 to 64 km). Each latitude was sampled 30 times per day between latitudes 34øS and 80øN, or 34øN and 80øS depending on the yaw direction of the UARS, and nearly all local times were sampled in about 36 days. This data set extends the altitude, latitude, and seasonal coverage of previous experiments, particularly in relation to measurements at high winter latitudes. To arrive at estimates of experiment error, we compared CLAES profiles for both gases with a wide variety of correlative data from ground-based, rocket, aircraft, balloon, and space-borne sensors, looked at the repeatability of multiple profiles in the same location, and carried out empirical estimates of experiment error based on knowledge of instrument characteristics. These analyses indicate an average single-profile CH 4 systematic error of about 15% between 46 and 0.46 mbar, with CLAES biased high. The CH 4 random error over this range is 0.08 to 0.05 parts per million, which translates to about 7% in the midstratosphere. For N20 the indicated systematic error is less than 15% at all altitudes between 68 and 2 mbar, with CLAES tending to be high below 6.8 mbar and low above. The N20 random error is 20 to 5 ppb between 46 and 2 mbar, which also translates to 7% in the low to midstratosphere. Both tracers have useful profile information to as low as 68 mbar, excluding the tropics, and as high as 0.2 mbar (CH4) and 1 mbar (N20). The global fields show generally good spatial correlation and exhibit the major morphological and seasonal features seen in previous global field data. Several morphological features are pointed out for regions and conditions for which there have been essentially no previous data. These include the differential behavior of the tracer isopleths near and inside the Antarctic winter vortex, and local maxima in the tropics in 1992, probably associated with the Mount Pinatubo sulfate aerosol layer. Overall, the results of this validation exercise indicate that the version 7 CH 4 and N20 data sets can be used with good confidence for quantitative and qualitative studies of stratospheric and lower-mesospheric atmospheric structure and dynamics.

This paper discusses simultaneous measurements of stratospheric ClONO2, HNO3, temperature, and aerosol extinction coefficient by the Cryogenic Limb Array Etalon Spectrometer (CLAES) on the NASA Upper Atmosphere Research Satellite (UARS), obtained over the period 9 January 1992 through 23 April 1993. The discussion concentrates on the stratosphere region near 21 km of particular interest to heterogeneously driven ozone depletion. For periods between 12 June and 1 September 1992 at latitudes poleward of about 60-degrees-S, when temperatures were below type I polar stratospheric cloud (PSC) formation thresholds throughout the lower stratosphere, CLAES observed high levels of PSCs coincident with highly depleted fields of both HNO3 and ClONO2. By 17 September, the incidence of PSCs had greatly diminished in the lower stratosphere, but both ClONO2 and HNO3 remained highly depleted. These observations are consistent with the removal of gaseous HNO3 through the formation of nitric acid trihydrate (NAT) particles and the removal of ClONO2 through heterogeneous reactions on the particle surfaces. They also suggest substantial denitrification of the lower Antarctic vortex through sedimentation of PSC particles. In the Northern Hemisphere winter of 1992/93 far fewer PSCs were observed in the Arctic lower-stratosphere vortex, which had shorter periods and more localized regions of cold temperatures. Both HNO3 and ClONO2 maintained much higher levels inside the Arctic vortex than those seen in the Antarctic throughout the winter/spring period. Following 28 February 1993 when Arctic vortex temperatures rose above 195 K, ClONO2 was observed in large quantities [> 2.1 ppbv near 21 km] inside the vortex. The persistence of relatively high levels of HNO3 inside the Arctic spring vortex compared with the low levels seen in the Antarctic spring vortex suggest a much lower level of denitrification in the Arctic.

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.

The Cryogenic Limb Array Etalon Spectrometer (CLAES) will derive Stratospheric temperatures and constituent number densities from the measurement of infrared spectral emissions, during its 18 month mission on board the NASA Upper Atmosphere Research Satellite (UARS). Overviews of the CLAES experiment and hardware are given by Roche et al (Ref 1) and Burriesci et al. (Ref 2). CLAES earthlimb spectral measurements consist of discrete narrow band spectral measurements within a spectral micro-window defined by a some what broader band blocker filter. The narrow spectral channels are of the order 0.2 to 0.6 cm-1, depending on spectral region. The blocker filter bands are of the order 3 to 12 cm-1. There are 9 blocker regions spaced across the range 3.5 to 12 micrometers wavelength. The blocker regions are selected for retrieval of HCI (~ 2843 cm-1), NO (~ 1897 cm-1), H2O and NO2 (~ 1605 cm-1), CH4, N2O, and N2O5 (~ 1257 cm-1), F12 (~925 cm-1), HNO3 (879 cm-1), F11 (843 cm-1), temperature (CO2) and 03 (~792 cm-1) and ClONO2 (780 cm-1).

Measurements of the optical refractive index structure coefficient Cn2 and the temperature structure coefficient CT2 were made over the Tularosa Basin of south central New Mexico using both tower and aircraft mounted instruments. The height dependence of CT2 agrees reasonably well with the predictions of similarity theory in the daytime. However, the nighttime profiles disagree significantly from the surface-layer predictions for z/L > 0.05. Two factors can explain this disagreement: 1) for strong stabilities, the boundary layer is not fully turbulent, and 2) in the absence of strong synoptic forcing, mountain drainage flows may modify the profiles. The magnitude of CT2 during the daytime is found to be closely correlated with the difference in temperature between the surface and the air; in addition, there is a small dependence on wind speed. Measurements of CT2 through the depth of the convective mixing layer during the day agree closely with the model of Kaimal et al. (1976). These results imply that a single measurement or estimate of CT2 in the surface layer can be used to estimate the average profile of CT2 up to the inversion height during the day.