[1] The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument measured stratospheric temperatures and trace species concentrations with high precision and spatial resolution during two missions. The measuring technique is infrared limb-sounding of optically thin emissions. In a general approach, we investigate the applicability of the technique to measure gravity waves (GWs) in the retrieved temperature data. It is shown that GWs with wavelengths of the order of 100-200 km horizontally can be detected. The results are applicable to any instrument using the same technique. We discuss additional constraints inherent to the CRISTA instrument. The vertical field of view and the influence of the sampling and retrieval imply that waves with vertical wavelengths $3-5 km or larger can be retrieved. Global distributions of GW fluctuations were extracted from temperature data measured by CRISTA using Maximum Entropy Method (MEM) and Harmonic Analysis (HA), yielding height profiles of vertical wavelength and peak amplitude for fluctuations in each scanned profile. The method is discussed and compared to Fourier transform analyses and standard deviations. Analysis of data from the first mission reveals large GW amplitudes in the stratosphere over southernmost South America. These waves obey the dispersion relation for linear two-dimensional mountain waves (MWs). The horizontal structure on 6 November 1994 is compared to temperature fields calculated by the Pennsylvania State University (PSU)/National Center for Atmospheric Research (NCAR) mesoscale model (MM5). It is demonstrated that precise knowledge of the instrument's sensitivity is essential. Particularly good agreement is found at the southern tip of South America where the MM5 accurately reproduces the amplitudes and phases of a large-scale wave with 400 km horizontal wavelength. Targeted ray-tracing simulations allow us to interpret some of the observed wave features. A companion paper will discuss MWs on a global scale and estimates the fraction that MWs contribute to the total GW energy (Preusse et al., in preparation, 2002).
Abstract. The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument was built to determine whether and to what extent small-scale structures in global trace gas distributions and in dynamics are present in the middle atmosphere. To achieve this, trace gases were measured in the middle infrared by the limb scan technique at the highest possible horizontal and vertical resolution. CRISTA uses three telescopes (i.e., three view directions) simultaneously, and has three grating spectrometers for the middle IR (4-14/xm) and one spectrometer for the far IR (15-71 /xm). The optics and detectors are cooled to cryogenic temperatures by supercritical helium or subcooled helium, respectively, in a double cryostat. An instrument overview is given, and the design guidelines are sketched. The CRISTA experiment was flown on the space shuttle STS 66 as part of NASA mission ATLAS 3 on November 3-14, 1994. Orbit altitude was 300 km, and inclination was 57 ø. A campaign of ground-based, balloon, and rocket validation and complementary measurements was performed simultaneously. The CRISTA instrument performed flawlessly. A horizontal resolution of 200 km x 650 km was achieved at the equator, with higher horizontal resolution at higher latitudes. A vertical resolution of 2.5 km (or better) was obtained. The middle atmosphere was found to be highly variable at scales of <1000 km in the stratosphere. Three streamers of tropic/ subtropic air extending to higher latitudes are described. Their meridional scale is -<1000 km, while the zonal scale is of the order of 10,000 km and more. The streamers appear to be typical of specific winter conditions and to play a role in meridional transport. At mesospheric heights a strong tidal temperature oscillation was observed which extended well into the lower thermosphere.
Abstract. The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment aboard the Shuttle Pallet Satellite (SPAS) was successfully flown in early November 1994 (STS 66) and in August 1997 (STS 85). This paper focuses on the first flight of the instrument, which was part of the Atmospheric Laboratory for Application and Science 3 (ATLAS 3) mission of NASA. During a free flying period of 7 days, limb scan measurements of atmospheric infrared emissions were performed in the 4 to 71 /am wavelength region. For improved horizontal resolution, three telescopes (viewing directions) were used that sensed the atmosphere simultaneously. Atmospheric pressures, temperatures, and volume mixing ratios of various trace gases were retrieved from the radiance data by using a fast onion-peeling retrieval technique. This paper gives an overview of the data system including the raw data processing and the temperature and trace gas profile retrieval. Examples of version 1 limb radiance data (level 1 product) and version 1 mixing ratios (level 2 product) of ozone, C1ONO2, and CFC-11 are given. A number of important atmospheric transport processes can already be identified in the level 1 limb radiance data. Radiance data of the lower stratosphere (18 km) indicate strong upwelling in some equatorial regions, centered around the Amazon, Congo, and Indonesia. Respective data at the date line are consistent with convection patterns associated with E1 Nifio. Very low CFC-11 mixing ratios occur inside the South Polar vortex and cause low radiance values in a spectral region sensitive to CFC-11 emissions. These low values are a result of considerable downward transport of CFC-11 poor air that occurred during the winter months. Limb radiance profiles and retrieved mixing ratio profiles of CFC-11 indicate downward transport over -5 km. The accuracy of the retrieved version 1 mixing ratios is rather different for the various trace gases. In the middle atmosphere the estimated systematic error of ozone is -14%. Ozone data of correlative satellite measurements are well within this error bar. CRISTA agrees, for example, with Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) sunset measurements typically within 5%. The random error of version 1 ozone mixing ratios is 4%. Similar values apply to other trace gases. These low random errors allow the identification of small and medium scale horizontal and vertical structures in the measured trace gas distributions. Examples of structures in mixing ratio fields of ozone, C1ONO2, and CFC-11 are given.
Abstract. Modeling and observations provide evidence of the existence of a tertiary ozone maximum in the middle mesosphere restricted to winter high-latitudes. This local maximum occurs at approximately 72 km altitude, at latitudes just equatorward of the polar night terminator. Model analysis indicates that this maximum is the result of a decrease in atomic oxygen losses by catalytic cycles involving the odd-hydrogen species OH and HO2. In the middle mesosphere, at high latitudes, the atmosphere becomes optically thick to ultra-violet radiation at wavelengths below 185 nm. Since photolysis of water vapor is the primary source of oddhydrogen, reduced ultra-violet radiation results in less oddhydrogen and consequently lower oxygen loss rates. The consequent increase in atomic oxygen results in higher ozone because atomic oxygen recombination remains the only significant source of ozone in the mesosphere.
The second mission of the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment took place in August 1997. The experiment was flown aboard the ASTROnomical Shuttle PAllet Satellite (ASTRO‐SPAS) free‐flying platform launched by the NASA space shuttle. CRISTA analyzes the infrared radiation emitted by trace gases from the Earth limb in the altitude regime from the upper troposphere to the lower thermosphere. The main aim of CRISTA is to detect small‐scale dynamically induced structures in the distribution of trace constituents in the middle atmosphere. The instrument is therefore equipped with three telescopes that simultaneously collect the infrared radiation from three different air volumes. The high spatial density of the measurement grid obtained during the first CRISTA mission in November 1994, as well as the latitudinal coverage, was considerably improved by making use of newly developed satellite pointing and maneuvering capabilities. The altitude coverage was extended to include the upper troposphere where water vapor distributions are analyzed. Dynamically induced features are observed in practically all trace gases and at various spatial scales. The smallest scales that could be analyzed on the basis of the CRISTA data set are well below 100 km. Compared to the first mission, much more emphasis was laid on measurements in the upper mesosphere and lower thermosphere—this was possible because of higher radiometric sensitivities in some channels. Atomic oxygen, carbon dioxide, and ozone densities are derived in the upper mesosphere and lower thermosphere. The mission conditions allowed the study of polar stratospheric clouds (PSC) over the Antarctic and of polar mesospheric clouds (PMC) at high northern latitudes. For the first time, summer high latitude mesopause temperatures were retrieved from CO2 15‐μm spectra using a nonlocal thermodynamic equilibrium model. The derived temperatures compare well with a temperature climatology based on rocket soundings.
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