Trace gas distributions and temperatures in the mesosphere and lower thermosphere were derived from infrared spectra measured by the two CRISTA experiments flown in November 1994 and in August 1997. CRISTA (CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere) is a triple telescope cryogenically cooled infrared spectrometer which senses the Earth limb from a Shuttle orbit. The geographical coverage was -57°/+68° and -74°/+74° during the two missions, respectively. Each mission lasted slightly more than one week. The mesospheric set of trace gases include ozone, carbon dioxide and carbon monoxide, methane, water vapor, and atomic oxygen. In addition temperatures and pressures are obtained from the CO2 15 μm band. The temperature/pressure results are used to derive geostrophic wind fields. Most of the data reduction required non-LTE modelling of the radiation properties of the species. Practically all data exhibit considerable large scale structures in both latitude and longitude due to planetary waves or interhemispheric transport.
The new airborne CRyogenic Infrared Spectrometers and Telescope for the Atmosphere experiment (CRISTA-New Frontiers) succeeds the CRISTA satellite instrument operated twice during NASA space shuttle flights in November 1994 (STS 66) and August 1997 (STS 85). The first mission of the instrument will take place aboard the high altitude research aircraft M55-Geophysica in a campaign in the tropics in 2005/06. CRISTA-NF is a limb-scanning instrument measuring thermal emissions of various atmospheric trace gases (e.g. water vapor, ozone, chlorofluorocarbons), clouds and aerosols in the mid-infrared spectral region. The incoming radiation entering the optics through a Herschel telescope is analyzed by two Ebert-Fastie grating spectrometers with moderate spectral resolution and finally registered by cryogenic semiconductor-detectors. The optical system is integrated into a compact cryostat which reaches temperatures down to 10K by cooling with supercritical helium. This allows fast measurements and provides good signal-to-noise ratio. A narrow vertical field of view (200m) results in high vertical resolution which is neccessary for the analysis of small scale dynamic processes especially in the upper troposphere and lower stratosphere. This paper gives a scientific motivation, some remarks on the measurement technique and an overview of instrument design and technology.
Gravity wave variances in CLAES temperature data are isolated by a 0-6 zonal wavenumber Kalman filter. Resulting vertical profiles of temperature residuals are analyzed by a combination of Maximum Entropy Method (MEM) and harmonic analysis for gravity waves (GWs). This is the same method previously employed to study GWs in CRISTA data. We obtain nearly 1.5 years of continuous GW data between 34S and 34N and good coverage at higher latitudes depending on UARS yaw maneuvers. Results are compared to CRISTA data and interpreted for different wave sources. A time series of zonal mean GW variance shows
the seasonal shift of the tropical maximum of GW variance around the equator. Maximum variances are reached 1-2 months after summer solstice, consistent with the shift of the inner tropical convergence zone. Quiet summer and enhanced winter values at mid and high latitudes are due to a combination of wind filtering and wind modulation. Wind filtering occurs when GWs propagate from tropospheric west winds into the lower stratosphere. There prevailing winds reverse from west wind in winter to east wind in summer, thus causing a critical layer for low phase speed GWs during summer. The term wind modulation is used for the Doppler shift of the GW spectrum
by the wind at the observation altitude shifting parts of the GW spectrum in and out the vertical-wavelength visibility limits of the instrument. We find evidence for both processes in the data and indication that GW filtering might be the more important one.
The CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment measured mid- and far-infrared limb spectra during two Shuttle missions in November 1994 and August 1997 from the upper troposphere to the lower thermosphere. From the CO2 15μm spectra temperatures in the mesosphere and lower thermosphere were derived using a non-LTE model coupled to a line-by-line radiative transfer code. CO2 and atomic oxygen densities were calculated from the simultaneously recorded 4.3 μm (CO2) and 9.6 μm (ozone) measurements. The retrieved temperatures reveal the very low high latitude summer mesopause temperatures. Zonal structures are found at all altitudes and in the summer hemisphere as well as in the winter hemisphere. The north polar temperature distribution near the mesopause is dominated by a wave 1 structure with some wave 2 contribution. The same pattern is observed in the distribution of polar mesospheric clouds (PMC) which were detected via their thermal emission near 12 μm. The appearance of the PMCs thus verifies the temperatures obtained from the non-LTE modeling. The wave structures extend well into the thermosphere.
The CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument measured atmospheric trace gas emissions in the infrared using the limb scanning technique. For the first time three viewing directions were used by a satellite instrument in near-earth orbit (300 km) to obtain an unprecedented spatial density of the daily global measurement net. The high measurement speed needed for an enhanced horizontal resolution was achieved by cooling the instrument with supercritical and subcooled helium and by using Si:Ga bulk or Si:As blocked impurity band (BIB) detectors for the wavelength range 4-17 micrometers and Ge:Ga bulk detectors for longer wavelengths. The detectors were operated at temperatures between 2.5 and 13 Kelvin. Under these conditions the signal of the detectors shows non-stationary effects (relaxation effects) degrading measured spectra to some extent.These effects are difficult to account for as they can only be described by using at least 6 parameters depending on signal height and illumination history. In this paper an empirical model to correct the non-stationary effects of the Si:Ga detectors is presented. The model is based on measured signal responses after step-like illumination changes. Several tests using different data sets show that the model works well under various conditions.
During its two missions of about one week duration each in November 1994 and in August 1997 the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment observed spectrally resolved mid- and far- infrared emissions from the earth limb in the altitude regime from the troposphere to the lower thermosphere. The measurements concentrated on high spatial resolution in all three dimensions in the lower part of the height range. At upper mesosphere/lower thermosphere altitudes global ozone concentrations during day and night, daytime carbon-dioxide densities, and atmospheric temperatures were derived using a comprehensive non-LTE model. The derived parameters compare well with other experimental data. Pronounced horizontal structures in latitude as well as in longitude are found in all parameters showing that dynamical influences are of importance also in the upper mesosphere/lower thermosphere. Carbon dioxide mixing ratios start to depart from their tropospheric values at altitudes as low as 70 - 80 km. Atmospheric temperatures of 140 K and below were retrieved near the mesopause at high northern latitudes in August. These data are supported by the simultaneous observation of polar mesospheric clouds.
The CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment is an infrared limb sounder designed to analyze the distribution of trace gases in the terrestrial middle and upper atmosphere with high spatial and temporal resolution. CRISTA was successfully flown aboard the CRISTA-SPAS freeflier together with ATLAS-3 during the Space Shuttle mission STS-66 in November 1994. A second and also very successful flight of CRISTA took place in August 1997 as part of the Space Shuttle mission STS-85. It was found that the measured trace gas distributions exhibited strong structures with scales from a few 100 km horizontally and from a few km vertically. Only under summer conditions trace gas concentrations were observed which followed latitudinal gradients alone. At other times pronounced longitudinal variations were found at all latitudes and at all altitudes. Streamers were seen in the distribution of several trace gases in both CRISTA missions. At high southern latitudes polar stratospheric clouds were detected which exhibited a significant spatial and temporal variability.
A limb sounding cryogenic IR telescope named CRISTA (cryogenic infrared spectrometers and telescopes for the atmosphere) has been developed to study dynamic disturbances in the middle atmosphere with high spatial (horizontal and vertical) resolution. For this purpose, it measures mid and far IR emissions of several trace constituents at earth's limb using three independent telescopes with high off-axis rejection performance. Height profiles are derived from simultaneous scans of the three telescope LOS. The radiation received is spectrally analyzed by grating spectrometers followed by Si:Ga and Ge:Ga detectors. High sensitivity together with improved spatial resolution leads to a spacing of only 500 km to 600 km between two adjacent measurement points and thus to a far more detailed picture of the atmosphere compared to present day satellite experiments. CRISTA, integrated in the free-flyer ASTROSPAS, is launched in 1994 by the space shuttle for a short duration mission and will be part of ATLAS 3.
The CRISTA experiment (CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere) is a limb sounding instrument designed for high spatial resolution measurements of infrared emissions from the Earth's middle atmosphere. The principal scientific aim is to study small and medium scale structures in the concentrations of minor constituents which serve as tracers for the dynamical processes acting on these species. In order to achieve a high spatial resolution CRISTA is equipped with three telescopes each followed by its own grating spectro-meter. The spectrometers cover a wavelength range of 4 micrometers to 17 micrometers (all three viewing directions) and 55 micrometers to 71 micrometers (one telescope only) with a resolving power of about 300. Up to 15 trace gases will thus be measured simultaneously on a 500 X 650 km2 grid reaching from the lower strato-sphere to the upper mesosphere. For special soundings the measurements will occasionally be extended to an altitude of 150 km. The launch of CRISTA is planned for autumn 1994. CRISTA will be integrated into the free- flying platform CRISTA-SPAS and carried to a 57 degree(s) inclination orbit by the Space Shuttle. In the free-flying phase a measuring time of approximately on week is expected. The launch of CRISTA on CRISTA-SPAS will be together with the ATLAS-3 mission.
This paper presents details of the optical and mechanical layout of a cryogenically cooled IR-sensor named CRISTA (CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere). The instrument is designed to analyze dynamical processes in the middle atmosphere. For this purpose, it measures IR emissions of several trace gases at the limb using three independent telescopes with high off axis rejection performance. CRISTA, integrated in the free-flyer ASTRO-SPAS, will be launched in 1993 by the Space Shuttle for a 9 day mission.
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