Cryogenic Infrared Spectrometers And Telescopes For The Atmosphere Research Articles

General approach to the formulation and solution of the multi-parameter inverse problems of atmospheric remote sensing with measurements and constraints of different types

A general approach to the formulation and solution of the multi-parameter inverse problems of atmospheric remote sensing with measurements and constraints of different types is considered, which is based on the concept of the presentation of constraints as virtual measurements of finite accuracy. The advantages of the approach are (1) the possibility to account for all kinds of available information (remote and in situ measurements, physical constraints, model predictions); (2) the unified description of different measurements, a priori information and constraints in the retrieval algorithm; (3) the possibility to use measurements and a priori information of different types in any combination and to assess individual contributions to information content. The approach can be considered as a convenient tool for implementation of different synergistic remote-sensing schemes and for utilization of maximum available information on sought parameters for the purpose of increasing the accuracy of atmospheric remote sensing and providing self-consistency of sets of retrieved parameters. The known formulae for degrees of freedom for signal, averaging kernels, error components, and parameters describing spatial resolution are generalized to the case of multiple sought variables, measurements, and constraints, and the peculiar features of such generalization are discussed. The example is given of the application of the approach to the interpretation of the middle atmosphere limb infrared radiance data obtained in CRISTA (Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere) experiments with special emphasis on the constraints describing coupling of the parameters due to physical processes.

Satellite observations of cirrus clouds in the Northern Hemisphere lowermost stratosphere

Abstract. Here we present observations of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) of cirrus cloud and water vapour in August 1997 in the upper troposphere and lower stratosphere (UTLS). The observations indicate a considerable flux of moisture from the upper tropical troposphere into the extratropical lowermost stratosphere (LMS), resulting in the occurrence of high-altitude optically thin cirrus clouds in the LMS. The locations of the LMS cloud events observed by CRISTA are consistent with the tropopause height determined from coinciding radiosonde data. For a hemispheric analysis in tropopause relative coordinates an improved tropopause determination has been applied to the European Centre for Medium-Range Weather Forecasts (ECMWF) temperature profiles. We found that a significant fraction of the cloud occurrences in the tropopause region are located in the LMS, even if a conservative overestimate of the cloud top height (CTH) determination by CRISTA of 500 m is assumed. The results show rather high occurrence frequencies (~ 5%) up to high northern latitudes (70° N) and altitudes well above the tropopause (> 500 m at ~350 K and above) in large areas at mid- and high latitudes. Comparisons with model runs of the Chemical Lagrangian Model of the Stratosphere (CLaMS) over the CRISTA period show a reasonable consistency in the retrieved cloud pattern. For this purpose a limb ray tracing approach was applied through the 3-D model fields to obtain integrated measurement information through the atmosphere along the limb path of the instrument. The simplified cirrus scheme implemented in CLaMS seems to cause a systematic underestimation in the CTH occurrence frequencies in the LMS with respect to the observations. The observations together with the model results demonstrate the importance of isentropic, quasi-horizontal transport of water vapour from the subtropics and the potential for the occurrence of cirrus clouds in the lowermost stratosphere and tropopause region.

Global ray tracing simulations of the SABER gravity wave climatology

Since February 2002, the SABER (sounding of the atmosphere using broadband emission radiometry) satellite instrument has measured temperatures throughout the entire middle atmosphere. Employing the same techniques as previously used for CRISTA (cryogenic infrared spectrometers and telescopes for the atmosphere), we deduce from SABER V1.06 data 5 years of gravity wave (GW) temperature variances from altitudes of 20 to 100 km. A typical annual cycle is presented by calculating averages for the individual calendar months. Findings are consistent with previous results from various satellite missions. Based on zonal mean, SABER data for July and zonal mean GW momentum flux from CRISTA, a homogeneous and isotropic launch distribution for the GROGRAT (gravity wave regional or global ray tracer) is tuned. The launch distribution contains different phase speed mesoscale waves, some of very high‐phase speed and extremely low amplitudes, as well as waves with horizontal wavelengths of several thousand kilometers. Global maps for different seasons and altitudes, as well as time series of zonal mean GW squared amplitudes based on this launch distribution, match the observations well. Based on this realistic observation‐tuned model run, we calculate quantities that cannot be measured directly and are speculated to be major sources of uncertainty in current GW parameterization schemes. Two examples presented in this paper are the average cross‐latitude propagation of GWs and the relative acceleration contributions provided by saturation and dissipation, on the one hand, and the horizontal refraction of GWs by horizontal gradients of the mean flow, on the other hand.

Global water vapour distribution in the upper troposphere and lower stratosphere during CRISTA 2

Water vapour measurements during the second mission of the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument are presented in the altitude regime 8–20 km. Mixing ratios are shown on isentropic surfaces (300–500 K) as global zonal means and as averages in 60° longitude sectors. Transports are indicated to occur preferentially on isentropic surfaces in the northern hemisphere, but not in the tropics and in the south. The hygropause is found shifted away from the equator towards the winter hemisphere. The amount of shift is longitude dependent and can be as great as 20–30°. The water content of the hygropause area shows considerable zonal asymmetries. A circumpolar toroidally shaped layer of enhanced water vapour is observed at high southern latitudes (60°S). This belt extends from somewhat above the tropopause up to the 450 K level. Polar stratospheric clouds (PSC) are observed near and above the area of highest water vapour mixing ratios. Evaporation of PSC particles and rehydration of the atmosphere are thus suggested as the origin of the enhanced water vapour belt. A tongue-like ridge of enhanced water vapour extends at 30°W from the belt northward to the equator and beyond. It appears to moisten the TTL and tropical lower stratosphere. Related time scales are one or a few days. Intrusions of this kind appear to be not unfrequent and may therefore play a role for the water vapour budget of this atmospheric region.

Simulation of transport and composition changes during a blocking episode over the East Atlantic and North Europe

Transport of atmospheric trace gases during a blocking event in the troposphere and lower stratosphere (UTLS) in August 1997 is studied. Considering the frequency of such events it is obvious that they play a significant role for climate and air chemistry and thus the atmospheric environment. The event has been selected because a unique set of composition observations carried out by the CRISTA (Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere) instrument in the UTLS was available for the period of blocking. The regional European Atmospheric Dispersion (EURAD) model system was used for a detailed analysis focusing on ozone and CFC 11 (CFCl 3, Freon) distributions and their temporal and spatial variability. The combination of the CRISTA data and a regional transport chemistry model enabled a unique analysis of transport behaviour of a blocking. This developed an Ω-structure with a deep cut-off low at the western flank of the blocking high and a trough with highly perturbed trace gas fields on the eastern side. Tropopause heights varied intensively and were bended down to rather low levels in the cut-off low and folds appearing in the eastern trough. Results of artificial tracer experiments are presented which show that polluted air from lower tropospheric levels and – in this case – lower latitudes as well as the North American continent may be lifted up to the UTLS in the anticyclonic part of the Ω-block and transported from there over large distances in streamers. Quasi-periodic variations of CFC 11 flux divergence indicate dynamical coupling of the different domains of the block.

Atmospheric neutral temperature distribution at the mesopause altitude

In November 1994 and August 1997 the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument performed a global measurement ( 72 ∘ S – 72 ∘ N ) of infrared limb radiance from 4 to 71 μ m in the altitude range 6–180 km. Using a non-local thermodynamic equilibrium (non-LTE) model that couples the collisional, radiative and photochemical processes, the kinetic temperature was recovered from 15 μ m CO 2 emission for CRISTA-1 and -2 missions by direct assimilation of the integrated limb radiances between 72 and 120 km. Falling sphere and airglow validation measurements at NASA/GSFC Wallops Flight Facility (WFF) and the Mesosphere–Thermosphere Emissions for Ozone Remote Sensing (METEORS) experiment at White Sands Missile Range were coordinated with CRISTA during the field campaign. The derived temperatures show good agreement with these rocket soundings, partial climatology obtained from Rayleigh scattering observations by Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) and NRLMSISE-00 model.

The distribution of carbon monoxide in the upper mesosphere and lower thermosphere during CRISTA-1 and -2

Carbon monoxide concentrations are derived from the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) measurements in November 1994 and in August 1997. CRISTA is a helium-cooled infrared limb sounder. Its measurements include daytime spectra of the CO (Δ v=1) band at 4.7 μm. From the spectra CO densities are derived using a state of the art non-LTE model. During the first mission data were recorded between 58°S and about 68°N. In the second mission the latitude coverage was extended to ±71° in the mesosphere. The orbital characteristics, however, were such that daytime conditions prevailed in the northern (summer) hemisphere only. The derived CO concentrations agree well with other experimental data. As the CO mixing ratio increases steeply with altitude in the mesosphere and as the chemical lifetime is much longer than the time constants of dynamical motions this gas is an excellent tracer for dynamics. During the two CRISTA missions the CO distribution was found extremely variable both in time and in space, which is a result of the complex dynamics at these altitudes. The variations are compatible with the large-scale transport from the summer to the winter hemisphere. The influence of planetary waves is observed under winter as well as under summer conditions. Large tidal amplitudes were found at mid-latitudes during the second CRISTA mission. The overall wave activity observed in August by CRISTA suggests an abrupt change of wave damping in the vicinity of 97 km.

Use of CRISTA mesopause region temperatures for the intercalibration of ground-based instruments

Most available ground-based (GB) techniques for measuring temperatures in the upper mesosphere to lower thermosphere (or mesopause region) have systematic errors that are comparable to those of orbiting instruments. Determining these unknown biasses would normally require colocated observations that are only seldom feasible. Satellite measurements can be used as a “transfer standard” between GB observations that are not colocated. In this context, even with a reproducible or known bias in the satellite data, the comparison is still meaningful. Since Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) temperatures cover the mesopause region with very good accuracy (statistical errors do not exceed 1.5 K and systematic uncertainties range from about 3–7.5 K), they are quite suitable for this purpose. Because of the nearly constant precision over the height range of interest, also rotational temperatures of airglow emissions from different altitudes like the OH and O 2 bands (or the OI 558 nm line) can be successfully compared with each other. In spite of the limited number of overpasses during the relatively short CRISTA missions, the feasibility of such an intercalibration is demonstrated for widely separated GB sites. Here, the results obtained for GB measurements at eight different sites, using CRISTA-1 and CRISTA-2 data, are presented. For OH temperatures, the standard deviation between the different instruments is only 5.4 K, confirming previous estimates.

Mesospheric surf zone and temperature inversion layers in early November 1994

Carbon monoxide, temperature, and potential vorticity data (November, 1994) from the cryogenic infrared spectrometers and telescopes for the atmosphere (CRISTA) experiment are used to analyze the relationship between the mesospheric surf zone in the winter hemisphere and simultaneously observed thermal inversions just above. The observed upward propagating planetary waves rapidly decay when they approach the critical wind line in the upper mesosphere and a distinct surf zone is formed between 60–75 km. Above 85 km, the planetary wave activity increases again revealing an out-of-phase behavior with the waves below. This is likely due to momentum forcing associated with breaking gravity waves that have been filtered by the stratospheric and lower mesospheric planetary waves. The abrupt vertical phase shift of the planetary waves thus induces a strong vertical geopotential curvature that is sufficiently large, through hydrostatic equilibrium, to invert the thermal structure around 80 km. The CRISTA observations and their interpretation are consistent with simulations of the thermosphere–ionosphere–mesosphere-electrodynamics general circulation model (TIME-GCM) that was run for the same time period. Both the observation and the model results rather point to a more indirect, though essential, role of the gravity waves in the formation of the mesospheric inversion layers in early winter 1994.

Global wave activity from upper stratosphere to lower thermosphere: A new turbopause concept

Global temperature measurements are available from CRISTA (CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere) and from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) up to 110 km . Standard deviation from zonal mean temperature is used as a wave activity indicator (proxy). Altitude/latitude plots of these standard deviations σ or variances σ 2 show a structure that is dependent on the season. There is also substantial zonal asymmetry. Vertical cuts through the σ -field show a remarkable transition between 90 and 100 km : linear fit curves above 100 km have a gradient similar to the amplitude increase of freely (upward) propagating waves. The corresponding gradients below 90 km are much flatter and thus indicate considerable wave damping. The intersection of the two fit curves is dubbed the “wave-turbopause” here, and is believed to be near the turbulent or transport turbopause. This wave-turbopause is found in the vicinity of 90 – 95 km for CRISTA-1, CRISTA-2, and SABER. It is compared to the corresponding cold point mesopause and to the isolines of estimated potential vorticities to show similarities with the tropopause. The height of the wave-turbopause depends on latitude. It also has considerable seasonal variation, which is very different at high and low latitudes.

Absolute values of gravity wave momentum flux derived from satellite data

Temperature data obtained by the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) are analyzed for gravity waves (GWs). Amplitude, phase and vertical wavelength are determined from detrended temperature height profiles. The retrieved phases are utilized to estimate the horizontal wavelengths. At 25 km altitude an equatorial maximum of horizontal wavelength with a decrease toward mid and high latitudes is found. Simultaneous estimates of both horizontal and vertical wavelengths and temperature amplitudes allow the direct calculation of GW momentum flux (MF) from satellite observations for the first time. However, histograms of horizontal wavelength distributions indicate severe undersampling which prevents the retrieval of the propagation directions of the waves, and suggests our MF estimates may be too low, particularly at the high latitudes. Therefore an empirical aliasing correction has been applied. A world map of MF at 25 km altitude shows high variability and pronounced source regions and deviates in structure from a map of GW variances at the same altitude. Results from the Warner and McIntyre GW parameterization scheme (three‐part model) show better agreement with CRISTA MF estimates than with CRISTA squared GW amplitudes. Best agreement is found for low model launch levels. Large error ranges of the estimated MF values obtained in this paper could be substantially reduced by improved horizontal sampling in future satellite missions.

A review of the scientific results from the CRISTA missions

The CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment measured atmospheric limb infrared emissions in the altitude regime from the upper troposphere to the lower thermosphere during two Shuttle missions in November 1994 and August 1997. From the recorded spectra trace gas densities and temperature fields were derived on a very dense spatial grid. In the mesosphere and lower thermosphere trace gas and temperature retrievals were carried out with the help of a state of the art non-LTE (non-local thermodynamic equilibrium) model coupled to a line-by-line radiative transfer code. The upper atmosphere data include densities of carbon dioxide, ozone, atomic oxygen, and temperature. All parameters were derived for day and night with the exception of CO 2 which is available for daytime only. Additional trace gases in the mesosphere include water vapor, methane, and carbon monoxide. The main findings are a substantial depletion of CO 2 between 80 and 100 km, high ozone concentrations in the secondary maximum (upper mesosphere) during night, a tertiary ozone maximum near the winter polar terminator in the middle mesosphere and well developed dynamically induced structures in latitude as well as in longitude. Such structures are also observed in the lower thermosphere where the distribution of atomic oxygen was measured up to about 180 km altitude. The atomic oxygen concentrations encountered in the thermosphere during solar minimum are much lower than predicted by MSIS.

Colour indices for the detection and differentiation of cloud types in infra-red limb emission spectra

Simple radiance ratios have been used for the detection of clouds around the tropopause and in the winter polar stratosphere from the infra-red spectra of two remote sensing instruments, the cryogenic infrared spectrometers and telescopes for the atmosphere (CRISTA) flown on two space shuttle missions in 1994 and 1997 and the Michelson interferometer for passive atmospheric sounding (MIPAS) launched on ENVISAT in March 2002. This very successful approach was first applied to different wavelength regions of the CRISTA measurements and was then used as a pre-flight validation test for a cloud detection algorithm of the operational retrieval processor for MIPAS. Preliminary results are now available from the MIPAS instrument and are presented here. First, cloud top heights have been derived down to 12 km by the detection method and show quite reasonable results. In addition, modelled spectra and measurements show that the extension of the method to lower altitudes – potentially down to 6 km – should be possible. Second, the high spectral resolution of the MIPAS measurements allows in addition the detection of scattering effects in the spectra, which gives the future opportunity to retrieve information about the size of the scattering particles. In particular, an index has been developed which allows large particle clouds to be identified. Finally, investigations of CRISTA spectra have already shown that the differentiation of polar stratospheric cloud (PSC) types is possible based on their characteristic spectral features. Application of the differentiation method to the tropics shows no indication for clouds containing PSC-like nitric-acid-hydrate particles.

Trace gas variability in the stratosphere

During the second mission of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) from August 8 to 16, 1997, over 45,000 altitude profiles of infrared spectra were collected. A variety of atmospheric trace gases have been retrieved. Due to its unprecedented spatial and temporal resolution CRISTA data is especially suited to study variability on small scales. Variability of selected trace gases is presented in terms of standard deviations from the zonal means in 5° latitude bands: altitude range is about 15–50 km for the mixing ratios of O 3, N 2O, CH 4, CFC 11, and HNO 3. Results are compared to CIRA 1996, Part III, and agreements or disagreements are discussed. Variability is found to be not constant, but quite variable itself. It is generally higher in winter than in summer. Beyond that there are considerable variations of standard deviations with latitude and with altitude. They show interesting peculiarities that will be discussed. The results indicate that most part of the data variability are atmospheric fluctuations rather than measurement errors.

Quantitative transport studies based on trace gas assimilation

Trace gas assimilation is an attractive method for the generation of synoptic trace gas fields from asynoptic satellite observations. Moreover, it allows for quantitative transport studies based on observational data. In this paper, we present a case study based on CFC-11 measurements of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment in November 1994. It is shown that assimilation of CFC-11 into a transport model significantly influences calculated transport quantities compared to results obtained from simulations without trace gas assimilation.

A global view of tidal temperature perturbations above the mesopause: Preliminary model/observation intercomparison

Migrating and nonmigrating diurnal tides in the temperature data from the satellite borne, Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment are compared to model predictions from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) and from the Global Scale Wave Model (GSWM). The comparative model/observation analysis is performed between 75–120 km altitude and at 7.5°N. The results suggest that interactions between quasi-stationary planetary waves and radiative and latent heat forced tidal components may play an important role in generating the thermal tidal structure above the mesopause though more extended model studies are necessary.

Satellite observations of daytime and nighttime ozone in the mesosphere and lower thermosphere

The global distribution of mesospheric and lower thermospheric ozone 9.6 μm infrared emissions was measured by the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment during two Space Shuttle missions in November 1994 and August 1997. The radiances measured by CRISTA have been inverted to O3 number densities in the 50–95 km range by using a nonlocal thermodynamic equilibrium model. A detailed sensitivity study of retrieved O3 number densities has been carried out. The ozone abundance profiles show volume mixing ratios of 1–2 ppmv at the stratopause, 0.5 ppmv or less around 80 km, and typically 1 ppmv during daytime and 10 ppmv during nighttime at the secondary maximum. The agreement with other experiments is typically better than 25%. The global distribution of upper mesospheric ozone shows significant latitudinal gradients and an enhancement in the equatorial upper mesosphere. At the polar night terminator a third ozone maximum is observed. Three‐dimensional model results indicate that the latitudinal gradients are significantly influenced by solar tides.

Calibration procedures and correction of detector signal relaxations for the CRISTA infrared satellite instrument.

Remote sensing from space has become a common method for deriving geophysical parameters such as atmospheric temperature and composition. The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument was designed to sound the middle and the upper atmosphere (10-180 km) with high spatial resolution. Atmospheric IR emissions were measured with Si:Ga bulk or Si:As blocked impurity band detectors for a wavelength interval of 4-17 microm and Ge:Ga bulk detectors for 56-71 microm. An overview of the calibration of the instrument and the correction of detector signal relaxations for the Si:Ga detectors are given, both of which are necessary to provide high-quality IR radiance data as input for the retrieval of atmospheric temperature and trace gas mixing ratios. Laboratory and flight data are shown to demonstrate the quality of the results.

Observation of migrating and nonmigrating diurnal tides in the equatorial lower thermosphere

During 9 November 1994, the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment measured vertical profiles of temperature up to an altitude of 120 km. Temperatures above 75 km are retrieved from 15 μm CO2 emissions, accounting for the deviation from the local thermodynamical equilibrium (non‐LTE, NLTE). This study presents the first amplitude and phase measurements of global temperature tides in a region of Earth's atmosphere where prior to CRISTA no daytime and nighttime temperature measurements were available. The migrating and 8 nonmigrating components of the diurnal tide are analyzed from 75–120 km and at 7.5°N. Combined amplitudes exceed 80 K with the nonmigrating components dominant above ∼90 km.

Sources of nonmigrating tides in the tropical middle atmosphere

Temperature measurements from the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment taken during the U.S. Space Shuttle mission STS‐66 in November 1994 provide a variety of zonally symmetric and asymmetric tidal signatures in the altitude range from 40–90 km. The most prominent zonally asymmetric tidal pattern is identified to be the westward propagating nonmigrating diurnal tide of zonal wavenumber 2 (s = −2). This mode has an amplitude of approximately half the amplitude of the migrating (s = −1) component of the diurnal tide. The observational findings are compared to model results from the Global Scale Wave Model (GSWM) and from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME‐GCM). GSWM and TIME‐GCM account for different tidal sources and therefore allow an analysis of the tidal forcing responsible for the observed signatures. The GSWM tidal forcing in the model version used is based upon latent heat release associated with tropical deep convection while nonmigrating tides in the TIME‐GCM are predominantly forced by nonlinear interactions between the migrating diurnal tide and stationary planetary waves. It is shown that the latter mechanism forces a large part of the s = −2 mode while the stationary, zonally uniform (s = 0) diurnal nonmigrating tide is mainly driven by latent heat release. This result suggests that dynamical models for the mesosphere/lower thermosphere (MLT) region need to account for the tropospheric latent heat source and stationary planetary wave activity in order to predict realistic longitudinal diurnal tidal variability.