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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 O3, N2O, CH4, CFC 11, and HNO3. 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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

The CRISTA experiment provided global measurements of atmospheric trace gases in the stratosphere and upper troposphere during its second mission in August 1997. A new data product has recently been developed, yielding water vapor mixing ratios around the tropopause. The high data density of CRISTA makes an efficient assimilation of the water vapor field (by means of the NCAR ROSE CTM) possible. From these data turbulent trace gas fluxes v′χ′ are derived. The global distribution of the H2O fluxes is found to be highly structured at a given pressure level. Zonal means of fluxes indicate transport barriers at the equator and near the tropopause. This is compared to effective diffusivities of P. Haynes and E. Shuckburgh [J. Geophys. Res. 105 (2000) 22795] and general agreement is obtained. There is one important discrepancy, though: the effective diffusivities show a transequatorial “bridge” at about 350 K potential temperature (about 12 km), a “bridge” which is also seen in the CRISTA water vapor data, but at a considerably higher altitude. This finding is confirmed by ozone data from CRISTA and from UARS. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]