Peter Knieling

Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment and middle atmosphere variability

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 μm) and one spectrometer for the far IR (15-71 μm). 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°. 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 × 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.

Quasi 2 day waves in the summer mesosphere: Triple structure of amplitudes and long‐term development

Upper mesosphere OH temperature measurements are compared at the stations of Wuppertal (51 degrees N, 7 degrees E) and Hohenpeissenberg (48 degrees N, 11 degrees E) for 2004-2009 in order to form a combined data set which considerably improves the measurement statistics. This allows time analyses near the Nyquist frequency (2 days) which is used for a study of the quasi 2 day wave (QTDW) in summer. The well-known maximum near solstice is observed. In addition, there are two unexpected side maxima about 45-60 days before and after the center peak. A similar triplet is seen in the QTDW analysis of Microwave Limb Sounder temperature data. The triple structure is also found in a very similar form 15 years earlier in the interval 1988-1993 in early Wuppertal data. In these 15 years the time distance between the first and last triple peak has increased by about 22 days. Amplitudes of the QTDW correspond to the meridional gradient of the quasi-geostrophic potential vorticity (from MLS data) and baroclinic instabilities (bc) from radar winds (at Juliusruh, 55 degrees N, 13 degrees E). Parameter bc also shows a triple structure, when mean values 2003-2008 are calculated. The QTDW triplet results from the combination of atmospheric (in) stability and critical wind speed. The widening of the QTDW triple structure suggests a long-term change of mesospheric stability and wind structure. This is found, indeed, in the bc and zonal wind data. The changes likely reflect a long-term circulation change in the middle atmosphere extending up to the mesopause.

Indications of long-term changes in middle atmosphere transports

Upper mesosphere temperatures are derived from Meinel OH∗ emissions. They show large variations of various kinds. Annual mean temperatures measured at Wuppertal (51°N, 7°E) since 1981 do not show a significant long-term trend: the value obtained is 0.02 K ± 0.09 K per year. Monthly trends, on the contrary, are fairly substantial. To take a new and different approach to middle atmosphere long-term behavior, two new parameters are suggested for analysis: the short-period variance σ2 of the temperature, and the Equivalent Summer Duration (ESD). 1.) The variance σ2 itself shows long-term variations, which are correlated with temperature fluctuations at some lower altitude. This behavior is in line with the “downward control principle” and thus indicative of changes in atmospheric transports. 2.) The ESD parameter is defined in analogy to the duration of the vegetation period on the ground. A threshold temperature of 200 K at 87 km is chosen to define the beginning and end of summer. This yields an ESD on the order of 150 days. The ESD values at Wuppertal show a solar cycle effect which needs to be corrected for. Sensitivity of OH temperatures to solar activity at Wuppertal has been analyzed for this purpose. A sensitivity of 0.03 K ± 0.016 K per F10.7cm flux unit was obtained. The corrected ESD values at the mesopause show a substantial increase of 18 days (11%) in 20 years (extrapolated). Respective vegetation period data have been published recently and show an increase of 20 days (13%) in 20 years (Zhou et al. 2001). They are in line with phenological data presented here. In the stratosphere summer length is estimated from the spring/autumn circulation reversals. Also here substantial changes are found, with a (negative) gradient of 19 days (13%) in 20 years. Considerable changes in middle atmosphere dynamics are thus indicated even though the statistics of some of the data are still limited. The mesopause ESD increases are compatible with a long-term change of the semi-annual oscillation (SAO). The stratospheric data suggest that the variations seen could be (in part) a climate fluctuation rather than a manmade trend, as data from two earlier decades show behavior that is opposite.

A highly miniaturized satellite payload based on a spatial heterodyne spectrometer for atmospheric temperature measurements in the mesosphere and lower thermosphere

A highly miniaturized limb sounder for the observation of the O2 A-Band to derive temperatures in the mesosphere and lower thermosphere is presented. The instrument consists of a monolithic spatial heterodyne spectrometer (SHS), which is able to resolve the rotational structure of the R-branch of that band. The relative intensities of the emission lines follow a Boltzmann distribution and the ratio of the lines can be used to derive the kinetic temperature. The SHS operates at a Littrow wavelength of 761.8 nm and heterodynes a wavelength regime between 761.9 nm and 765.3 nm with a resolving power of 5 about 8,000 considering apodization effects. The size of the SHS is 38x38x27 mm and its acceptance angle is ±5o. It has an etendue of 0.014 cm sr. Complemented by a front optics with a solid angle of 0.65 and a detector optics, the entire optical system fits into a volume of about 1.5 liters. This allows to fly this instrument on a 3 or 6 unit CubeSat. The vertical field of 1 Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-437 Manuscript under review for journal Atmos. Meas. Tech. Discussion started: 9 January 2018 c

New results from CRISTA

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.