Peter Preusse

Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) data processing and atmospheric temperature and trace gas retrieval

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 μm 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, ClONO 2 , 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 El Nino. 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, ClONO 2 , and CFC-11 are given.

CRISTA observations of cirrus clouds around the tropopause

[1]xa0The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument observed thin cirrus clouds at and above the tropopause during its two missions in November 1994 and August 1997. A simple cloud detection scheme was developed for extinctions greater than 2 × 10−3 km−1 through analysis of the measured infrared spectra in the 12-μm range. Horizontal and vertical distributions of cloud occurrence frequencies are in good agreement with the Stratospheric Aerosol and Gas Experiment (SAGE) II subvisual cirrus cloud (SVC) climatology as well as SAGE measurements for the 1997 period. Seasonal variations, strong longitudinal variability, and indications of enhanced cloud occurrence frequencies in separated regions caused by El Nino events were detected in the CRISTA data set. A substantial day-to-day variability could be found throughout the tropics, and several regions with enhanced variability have been identified. In addition, a significant amount of cloud was found above the midlatitude tropopause. Backward trajectories in relation to outgoing longwave radiation (OLR) measurements and cloud observation in the troposphere by meteorological satellites suggest that about three fourths of the high clouds (>15 km) observed by CRISTA in the tropics stem from deep convection systems and the outflow of these systems. This would imply that on the order of at least one fourth of the observed cloud events are originated by other mechanisms, such as in situ formation due to cooling events on synoptic and/or gravity wave scales. For the convective generated cirrus clouds, a maximum lifetime of around 3–4 days was estimated over a wide range of latitudes. Such a long lifetime could be important for modeling the impact of cirrus clouds on radiation budget (climate) and heterogeneous chemical processes around the tropopause.

Tidal signatures in temperature data from CRISTA 1 mission

Temperature measurements in the stratosphere and mesosphere were taken during the first Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA 1) mission using CO2 emissions. These measurements range from 13 to close to 100 km, and individual temperature measurements have a precision of 1 K. The CRISTA orbit was circular at an inclination of 57°, so local time variations during the 7 day mission were small for a given latitude and orbit leg. Zonal averages of the data show significant structure in the vertical and as a function of latitude. Temperature differences between the zonal mean data from the ascending and descending portions of the orbit are of the form expected from the diurnal tide. The maximum zonal mean difference is ≈20 K and occurs over the equator at an altitude of 75 km. Zonal variations in the temperature difference indicate that the tidal amplitude is not uniform at all longitudes. At the equator the maximum amplitude (30 K) appears over the African sector and the minimum (10 K) over the Pacific sector. This variation is most likely a nonmigrating wavenumber 2 diurnal tide although other less plausible possibilities exist. To facilitate comparisons with model results the temperature variations are converted to equivalent vertical displacements, assuming the tidal motions are adiabatic. Such an approach is appropriate in the mesosphere where diurnal variations due to radiative effects are small and reduces the dependence of the measured temperature amplitude on the background temperature profile. Equivalent vertical displacements are also calculated using results from the global scale wave model. For the most part the model results and observations are in excellent qualitative and good quantitative agreement from the tropopause to the mesopause. However, the observed vertical wavelength is smaller, and its amplitude in terms of equivalent displacement is smaller in the upper mesosphere than that in the model. The decrease in amplitude is consistent with that expected from the transition from equinox to solstice conditions.

Satellite observations of upper stratospheric and mesospheric OH: The HOxdilemma

We report the first observations of the vertical distribution of hydroxyl (OH) from the upper stratosphere to the mesopause. The Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) made these measurements in August 1997. The data confirm the results from the earlier November 1994 MAHRSI mission that were confined to altitudes above 50 km, namely that mesospheric OH densities are 25 to 35% lower than predicted by standard photochemical theory. However, the new observations show that below 50 km the OH density increases rapidly and at 43 km altitude it is larger than that expected from standard theory. This represents a serious dilemma for our understanding of odd-hydrogen chemistry because the same key reactions are thought to dominate OH/HO2 partitioning in both regions. We show that neither standard photochemical theory nor any previously proposed changes are adequate to explain the OH observations in both the upper stratosphere and mesosphere.

Gravity waves resolved in ECMWF and measured by SABER

[1]xa0The limited resolution of most general circulation models (GCMs) is not sufficient to simulate gravity waves (GWs) explicitly. ECMWF (European Center for Medium-Range Weather Forecasts) data have now a horizontal resolution of °, so parts of the mesoscale GWs can be resolved although most source processes still contain sub-grid phenomena. We validate the GWs resolved in ECMWF by comparison with corresponding results obtained from global SABER (Sounding of the Atmosphere Using Broadband Emission Radiometry) satellite observations. For this comparison, effects of the radiative transfer and satellite retrieval procedure are accounted for. Globally, GWs can be attributed to various GW sources and the GW spectrum is modulated by the background winds. Correlation analysis comparing SABER and ECMWF temperature fluctuations indicate good agreement with respect to mountain waves, for example, over the southern tip of south America or over Scandinavia, as well as GWs at the edge of the winter polar vortex.

Measurements of trace gases by the cryogenic infrared spectrometers and telescopes for the atmosphere (CRISTA) experiment

Abstract The CRISTA experiment aboard the Shuttle Pallet Satellite (SPAS) was flown on STS 66 in early November 1994. During a free flying period of seven days measurements of atmospheric temperatures and of 15 trace gases were performed with unprecedented horizontal resolution. This paper gives a brief description of the instrument and of the observational technique. Preliminary results of CIONO 2 retrievals are presented and discussed in terms of atmospheric dynamics and photochemistry.

Modulation of Gravity Waves by Tides as Seen in CRISTA Temperatures

Abstract During shuttle missions STS-66 (November, 1994) and STS-85 (August, 1997) the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) acquired temperature data with very high spatial resolution. These are analyzed for gravity waves (GW). The altitude range spans the whole middle atmosphere from the tropopause up to the mesopause. In the upper mesosphere tidal amplitudes exceed values of 10 K. Modulation of GW activity by the tides is observed and analyzed using CRISTA temperatures and tidal predictions of the Global Scale Wave Model (GSWM). The modulation process is identified as a tidally-induced change of the background buoyancy frequency. The findings agree well with the expectations for saturated GW and are the first global scale observations of this process.

Indications of convectively generated gravity waves in crista temperatures

Abstract During shuttle missions STS-66 (November, 1994) and STS-85 (August, 1997) the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) acquired temperature data and mixing ratios of, among other trace gases, tropospheric water vapor with very high spatial resolution. Vertical profiles of temperature are analyzed for gravity waves (GW). Enhanced GW activity is found at the equator and in the northern hemispheric subtropics. The patterns of high GW excitation resemble regions of upward tropopause displacement, indicated by high water vapor mixing ratio, suggesting that the waves are generated by deep convection. The observed GWs have non—zero phase speeds with respect to the ground. The horizontal wavelengths of the waves are discussed in conjunction with the wave source.

Evidence for gravity waves in CRISTA temperatures

Abstract Detectability of gravity waves (GW) for a limb sounding experiment is investigated: Limb radiances emitted from a modeled GW field are calculated. Horizontal and vertical wavelengths of the GW are varied. Distinguishable amplitudes are found in altitude radiance profiles, even if wavelengths are short compared to the weighting function of radiative transfer. Altitude profiles of temperature retrieved from CRISTA limb radiances are analysed for small vertical scale waves. Because of their short spatial scales, they are tentatively interpreted here as GW. Amplitudes are deduced from single height profiles. This leads to a high resolution spatial distribution of GW activity. Results for the first CRISTA flight are presented and compared to recent satellite-based measurements of GW.

Middle atmosphere Kelvin waves observed in Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) 1 and 2 temperature and trace species

[1]xa0A number of tropical perturbations that have all the characteristics of Kelvin waves are identified in temperature measurements from the two flights of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument. The background wind conditions during the two flights were quite different due to the different phases of the quasi-biennial oscillation (QBO), and there were differences in the Kelvin waves observed. During each flight, there were several different zonal wave numbers and/or frequencies present simultaneously. The observed waves conform well to theory. In particular, lower-frequency waves are confined to the lower stratosphere, while higher-frequency waves appear in the upper stratosphere and mesosphere; the waves are centered on the equator; and the frequency and structure satisfy the dispersion relation. Wave signals also appear in several stratospheric trace species: O3, CFC-11 (CFCl3), HNO3, N2O, and CH4. The sense of the correlation of these trace species perturbations with temperature (negative for CFC-11, N2O, and CH4; positive for lower stratospheric HNO3 and O3) confirms that vertical velocity is responsible for the perturbations. There is a shift in the relative phases as photochemical processes become more important with increasing altitude. Upper stratospheric ozone correlates negatively with temperature due to temperature-dependent reaction rates that destroy ozone.