Near-infrared laboratory spectra of solid H2O/CO2 and CH3OH/CO2 ice mixtures

We present near-IR spectra of solid CO₂ in H₂O and CH₃OH, and find they are significantly different from that of pure solid CO₂. Peaks not present in either pure H₂O or pure CO₂ spectra become evident when the two are mixed. First, the putative theoretically forbidden CO₂ (2ν₃) overtone near 2.134 μm (4685 cm⁻¹), that is absent from our spectrum of pure solid CO₂, is prominent in the spectra of H₂O/CO₂=5 and 25 mixtures. Second, a 2.74-μm (3650 cm⁻¹) dangling OH feature of H₂O (and a potentially related peak at 1.89 μm) appear in the spectra of CO₂-H₂O ice mixtures, but are probably not diagnostic of the presence of CO₂. Other CO₂ peaks display shifts in position and increased width because of intermolecular interactions with H₂O. Warming causes some peak positions and profiles in the spectrum of a H₂O/CO₂=5 mixture to take on the appearance of pure CO₂. Absolute strengths for absorptions of CO₂ in solid H₂O are estimated. Similar results are observed for CO₂ in solid CH₃OH. Since the CO₂ (2ν₃) overtone near 2.134 μm (4685 cm⁻¹) is not present in pure CO₂ but prominent in mixtures, it may be a good observational (spectral) indicator of whether solid CO₂ is a pure material or intimately mixed with other molecules. These observations may be applicable to Mars polar caps as well as outer Solar System bodies.     

The dependence of the climate sensitivity on convective parametrization: statistical evaluation

Two sensitivity experiments, in which CO₂ is instantaneously doubled, have been performed with a general circulation model to determine the influence of the convective parametrization on simulated climate change. We have examined the spatial structure of changes in the annual mean and annual cycle for surface temperature and precipitation for both experiments; similarly we have examined changes in the variance for these two fields. We have also computed a range of test statistics in order to obtain reliable measures of the signal-to-noise ratio in the climate change signal from each experiment. We have computed test statistics for the entire globe and for five different region and we contrast the global response with the response in the Australian region taken as a representative sample.We find that the highest signal-to-noise ratios in the change from 1 * CO₂ to 2 * CO₂ are for the change in surface temperature for both experiments with little difference in the global averages between the experiments. Globally averaged precipitation shows a greater noise level but perhaps the greatest contrast between experiments. There are generally significant increases in the temporal and spatial variability of precipitation in the change from the 1 * CO₂ to 2 * CO₂ and with some differences apparent between the two experiments. The temporal variability of surface temperature does not change significantly in any of the 2 * CO₂ cases, and there is little difference between the experiments. There is a significant decrease in the spatial variability of surface temperature in all 2 * CO₂ experiments in all cases and with significant differences in the seasonal variations between different experiments. The spatial variability of precipitation increases in all 2 * CO₂ cases and also with substantial differences in the seasonal variations between the experiments. There are accompanying significantly different spatial pattern correlations for both surface temperature and precipitation. In general we find that the global changes are fairly robust with the differences associated with convective parametrization schemes being very small. However, at the regional level, there are marked differences between experiments with changes both in the means and in the spatial and temporal variances but often with low levels of significance.     

The mid-infrared transmission spectra of Antarctic ureilites

Abstract— The mid-infrared (4000–450 cm^?1; 2.5–22.2 μm) transmission spectra of seven Antarctic ureilites and 10 Antarctic H-5 ordinary chondrites are presented. The ureilite spectra show a number of absorption bands, the strongest of which is a wide, complex feature centered near 1000 cm^?1 (10 μm) due to Si-O stretching vibrations in silicates. The profiles and positions of the substructure in this feature indicate that Mg-rich olivines and pyroxenes are the main silicates responsible. The relative abundances of these two minerals, as inferred from the spectra, show substantial variation from meteorite to meteorite, but generally indicate olivine is the most abundant (olivine:pyroxene = 60:40 to 95:5). Both the predominance of olivine and the variable olivine-to-pyroxene ratio are consistent with the known composition and heterogeneity of ureilites. The H-5 ordinary chondrites spanned a range of weathering classes and were used to provide a means of addressing the extent to which the ureilite spectra may have been altered by weathering processes. It was found that, while weathering of these meteorites produces some weak bands due to the formation of small amounts of carbonates and hydrates, the profile of the main silicate feature has been little affected by Antarctic exposure in the meteorites studied here. The mid-infrared ureilite spectra provide an additional means of testing potential asteroidal parent bodies for the ureilites. At present, the best candidates include the subset of S-type asteroids having low albedos and weak absorption features in the near infrared.     

AN AUTOMATIC PROCEDURE FOR ESTIMATING SPRING SMALL GRAINS ACREAGE FROM LANDSAT DATA

The development and testing of a computerized technique for utilizing multitemporal Landsat multispectral scanner data to estimate spring small grains acreage are described. The Kauth-Thomas green number transformation is applied to the data prior to application of the pixel-level standardized logic. Four years of data from the U.S. and Canada are used in testing. A comparison of the test results to those of the analyst-intensive procedures indicates a potential for increase in near-harvest estimation efficiency with little sacrifice in accuracy.