Showing papers by "Prasad Varanasi published in 1992"

Intensity and linewidth measurements in the 13.7 μm fundamental bands of 12C2H2 and 12C13CH2 at planetary atmospheric temperatures

Abstract: The absolute intensities and collision-broadened half-widths of several lines in the P-,Q-, and R-branches of the nu5-fundamental band of (C-12)2H2 have been measured at various temperatures between 147 and 295 K employing the Doppler-limited spectral resolution (about 10 exp -4/cm) of a tunable diode laser spectrometer. The absolute intensities of R(5), R(7), R(9), and R(20) in the same fundamental belonging to (C-12)(C-13)H2 have also been measured at 294 K. The temperature dependence of the collision-broadened half-width has been determined for some of the lines broadened by planetary atmospheric gases, namely, He, Ar, H2, and N2. Four self-broadened linewidths of (C-12)2H2, as well as three H2-broadened linewidths and a self-broadened half-width of (C-12)(C-13)H2, have also been retrieved from the measurements.

Tunable diode laser measurements on the 951.7393 cm-1 line of 12C2H4 at planetary atmospheric temperatures

Abstract: The absolute intensity and the collision broadened half-widths of the 951.7393/cm line, which belongs to the nu7-fundamental band (C-12)2H4, at 152, 202, 252, and 294 K are presented using He, H2, and N2 as broadeners. The temperature dependence of the half-width is determined for line broadening by the planetary atmospheric gases He, H2, and N2.

Absorption coefficients of CFC-11 and CFC-12 needed for atmospheric remote sensing and global warming studies

Abstract: Spectral absorption coefficients k(v) in the atmospheric window are reported for CFC-11 and CFC-12. Data obtained with a grating spectrometer are compared with NCAR cross sections and measurements of k(v) made with a tunable diode laser spectrometer at various temperature-pressure combinations representing tangent heights or layers in the atmosphere are presented. The results are suitable for atmospheric remote sensing and global warming studies.

Absorption spectra of HCFC-22 around 829 cm-1 at atmospheric conditions

Abstract: Spectral absorption coefficients of HCFC-22 have been measured around 829/cm in the laboratory at various temperature-pressure combinations chosen to represent tangent heights (as in solar-occultation experiments) or layers in the atmosphere. The data measured employing the Doppler-limited spectra resolution (about 10 exp -4/cm) of a tunable diode laser spectrometer are free of instrumental distortion and are more practical in this case than the spectral line parameters adapted in conventional line-by-line procedures for analyzing atmospheric spectra. The present data obtained with N2 as the broadening gas are shown to be directly applicable to the real atmosphere.

A reexamination of the greenhouse effect due to CFC-11 and CFC-12

Abstract: Employing the most recent laboratory absorption-coefficient data1 on the thermal infrared (i.r.) bands of CFC-11 (CFCl3) and CFC-12 (CF2Cl2), which were measured at several temperatures relevant to the troposphere and the stratosphere, the greenhouse effect produced by these two CFCs has been reexamined. The effect upon the atmospheric radiative fluxes due to the temperature dependence of the absorption coefficient, especially in the many hot bands present in this spectral region, has been studied. The validity of the often used optically-thin approximation has been scrutinized in view of the observed enhancement in the absorption by the CFCs at low temperatures. The influence of absorption by water vapor on the radiative transfer through columns of CFC-11 and CFC-12 has also been considered. It has been shown that, even though each of these individual refinements may modify the previously estimated effect due to the CFCs by a small amount only, the collective effect may be a non-negligible 35% change in the surface-troposphere heating for every ppbv of CFC-11 and CFC-12 each introduced into a model atmosphere.

Infrared absorption-coefficient data on SF6 applicable to atmospheric remote sensing

Abstract: Spectral absorption coefficients, k(nu)/cm per atm, of SF6 have been measured in the central Q-branches of the nu(3)-fundamental at 947/cm at various temperature-pressure combinations representing tangent heights in solar-occultation experiments or layers in the atmosphere. The data obtained with the Doppler-limited spectral resolution (about 0.0001/cm) of a tunable-diode laser spectrometer are useful in the atmospheric remote sensing of this trace gas.