Abstract
An important goal of the study of atmospheres of planets is to provide an understanding of the relationship and interaction among phenomena occurring at different altitude and pressure regions and the effects of external influences on these phenomena. To probe multiple pressure regimes in general requires measurements in different spectral regions and with a wide range of spectral resolutions. This presents formidable technical challenges. To directly probe phenomena in the upper neutral atmosphere (pressures ⩽30 mbar) is particularly difficult. Much of the information on local chemistry and physics is contained in the near Doppler profiles of infrared molecular lines formed in these regions and spectral resolving powers λ Δλ > 10 6 are required to adequately measure the lineshapes. The very high spectral resolution technique of infrared heterodyne spectroscopy capable of making such line measurements is briefly described. Several investigations are described to illustrate the range of phenomena that can be studied and the unique physical and chemical parameters that can be retrieved. These investigations include direct measurement of global thermospheric circulation on Venus using Doppler shifts of nonthermal CO 2 emission lines near 10 μm; the study of Jupiter's deep interior utilizing spectroscopy of H 2 quadrupole lines (17 and 28.2 μm>) formed in the stratosphere; the evaluation of photochemical processes which determine the composition of Mars and the outer planets by retrieving constituent abundances (O 3 near 9.5 μm on Mars and hydrocarbons on Jupiter and Neptune); and the determination of the compositional and thermal structure in Jupiter's auroral region using line profiles of auroral ethylene (C 2H 4) and ethane (C 2H 6) emission near 10.5 and 12 μm. The value of multispectral and temporal observations for more comprehensive studies of atmospheric phenomena and the internal and external processes driving them are also discussed.
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