F. Espenak

Direct measurement of winds on Titan

We report the first direct measurement of wind velocity in the atmosphere of Titan, one of only two examples in our solar system of a slowly-rotating body with a dense atmosphere and a prime target of the Cassini mission. Zonal wind velocity was determined from Doppler shift of ethane lines emitted from Titans stratosphere (∼0.1–7 mbar) measured by infrared heterodyne spectroscopy near 12 µm (λ/Δ λ ≥ 106). Prograde zonal circulation, in the direction of global rotation, is established with 94% statistical confidence. Results provide information regarding Titan meteorology constraining dynamical theories for slowly-rotating bodies, provide otherwise unobtainable data to optimize the Cassini Huygens Probe investigations, and demonstrate the capability for remotely measuring winds on a small, distant object.

Absolute wind velocities in the lower thermosphere of Venus using infrared heterodyne spectroscopy

Abstract Absolute wind velocities in the thermosphere of Venus were retrieved using NASA/Goddard Space Flight Center infrared heterodyne spectrometers at the NASA Infrared Telescope Facility (IRTF) and the McMath Solar Telescope, December 1985 to March 1987. Measurement of beam-integrated Doppler shifts in the nonthermal emission core of the 12C16O2 10.33-μm R(8) line provided sampling of the lower thermospheric wind field (100–120 km) projected along the line of sight. The spectrometers 1–2 arc-sec diffraction-limited beam yielded the spatial resolution necessary for circulation model discrimination. Saturated resonance (Lamb dip) stabilization of the reference CO2 laser local oscillator provided continuous absolute frequency calibration of the spectrometer to

Collision of comet Shoemaker-Levy 9 with Jupiter observed by the NASA infrared telescope facility

The National Aeronautics and Space Administration (NASA) Infrared Telescope Facility was used to investigate the collision of comet Shoemaker-Levy 9 with Jupiter from 12 July to 7 August 1994. Strong thermal infrared emission lasting several minutes was observed after the impacts of fragments C, G, and R. All impacts warmed the stratosphere and some the troposphere up to several degrees. The abundance of stratospheric ammonia increased by more than 50 times. Impact-related particles extended up to a level where the atmospheric pressure measured several millibars. The north polar near-infrared aurora brightened by nearly a factor of 5 a week after the impacts.

Variability of ethane on Jupiter

Abstract Abundances and spatial distributions of ethane in Jupiters stratosphere were obtained from ultrahigh-resolution ( Λ ΔΛ ∼ 10 6 ) spectra of individual C2H6 emission lines in the ν9 band near 12 μm. The accuracy of the retrieved C2H6 mole fractions was evaluated in the context of varying stratospheric temperature profiles and C2H6 altitude distributions. A twofold uncertainty in the accuracy of the obtained abundances is possible. A mean equatorial value for the C2H6 mole fraction of 2.8 ± 0.6 × 10t-6 was retrieved. Significant variability in the ethane line emission and retrieved mole fractions was found near the footprint of Ios flux tube and within the auroral regions. An increase in the ethane emission and abundance is obtained near the south polar region, relative to equatorial and northern latitudes. A significant decrease in ethane emission and abundance was observed in April 1983 near the known “hot spot” at 180° long (System III, 1965) and 60°N lat, where enhanced CH4 and C2H2 emission was previously observed. We suggest that these observed phenomena are caused by a modification of local stratospheric chemistry, possibly by higher order effects of charged particles precipitating along magnetic field lines.

Ground-based infrared measurements of the global distribution of ozone in the atmosphere of Mars

We report measurements of the global distribution of ozone in the atmosphere of Mars, based on Doppler-limited infrared spectroscopy during the period 3–7 June 1988. The Martian spectrum was measured in the region of the P36 transition of 12C16O2 (1031.4774 cm−1) in a search for two O3 lines arising in the ν3 band at 1031.4515 and 1031.4559 cm−1. Surface pressures and temperature profiles were retrieved by inversion of the fully resolved 12C16O2 line. Ozone measurements were obtained at eight beam positions over a range of Martian latitudes (80° S to 20° N) and local solar hour angles (−0.5h to +5.5h). The total O3 column abundance at each position was retrieved by fitting the lines with synthetic spectra generated by a radiative transfer program. The only previous ozone measurement at this season (Ls ∼ 204°) was made above the south polar cap by Mariner 7 and revealed an abundance of 10 μm-atm. However, the retrieved O3 column burdens of this investigation are less than 2.2 μm-atm for all latitudes sampled, consistent with seasonal abundances predicted by the models of Liu and Donahue, and Shimazaki and Shimizu.

Infrared spectral measurement of space shuttle glow

The U.S. Air Force and NASA successfully conducted infrared spectral measurements of the space shuttle glow during STS-39. Preliminary analysis indicates that NO, NO+, OH, and CO produce infrared glow during quiescent orbiter conditions. During orbiter thruster firings the glow intensities in the infrared are enhanced by factors of 10X to 100X with significant changes in spectral distribution. These measurements were obtained with the Spacecraft Kinetic Infrared Test (SKIRT) payload which included a cryogenic infrared circular variable filter infrared spectrometer covering the 0.7 to 5.4 μm wavelength region. Approximately 14,000 spectra of shuttle glow, airglow, aurora, and the orbiter environment were obtained during the eight day mission. The STS-39 Space Shuttle Discovery was launched from the NASA Kennedy Space Center on 28 April 1991 into a 57 deg inclination circular orbit at an altitude of 260 km.

Polar warming in the middle atmosphere of Mars

Abstract We report ground-based laser heterodyne spectroscopy of non-thermal emission in the cores of the 10.33-μmR(8) and 10.72-μmP(32) lines of 12C16O2, obtained at 23 locations on the disk of Mars during the 1984 opposition, at Ls = 130°. The data were obtained at a sub-Doppler spectral resolution, and the temperature of the middle Martian atmosphere (50–85 km) is derived from the frequency width and intensity of the R(8) emission, and from the total intensity of the P(32) emission. We find that the temperature of the middle Martian atmosphere varies with latitude. Near the subsolar latitude, the average 50- to 85-km temperature is close to the radiative equilibrium value for a CO2 atmosphere. However, at high latitudes in both the northern (summer) and southern (winter) hemispheres the 50- to 85-km temperature exceeds the CO2 radiative equilibrium value; a meridional gradient in the range of 0.4 – 0.9°K per degree of latitude is indicated by our data. The highest temperatures are seen at high latitudes in the winter hemisphere, reminiscent of the seasonal effects seen at the Earths mesopause. As in the terrestrial case, this winter polar warming in the Martian middle atmosphere necessitates departures from radiative equilibrium; dynamical heating of order 4 × 102 ergs g−1 sec−1 is required at the edge of the winter polar night. A comparison with 2-D circulation models shows that the presence of atmospheric dust may enhance this dynamical heating at high winter latitudes, and may also account for heating at high latitudes in the summer hemisphere.

Infrared studies of hydrocarbons on Jupiter

Measurements of ethane and ethylene emission lines on Jupiter were made using a dual CO2 laser heterodyne spectrometer. Retrieved abundances of these products of methane photolysis in the Jovian stratosphere were used to test existing photochemical models and to investigate a localized “hot spot” in the northern auroral region.

On the apparent velocity of integrated sunlight. I - 1983-1985

Frequency measurements for the Delta V = 2 transitions of CO in the integrated light spectrum of the sun are presented. The nature and magnitude of systematic errors which typically arise in absolute velocity measurements of integrated sunlight are explored in some detail, and measurements believed accurate at the level of about 5 m/s or less are presented. It is found that the integrated light velocity varies by about 3 m/s or less over a one-day period. Over the long term, the data indicate an increasing blue-shift in these weak infrared lines amounting to 30 m/s from 1983 to 1985. The sense of the drift is consistent with a lessening in the magnetic inhibition of granular convection at solar minimum. Such an effect has implications for the spectroscopic detectability of planetary-mass companions to solar-type stars.

Ethane abundance on Titan

Abstract Ethane (C2H6) abundance in Titans stratosphere is determined from recent ground based high spectral resolution measurements of individual ethane emission line spectra. Lines near 12 μm in the ν9 band of C2H6 were measured at a resolving power of λ/Δλ ∼ 106 with infrared heterodyne spectroscopy at the NASA Infrared Telescope Facility (IRTF). Globally averaged constant-with-height C2H6 mole fractions are retrieved for various possible thermal profiles on Titan. A range of possible stratospheric temperatures is investigated with respect to the data and a corresponding range of acceptable globally averaged ethane mole fractions is retrieved. The data and physical constraints imposed by the observations limit the temperatures in Titans upper stratosphere to 160–180 K. Corresponding acceptable mole fractions can range from 4 × 10−6 to 1.6 × 10−5 depending on the thermal profile used. For a currently “recommended” thermal profile a mole fraction of 9.4(−4.7, +9.4) × 10−6 is retrieved, some-what lower than previous results, but centrally placed in the acceptable temperature-abundance parameter space.