Engineering topics

Conrath, B. J.

Publications and source records attributed to Conrath, B. J..

At least 37 records · Page 2

NASA NTRS1992

A seasonal radiative-dynamic model of Saturn's troposphere

The present steady-state, linearized and zonally-averaged model of the thermal response of Saturn's atmosphere to seasonal insolation is compared with extant data in order to extract diagnostic information on the planet's troposphere and stratosphere. The planet's rings are shown to constitute a strong modulator of the seasonal insolation function. A detailed comparison of the model with existing temperature measurements shows that the large thermal inertia of Saturn and uncertainties in the wind and thermal measurements overwhelm the rings' thermal effects. A meridional asymmetry in heating is noted which is consistent with an enhancement of aerosols and of photochemically generated ethane and acetylene in the southern hemisphere's summer.

Barnet, C. D.↗

NASA NTRS1992

Exploration of the solar system by infrared remote sensing

The remote sensing of objects in the solar system using infrared radiation is discussed. Theories of radiative transfer, molecular spectroscopy, and atmospheric physics are used to show how infrared spectra of model planetary atmospheres are calculated. Instrumental techniques are described and the effect of instruments on the measurement of the emerging radiation field is addressed. Techniques that allow the retrieval of atmospheric and surface parameters from observations are examined. All the planets except Pluto are studied, and many of the planetary satellites.

Hanel, R. A.↗

NASA NTRS1991

The helium abundance of Neptune from Voyager measurements

The He abundance in the Neptunian atmosphere is estimated using results from Voyager radio occultation and IR spectrometer measurements. It is found that the shape of the measured spectrum cannot be matched by spectra calculated from atmospheric models that include only gaseous opacity, indicating that there might exist an additional opacity source associated with clouds or hazes. The data obtained could be fit with either of the two general classes of horizontally homogeneous cloud opacity models: (1) a model consisting of a tropospheric cloud with an optical thickness at 200/cm between 1 and 8; and (2) a stratospheric cloud with an optical thickness between 0.2 and 0.8.

Conrath, B. J.↗

NASA NTRS1991

The albedo, effective temperature, and energy balance of Neptune, as determined from Voyager data

Data from the Voyager infrared spectrometer and radiometer (IRIS) investigation are used in determining the albedo, effective temperature, and energy balance of Neptune. From broadband radiometric observations made at phase angles of 14 deg and 134 deg, together with measurements at intermediate phase angles from the literature, an orbital mean value of 0.290 +/-0.067 is obtained for the bolometric Bond albedo. This yields an equilibrium temperature Teq = 46.6 +/-1.1 K. From thermal spectra obtained over latitudes from pole to pole an effective temperature Teff = 59.3 +/-0.8 K is derived. This represents a substantial improvement over previously determined values. The energy balance of Neptune is therefore E = 2.61 +/-0.28, which is in agreement with previous results. The reduced uncertainty in this value is due to the improved determination of the effective temperature.

Pearl, J. C.↗

NASA NTRS1991

Thermal structure and dynamics of Neptune's atmosphere from Voyager measurements

The thermal structure of the Neptunian atmosphere between 50 and 10 mbar is characterized using spatially resolved Voyager IR spectra from a global mapping sequence. A zonal mean meridional temperature cross section was obtained which shows a minimum in the upper tropospheric and lower stratospheric temperatures at the southern mid-latitudes, and maxima at the equator and at high southern latitudes. This structure is qualitatively similar to the thermal structure of the Uranian atmosphere, even though the obliquities and the internal heat fluxes of the two planets are quite different.

Conrath, B. J.↗

NASA NTRS1991

Thermal structure and energy balance of Uranus

The present study determines the basic properties of the atmospheric temperature field of Uranus through a combination of earth-based and Voyager measurements. Stellar occultation observations indicate both spatial and temporal variability at microbar pressure levels. The tropospheric and stratospheric vertical structure are established via Voyager radio occultation and infrared measurements as well as earth-based full-disk infrared observations. It is found that the measured lapse rate at pressures greater than about 600 microbar exceeds that for fully equilibrated ortho and para hydrogen. The latitude dependence of the upper tropospheric temperatures is determined from Voyager infrared measurements; remarkably little contrast is found. The weak horizontal structure is consistent with tropospheric zonal winds which decay with height and are directed prograde at midlatitudes but retrograde at low latitudes.

Conrath, B. J.↗

NASA NTRS1990

Titan's stratospheric temperatures - A case for dynamical inertia?

Voyager IRIS spectral radiances in the nu4-band of CH4 for the Titan atmosphere exhibit a hemispheric asymmetry. While asymmetry in the meridional distribution of opacity about the equator cannot be discounted, attention is given to the need for angular momentum transport concurrent with seasonally varying temperatures in the Titan stratosphere, which would maintain the cyclostrophic thermal wind relation between zonal winds and temperatures. The adiabatic heating and cooling associated with these motions can produce the observed temperature asymmetry.

Flasar, F. M.↗

NASA NTRS1990

The albedo, effective temperature, and energy balance of Uranus, as determined from Voyager IRIS data

The albedo, T(eff), and energy balance of Uranus are presently derived from Voyager IR Spectrometer and Radiometer data. By obtaining the absolute phase curve of Uranus, it has become possible to evaluate the Bond albedo without making separate determinations of the geometric albedo and phase integral. An orbital mean value for the bolometric Bond albedo of 0.3 + or - 0.049 yields an equilibrium temperature of 58.2 + or - 1.0 K. Thermal spectra from pole-to-pole latitude coverage establish a T(eff) of 59.1 + or - 0.3 K, leading to an energy balance of 1.06 + or - 0.08 for Uranus.

Pearl, J. C.↗

NASA NTRS1990

Thermal emission spectroscopy of the middle atmosphere

The general objective of this research is to obtain, via remote sensing, simultaneous measurements of the vertical distributions of stratospheric temperature, ozone, and trace constituents that participate in the catalytic destruction of ozone (NO(sub y): NO, NO2, NO3, HNO3, ClONO2, N2O5, HNO4; Cl(sub x): HOCl), and the source gases for the catalytic cycles (H2O, CH4, N2O, CF2Cl2, CFCl3, CCl4, CH3Cl, CHF2Cl, etc.). Data are collected during a complete diurnal cycle in order to test our present understanding of ozone chemistry and its associate catalytic cycles. The instrumentation employed is an emission-mode, balloon-borne, liquid-nitrogen-cooled Michelson interferometer-spectrometer (SIRIS), covering the mid-infrared range with a spectral resolution of 0.020 cm(exp -1). Cryogenic cooling combined with the use of extrinsic silicon photoconductor detectors allows the detection of weak emission features of stratospheric gaseous species. Vertical distributions of these species are inferred from scans of the thermal emission of the limb in a sequence of elevation angles. The fourth SIRIS balloon flight was carried out from Palestine, Texas on September 15-16, 1986 with 9 hours of nighttime data (40 km). High quality data with spectral resolution 0.022 cm(exp -1), were obtained for numerous limb sequences. Fifteen stratospheric species have been identified to date from this flight: five species from the NO(sub y) family (HNO3, NO2, NO, ClONO2, N2O5), plus CO2, O3, H2O, N2O, CH4, CCl3F, CCl2F2, CHF2Cl, CF4, and CCl4. The nighttime values of N2O5, ClONO2, and total odd nitrogen have been measured for the first time, and compared to model results. Analysis of the diurnal variation of N2O5 within the 1984 and 1986 data sets, and of the 1984 ClONO2 measurements, were presented in the literature. The demonstrated ability of SIRIS to measure all the major NO(sub y) species, and therefore to determine the partitioning of the nitrogen family over a continuous diurnal cycle, is a powerful tool in the verification and improvement of photochemical modeling.

Kunde, V. G.↗

NASA NTRS1989

Slowly moving thermal features on Jupiter

Maps of the Jovian upper troposphere temperatures derived from Voyager 1 and Voyager 2 infrared interferometer spectrometer (IRIS) spectra show large-scale features which move very slowly. The motion is very different from the inferred local fluid velocity. It is suggested that these features may indicate a deeply-rooted fluid dynamical regime beneath the surface meteorology.

Magalhaes, J. A.↗

NASA NTRS1989

Thermal structure and heat balance of the outer planets

Current knowledge of the thermal structure and energy balance of the outer planets is summarized. The Voyager spacecraft experiments have provided extensive new information on the atmospheric temperatures and energetics of Jupiter, Saturn and Uranus. All three planets show remarkably small global-scale horizontal thermal contrast, indicating efficient redistribution of heat within the atmospheres or interiors. Horizontal temperature gradients on the scale of the zonal jets indicate that the winds decay with height in the upper troposphere. This suggests that the winds are driven at deeper levels and are subjected to frictional damping of unknown origin at higher levels. Both Jupiter and Saturn have internal power sources equal to about 70 percent of the absorbed solar power. This result is consistent with the view that significant helium differentiation has occurred on Saturn. Uranus has an internal power no greater than 13 percent of the absorbed solar power, while earth-based observations suggest Neptune has an internal power in excess of 100 percent of the absorbed solar power.

Conrath, B. J.↗

NASA NTRS1987

Voyager infrared observations of Uranus' atmosphere - Thermal structure and dynamics

The temperature structure of the Uranus atmosphere is investigated on the basis of 325/cm and 225/cm Voyager 2 IRIS observations of a layer between 60 and 200 mbar (including the tropopause). The data are presented in graphs and analyzed in detail. The latitudinal variations of the temperature near the tropopause and the inferred thermal winds are shown to be in good agreement with the findings reported for lower altitudes by Hanel et al. (1986), although greater in amplitude. A linear zonally symmetric circulation model with no solar and condensation heating, a frictional damping time 1-2 times the radiative damping time, a subrotating atmosphere at low latitudes, and zonal winds decaying with altitude is proposed to account for the observed structures.

Flasar, F. M.↗

NASA NTRS1987

Atmospheric infrared emission of ClONO2 observed by a balloon-borne Fourier spectrometer

ClONO2 was observed in high-resolution infrared emission spectra obtained on Nov. 6, 1984, by a balloon-borne Fourier spectrometer. The observations took place near 0300 LT at a latitude of 35 N. Spectral simulations are used to determine the mixing ratios of ClONO2. This analysis incorporates line by line calculations and new ClONO2 cross sections measured in the laboratory at 223 K. The inferred mixing ratios of ClONO2 are 1.3 + or - 0.45 ppb and 0.98 + or - 0.35 ppb at 14 and 34 mbar. One-dimensional photochemical model predictions are compared to the observations. The ClONO2 mixing ratio at 34 mbar appears to be larger than theory, while there is agreement at 14 mbar.

Massie, S. T.↗

NASA NTRS1987

Simultaneous measurement of stratospheric O3, H2O, CH4, and N2O profiles from infrared limb thermal emissions

Thermal emission measurements of the earth's stratospheric limb were made with a cryogenically cooled high-resolution Michelson interferometer on a balloon flight launched from Palestine, TX, on Nov. 6, 1984. Infrared spectra for complete limb sequences were obtained over portions of the 700-1940/cm range with an unapodized spectral resolution of 0.03/cm for tangent heights varying from 13 to 39 km. The observed data from 1125 to 1425/cm have been analyzed for simultaneous measurement of O3, H2O, CH4, and N2O profiles. The analysis employs line-by-line and layer-by-layer radiative-transfer calculations, including curvature and refraction effects. The optimum use of geometric and spectral effects is made to obtain sharply peaked weighting functions. Contributions from stratospheric aerosol are included by measuring the light extinction within the window regions of the observed spectra. The retrieved constituent profiles are compared with measurements made with a variety of techniques by other groups. The comparison shows good agreement with the published data for all gases, indicating the capability of retrieving trace gas profiles from high-resolution thermal emission limb measurements.

Abbas, M. M.↗

NASA NTRS1987

Infrared spectroscopy of the lower stratosphere with a balloon-borne cryogenic Fourier spectrometer

The IR limb emission of the lower stratosphere has been measured using a balloon-borne liquid nitrogen-cooled Michelson interferometer with liquid helium-cooled Si:Ga detectors. Portions of the thermal emission spectrum have been recorded between 650 and 2000/cm with an unapodized spectral resolution of 0.03/cm. This is the highest spectral resolution limb emission thus far obtained. A preliminary description is given of these data along with a discussion of the significant features. Species identified to date include CO2, O3, CFCl3, CF2Cl2, H2O, CH4, HNO3, N2O, NO2, and ClONO2. A tentative identification is made for NO, representing the first direct spectroscopic detection of NO in emission.

Kunde, Virgil G.↗

NASA NTRS1986

Retrieval of ammonia abundances and cloud opacities on Jupiter from Voyager IRIS spectra

Gaseous ammonia abundances and cloud opacities are retrieved from Voyager IRIS 5- and 45-micron data on the basis of a simplified atmospheric model and a two-stream radiative transfer approximation, assuming a single cloud layer with 680-mbar base pressure and 0.14 gas scale height. Brightness temperature measurements obtained as a function of emission angle from selected planetary locations are used to verify the model and constrain a number of its parameters.

Conrath, B. J.↗

NASA NTRS1986

Zonal mean properties of Jupiter's upper troposphere from Voyager infrared observations

Voyager IRIS spectra of Jupiter are used to derive zonal averages for 270- and 150-mb temperatures, as well as optical depths through the troposphere at two temperatures, ammonia concentrations near the 680-mb level, and the parahydrogen fraction near the 270-mb level. Simple modeling of an axisymmetric circulation incorporating the linear damping of perturbations from a uniform state for both winds and temperature yields results that are consistent with observed thermal wind shears and with the vertical motion field.

Gierasch, P. J.↗

NASA NTRS1985

Finite field of view effects on inversion of limb thermal emission observations

It is pointed out that the technique of thermal emission spectroscopy provides an effective means for remote sounding of stratospheric temperature structure and constituent distributions. One procedure for measuring the stratospheric infrared spectrum involves the conduction of observations along ray paths tangent to the stratospheric limb. Thermal emission limb tangent observations have certain advantages compared to other types of observations. The techniques for determining temperature and trace gas distributions from limb thermal emission radiances are based on the assumption that the bulk of opacity lies near the tangent point. Ideally, the field of view (FOV) of the observing instrument should be very small. The effect of a finite FOV is to reduce the spatial resolution of the retrieved temperature and constituent profiles. The present investigation is concerned with the effects of the FOV on the inversion of infrared thermal emission measurements for balloon platforms. Attention is given to a convenient method for determining the weighting functions.

Abbas, M. M.↗