Joseph A. Pirraglia

Infrared observations of the neptunian system.

The infrared interferometer spectrometer on Voyager 2 obtained thermal emission spectra of Neptune with a spectral resolution of 4.3 cm-1. Measurements of reflected solar radiation were also obtained with a broadband radiometer sensitive in the visible and near infrared. Analysis of the strong C2H2 emission feature at 729 cm-1 suggests an acetylene mole fraction in the range between 9 x 10-8 and 9 x 10-7. Vertical temperature profiles were derived between 30 and 1000 millibars at 70� and 42�S and 30�N. Temperature maps of the planet between 80�S and 30�N were obtained for two atmospheric layers, one in the lower stratosphere between 30 and 120 millibars and the other in the troposphere between 300 and 1000 millibars. Zonal mean temperatures obtained from these maps and from latitude scans indicate a relatively warm pole and equator with cooler mid-latitudes. This is qualitatively similar to the behavior found on Uranus even though the obliquities and internal heat fluxes of the two planets are markedly different. Comparison of winds derived from images with the vertical wind shear calculated from the temperature field indicates a general decay of wind speed with height, a phenomenon also observed on the other three giant planets. Strong, wavelike longitudinal thermal structure is found, some of which appears to be associated with the Great Dark Spot. An intense, localizd cold region is seen in the lower stratosphere, which does not appear to be correlated with any visible feature. A preliminary estimate of the effective temperature of the planet yields a value of 59.3 � 1.0 kelvins. Measurements of Triton provide an estimate of the daytime surface temperature of 38+3-4 kelvins.

Thermal structure of Saturn from Voyager infrared measurements: Implications for atmospheric dynamics

Abstract Saturn atmospheric temperatures at the 150-mbar level retrieved from Voyager IRIS measurements indicate the presence of small-scale meridional gradients which are approximately symmetric with respect to the equator, but are superposed on a large-scale hemispheric thermal asymmetry. Under the assumption that the retrieved values at this atmospheric level represent kinetic temperatures on a constant pressure surface, it is suggested that the small-scale structure is produced by a meriodional circulation associated with the dissipative decay of the zonal winds with height, while the hemispheric asymmetry represents a thermal response to the seasonally varying insolation. The small-scale gradients are correlated with zonal winds derived from Voyager images at mid and high latitudes through the thermal wind relation; the calculated thermal wind shears suggest a decay with height of the jet system toward a state of uniform eatward flow. The existence of the approximately symmetric zonal winds and associated temperature gradients in the presence of a large-scale seasonal thermal response suggests that the jet system is driven at depths substantially below the levels where seasonally modulated insolation is important ( p⪆0.5 bar ).

Albedo, internal heat flux, and energy balance of Saturn

Full-disk and high-resolution measurements recorded during the Voyager 1 flyby of Saturn by the radiometer of the infrared instrument, IRIS, indicate a geometric albedo of 0.242 ± 0.012, which is lower than previous estimates. The given error is largely due to uncertainties in systematic corrections; random effects are small. Combining this measurement with the Pioneer-derived phase integral yields a Bond albedo of 0.342 ± 0.030. Infrared spectra recorded at the same time by the Michelson interferometer, along with a model extrapolation to wavenumbers not covered by the instrument, yield an effective temperature of 95.0 ± 0.4°K. As in the case of the radiometer, random instrumental errors are small, and the quoted error in the effective temperature reflects primarily uncertainties in systematic corrections. The rings of Saturn significantly affect both the short- and long-wavelength fluxes. From these measurements the internal heat flux of Saturn is 2.01 ± 0.14 10−4W cm−2, and the energy balance, defined as the ratio of total emitted to total absorbed energy, is 1.78 ± 0.09.

Infrared Observations of the Uranian System

The infrared interferometer spectrometer (IRIS) on Voyager 2 recorded thermal emission spectra of Uranus between 200 and 400 cm-1 and of Miranda and Ariel between 200 and 500 cm-1 with a spectral resolution of 4.3 cm-1. Reflected solar radiation was also measured with a single-channel radiometer sensitive in the visible and near infrared. By combining IRIS spectra with radio science results, a mole fraction for atmospheric helium of 0.15 � 0.05 (mass fraction, 0.26 � 0.08) is found. Vertical temperature profiles between 60 and 900 millibars were derived from average polar and equatorial spectra. Temperatures averaged over a layer between 400 to 900 millibars show nearly identical values at the poles and near the equator but are 1 or 2 degrees lower at mid-latitudes in both hemispheres. The cooler zone in the southern hemisphere appears darker in reflected sunlight than the adjacent areas. An upper limit for the effective temperature of Uranus is 59.4 kelvins. Temperatures of Miranda and Ariel at the subsolar point are 86 � 1 and 84 � 1 kelvins, respectively, implying Bond albedos of 0.24 � 0.06 and 0.31 � 0.06, respectively. Estimates of phase integrals suggest that these satellites have unusual surface microstructure.

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

Data from the Voyager infrared spectrometer and radiometer (IRIS) investigation are used to determine the albedo, effective temperature, and energy balance of Uranus. From broadband radiometric observations made over a range of phase angles 15° < α < 155°, an orbital mean value for the bolometric Bond albedo, A = 0.300 ± 0.049, is obtained, which yields an equilibrium temperature Teq = 58.2 ± 1.0°K. From thermal spectra obtained over latitudes from pole to pole, an effective temperature Teff = 59.1 ± 0.3°K is derived. This represents a substantial improvement over previously determined values. The energy balance of Uranus is therefore E = 1.06 ± 0.08; the one-standard-error upper limit of 1.14 is lower than previous results.

Martian Tidal Pressure and Wind Fields Obtained from the Mariner 9 Infrared Spectroscopy Experiment

Abstract Using temperature fields derived from the Mariner 9 infrared spectroscopy experiment, the Martian atmospheric tidal pressure and wind fields are calculated. Temperature as a function of local time, latitude, and atmospheric pressure level is obtained by secular and longitudinal averaging of the data. The resulting temperature field is approximated by a spherical harmonic expansion, retaining one symmetric and one asymmetric term each for wavenumber zero and wavenumber one. Vertical averaging of the linearized momentum and continuity equations results in an inhomogeneous tidal equation for surface pressure fluctuations with the driving function related to the temperature field through the geopotential function and the hydrostatic equation. Solutions of the tidal equation show a diurnal fractional pressure amplitude approximately equal to one-half the vertically averaged diurnal fractional temperature amplitude. These results indicate that a diurnal pressure fluctuation of 6–7% existed during the p...

Meridional energy balance of Jupiter

Abstract The meridional energy balance of Jupiter is calculated from high spatial resolution observations by the Voyager 1 infrared spectrometer and radiometer. On a hemispheric scale Jupiter radiates thermal energy to space approximately uniform with latitude while solar energy absorption varies approximately as the solar angle. This implies internal adjustment to the solar energy with a larger contribution poleward of ±45° than in the equatorial zone. The internal flux is modulated by the major visible features of the zone and belt system but, unlike the hemispheric scale where increased internal flux is correlated with decreased solar absorption, on smaller scales the inverse occurs. The energy balance is very likely to be controlled by dynamics, but the relative influence of the upper atmosphere and the interior is not yet clear. Models have been proposed that would explain the pole-to-equator variation in the thermal emission and it is suggested that the smaller scale variations may be the result of forced convective circulation.

Polar Symmetric Flow of a Viscous Compressible Atmosphere: An Application to Mars

Abstract The atmosphere is assumed to be driven by a polar symmetric temperature field and the equations of motion in pressure ratio coordinates are linearized by considering the zero order in terms of a thermal Rossby number RδT(2aΩ)2 where δT is a measure of the latitudinal temperature gradient. When the eddy viscosity is greater than 106 cm2S−1 boundary layer extends far up into the atmosphere making the geostrophic approximation invalid for the bulk of the atmosphere. The surface pressure gradient exhibits a latitudinal dependence opposite that of the depth-averaged temperature. The magnitude of the gradient is dependent upon the depth of the boundary layer, which depends upon the eddy viscosity, the boundary conditions imposed at the surface, and upon the temperature lapse rate. Using a temperature model for Mars based on Mariner 9 infrared spectral data with a 30% increase in the depth-averaged temperature from the winter pole to the subsolar point, the following results were obtained for the increa...

Results from the Infrared Spectroscopy Experiment on Mariner 9

Over 20000 thermal emission spectra of Mars have been obtained, providing extensive diurnal, seasonal and spatial coverage of the planet. Each spectrum covers the spectral range from 200 to 2000 cm−1 with an apodized spectral resolution of 2.4 cm−1; the noise equivalent radiance of the instrument is 0.5 × 10−7 W cm−2 sr−1 (cm−1)−1.