I. G. Nolt

Spatially resolved infrared observations of Saturn II. The temperature enhancement at the South pole of Saturn

Abstract North-South scans of Saturn at 17.8, 19.7, and 22.7 μm show enhanced emission from the South polar region. This effect is consistent with the polar brightening observed in the 12 μm ethane band (Gillett and Orton, 1975; Rieke, 1975), and it indicates that the temperature inversion is hotter at the South pole than at the equator. A model for the temperature inversion of the South pole is constructed and compared to the observations.

Spatially resolved infrared observations of Saturn: I. Equatorial limb scans at 20 μm

Abstract Drift scans of the equator of Saturn have been obtained through narrow band filters at 17.8, 19.7, and 22.7 μm. Spatial resolution was ≃17% of the equatorial diameter. These observations clearly differentiate otherwise tenable atmospheric models. A published model by A. Tokunaga and R.D. Cess [Icarus 32, 321–327 (1977)] is shown to represent these new observations significantly better than other models from the literature.

Multifrequency observations of blazars. II - The variability of the 1 micron to 2 MM continuum

The results of monitoring, over a period of two years, a sample of 12 blazars, in 11 wave bands between 1 micron and 2 mm are presented. All sources exhibit some variability, both in flux density and spectral shape. The infrared variability is consistent with repeated injections of reaccelerations of electrons, which subsequently suffer radiative losses. For OJ 287, 3C 279, and 3C 345, a decay and steepening of the infrared spectrum occurred as the submillimeter turnover evolved to lower frequencies, consistent with expansion of the emitting region. The peak flux, however, increased during this evolution. This behavior is inconsistent with most models for compact extragalactic sources, but it is naturally explained by shock waves traveling in an adiabatically expanding relativistic jet (Marscher and Gear, 1985).

Temporal characteristics of the Jovian atmosphere

Drift scans along the central meridian of Jupiter have been obtained at wavelengths of 7.9, 17.8, and 19.7 microns. These observations indicate a significant north-south temperature asymmetry within the Jovian stratosphere but not within its troposphere, results which agree with the recent Voyager 1 observations. Employing a time-dependent stratospheric model, it is found that the observed north-south asymmetry is consistent with seasonal stratospheric variability. In the model, the primary cause for this variability is the time-dependent absorption of sunlight by aerosols.

Spatially resolved infrared observations of Saturn III. 10- and 20-μm disk scans at B′ = −11°.8

Abstract Disk scans of Saturn at 10 and 20 μm were obtained when the Saturnicentric solar declination ( B ′) was −11°.8. The scans show little change from scans obtained when B ′ was −16°.3, and this could result from the long radiative time constant of the Saturnian atmosphere. The observations at 20 μm, in the H 2 continuum, show positively that the temperature inversion at the south pole has a higher temperature than at any other point on the disk. In addition, the 12.1- and 20-μm scans indicate that the temperature of the inversion region is higher at the equator compared to the temperate zone. The data also suggest that enhanced 20-μm emission is correlated with the strength of the ultraviolet absorption.

Millimeter and submillimeter observations of 3C 273

The first detection of 3C 273 (1226 + 023) at wavelengths of 107, 240, and 400 microns together with contemporary measurements at 800 microns, 1.1, 1.9, 3.3, and 8.9 mm, is reported. These observations show that the continuum spectrum of 3C 273 can be extrapolated smoothly from the submillimeter to the infrared with a constant spectral index. There is no evidence of thermal emission from dust. It is shown that the spectrum is consistent with optically thin synchrotron emission from a relativistic beam at a small angle to the line of sight.

Infrared passbands for clear-air-turbulence detection

Clear air turbulence (CAT) ahead of an aircraft can be detected in real time by an infrared radiometer. The alert time and reliability depend on the passband of the infrared filter used and the altitude of the aircraft. Preliminary results and analyses show that a nominal passband of 26 to 35 microm appears optimal to alert CAT from 1.5 to 6.0 min ahead of the encounter. The alert time increases with higher altitude as the atmospheric absorption, determining the horizontal weighting, is reduced.

Latitudinal variations in Jovian stratospheric temperature

Ground-based observations of Jupiter show that the planets stratospheric and tropospheric thermal emission are anticorrelated. The observations can possibly be explained by latitudinal variations in cloud altitude. These variations cause differential stratospheric heating by sunlight which is reflected off the clouds and then absorbed within the stratosphere by visible and near-infrared bands of methane.

Millimeter-wave observations of flat spectrum radio sources

Measurements at wavelengths between 0.4 and 2.0 mm of a sample of 26 compact, flat spectrum radio sources are presented. These observations extend the known radio spectra of this class of sources to higher frequencies and show that most of these sources are still flat at short millimeter wavelengths. The spectral shapes are consistent with an inhomogeneous synchrotron model (with some degree of relativistic beaming); however, the lack of concurrent multifrequency data prevents more definite conclusions at this stage.

Far-infrared spectroscopy of the earth's stratosphere

This paper discusses the spectrum of the earths stratosphere in the far-infrared, from 5 to 250/cm. Many of the trace gases that are important in stratospheric photochemistry have been measured, or are potentially measurable in the far-infrared. The spectral features of these gases are discussed with application to spacecraft measurements. In particular, the suitability of the spectrum for measurements of the HO(x) and ClO(x) families and of O3 are compared for different classes of instruments: Fourier transform spectrometers, filter radiometers, and scanning high-resolution Fabry-Perot instruments. It is found that these types of instruments have complementary capabilities that would best be used in combination in a comprehensive multispecies measurement scheme.