Lunar studies

Two research projects to classify lunar photographic images are reported. The feasibility of using polarimetry to study large scale features on the moon was investigated. A system was built that measured polarization by subtracting two film images taken through perpendicular Polaroid filters, however, no new boundaries were discovered in the pictures which are not already discernable in ordinary photographs. The present status and equipment of a microfiche library system which would allow easy access to selected lunar photographs from all space missions is also reported

Convection without eddy viscosity: An attempt to model the interiors of giant planets

In the theory of hydrostatic quasi-geostrophic flow in the Earth's atmosphere the principal results do not depend on the eddy viscosity. This contrasts with published theories of convection in deep rotating fluid spheres, where the wavelength of the fastest growing disturbance varies as E sup 1/3, where E, the Ekman number, is proportional to the eddy viscosity. A new theory of quasi-columnar motions in stably stratified fluid spheres attempts to capture the luck of the meteorologists. The theory allows one to investigate the stability of barotropic and baroclinic zonal flows that extend into the planetary interior. It is hypothesized that the internal heat Jupiter and Saturn comes out not radially but on sloping surfaces defined by the internal entropy distribution. To test the hypothesis one searches for basic states in which the wavelength of the fastest-growing disturbance remains finite as E tends to zero, and is which the heat flux vector is radially outward and poleward

Science support for the Earth radiation budget sensor on the Nimbus-7 spacecraft

Experimental data supporting the Earth radiation budget sensor on the Nimbus 7 Satellite is given. The data deals with the empirical relations between radiative flux, cloudiness, and other meteorological parameters; response of a zonal climate ice sheet model to the orbital perturbations during the quaternary ice ages; and a simple parameterization for ice sheet ablation rate

Thermal balance of the atmospheres of Jupiter and Uranus

Two-dimensional, radiative-convective-dynamical models of the visible atmospheres of Jupiter and Uranus are presented. Zonally-averaged temperatures and heat fluxes are calculated numerically as functions of pressure and latitude. In addition to radiative heat fluxes, the dynamical heat flux due to large-scale baroclinic eddies is included and is parametrized using a mixing length theory which gives heat fluxes similar to those of Stone. The results for Jupiter indicate that the internal heat flow is non-uniform in latitude and nearly balances the net radiative flux leaving the atmosphere. The thermal emission is found to be uniform in latitude in agreement with Pioneer and Voyager observations. Baroclinic eddies are calculated to transport only a small amount of the meridional heat flow necessary to account for the uniformity of thermal emission with latitude. The bulk of the meridional heat transfer is found to occur very deep in the stable interior of Jupiter as originally proposed by Ingersoll and Porco. The relative importance of baroclinic eddies vs. internal heat flow in the thermal balance of Uranus depends on the ratio of emitted thermal power to absorbed solar power. The thermal balance of Uranus is compared to that of Jupiter for different values of this ratio

Saturn's aurora observed by the Cassini camera at visible wavelengths

The first observations of Saturn's visible-wavelength aurora were made by the Cassini camera. The aurora was observed between 2006 and 2013 in the northern and southern hemispheres. The color of the aurora changes from pink at a few hundred km above the horizon to purple at 1000-1500 km above the horizon. The spectrum observed in 9 filters spanning wavelengths from 250 nm to 1000 nm has a prominent H-alpha line and roughly agrees with laboratory simulated auroras. Auroras in both hemispheres vary dramatically with longitude. Auroras form bright arcs between 70 and 80 degree latitude north and between 65 and 80 degree latitude south, which sometimes spiral around the pole, and sometimes form double arcs. A large 10,000-km-scale longitudinal brightness structure persists for more than 100 hours. This structure rotates approximately together with Saturn. On top of the large steady structure, the auroras brighten suddenly on the timescales of a few minutes. These brightenings repeat with a period of about 1 hour. Smaller, 1000-km-scale structures may move faster or lag behind Saturn's rotation on timescales of tens of minutes. The persistence of nearly-corotating large bright longitudinal structure in the auroral oval seen in two movies spanning 8 and 11 rotations gives an estimate on the period of 10.65 $\pm$0.15 h for 2009 in the northern oval and 10.8$\pm$ 0.1 h for 2012 in the southern oval. The 2009 north aurora period is close to the north branch of Saturn Kilometric Radiation (SKR) detected at that time.Comment: 39 pages, 8 figures, 1 table, 6 supplementary movies, accepted to Icaru

Lunar and planetary studies

This grant supports the core program in planetary astronomy at Caltech. The research includes observations in the IR, sub-mm, mm and cm wavelengths at national and Caltech observatories with a strong emphasis on integrating the observations with spacecraft data and with models of atmospheric structure, dynamics and chemistry. Muhleman's group made extensive observations of Saturn, Uranus and Neptune which are being interpreted in terms of deep atmospheric structures which are obvious in the 2 and 6 cm maps of Saturn and Uranus. The microwave measurements are one of the few sources of information below the 2 bar level. Goldreich is investigating the dynamics of narrow rings with postdoctoral fellow, Pierre-Yves Longaretti. Their work has focused on the role of collisional stresses on the precession of the rings, since the Voyager radio science results imply that the previous model based on the ring's self-gravity is not the entire story. In addition Borderies, Goldreich and Tremaine have completed an investigation of the dynamics of the Encke division in Saturn's A ring

Temperature Variation and the Solar Oblateness

Dicke and Goldenberg's oblateness measurement may be explained by an equatorial temperature excess of 30° K, smoothly distributed in optical depths ≤ 0 01 The resulting brightness variation with solar latitude is concentrated close to the limb, and it is not possible, with data presently available, to distinguish such variation from true oblateness

Temperature variation with latitude in the upper solar photosphere: Relevance to solar oblateness measurements and facular models

Altrock and Canfield's observations of temperature variation with latitude in the upper solar photosphere refer to higher levels (smaller optical depths) than those to which Dicke and Goldenberg's solar oblateness observations refer. These higher levels account for only 1% of Dicke and Goldenberg's observed intensity. Thus Altrock and Canfield's observations are not inconsistent with models which have been proposed to account for solar oblateness observations by means of a brightness variation with solar latitude

The Co-Evolution of Mars’ Atmosphere and Massive South Polar CO₂ Ice Deposit

A Massive CO₂ Ice Deposit (MCID) that rivals the mass of Mars’ current, 96% CO₂ atmosphere was recently discovered to overlie part of Mars’ southern H₂O cap [1]. The MCID is layered: a top layer of 1-10 m of CO₂, the Residual South Polar Cap (RSPC) [2], is underlain by ~10-20 m of H₂O ice, followed by up to three 100s-meter-thick layers of CO2 ice, separated by two layers of ~20-40 m of H₂O ice [3] (Fig. 1). Previous studies invoked orbital cycles to explain the layering, assuming the H₂O ice insulates and seals in the CO₂, allowing it to survive periods of high obliquity [3,4]. We also model that orbital cycles [5] drive the MCID’s development, but instead assume the MCID is in continuous vapor contact with the atmosphere rather than sealed. Pervasive meter-scale polygonal patterning and km-scale collapse pits observed on the sub-RSPC H₂O layer [1,3] are consistent with it being fractured and permeable to CO₂ mass flux. Using currently observed optical properties of martian polar CO₂ ice deposits [6], our model demonstrates that the present MCID is a remnant of larger CO₂ ice deposits laid down during epochs of decreasing obliquity that are eroded, liberating a residual lag layer of H₂O ice, when obliquity increases. With these assumptions, our energy balance model ex-plains why only the south polar cap hosts an MCID, why the RSPC exists, and the observed MCID stratigraphy. We use our model to calculate Mars’ pressure history and the age of the MCID