Sanjay S. Limaye

Voyager 2 at Neptune: Imaging Science Results

Voyager 2 images of Neptune reveal a windy planet characterized by bright clouds of methane ice suspended in an exceptionally clear atmosphere above a lower deck of hydrogen sulfide or ammonia ices. Neptunes atmosphere is dominated by a large anticyclonic storm system that has been named the Great Dark Spot (GDS). About the same size as Earth in extent, the GDS bears both many similarities and some differences to the Great Red Spot of Jupiter. Neptunes zonal wind profile is remarkably similar to that of Uranus. Neptune has three major rings at radii of 42,000, 53,000, and 63,000 kilometers. The outer ring contains three higher density arc-like segments that were apparently responsible for most of the ground-based occultation events observed during the current decade. Like the rings of Uranus, the Neptune rings are composed of very dark material; unlike that of Uranus, the Neptune system is very dusty. Six new regular satellites were found, with dark surfaces and radii ranging from 200 to 25 kilometers. All lie inside the orbit of Triton and the inner four are located within the ring system. Triton is seen to be a differentiated body, with a radius of 1350 kilometers and a density of 2.1 grams per cubic centimeter; it exhibits clear evidence of early episodes of surface melting. A now rigid crust of what is probably water ice is overlain with a brilliant coating of nitrogen frost, slightly darkened and reddened with organic polymer material. Streaks of organic polymer suggest seasonal winds strong enough to move particles of micrometer size or larger, once they become airborne. At least two active plumes were seen, carrying dark material 8 kilometers above the surface before being transported downstream by high level winds. The plumes may be driven by solar heating and the subsequent violent vaporization of subsurface nitrogen.

Models of the structure of the atmosphere of Venus from the surface to 100 kilometers altitude

From a critical comparison and synthesis of data from the four Pioneer Venus Probes, the Pioneer Venus Orbiter, and the Venera 10, 12, and 13 landers, models of the lower and middle atmosphere of Venus are derived. The models are consistent with the data sets within the measurement uncertainties and established variability of the atmosphere. The models represent the observed variations of state properties with latitude, and preserve the observed static stability. The rationale and the approach used to derive the models are discussed, and the remaining uncertainties are estimated.

Jupiter: New estimates of the mean zonal flow at the cloud level

Abstract Previous estimates of the mean zonal flow on Jupiter from Voyager images by Ingersoll et al. ( A. P. Ingersoll, R. F. Beebe, J. L. Mitchell, G. W. Garneau, G. M. Yagi, and J. P. Mueller (1981) . J. Geophys. Res. 86 , 8733–8743) and by Limaye et al. ( S. S. Limaye, H. E. Revercomb, L. A. Sromovsky, R. J. Krauss, V. E. Suomi, S. A. Collins, and C. C. Avis (1982) . J. Atmos. Sci. 39 , 1413–1432) showed good agreement in the locations of the easterly and westerly jets but differed somewhat in magnitude. Recent measurements of the high-speed jet located near 24° north (plane-topographic) latitude by T. Maxworthy ((1984) . Planet. Space Sci. 32 , 1053–1058) from high spatial and temporal resolution Voyager images indicate that both Ingersoll et al. and Limaye et al. underestimated the magnitude of the jet by more than 30–40 msec −1 . In an attempt to examine the differences in the magnitude of the Jovian jets determined from Voyager 1 and 2 images, a new approach to determine the zonal mean east-west component of motion was investigated. The new technique, based on simple, digital pattern matching approach and applied on pairs of mapped images (cylindrical mosaics) yields a profile of the mean zonal component that reproduces the exact locations of the easterly and westerly jets between ±60° latitude. Not only do the jet magnitudes but also the wings of the jets agree remarkably well from mosaic pair to pair. Further, the latitudinal resolution is five (midlatitudes) to eight times (equatorial) greater than previous results. Results have been obtained for all of the Voyager 1 and 2 cylindrical mosaics. The correlation coefficient between Voyager 1 and Voyager 2 average mean zonal flow between ±60° latitude determined from violet filter mosaics is 0.998. A slight latitude offset, possibly due to navigation errors, is detectable (+0.2 latitude average) in the Voyager 1 data. Independent cloud motion measurements in two high-resolution image pairs (orange and violet) acquired from Voyager 1 cameras agree well with the average mean zonal flow for the fastest Jovian jet at 23.8°N latitude. Comparison with Maxworthys (1984) results suggests longitudinal variations in cloud motions approaching about 20 msec −1 . In particular, the jet magnitude is about 163 ±7 (RMS) msec −1 , which compares well with 182 ± 10 msec −1 reported by Maxworthy. There is excellent agreement in the location of the peak magnitude as well as its shape. The time average Voyager 2 mean zonal flow profile with latitude is presented in a table.

Morphology and dynamics of the upper cloud layer of Venus

Venus is completely covered by a thick cloud layer, of which the upper part is composed of sulphuric acid and some unknown aerosols. The cloud tops are in fast retrograde rotation (super-rotation), but the factors responsible for this super-rotation are unknown. Here we report observations of Venus with the Venus Monitoring Camera on board the Venus Express spacecraft. We investigate both global and small-scale properties of the clouds, their temporal and latitudinal variations, and derive wind velocities. The southern polar region is highly variable and can change dramatically on timescales as short as one day, perhaps arising from the injection of SO2 into the mesosphere. The convective cells in the vicinity of the subsolar point are much smaller than previously inferred, which we interpret as indicating that they are confined to the upper cloud layer, contrary to previous conclusions, but consistent with more recent study.

Cloud Motions on Venus: Global Structure and Organization

Abstract We present results on cloud motions on Venus obtained over a period of 3.5 days from Mariner 10 television images. The implied atmosphere flow is almost zonal everywhere on the visible disk, and is in the same retrograde sense as the solid planet. Objective analysis of motions suggests presence of jet cores (−130 m s−1) and organized atmospheric waves. The longitudinal mean meridional profile of the zonal component of motion of the ultraviolet features shows presence of a midlatitude jet stream (−110 m s−1). The mean zonal component is −97 m s−1 at the equator. The mean meridional motion at most latitudes is directed toward the pole in either hemisphere and is at least an order of magnitude smaller so that the flow is nearly zonal. A tentative conclusion from the limited coverage available from Mariner 10 is that at the level of ultraviolet features mean meridional circulation is the dominant mode of poleward angular momentum transfer as opposed to the eddy circulation.

Earth-Based Observations of the Galileo Probe Entry Site

Earth-based observations of Jupiter indicate that the Galileo probe probably entered Jupiters atmosphere just inside a region that has less cloud cover and drier conditions than more than 99 percent of the rest of the planet. The visual appearance of the clouds at the site was generally dark at longer wavelengths. The tropospheric and stratospheric temperature fields have a strong longitudinal wave structure that is expected to manifest itself in the vertical temperature profile.

McIDAS III: A Modern Interactive Data Access and Analysis System

Abstract A powerful facility for meteorological analysis called the Man Computer Interactive Data Access System (McIDAS) was designed and implemented in the early 1970s at the Space Science and Engineering Center of the University of Wisconsin-Madison. Hardware and software experience gained via extensive use of that facility and its derivatives have led to a newer implementation of McIDAS on a larger computer with significant enhancements to the supporting McIDAS software. McIDAS allows remote and local access to a wide range of data from satellites and conventional observations, time lapse displays of imagery data, overlaid graphics. and current and past meteorological data. Available software allows one to perform analysis of a wide range of digital images as well as temperature and moisture sounding data obtained from satellites. McIDAS can generate multicolor composites of conventional and satellite weather data, radar and forecast data in a wide variety of two- and three-dimensional displays as wel...

Jovian winds from Voyager 2. I - Zonal mean circulation

Abstract Independent measurements of Jovian cloud motions confirm previously published results on the general structure of Jupiters zonal mean circulation. The new results are based on Voyager 2 images and measurement techniques which are different from those used in previous studies. The latitudes of the zonal jets agree with previous results, but there are some differences in the measured speed of the jets which exceed uncertainty estimates. These differences may be due to differences in sampling strategies. The structure of the zonal mean meridional velocity profile has still not been clearly resolved: mean meridional velocities generally differ from zero by no more than their estimated uncertainty. An analysis of successive measurements of the same cloud targets shows that most of the variance of individual velocity measurements is due to true variability of the winds. In agreement with the previous results the curvature of the zonal velocity profile is consistent with barotropic instability within m...

Orbiter Cloud Photopolarimeter Investigation

The first polarization measurements of the orbiter cloud photopolarimeter have detected a planet-wide layer of submicrometer aerosols of substantial visible optical thickness, of the order of 0.05 to 0.1, in the lower stratosphere well above the main visible sulfuric acid cloud layer. Early images show a number of features observed by Mariner 10 in 1974, including planetary scale markings that propagate around the planet in the retrograde sense at roughly 100 meters per second and bright- and dark-rimmed cells suggesting convective activity at low latitudes. The polar regions are covered by bright clouds down to latitudes aproximately 50 degrees, with both caps significantly brighter (relative to low latitudes) than the south polar cloud observed by Mariner 10. The cellular features, often organized into clusters with large horizontal scale, exist also at mid-latitudes, and include at least one case in which a cell cuts across the edge of the bright polar cloud of the northern hemisphere.

Winds of Neptune: Voyager observations of cloud motions

High temporal and spatial resolution images acquired from Voyager cameras have been used to measure cloud motions to improve the meridional profile of the zonal mean circulation on Neptune. A wide range of atmospheric periods between 12 and 21 hours is revealed by the average cloud motions, consistent with the previous observations. New observations have expanded latitudinal coverage, improved the determination of streak motions, especially near 30°N, and added statistical weight to latitudes already covered by previous measurements. Both new and earlier observations have been subjected to quality control procedures to reduce dispersion caused by erroneous observations. The resulting data set emphasizes short time intervals to maximize target recognition. Most reliable cloud targets last less than one Neptune rotation, many only a fraction of it. A broad equatorial retrograde jet extends from approximately 50°S to at least 45°N (the northernmost latitude at which discrete cloud features have been seen). A relatively narrow prograde jet of at least 300 m s−1 is found near 70°S. The wind observations have a high degree of variability, some of which is due to variability of motions; but at many latitudes it reflects observation errors arising from rapid evolution of Neptunes clouds. A bias observed in the measured meridional component is most likely due to a small discrepancy between the true rotation pole of Neptune and the pole position used in the data reduction. Zonal motions and morphology suggest the global circulation to be symmetric about the equator.