Velocity variations of an equatorial plume throughout a Jovian year
Abstract
Analysis of features in the Equatorial Zone of Jupiter has shown that the equatorial plume reported by Pioneer 10 has existed for an 11-yr interval. During this interval the plume has shown an acceleration which can be interpreted as a constant component of 3 × 10−8 m/sec2 and a sinusoidal component which anticorrelates with the planetocentric declination of the Sun, DS, and has an amplitude of −0.96 m/sec per degree change of DS. The sinusoidal component has been interpreted in terms of solar heating. Throughout this interval of time the Equatorial Zone has appeared abnormally dark and has contained many dark projections along the northern edge. When the plume approaches to within 25 to 30° of these features they are deflected in the direction of motion of the plume and then dissipate or become obscured as the plume passes. After passage of the plume normal features are again observed.
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Cited by (11)
Meteorology of Jupiter's equatorial hot spots and plumes from Cassini
2013, IcarusCitation Excerpt :A more recent study by Arregi et al. (2006) that examined hot spots in visible observations stated that hot spots exhibited a dispersion relationship between drift speed and wave number, which was dominant between 8 and 12. Equatorial plumes are immense white cloud streaks located in between hot spots and embedded within the Equatorial Zone (Reese and Beebe, 1976). Stoker (1986) proposed that the plumes were thunderstorm anvil-like structures generated from moist convection within a storm center.
We present an updated analysis of Jupiter’s equatorial meteorology from Cassini observations. For two months preceding the spacecraft’s closest approach, the Imaging Science Subsystem (ISS) onboard regularly imaged the atmosphere. We created time-lapse movies from this period in order to analyze the dynamics of equatorial hot spots and their interactions with adjacent latitudes. Hot spots are relatively cloud-free regions that emit strongly at 5 μm; improved knowledge of these features is crucial for fully understanding Galileo probe measurements taken during its descent through one. Hot spots are quasi-stable, rectangular dark areas on visible-wavelength images, with defined eastern edges that sharply contrast with surrounding clouds, but diffuse western edges serving as nebulous boundaries with adjacent equatorial plumes. Hot spots exhibit significant variations in size and shape over timescales of days and weeks. Some of these changes correspond with passing vortex systems from adjacent latitudes interacting with hot spots. Strong anticyclonic gyres present to the south and southeast of the dark areas appear to circulate into hot spots. Impressive, bright white plumes occupy spaces in between hot spots. Compact cirrus-like ‘scooter’ clouds flow rapidly through the plumes before disappearing within the dark areas. These clouds travel at 150–200 m s−1, much faster than the 100 m s−1 hot spot and plume drift speed. This raises the possibility that the scooter clouds may be more illustrative of the actual jet stream speed at these latitudes. Most previously published zonal wind profiles represent the drift speed of the hot spots at their latitude from pattern matching of the entire longitudinal image strip. If a downward branch of an equatorially-trapped Rossby wave controls the overall appearance of hot spots, however, the westward phase velocity of the wave leads to underestimates of the true jet stream speed.
Galileo Imaging of Jupiter's Atmosphere: The Great Red Spot, Equatorial Region, and White Ovals
1998, IcarusDuring the first six orbits of the Galileo spacecraft's prime mission, the Solid State Imaging (SSI) system acquired multispectral image mosaics of Jupiter's Great Red Spot, an equatorial belt/zone boundary, a “5-μm hot spot” similar to the Galileo Probe entry site, and two of the classic White Ovals. We present mosaics of each region, approximating their appearance at visible wavelengths and showing cloud height and opacity variations. The local wind field is derived by tracking cloud motions between multiple observations of each region with time separations of roughly 1 and 10 hr. Vertical cloud structure is derived in a companion paper by Banfieldet al. (Icarus135, 230–250). Galileo's brief, high-resolution observations complement Earth-based and Voyager studies and offer local meteorological context for the Galileo Probe results. Our results show that the dynamics of the zonal jets and large vortices have changed little since Voyager, with a few exceptions. We detect a cyclonic current within the center of the predominantly anticyclonic Great Red Spot. The zonal velocity difference between 0° S and 6° S has increased by 20 m sec−1. We measure a strong northeast flow approaching the hot spot. This flow indicates either massive horizontal convergence or the presence of a large anticyclonic vortex southeast of the hot spot. The current compact arrangement of two White Ovals and a cyclonic structure greatly perturbs the zonal jets in that region.
Ground-based imaging of Jovian cloud morphologies and motions. II. The northern hemisphere from 1975 to 1985
1988, IcarusTelescopic photographs of Jupiter obtained during one Jovian year (1975–1985) have been analyzed in order to study the morphology and motions of the great-scale cloud systems present in the northern hemisphere during the epoch pre- and post-Voyager flyby spacecraft mission (see Sanchez-Lavega and Rodrigo 1985, Astron. Astrophys. 148, 67–78, for a similar work in the southern hemisphere). The texture of the north equatorial belt (NEB) was characterized by a variable number of plumes, between 11 and 15 (a mean of 25% have high-albedo heads), rifts (tilted high-albedo clouds crossing the belt in the shear flow sense), and turbulent wavy patterns in the northern edge. We present interactions between these features as observed in 1985. Elongated dark “barges” and rows of small dark spots were observed near the northern edge of the NEB during specific epochs. The high-albedo north tropical zone (NTrZ) was generally homogeneous from 1977 to 1984, but in 1976 little red spots were observed in its interior, and a contrasting (visible and red wavelengths) narrow belt located in its center was present in 1985. However, the most interesting feature in this region was the development of a prominent double disturbance (NTrZD) during 1975 in the high-speed eastward jet at 24°N, of which we present a study of its morphology and kinematics. Pronounced albedo changes were observed in the NTB during the whole period analyzed. Color contrasts in the NTrZ-NTB-NTZ regions were measured in 1985 from broadband relative photometry. North of 34°N there were alternating albedo bands characterized by their longitudinal variability, by the presence of small light spots in the equatorial side of the eastward jets, and by elongated dark sections of the belts on the polar side. The zonal wind profile u(ϕ) measured during this Jovian year is in good agreement with that obtained from Voyager's images and from previous ground-based analysis.
Moist convection: A mechanism for producing the vertical structure of the Jovian Equatorial Plumes
1986, IcarusThis paper examines cumulus cloud formation and vertical motion on Jupiter as a potential mechanism for producing the Equatorial Plumes. A one-dimensional diagnostic model of a Jovian cumulus cloud is developed to calculate profiles of cloud temperature and vertical velocity. Model results depend on the temperature and relative humidity structure of the atmosphere in the vicinity of the cloud and the rate that surrounding air mixes with cloud air. Since these parameters are highly uncertain on Jupiter, model cases are examined for a range of assumed values. The cloud model results are used to demonstrate that, for appropriate choices of model parameters, moist convection can produce the Equatorial Plumes and account for the vertical distribution of aerosols associated with them. The model results are consistent with the following scenario for plume formation. The plumes form in the ammonia cloud deck when ammonia sublimes in rising air parcels. Condensation of ammonia alone cannot provide the vigorous rising motion observed in the Plume cores. Rather, clouds which originate at the water cloud level can lift air to the ammonia cloud level and higher. Water clouds with entrainment rates similar to terrestrial cumulonimbus clouds rise and form the plume anvil clouds when they reach the stable layer above 700 mbar. The high altitude haze which uniformly blankets the equatorial region can also be formed by overshooting water cumulus if some of the rising cloud parcels are relatively undiluted by entrainment.
A model for the vertical cloud structure of Jupiter's Equitorial Plumes is deduced based on an analysis of Voyager images of the equitorial region in the 6190Å methane band and the 6000-Å continuum, and ground-based 8900-Å methane band images of Jupiter. A computer code that represents scattering and absorption from aerosol and gas layers was applied to a heirarchy of increasingly complex model aerosol structures to match the observations in the three wavelengths. The observations are consistent with a model for the vertical cloud structure of the equitorial region that consists of four aerosol layers. A high-altitude haze layer (HAL) with optical depth τ = 1 uniformly blankets the equitorial region at an altitude between 100 and 250 mbar. Below that, a middle-level cloud layer between 400 and 800 mbar contains the well-known Equatorial Plumes. The Plume clouds are optically thick (τ ≥ 12), bright clouds with single scattering albedo . They are probably composed of ammonia ice. The darker () interplume regions contain optically thinner clouds (2 ≤ τ ≤ 5) at the same altitude as the Plumes. An opaque cloud deck between 4000 and 6000 mbar, which is probably composed of water, forms the lowest model layer. In addition to these three layers, a thin forward scattering haze layer above 100 mbar was included in the models for consistency with previous work (Tomasko et al., 1978). We conclude that the vertical structure of the Equatorial Plume clouds is consistent with the hypothesis (Hunt et al., 1981) that the Plumes are caused by upwelling at the ammonia condensation level produced by bouyancy due to latent heat release from the condensation of water clouds nearly three scale heights below the Plumes.
The 1974/1975 Jupiter apparition is described. Photographic images have been measured and zonal velocities are given for all spots observed on four or more dates. Global and localized zonal flow patterns are graphically presented. Methane absorption band imagery at 890 nm indicates that white ovals and red spots are high in altitude, and blue features are cloud-free areas. The motions of blue features are complex and unlike the motions of other features. Interactions or associations between spots at five adjacent atmospheric currents have been observed. Zonal motion within an equatorial plume has been observed. Evidence is presented for a probable source of red spots in the North Tropical Zone.