Plume Development of the Shoemaker-Levy 9 Comet Impact

We have studied plume formation after a Jovian comet impact using the ZEUS-MP 2 hydrodynamics code. The three-dimensional models followed objects with 500, 750, and 1000 meter diameters. Our simulations show the development of a fast, upward-moving component of the plume in the wake of the impacting comet that "pinches off" from the bulk of the cometary material ~50 km below the 1 bar pressure level, ~100 km above the depth of greatest mass and energy deposition. The fast-moving component contains about twice the mass of the initial comet, but consists almost entirely (>99.9%) of Jovian atmosphere rather than cometary material. The ejecta rise mainly along the impact trajectory, but an additional vertical velocity component due to buoyancy establishes itself within seconds of impact, leading to an asymmetry in the ejecta with respect to the entry trajectory. The mass of the upward-moving component follows a velocity distribution M(>v) approximately proportional to v^-1.4 (v^-1.6 for the 750 m and 500 m cases) in the velocity range 0.1 < v < 10 km/s.Comment: 5 pages, 4 figures. Accepted for publication in The Astrophysical Journa

Network analysis of protein dynamics

The network paradigm is increasingly used to describe the topology and dynamics of complex systems. Here we review the results of the topological analysis of protein structures as molecular networks describing their small-world character, and the role of hubs and central network elements in governing enzyme activity, allosteric regulation, protein motor function, signal transduction and protein stability. We summarize available data how central network elements are enriched in active centers and ligand binding sites directing the dynamics of the entire protein. We assess the feasibility of conformational and energy networks to simplify the vast complexity of rugged energy landscapes and to predict protein folding and dynamics. Finally, we suggest that modular analysis, novel centrality measures, hierarchical representation of networks and the analysis of network dynamics will soon lead to an expansion of this field.Comment: 10 pages, 2 figures, 1 tabl

Moist Convection in the Giant Planet Atmospheres

The outer planets of our Solar System display a myriad of interesting cloud features, of different colors and sizes. The differences between the types of observed clouds suggest a complex interplay between the dynamics and chemistry at play in these atmospheres. Particularly, the stark difference between the banded structures of Jupiter and Saturn vs. the sporadic clouds on the ice giants highlights the varieties in dynamic, chemical and thermal processes that shape these atmospheres. Since the early explorations of these planets by spacecrafts, such as Voyager and Voyager 2, there are many outstanding questions about the long-term stability of the observed features. One hypothesis is that the internal heat generated during the formation of these planets is transported to the upper atmosphere through latent heat release from convecting clouds (i.e., moist convection). In this review, we present evidence of moist convective activity in the gas giant atmospheres of our Solar System from remote sensing data, both from ground- and space-based observations. We detail the processes that drive moist convective activity, both in terms of the dynamics as well as the microphysical processes that shape the resulting clouds. Finally, we also discuss the effects of moist convection on shaping the large-scale dynamics (such as jet structures on these planets)

Addition Of Water And Ammonia Cloud Microphysics To The Epic Model

An active hydrological cycle has been added to the EPIC general circulation model (GCM) for planetary applications, with a special emphasis on Jupiter. Scientists have suspected for decades that clouds, and in particular latent heating, strongly influence Jupiter\u27s atmospheric dynamics and this research provides a tool to investigate this phenomenon. Components of the model have been adapted for the planetary setting from recently published Earth microphysics schemes. The behavior of the cloud model is investigated in two steps. First, we explore in detail the runtime properties of a nominal model, and second, through sensitivity tests we determine how the full microphysics and selected components of the scheme affect the formation and evolution of clouds and precipitation. Results from our one-dimensional (vertical) simulations match expectations based on thermochemical models about the vertical positioning of ammonia and water clouds, and the nature of precipitation. Using (two-dimensional) meridional plane simulations, we investigate the latitudinal variation of clouds. We conclude that the zonal-wind structure under the visible cloud deck strongly affects the position of the cloud bases, also that the atmospheric dynamics modifies the resulting cloud structure that we can determine in 1D models. We describe in detail an equatorial storm system observed in our 2D simulations. We also show that simplification of our microphysics scheme would improperly simulate large-scale weather phenomena on Jupiter. We support future laboratory tests and in situ measurements that would improve the cloud parameterization scheme and would also add more constraints on the global distribution of condensibles and on the zonal wind-structure. The complete computer program resulting from this research can be downloaded as open-source software from NASA\u27s Planetary Data System (PDS) Atmospheres node. © 2007 Elsevier Inc. All rights reserved

Drifting Ice Giant Dark Spots And Their Potential Connections To Terrestrial Hurricanes

The natural disasters associated with hurricane Sandy are but one example of the dangers presented by hurricanes and typhoons. Predicting the track of these features remains a significant meteorological challenge, with predictive models often diverging significantly within a couple of days. The difficulty of hurricane prediction is linked to the number of factors influencing their movement, including ocean temperature and currents, land masses, broader weather patterns, the jet stream, cloud microphysics, and the coriolis effect. All of these factors help mask the underlying mechanisms driving hurricane drift and thereby limiting our understanding of these phenomena. However, terrestrial hurricanes are not the only example of coherent, drifting atmospheric vortices. The first Great Dark Spot, a geophysical vortex discovered by Voyager II on Neptune in 1989, drifted about 10 degrees in latitude over eight months of direct observation. In 2005, a long lived cloud feature on Uranus called the “Berg” suddenly began to drift towards the equator at a rate of several degrees per year, an event possibly linked to a hidden vortex beneath the clouds. These systems, with no land or oceans and simpler background weather patterns, may provide a more straightforward analysis of vortex drift than terrestrial features while sharing fundamental mechanisms that drive the motion. Improvements to a current General Circulation Model used to analyze the Ice Giant atmospheres now allow a more detailed investigation of these drifting vortices and the possible connections between their motions and those of hurricanes

Numerical Investigation Of Orographic Cloud And Vortex Dynamics On Ice Giant Planets

Farther out and smaller than Jupiter and Saturn, Neptune and Uranus form a pair of planets known as the ice giants. These ice giants share similar atmospheric conditions and chemistry, including strikingly bright methane cloud features. These features are typically the most visible phenomena in these atmospheres as observed from earth. Some of these clouds are orographic in nature, tracking the motions of large vortex features known as Dark Spots. In 1989, the Voyager II encounter with Neptune revealed such a pairing, with first Great Dark Spot (GDS-89), arguably the most dynamic large vortex feature in the outer solar system, matched with an orographic bright companion cloud. Later Hubble Space Telescope observations revealed two other Dark Spots on Neptune in the northern hemisphere, dubbed NGDS-32 and NGDS-15, the former of which appeared to have an orographic feature. All of the Neptune Dark Spots are transient, lasting months to a few years, and the most recent HST observations evidenced no GDS activity. In contrast, Uranus showed no vortex features during the Voyager II encounter in 1986, but in the summer of 2006 what is likely the first observed GDS on Uranus was spotted. There is some evidence that a bright, possibly orographic cloud feature tracked this vortex at certain times. This paper numerically investigates the source of these orographic features and their influence on the vortex dynamics through simulations with a general circulation model called EPIC. Understanding these features will provide increased insight into the planetary atmosphere environment on the ice giants, enabling comparative meteorology and enhancing our ability to design future missions to this planet

Influence Of Persistent Companion Clouds On Geophysical Vortex Dynamics

Large geophysical vortices provide some of the most dramatic features in the known atmospheres, from hurricanes on Earth to the Great Red Spot on Jupiter. A notable difference between the Great Red Spot and terrestrial hurricanes is that hurricanes are more dynamic, changing shape and location in response to internal and external conditions. In contrast, large vortices on the outer two gas giant planets, Uranus and Neptune, have exhibited a greater tendency toward dynamics more akin to hurricanes. The most notable of these dynamic vortices was the original Great Dark Spot observed by Voyager II in 1989, which through eight months of observation drifted towards the equator by ten degrees in latitude and oscillated in shape over an eight-day period during the month of closest observation. Also like hurricanes, it now appears that clouds also play a critical role in governing the dynamics of these features, most importantly in terms of persistent orographic companion clouds that form in the vicinity of some of these vortices. However, to better understand the vertical as well as horizontal motions requires highest resolution simulations of these features. This paper will discuss the evidence of cloud effects on the vortex dynamics and progress on achieving the higher resolution vortex simulations that more accurately simulate the cloud physics. A deeper exploration of the cloud-vortex interaction will give us a better understanding of the physics of the ice giant atmospheres. In turn, this may help elucidate the motions of hurricanes on Earth through the application of comparative planetology. © 2010 by the authors