The problem of small divisors in planetary motion

Small divisors caused by certain linear combinations of frequencies appear in all analytical planetary theories. With the exception of the deep resonance between Neptune and Pluto, they can be removed at the expense of introducing secular and mixed secular terms, limiting the domain in which the solution is valid. Because of them classical solutions are known not to converge uniformly; Poincaré referred to them as asymptotic. The KAM theory shows that if one is far enough from exact commensurability and has small enough planetary masses, expansions exist which will converge to quasi-periodic orbits. Solutions showing very small divisors are excluded from this region of convergence. The question of whether they are intrinsic to the problem or are just manifestations of the method of solution is not settled. Problems with a single commensurabily that can be isolated from the rest of the Hamiltonian may have solutions with no small divisors. The problem of two or more commensurabilities remains unsolved.     

The final Galileo SSI observations of Io: orbits G28-I33

We present the observations of Io acquired by the Solid State Imaging (SSI) experiment during the Galileo Millennium Mission (GMM) and the strategy we used to plan the exploration of Io. Despite Galileo's tight restrictions on data volume and downlink capability and several spacecraft and camera anomalies due to the intense radiation close to Jupiter, there were many successful SSI observations during GMM. Four giant, high-latitude plumes, including the largest plume ever observed on Io, were documented over a period of eight months; only faint evidence of such plumes had been seen since the Voyager 2 encounter, despite monitoring by Galileo during the previous five years. Moreover, the source of one of the plumes was Tvashtar Catena, demonstrating that a single site can exhibit remarkably diverse eruption styles—from a curtain of lava fountains, to extensive surface flows, and finally a ∼400 km high plume—over a relatively short period of time (∼13 months between orbits I25 and G29). Despite this substantial activity, no evidence of any truly new volcanic center was seen during the six years of Galileo observations. The recent observations also revealed details of mass wasting processes acting on Io. Slumping and landsliding dominate and occur in close proximity to each other, demonstrating spatial variation in material properties over distances of several kilometers. However, despite the ubiquitous evidence for mass wasting, the rate of volcanic resurfacing seems to dominate; the floors of paterae in proximity to mountains are generally free of debris. Finally, the highest resolution observations obtained during Galileo's final encounters with Io provided further evidence for a wide diversity of surface processes at work on Io.     

The Sensitivity of Australian Fire Danger to Climate Change

Global climate change, such as that due to the proposed enhanced greenhouseeffect, is likely tohave a significant effect on biosphere-atmosphere interactions, includingbushfire regimes. Thisstudy quantifies the possible impact of climate change on fire regimes byestimating changes infire weather and the McArthur Forest Fire Danger Index (FDI), an index thatis used throughoutAustralia to estimate fire danger. The CSIRO 9-level general circulation model(CSIRO9 GCM)is used to simulate daily and seasonal fire danger for the present Australianclimate and for adoubled-CO₂ climate. The impact assessment includes validation ofthe GCMs daily controlsimulation and the derivation of correction factors which improve theaccuracy of the firedanger simulation. In summary, the general impact of doubled-CO₂is to increase firedanger at all sites by increasing the number of days of very high and extremefire danger.Seasonal fire danger responds most to the large CO₂-induced changesin maximumtemperature.     

Effects of the passage of an IMF discontinuity on the polar cap geometry and the formation of a polar cap arc

Changes of the geometry of the open field line region (namely, the polar cap) caused by the passage of a tangential IMF discontinuity are simulated using the model constructed by Akasofu and Roederer (1983). A singly-bounded open field line region tends to split into two, forming a narrow closed field line region and thus allowing the formations of a plasma sheet and of an auroral arc across the highest latitude region of the Earth. The three-dimensional geometry of some of the closed field lines in the narrow closed region is examined. In this connection, an interesting observation of the formation of an auroral arc over Thule, Greenland, is reported.     

Wind forced transport fluctuations of the Florida Current within the straits of Florida

Volume transport fluctuations of the Florida Current (Gulf Stream), generated within the Straits of Florida by local meridional wind stress, is investigated. A simple coastal response model was applied to the Straits of Florida and forced by along-channel winds only. The predicted volume transports were in good agreement with transport estimates derived from moored current meters and cable voltages for winter winds. Surprisingly, good agreement was also found for the annual transport cycle for the two years of available data, suggesting that the seasonal change in local along-channel wind forcing provides a significant contribution to the annual transport cycle of the Gulf Stream.     

The floccule theory for planetary formation

The accumulation of floccules into protoplanets is discussed, and it is pointed out that the simplifications which have been introduced into recent numerical models may result in the incorrect conclusion being reached.     

Possible mechanism for limiting grain sizes

It is suggested that grains are driven out of interstellar clouds by galactic radiation pressure and it is shown that the corresponding sizes which they can achieve within the cloud due to condensation is in reasonable agreement with observations.     

Tectonic implications of new Appalachian Ultradeep Core Hole (ADCOH) seismic reflection data from the crystalline southern Appalachians

Summary. Some 180 km of new VIBROSEIS profiles have been acquired in the southern Appalachian Inner Piedmont, Brevard fault zone and eastern Blue Ridge as part of the ADCOH Project site investigation. These data are of the highest quality yet obtained in a crystalline terrane in the US, perhaps in the world, and reveal several conclusions that should have a direct bearing upon the world-wide nature of composite crystalline thrust sheets and their modes of interaction with the platform rocks beneath. Strong reflections previously interpreted as the base of the crystalline sheet are clearly part of the platform sedimentary (clastic rocks) sequence resting upon the autochthonous basement and early Palaeozoic rift basins. This reflection package and related transparent zones are clearly repeated beneath the crystalline sheet indicating a complex of thrusts repeating units within the platform succession. Reflectors (granitoid-amplibolite contacts) in the crystalline sheet in the Inner Piedmont represent recumbent folds of similar wavelengths and amplitudes to folds mappable on the surface. Duplexing of platform rocks beneath the crystalline sheet appears to have resulted in doming of the crystalline sheet. Similarly, duplex formation in the platform was probably controlled by both the thickness of the crystalline sheet and the rheological properties of the platform succession.     

BASS measurements of currents, waves, stress, and turbulence in theNorth Sea bottom-boundary layer

Shallow-water-boundary layers are affected by current, waves, bottom topography, and stratification. Precise turbulence measurements through such regions are difficult. A deployment of a BASS (Benthic Acoustic Stress Sensor) tripod in November 1997 in the North Sea in 15 m of water provides a data set to examine turbulent boundary layer models. The deployment spanned both calm and storm sea conditions, had strong tidal currents, the location was uniform horizontally, and the bottom-boundary layer was well mixed in temperature. Estimates of stress derived from the covariance, log-fit, drag-law, and inertial-dissipation method have been compared. The covariance stress estimate had the largest sample to sample scatter, but from theoretical considerations should give the best estimate in stratified flow. The drag-law estimate gave the least sampling variability but suffers from the user having to measure a drag coefficient by some other method. The inertial-dissipation method was more tolerant to sensor misalignment, had the second greatest sampling variability, and could not be used to measure stress during slack tide. Averaging many semidiurnal tidal cycles showed greater tidal asymmetry of the log-fit stress than the covariance or inertial-dissipation stress estimates. Turbulent energy generation and dissipation were measured and balanced individually for the upper two sensors and followed a one-over-height-above-bottom profile