3,306 research outputs found
A phase-space study of jet formation in planetary-scale fluids
The interaction between planetary waves and an arbitrary zonal flow is
studied from a phase-space viewpoint. Using the Wigner distribution, a
planetary wave Vlasov equation is derived that includes the contribution of the
mean flow to the zonal potential vorticity gradient. This equation is applied
to the problem of planetary wave modulational instability, where it is used to
predict a fastest growing mode of finite wavenumber. A wave-mean flow numerical
model is used to test the analytical predictions, and an intuitive explanation
of modulational instability and jet asymmetry is given via the motion of
planetary wavepackets in phase space.Comment: 10 pages, 10 figure
Peter Ackroydâs Chatterton, Thomas Chatterton, and postmodern romantic identities and attitudes: âThis is essentially a Romantic attitudeâ
Earthâs polar night boundary layer as an analogue for dark side inversions on synchronously rotating terrestrial exoplanets
A key factor in determining the potential habitability of synchronously rotating planets is the strength of the atmospheric boundary layer inversion between the dark side surface and the free atmosphere. Here we analyse data obtained from polar night measurements at the South Pole and Alert Canada, which are the closest analogues on Earth to conditions on the dark sides of synchronously rotating exoplanets without and with a maritime influence, respectively. On Earth, such inversions rarely exceed 30 K in strength, because of the effect of turbulent mixing induced by phenomena such as so-called mesoscale slope winds, which have horizontal scales of 10s to 100s of km, suggesting a similar constraint to near-surface dark side inversions. We discuss the sensitivity of inversion strength to factors such as orography and the global-scale circulation, and compare them to a simulation of the planet Proxima Centauri b. Our results demonstrate the importance of comparisons with Earth data in exoplanet research, and highlight the need for further studies of the exoplanet atmospheric collapse problem using mesoscale and eddy-resolving models
Winnerless Competition in Neural Dynamics; Cluster Synchronisation of Coupled Oscillators
Systems of globally coupled phase oscillators can have robust attractors that are heteroclinic networks. Such a heteroclinic network is generated, where the phases cluster into three groups, within a specific regime of parameters when the phase oscillators are globally coupled using the function . The resulting network switches between 30 partially synchronised states for a system of oscillators. Considering the states that are visited and the time spent at those states a spatio-temporal code can be generated for a given navigation around the network. We explore this phenomenon further by investigating the effect that noise has on the system, how this system can be used to generate a spatio-temporal code derived from specific inputs and how observation of a spatio-temporal code can be used to determine the inputs that were presented to the system to generate a given coding. We show that it is possible to find chaotic attractors for certain parameters and that it is possible to detail a genetic algorithm that can find the parameters required to generate a specific spatio-temporal code, even in the presence of noise. In closing we briefly explore the dynamics where and discuss this work in relation to winnerless competition.EPSR
Predictions of the atmospheric composition of GJ 1132b
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is
amongst the most highly characterizable small exoplanets currently known. In
this paper we study the interaction of a magma ocean with a water-rich
atmosphere on GJ 1132b and determine that it must have begun with more than 5
wt% initial water in order to still retain a water-based atmosphere. We also
determine the amount of O2 that can build up in the atmosphere as a result of
hydrogen dissociation and loss. We find that the magma ocean absorbs at most
~10% of the O2 produced, whereas more than 90% is lost to space through
hydrodynamic drag. The most common outcome for GJ 1132 b from our simulations
is a tenuous atmosphere dominated by O2, although for very large initial water
abundances atmospheres with several thousands of bars of O2 are possible. A
substantial steam envelope would indicate either the existence of an earlier H2
envelope or low XUV flux over the system's lifetime. A steam atmosphere would
also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2 or N2-rich atmospheres on GJ
1132 b.Comment: 14 pages, 11 figures, accepted at Ap
- âŠ