The observed Mars remnant magnetism suggests that there was an active dynamo in the Martian core. We use the MoSST core dynamics model to simulate the Martian historical dynamo, focusing on the variation of the dynamo...The observed Mars remnant magnetism suggests that there was an active dynamo in the Martian core. We use the MoSST core dynamics model to simulate the Martian historical dynamo, focusing on the variation of the dynamo states with the Rayleigh number Ra (a non-dimensional parameter describing the buoyancy force in the core). Our numerical results show that the mean field length scale does not vary monotonically with the Rayleigh number, and the field morphology at the core mantle boundary changes with Rayleigh number. In particular, it drifts westward with a speed decreasing with Rayleigh number.展开更多
Galileo mission detected the magnetic anomalies originated from Galilean moons.These anomalies are likely generated in the moons' interiors,under the influence of a strong ambient Jovian field.Among various possib...Galileo mission detected the magnetic anomalies originated from Galilean moons.These anomalies are likely generated in the moons' interiors,under the influence of a strong ambient Jovian field.Among various possible generation mechanisms of the anomalies,we focus on magneto-convection and dynamos in the interiors via numerical simulation.To mimic the electromagnetic environment of the moons,we introduce in our numerical model an external uniform magnetic field B0 with a fixed orientation but varying field strength.Our results show that a finite B0 can substantially alter the dynamo processes inside the core.When the ambient field strength B0 increases to approximately 40% of the field generated by the pure dynamo action,the convective state in the core changes significantly:the convective flow decreases by 80% in magnitude,but the differential rotation becomes stronger in much of the fluid layer,leading to a stronger field generated in the core.The field morphologies inside the core tend to align with the ambient field,while the flow patterns show the symmetry-breaking effect under the influence of B0.Furthermore,the generated field tends to be temporally more stable.展开更多
Observed Martian crustal magnetism shows that the Mars does not possess a global-scale,dynamo-driven intrinsic magnetic field.In addition,the remnant field at the surface is hemi-spherically asymmetric.Our earlier sim...Observed Martian crustal magnetism shows that the Mars does not possess a global-scale,dynamo-driven intrinsic magnetic field.In addition,the remnant field at the surface is hemi-spherically asymmetric.Our earlier simulation results suggest that the Martian dynamo could be sub-critical near its end(the energy required to sustain a subcritical dynamo is less than that to excite the dynamo)and the generated field morphology is non-dipolar.We further the study to examine the characteristics of the magnetic field via Empirical Orthogonal Function(EOF)analysis on the subcritical dynamo solutions with the Rayleigh number Rth = 2480(below the critical point for the onset of the Martian dynamo).Our results show that the magnetic field is dominantly equatorial dipolar.Reversals and excursions occur frequently,and the magnetic dipole moment does not vary monotonically in time.展开更多
基金Supported by National Natural Science Foundation of China (Grant No. 40328006)
文摘The observed Mars remnant magnetism suggests that there was an active dynamo in the Martian core. We use the MoSST core dynamics model to simulate the Martian historical dynamo, focusing on the variation of the dynamo states with the Rayleigh number Ra (a non-dimensional parameter describing the buoyancy force in the core). Our numerical results show that the mean field length scale does not vary monotonically with the Rayleigh number, and the field morphology at the core mantle boundary changes with Rayleigh number. In particular, it drifts westward with a speed decreasing with Rayleigh number.
基金supported by National Natural Science Foundation of China (Grant No. 40328006)
文摘Galileo mission detected the magnetic anomalies originated from Galilean moons.These anomalies are likely generated in the moons' interiors,under the influence of a strong ambient Jovian field.Among various possible generation mechanisms of the anomalies,we focus on magneto-convection and dynamos in the interiors via numerical simulation.To mimic the electromagnetic environment of the moons,we introduce in our numerical model an external uniform magnetic field B0 with a fixed orientation but varying field strength.Our results show that a finite B0 can substantially alter the dynamo processes inside the core.When the ambient field strength B0 increases to approximately 40% of the field generated by the pure dynamo action,the convective state in the core changes significantly:the convective flow decreases by 80% in magnitude,but the differential rotation becomes stronger in much of the fluid layer,leading to a stronger field generated in the core.The field morphologies inside the core tend to align with the ambient field,while the flow patterns show the symmetry-breaking effect under the influence of B0.Furthermore,the generated field tends to be temporally more stable.
文摘Observed Martian crustal magnetism shows that the Mars does not possess a global-scale,dynamo-driven intrinsic magnetic field.In addition,the remnant field at the surface is hemi-spherically asymmetric.Our earlier simulation results suggest that the Martian dynamo could be sub-critical near its end(the energy required to sustain a subcritical dynamo is less than that to excite the dynamo)and the generated field morphology is non-dipolar.We further the study to examine the characteristics of the magnetic field via Empirical Orthogonal Function(EOF)analysis on the subcritical dynamo solutions with the Rayleigh number Rth = 2480(below the critical point for the onset of the Martian dynamo).Our results show that the magnetic field is dominantly equatorial dipolar.Reversals and excursions occur frequently,and the magnetic dipole moment does not vary monotonically in time.