scholarly journals The Case Against an Early Lunar Dynamo Powered by Core Convection

2018 ◽  
Vol 45 (1) ◽  
pp. 98-107 ◽  
Author(s):  
Alexander J. Evans ◽  
Sonia M. Tikoo ◽  
Jeffrey C. Andrews-Hanna
Keyword(s):  
Core Convection

scholarly journals Heat transfer in rapidly rotating convection with heterogeneous thermal boundary conditions

2017 ◽  
Vol 828 ◽  
pp. 601-629 ◽  
Author(s):  
Jon E. Mound ◽  
Christopher J. Davies
Keyword(s):  
Heat Flux ◽  
Outer Boundary ◽  
Extreme Case ◽  
Creeping Flow ◽  
Supercritical Regime ◽  
Rotating Convection ◽  
Thermal Boundary Conditions ◽  
Core Convection ◽  
Rayleigh Numbers ◽  
Lateral Variations

Convection in the metallic cores of terrestrial planets is likely to be subjected to lateral variations in heat flux through the outer boundary imposed by creeping flow in the overlying silicate mantles. Boundary anomalies can significantly influence global diagnostics of core convection when the Rayleigh number, $Ra$, is weakly supercritical; however, little is known about the strongly supercritical regime appropriate for planets. We perform numerical simulations of rapidly rotating convection in a spherical shell geometry and impose two patterns of boundary heat flow heterogeneity: a hemispherical $Y_{1}^{1}$ spherical harmonic pattern; and one derived from seismic tomography of the Earth’s lower mantle. We consider Ekman numbers $10^{-4}\leqslant E\leqslant 10^{-6}$, flux-based Rayleigh numbers up to ${\sim}800$ times critical, and a Prandtl number of unity. The amplitude of the lateral variation in heat flux is characterised by $q_{L}^{\ast }=0$, 2.3, 5.0, the peak-to-peak amplitude of the outer boundary heat flux divided by its mean. We find that the Nusselt number, $Nu$, can be increased by up to ${\sim}25\,\%$ relative to the equivalent homogeneous case due to boundary-induced correlations between the radial velocity and temperature anomalies near the top of the shell. The $Nu$ enhancement tends to become greater as the amplitude and length scale of the boundary heterogeneity are increased and as the system becomes more supercritical. This $Ra$ dependence can steepen the $Nu\propto Ra^{\unicode[STIX]{x1D6FE}}$ scaling in the rotationally dominated regime, with $\unicode[STIX]{x1D6FE}$ for our most extreme case approximately 20 % greater than the equivalent homogeneous scaling. Therefore, it may be important to consider boundary heterogeneity when extrapolating numerical results to planetary conditions.

scholarly journals Simulations of Core Convection Dynamos in Rotating A-type Stars

2004 ◽  
Vol 215 ◽  
pp. 376-377
Author(s):  
Matthew Browning ◽  
Allan Sacha Brun ◽  
Juri Toomre
Keyword(s):  
Magnetic Field ◽  
Numerical Simulations ◽  
Differential Rotation ◽  
Three Dimensional ◽  
Dynamo Action ◽  
The Core ◽  
Core Convection ◽  
Seed Field ◽  
Initial Seed ◽  
Three Dimensional Simulations

We have conducted preliminary numerical simulations of a core convection dynamo operating within an A-type star of two solar masses. Convection within the core clearly can admit magnetic dynamo action. Magnetic field strengths in our three-dimensional simulations grow by many orders of magnitude, from an initial seed field to kilo-Gauss levels. We discuss the differential rotation and magnetic field sustained in our simulations.

scholarly journals An Idealized Numerical Study of Shear-Relative Low-Level Mean Flow on Tropical Cyclone Intensity and Size

2019 ◽  
Vol 76 (8) ◽  
pp. 2309-2334 ◽  
Author(s):  
Buo-Fu Chen ◽  
Christopher A. Davis ◽  
Ying-Hwa Kuo
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Numerical Study ◽  
Vertical Wind Shear ◽  
Development Stage ◽  
Surface Fluxes ◽  
Mean Flow ◽  
Low Level ◽  
Core Convection

Abstract Given comparable background vertical wind shear (VWS) magnitudes, the initially imposed shear-relative low-level mean flow (LMF) is hypothesized to modify the structure and convective features of a tropical cyclone (TC). This study uses idealized Weather Research and Forecasting Model simulations to examine TC structure and convection affected by various LMFs directed toward eight shear-relative orientations. The simulated TC affected by an initially imposed LMF directed toward downshear left yields an anomalously high intensification rate, while an upshear-right LMF yields a relatively high expansion rate. These two shear-relative LMF orientations affect the asymmetry of both surface fluxes and frictional inflow in the boundary layer and thus modify the TC convection. During the early development stage, the initially imposed downshear-left LMF promotes inner-core convection because of high boundary layer moisture fluxes into the inner core and is thus favorable for TC intensification because of large radial fluxes of azimuthal mean vorticity near the radius of maximum wind in the boundary layer. However, TCs affected by various LMFs may modify the near-TC VWS differently, making the intensity evolution afterward more complicated. The TC with a fast-established eyewall in response to the downshear-left LMF further reduces the near-TC VWS, maintaining a relatively high intensification rate. For the upshear-right LMF that leads to active and sustained rainbands in the downshear quadrants, TC size expansion is promoted by a positive radial flux of eddy vorticity near the radius of 34-kt wind (1 kt ≈ 0.51 m s−1) because the vorticity associated with the rainbands is in phase with the storm-motion-relative inflow.

Lagrangian Description of Air Masses Associated with Latent Heat Release in Tropical Storm Karl (2016) during Extratropical Transition

2019 ◽  
Vol 147 (7) ◽  
pp. 2657-2676 ◽  
Author(s):  
Christian Euler ◽  
Michael Riemer ◽  
Tobias Kremer ◽  
Elmar Schömer
Keyword(s):  
Inner Core ◽  
Vertical Wind Shear ◽  
Conveyor Belt ◽  
Tropical Storm ◽  
Vertical Shear ◽  
Lagrangian Description ◽  
Environment Impact ◽  
Extratropical Transition ◽  
Air Masses ◽  
Core Convection

Abstract Extratropical transition (ET) of tropical cyclones involves distinct changes of the cyclone’s structure that are not yet well understood. This study presents for the first time a comprehensive Lagrangian description of structure change near the inner core. A large sample of trajectories is computed from a convection-permitting numerical simulation of the ET of Tropical Storm Karl (2016). Three main airstreams are considered: those associated with the inner-core convection, inner-core descent, and the developing warm conveyor belt. Analysis of these airstreams is performed both in thermodynamic and physical space. Prior to ET, Karl is embedded in weak vertical wind shear and its intensity is impeded by excessive detrainment from the inner-core convection. At the start of ET, vertical shear increases and Karl intensifies, which is attributable to reduced detrainment and thus to the formation of a well-defined outflow layer. During ET, the thermodynamic changes of the environment impact Karl’s inner-core convection predominantly by a decrease of θe values in the inflow layer. Notably, notwithstanding Karl’s weak intensity, its inner core acts as a “containment vessel” that transports high-θe air into the increasingly hostile environment. Inner-core descent has two origins: (i) mostly from upshear-left above 4-km height in the environment and (ii) boundary layer air that ascends in the inner core first and then descends, performing rollercoaster-like trajectories. At the end of the tropical phase of ET, the developing warm conveyor belt comprises air masses from several different source regions, and only partly from the cyclone’s developing warm sector, as expected for extratropical cyclones.

An Electrical and Polarimetric Analysis of the Overland Reintensification of Tropical Storm Erin (2007)

2014 ◽  
Vol 142 (6) ◽  
pp. 2321-2344 ◽  
Author(s):  
Erica M. Griffin ◽  
Terry J. Schuur ◽  
Donald R. MacGorman ◽  
Matthew R. Kumjian ◽  
Alexandre O. Fierro
Keyword(s):  
Tropical Cyclones ◽  
Inner Core ◽  
Open Water ◽  
Tropical Storm ◽  
Sea Level Pressure ◽  
Core Convection ◽  
Lightning Detection ◽  
Mapping Array ◽  
Total Lightning ◽  
Abundant Data

Abstract While passing over central Oklahoma on 18–19 August 2007, the remnants of Tropical Storm Erin unexpectedly reintensified and developed an eyelike feature that was clearly discernable in Weather Surveillance Radar-1988 Doppler (WSR-88D) imagery. During this brief reintensification period, Erin traversed a region of dense surface and remote sensing observation networks that provided abundant data of high spatial and temporal resolution. This study analyzes data from the polarimetric KOUN S-band radar, total lightning data from the Oklahoma Lightning Mapping Array, and ground-flash lightning data from the National Lightning Detection Network. Erin’s reintensification was atypical since it occurred well inland and was accompanied by stronger maximum sustained winds and gusts (25 and 37 m s−1, respectively) and lower minimum sea level pressure (1001.3 hPa) than while over water. Radar observations reveal several similarities to those documented in mature tropical cyclones over open water, including outward-sloping eyewall convection, near 0-dBZ reflectivities within the eye, and relatively large updraft velocities in the eyewall as inferred from single-Doppler winds and ZDR columns. Deep, electrified convection near the center of circulation preceded the formation of Erin’s eye, with maximum lightning activity occurring prior to and during reintensification. The results show that inner-core convection may have played a role in the reinvigoration of the storm.

scholarly journals Gross thermodynamics of two-component core convection

2004 ◽  
Vol 157 (3) ◽  
pp. 1407-1414 ◽  
Author(s):  
David Gubbins ◽  
Dario Alfè ◽  
Guy Masters ◽  
G. David Price ◽  
Michael Gillan
Keyword(s):  
Core Convection ◽  
Two Component

scholarly journals Evolution of Stars with Suppressed Core Convection

1973 ◽  
Vol 180 ◽  
pp. 901 ◽  
Author(s):  
Richard Stothers ◽  
Chao-Wen Chin
Keyword(s):  
Core Convection

Inner core convection

Science ◽  
1996 ◽  
Vol 274 (5289) ◽  
pp. 893.4-0
Keyword(s):  
Inner Core ◽  
Core Convection
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