{"title":"Thermal convection and dynamo action with stable stratification at the top of the Earth's outer core","authors":"Priyabrata Mukherjee, Swarandeep Sahoo","doi":"10.1016/j.pepi.2023.107111","DOIUrl":null,"url":null,"abstract":"<div><p>The outer core of the Earth, filled with electrically conducting fluid, undergoes thermochemical convection due to super-adiabatic temperature gradients. Near the core-mantle boundary, fluid flow may be restricted due to sub-adiabatic temperature gradients or accumulated light elements forming a layer of stable stratification. The present study investigates the behavior of thermal convection with various buoyancy profiles, using non-uniform radial distribution of heat sources, mimicking the combined presence of convective and stable zones. Role of such modified convection in the evolution and resulting morphology of saturated magnetic fields is the main focus of this study. Apart from the reduction in the threshold for onset, the length scale of the convective instabilities is enhanced with stable stratification, while the frequency is reduced. Despite the confinement of convection to unstable regions, rapid rotation favors penetrative radial convective flows. In presence of a stably stratified layer, the dynamo action is suppressed due to the radial confinement of buoyancy, Coriolis, and Lorentz forces. The suppression of vortex stretching, indicated by the relative asymmetry in axial helicity provides further understanding of the mechanism behind the magnetic field structure. As the stratification becomes stronger, the dynamo action leads to magnetic fields with enhanced axial dipole field strength, although the strength of the dynamo is reduced. The confinement of the toroidal component of the magnetic field to localized concentrated patches in regions of stable stratification near the equatorial plane also inhibits the growth of magnetic fields. Nevertheless, enhanced buoyancy forcing may overcome the suppression of dynamo action and lead to strongly convecting dipolar dominated Earth-like dynamos even with moderate stratification.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"345 ","pages":"Article 107111"},"PeriodicalIF":2.4000,"publicationDate":"2023-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Physics of the Earth and Planetary Interiors","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0031920123001371","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
Abstract
The outer core of the Earth, filled with electrically conducting fluid, undergoes thermochemical convection due to super-adiabatic temperature gradients. Near the core-mantle boundary, fluid flow may be restricted due to sub-adiabatic temperature gradients or accumulated light elements forming a layer of stable stratification. The present study investigates the behavior of thermal convection with various buoyancy profiles, using non-uniform radial distribution of heat sources, mimicking the combined presence of convective and stable zones. Role of such modified convection in the evolution and resulting morphology of saturated magnetic fields is the main focus of this study. Apart from the reduction in the threshold for onset, the length scale of the convective instabilities is enhanced with stable stratification, while the frequency is reduced. Despite the confinement of convection to unstable regions, rapid rotation favors penetrative radial convective flows. In presence of a stably stratified layer, the dynamo action is suppressed due to the radial confinement of buoyancy, Coriolis, and Lorentz forces. The suppression of vortex stretching, indicated by the relative asymmetry in axial helicity provides further understanding of the mechanism behind the magnetic field structure. As the stratification becomes stronger, the dynamo action leads to magnetic fields with enhanced axial dipole field strength, although the strength of the dynamo is reduced. The confinement of the toroidal component of the magnetic field to localized concentrated patches in regions of stable stratification near the equatorial plane also inhibits the growth of magnetic fields. Nevertheless, enhanced buoyancy forcing may overcome the suppression of dynamo action and lead to strongly convecting dipolar dominated Earth-like dynamos even with moderate stratification.
期刊介绍:
Launched in 1968 to fill the need for an international journal in the field of planetary physics, geodesy and geophysics, Physics of the Earth and Planetary Interiors has now grown to become important reading matter for all geophysicists. It is the only journal to be entirely devoted to the physical and chemical processes of planetary interiors.
Original research papers, review articles, short communications and book reviews are all published on a regular basis; and from time to time special issues of the journal are devoted to the publication of the proceedings of symposia and congresses which the editors feel will be of particular interest to the reader.