177 citations · 2.4k across the 68 of their papers we have counts for
69 papers
Grand minima and intermittency in near-critical convection-driven dynamos
P. J. Käpylä
Context: Solar magnetism exhibits long-term variations on timescales of decades to centuries. Aims: The main aim is to study how the supercriticality of the dynamo affects the vari…
Global 3D simulations of convection and dynamos in Red Giants
Carolina Ortiz-Rodríguez, Petri Käpylä, Juan Pablo Hidalgo +2
Understanding the internal dynamics of red giants is essential for studying angular momentum transport and magnetic field generation during stellar evolution. We present three-dime…
Connecting mean-field theory with dynamo simulations
Petri J. Käpylä
Mean-field dynamo theory, describing the evolution of large-scale magnetic fields, has been the mainstay of theoretical interpretation of magnetism in astrophysical objects such as…
Magnetorotational instability in a solar near-surface mean-field dynamo
Axel Brandenburg, Gustav Larsson, Fabio Del Sordo +1
We address the question whether the magnetorotational instability (MRI) can operate in the near-surface shear layer (NSSL) of the Sun and how it affects the interaction with the dy…
Helicity effect on turbulent passive and active scalar diffusivities
Axel Brandenburg, Petri J. Käpylä, Igor Rogachevskii +1
Turbulent flows are known to produce enhanced effective magnetic and passive scalar diffusivities, which can fairly accurately be determined with numerical methods. It is now known…
Effects of rotation and surface forcing on deep stellar convection zones
Petri J. Käpylä
The canonical undestanding of stellar convection has recently been put under doubt due to helioseismic results and global 3D convection simulations. This "convective conundrum" is…
Simulations of solar and stellar dynamos and their theoretical interpretation
Petri J. Käpylä, Matthew K. Browning, Allan Sacha Brun +2
We review the state of the art of three dimensional numerical simulations of solar and stellar dynamos. We summarize fundamental constraints of numerical modelling and the techniqu…
Simulations of dynamo action in slowly rotating M dwarfs: Dependence on dimensionless parameters
C. A. Ortiz-Rodríguez, P. J. Käpylä, F. H. Navarrete +4
The aim of this study is to explore the magnetic and flow properties of fully convective M dwarfs as a function of rotation period Prot and magnetic Reynolds ReM and Prandlt number…
Effects of the centrifugal force in stellar dynamo simulations
Felipe H. Navarrete, Petri J. Käpylä, Dominik R. G. Schleicher +1
The centrifugal force is often omitted from simulations of stellar convection either for numerical reasons or because it is assumed to be weak compared to the gravitational force.…
Turbulent Prandtl number from isotropically forced turbulence
Petri J. Käpylä, Nishant K. Singh
Turbulent motions enhance the diffusion of large-scale flows and temperature gradients. Such diffusion is often parameterized by coefficients of turbulent viscosity () a…
Origin of eclipsing time variations in Post-Common-Envelope binaries: role of the centrifugal force
Felipe H. Navarrete, Dominik R. G. Schleicher, Petri J. Käpylä +2
Eclipsing time variations (ETVs) in post-common-envelope binaries (PCEBs) were proposed to be due to the time-varying component of the stellar gravitational quadrupole moment. This…
Magnetism, rotation, and nonthermal emission in cool stars -- Average magnetic field measurements in 292 M dwarfs
A. Reiners, D. Shulyak, P. J. Käpylä +16
Stellar dynamos generate magnetic fields that are of fundamental importance to the variability and evolution of Sun-like and low-mass stars, and for the development of their planet…
Reynolds number dependence of Lyapunov exponents of turbulence and fluid particles
Itzhak Fouxon, Joshua Feinberg, Petri Käpylä +1
The Navier-Stokes equations generate an infinite set of generalized Lyapunov exponents defined by different ways of measuring the distance between exponentially diverging perturbed…
Origin of eclipsing time variations: Contributions of different modes of the dynamo-generated magnetic field
Felipe H. Navarrete, Petri J. Käpylä, Dominik R. G. Schleicher +2
The possibility to detect circumbinary planets and to study stellar magnetic fields through eclipsing time variations (ETVs) in binary stars has sparked an increase of interest in…
Generation of mean flows in rotating anisotropic turbulence: The case of solar near-surface shear layer
A. Barekat, M. J. Käpylä, P. J. Käpylä +2
The radial gradient of the rotation rate in the near-surface shear layer (NSSL) of the Sun is independent of latitude and radius. Theoretical mean-field models have been successful…
Star-in-a-box simulations of fully convective stars
Petri J. Käpylä
(abridged) Context: Main-sequence late-type stars with masses less than are fully convective. Aims: The goal is to study convection, differential rotation, and dynam…
Common dynamo scaling in slowly rotating young and evolved stars
Jyri J. Lehtinen, Federico Spada, Maarit J. Käpylä +2
One interpretation of the activity and magnetism of late-type stars is that these both intensify with decreasing Rossby number up to a saturation level, suggesting that stellar dyn…
Antisolar differential rotation of slowly rotating cool stars
G. Rüdiger, M. Küker, P. Käpylä +1
Rotating stellar convection transports angular momentum towards the equator, generating the characteristic equatorial acceleration of the solar rotation while the radial flux of an…
-mode strengthening from a localized bipolar subsurface magnetic field
Nishant K. Singh, Harsha Raichur, Maarit J. Käpylä +3
Recent numerical work in helioseismology has shown that a periodically varying subsurface magnetic field leads to a fanning of the -mode, which emerges from the density jump at…
Bihelical spectrum of solar magnetic helicity and its evolution
Nishant K. Singh, Maarit J. Käpylä, Axel Brandenburg +3
Using a recently developed two-scale formalism to determine the magnetic helicity spectrum (Brandenburg et al. 2017), we analyze synoptic vector magnetograms built with data from t…
Magnetic and rotational quenching of the effect
Petri J. Käpylä
Context: Differential rotation in stars is driven by turbulent transport of angular momentum. Aims: To measure and parametrize the non-diffusive contribution to turbulent stress, k…
Transition from axi- to nonaxisymmetric dynamo modes in spherical convection models of solar-like stars
Mariangela Viviani, Jörn Warnecke, Maarit J. Käpylä +5
We seek to understand the transition from nearly axisymmetric configurations at solar rotation rates to nonaxisymmetric configurations for rapid rotation using 3D numerical simulat…
Extended subadiabatic layer in simulations of overshooting convection
Petri J. Käpylä, Matthias Rheinhardt, Axel Brandenburg +5
We present numerical simulations of hydrodynamic overshooting convection in local Cartesian domains. We find that a substantial fraction of the lower part of the convection zone (C…
Convection-driven spherical shell dynamos at varying Prandtl numbers
P. J. Käpylä, M. J. Käpylä, N. Olspert +2
(abidged) Context: Stellar convection zones are characterized by vigorous high-Reynolds number turbulence at low Prandtl numbers. Aims: We study the dynamo and differential rotatio…