Long-Term Solar Variability (LSV) Section
The long-term variability of solar magnetism is a key driver of the Earth's climate system and space environment. The goal of the LSV section is to understand long-term solar variability from the Sun's interior out to the heliosphere.
Solar Convection and Internal Rotation:
Turbulent convection in the solar envelope transports energy to the surface
where it is radiated into space and also redistributes momentum and entropy,
producing differential rotation and global meridional circulations. Of particular
importance is a layer of rotational shear near the base of the convection zone
known as the solar tachocline where much of the observed magnetic activity
of the Sun is thought to originate. HAO scientists investigate the multi-faceted
dynamics of the solar interior using a suite of theoretical and numerical models
ranging from three-dimensional magnetohydrodynamic (MHD) simulations to mean-field dynamo
models to tachocline models based on a hydromagnetic generalization of the shallow-water
equations commonly used in geophysics. Such models provide valuable
interpretive insight and guidance in support of ongoing investigations of solar
internal structure and dynamics based on helioseismology and on observations of
magnetic activity patterns in the solar atmosphere. Read more »
The Solar Dynamo:
The interaction of the solar dynamo with differential rotation and meridional flow is investigated through a coupled meanfield model including the Lorentz-force feedback on differential rotation and meridional flow. This feedback gives rise to periodic changes of the rotation rate, known as torsional oscillations. This dynamo model allows to incorporate the additional constraints given by observations of the variable internal rotation of the sun. It is also possible to address the energy budget of the dynamo. Read more »
Magnetic Flux Emergence:
The current prevailing picture is that magnetic active regions on the
solar surface originate from strong, predominantly toroidal magnetic
fields generated by the solar dynamo mechanism at the thin tachocline
layer at the base of the solar convection zone. Thus the magnetic fields
need to traverse the entire convection zone (the outer 30% of the solar
interior) before they reach the photosphere to form the observed sunspots and
solar active regions, which are centers of solar eruptions.
Understanding the process of magnetic flux emergence through the solar
convection zone is therefore crucial for understanding the link between the
observed magnetic activities at the surface and the dynamo-generated magnetic
fields in the interior. Using MHD numerical simulations, HAO scientists
have been modeling the formation and rise of buoyant of magnetic flux tubes
in the solar convection zone and their emergence through the
photosphere into the solar atmosphere. Read more »
Sunspots and Photospheric Dynamics:
In collaboration with the Max-Planck Institute for Solar System Research
(MPS) in Germany and the University of Utrecht in the Netherlands 2D and
3D MHD simulations with radiative transfer are used to investigate the
subsurface structure of sunspots. The simulations are based on the
MURaM code developed by the MPS and the University of Chicago. Read more »
The Solar-Stellar Connection:
Just as helioseismology revolutionized our understanding of the interior
structure of the Sun, asteroseismology is now placing this knowledge into a
broader context, by providing structural information for other solar-type
stars. Scientists at HAO are developing a stellar model-fitting pipeline, using a
parallel genetic
algorithm, to prepare for the asteroseismic data soon expected from
several satellite missions. Meanwhile, the Solar Oscillations Network Group (SONG)
is a concept for a global network of small ground-based telescopes dedicated to
asteroseismology and extrasolar planet searches, currently being organized
though the Danish AsteroSeismology Center (DASC) at the University of Aarhus. The High Altitude Observatory is
participating in the design and development phase of the SONG effort, with the
intent to build and operate one of the SONG telescopes at HAO's Mauna Loa
Observatory in Hawaii. Read more »
Effects associated with rotation can modify stellar properties, altering the luminosities, surface temperatures, sizes, and shapes of stars in ways that are unaccounted for in nonrotating models. HAO scientists have developed methods for constructing self-consistent models of differentially rotating, chemically homogeneous stars, whereby the equations of stellar structure and Poisson's equation for the gravitational potential are iteratively solved for an assumed conservative internal rotation law. Such models provide the means of interpreting observations of stars that are known to be rapid rotators. Read more »