Science Topics

Science Topics

A selection of articles representing various topics of Sun-Earth system science.

Transient coronal holes (TCHs) are associated with CMEs, and appear as dimmings in soft X-ray and extreme ultraviolet (e.g. right-most image)

CME Initiation, Evolution, and Interplanetary Consequences

HAO scientists have carried out 3D isothermal MHD simulations of the evolution of the large scale coronal magnetic field as a twisted magnetic flux tube is driven (slowly) through the lower boundary into a pre-existing coronal arcade field.

Line-of-sight-integrated Stokes linear polarization

Coronal and Heliospheric Evolution

The magnetic field in the Sun's atmosphere continuously evolves through processes of emergence, diffusion, and reconnection, resulting in ongoing reorganizations of the global coronal/helio- spheric magnetic morphology, as well as in the slow buildup of magnetic energy in twisted or sheared magnetic fields

Difference plots between simulations including and excluding SEPs

Impact of Energetic Particles on the upper Atmosphere

Energetic particles, namely electrons and protons, released from the magnetosphere cover a wide range of energies from a few electron volts (eV) to hundreds of milli-electron volts (MeV). Precipitating electrons of several kilo electron volts (keV) are deposited in the 90–150 km altitude range, and they are mostly responsible for producing auroras and creating the E-region ionosphere.

sun-heliosphere-Earth system for the last two solar minimum

Long-Term Solar Variability

HAO scientists pursue an interdisciplinary, system-wide view on the origins and impacts of solar and stellar cycle variation, with a particular focus on magnetic minima as times of low activity and relatively simple heliospheric structure.

The left panel shows the electric current density in a horizontal plane at height z=10 in the chromosphere. The middle and right panels show two perspective views of a set of 3D field lines traced from a few points along the current concentration shown in the left panel

Magnetic Flux Emergence

Understanding the process of magnetic flux emergence through the solar convection zone is crucial for understanding the link between the observed magnetic activities at the surface and the dynamo-generated magnetic fields in the interior.

High-resolution global magnetohydrodynamic simulation of bursty bulk flows

Modeling high-speed flows in the Earth’s Magnetotail

The magnetosphere is created by the interaction between the solar wind and the Earth’s magnetic field. On the dayside of the Earth pressure from the solar wind compresses the Earth’s dipole magnetic field and on the night side this interaction stretches it out forming a region of space commonly referred to as the magnetotail.

Global distribution of helium number densities at 250 km altitude during each season for solar minimum conditions

Satellite Drag Physical Modeling for Transition to Operations

The ionosphere and upper atmosphere play a major role in space operations, including communications, navigation, and satellite drag. Satellite drag, the drag force exerted by the tenuous upper atmosphere on orbiting bodies, is the leading cause of error in predicting the locations of objects in low-Earth orbit.

Convective patterns in a computer simulation of solar convection

Solar Convection and Mean Flows

Any inquiry into the ultimate origins of solar magnetic activity must soon confront turbulent thermal convection. Convection is a means by which the Sun shines. Energy liberated by nuclear fusion deep in the core of the Sun filters outward by the diffusion of photons. In the outer approximately 30% of the Sun by radius, the solar plasma is cooler and more opaque, making radiative diffusion less efficient. Convection takes over as the primary mechanism by which energy is transported from 0.7 R to the solar photosphere, where it is radiated into space.

WACCM simulation results on 4 February

Studying Atmosphere Coupling Using Mesoscale-resolving WACCM

An important pathway for the terrestrial weather to affect the space weather is through atmosphere waves, such as atmospheric tides, planetary waves and gravity waves. The impacts of the planetary-scale waves have been extensively studied observationally and numerically.

Sunspot simulation

Sunspots and Photospheric Dynamics

Sunspots are the most prominent manifestations of magnetic field in the visible layers of the solar atmosphere. Their origin is a dynamo process operating in the solar convection zone.

Volume visualization of the longitudinal magnetic field component in a 3D MHD simulation of solar convection

The Sun as a Dynamo

The ultimate origins of solar variability lie below the visible surface, where turbulent convection, differential rotation, and meridional flows work together to produce magnetic fields through the operation of a stellar dynamo, giving rise to the 22-year solar magnetic cycle.