Research Highlights

Research Highlights

A selection of highlights culled from publications by HAO staff.

3D view of the magnetic field lines in a simulation of the solar convective dynamo

Magnetic fields in the solar convection zone (major update)

It has been a prevailing picture that active regions on the solar surface originate from a strong toroidal magnetic field stored in the overshoot region at the base of the solar convection zone, generated by a deep seated solar dynamo mechanism. This article reviews the studies in regard to how the toroidal magnetic field can destabilize and rise through the convection zone to form the observed solar active regions at the surface.

Measured and modelled total solar irradiance

The Dimmest State of the Sun

How the solar electromagnetic energy entering the Earth’s atmosphere varied since pre-industrial times is an important consideration in the climate change debate.

Longitude-latitude maps of NmF2 from the NR (first column) and the difference of NmF2 between OSSEs and NR (second to fourth columns) at six different times.

Impact of Thermospheric Wind Data Assimilation on Ionospheric Electrodynamics using a Coupled Whole Atmosphere Data Assimilation System

The upward plasma drift and equatorial ionization anomaly (EIA) in the Earth's ionosphere are strongly influenced by the zonal electric field, which is generated by the wind dynamo. Specification and forecasting of thermospheric winds thus plays an important role in ionospheric weather prediction.

Maps of the magnetic field strength at depth of z = −7.5 Mm beneath the solar photosphere at different times (indicated in red in each panel)

On the (In)stability of Sunspots

The stability of sunspots is one of the long-standing unsolved puzzles in the field of solar magnetism and the solar cycle. The thermal and magnetic structure of the sunspot beneath the solar surface is not accessible through observations, thus processes in these regions that contribute to the decay of sunspots can only be studied through theoretical and numerical studies.

Snapshot from a two-dimensional test simulation setup with a 8x8Mm domain reaching from the upper convection zone into the transition region

Efficient numerical treatment of ambipolar and Hall drift as hyperbolic system

Partially ionized plasmas, such as the solar chromosphere, require a generalized Ohm's law including the effects of ambipolar and Hall drift. While both describe transport processes that arise from the multifluid equations and are therefore of hyperbolic nature, they are often incorporated in models as a diffusive, i.e. parabolic process. While the formulation as such is easy to include in standard MHD models, the resulting diffusive time-step constraints do require often a computationally more expensive implicit treatment or super-time-stepping approaches.

ν − z phase diagrams (cuts at constant horizontal wavenumber at approx. 2 and 4 Mm−1 through the stacks of the layer-by-layer two-dimensional k − ω phase difference diagrams) for various MURaM models

Acoustic-gravity wave propagation characteristics in three-dimensional radiation hydrodynamic simulations of the solar atmosphere

There has been tremendous progress in the degree of realism of three-dimensional radiation magneto-hydrodynamic simulations of the solar atmosphere in the past decades.

Control of ionospheric plasma velocities by thermospheric winds

Earth’s equatorial ionosphere exhibits significant and unpredictable day-to-day variations in density and morphology. The NASA Ionospheric Connection Explorer (ICON) makes the first coordinated space-based observations of the wind-driven dynamo and the plasma state to understand the relation of the plasma environment to the thermospheric weather below. 

Periodic variations in solar wind and responses of the magnetosphere and thermosphere in March 2017

TIMED/GUVI observed thermospheric column ∑O/N2 depletion in both hemispheres in March 2017. This long duration O/N2 depletion started with a geomagnetic storm between March 1 and 21, 2017 which was caused by large periodic variations in interplanetary magnetic field (IMF) and a high solar wind speed, thus likely associated with a solar wind co-rotating interaction region (CIR).

The enduring mystery of the solar corona

Physicists have long known that the Sun’s magnetic fields make its corona much hotter than the surface of the star itself. But how – and why – those fields transport and deposit their energy is still a mystery.