Research Highlights
Research Highlights
A selection of highlights culled from publications by HAO staff.
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.
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.
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.
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.
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.
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.
The Impact of Solar Activity on Forecasting the Upper Atmosphere via Assimilation of Electron Density Data
This study presents a comprehensive comparison of the impact of solar activity on forecasting the upper atmosphere through assimilation of radio occultation (RO)-derived electron density (Ne) into a physics-based model (TIE-GCM) using an ensemble Kalman filter.