Challenges to Understanding the Earth's Ionosphere and Thermosphere

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Thursday, October 3, 2019

In this paper we discuss, in a limited way, some of the challenges to advancing our understanding and description of the coupled plasma and neutral gas that make up the ionosphere and thermosphere (I-T).

Schematic of plasma and density structures in the IT system
Schematic of plasma and density structures in the IT system.

The I-T is strongly influenced by wave motions of the neutral atmosphere at the lower boundary near 90 km and is coupled to the magnetosphere, which supplies energetic particle precipitation and field-aligned currents at high latitudes. The resulting plasma dynamics are produced by currents generated by solar heating and upward propagating waves, by heating from energetic particles and electromagnetic energy from the magnetosphere and by the closure of the field-aligned currents applied at high latitudes. These three contributors to the current are functions of position, magnetic activity, and other variables that must be unraveled to understand how the I-T responds to coupling from the surrounding regions of geospace.

We have captured the challenges to this understanding in four major themes associated with coupling to the lower boundary, the generation of currents within the region, the coupling to the magnetosphere and the response of the region reflected in changes in the neutral and plasma density. We find that the wind field at the lower boundary of the I-T is poorly specified and the relative importance of processes affecting the propagation of waves through the I-T and their effects on the plasma is unknown. The currents that flow through the I-T are also dependent on the spatial and temporal development of the magnetospheric energy inputs, which are poorly specified. This development is strongly influenced by the coupling of electromagnetic energy and mass between the I-T and the magnetosphere for which the influences of the ionospheric conductivity are not well described. Finally, we find that the poorly understood spatial and temporal evolution of the I-T drivers produces large and small-scale structures in the plasma and neutral density that influence the stability of the region and the generation of plasma density irregularities within it.

Addressing these challenges requires advances in observing the neutral gas density, composition and velocity that are made simultaneously with observations of the plasma density and motions as well as the particles and fields describing the magnetospheric inputs. Additionally, our modeling capability must be advanced to include better descriptions of the processes affecting the propagation of waves through the region and to incorporate coupling to the regions below and the magnetosphere above at smaller spatial and temporal scales.

Link to article

Publication Name: AGU Centennial paper
First HAO Author's Name: Astrid Maute