Challenges to Understanding the Earth's Ionosphere and Thermosphere

• Published in: Journal of geophysical research. Space physics 2020-07, Vol.125 (7), p.n/a
• Main Authors: Heelis, R. A., Maute, A.
• Format: Article
• Language: English
• Subjects: Alignment; Atmosphere; Atmospheric models; Charged particles; Composition; Coupling; coupling to lower atmosphere; Descriptions; Earth; Earth ionosphere; Earth magnetosphere; Earth surface; Energetic particles; Ionosphere; ionosphere‐thermosphere; ionospheric current system; Latitude; Lower atmosphere; magnetosphere‐ionosphere coupling; Neutral gases; Neutral particles; Particle precipitation; Plasma; Plasma density; Plasma dynamics; plasma structures; Radiation; Radio communications; Solar heating; Sunspot activity; Sunspots; Thermosphere; Upper atmosphere; Wave propagation; Weather
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2019JA027497

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). The I‐T is strongly influenced by wave motions of the neutral atmosphere from the lower atmosphere and is coupled to the magnetosphere, which supplies energetic particle precipitation and field‐aligned currents at high latitudes. The resulting plasma dynamics are associated with 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 atmosphere, the generation and flow of currents within the I‐T region, the coupling to the magnetosphere, and the response of the I‐T region reflected in the neutral and plasma density changes. Addressing these challenges requires advances in observing the neutral density, composition, and velocity and simultaneous observations of the plasma density and motions as well as the particles and field‐aligned current describing the magnetospheric energy inputs. Additionally, our modeling capability must advance to include better descriptions of the processes affecting the I‐T region and incorporate coupling to below and above at smaller spatial and temporal scales. Plain Language Summary The ionosphere is the region of Earth's upper atmosphere made up of a mixture of charged and neutral gases between approximately 50 and 1,000 miles (80–1,600 km) above the Earth's surface. Sandwiched between the lower atmosphere and the magnetosphere, the ionosphere reacts to weather and climate near the Earth's surface and to eruptions and sunspot activity on the Sun. The ionosphere absorbs the harmful radiation from the Sun and determines the fidelity of all radio communication, navigation, and surveillance transmissions through it. It is part of a complex, coupled system that changes on scales from meters to the planetary radius, and from seconds to decades. Understanding how the behavior of this region is controlled, by internal interactions and by the external regi