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Beyond providing Earth with its predominant source of heat and light, the Sun affects the planet and human society in a variety of other ways. For instance, effects from storms propagating from the solar corona outward through space, can affect aviation, electrical grids, and satellite performance on Earth, often impinging on daily societal function directly. Due to distance from the Earth and few observing instruments, solar storms cannot currently be predicted. But, once observed, researchers can monitor a storm’s progress, tracking it through space into the magnetosphere, Earth’s outermost protective boundary. To isolate and identify storm characteristics and better forecast future events, scientists are turning to the Coupled Magnetosphere Ionosphere Thermosphere (CMIT) model developed by HAO scientists in collaboration with the NSF-funded Center for Integrated Space Weather Modeling.
Extreme space weather events include coronal mass ejections (CMEs). Not unlike hurricanes in space, CMEs expel a plasma of charged particles and elements like oxygen, helium, and iron, and cause the coronal magnetic field to propagate outward from the Sun, toward Earth. Despite the magnetosphere, which acts as a gatekeeper, protecting the lower atmosphere from solar winds by harnessing the energy and momentum of incoming ions and magnetic forces, CMEs can have serious repercussions on Earth.
In particular, aviation faces significant challenges during strong space storms. Pilots flying above 85 degrees latitude are outside the range of satellite communications and therefore must rely on radio communications for navigation. However, severe space weather disrupts radio transmissions; ionized particles and heightened magnetism affect radio wave propagation. A highly ionized atmosphere can also disrupt Global Positioning System (GPS) signals, throwing off the required triangulation of points that allows correct location of an object – such as an airplane – by GPS receivers. The more ions present in the atmosphere, the longer a signal takes to triangulate between points, so precise information on ionization level (the total electron content of the upper atmosphere) helps assess GPS accuracy. Also, the global wide area augmentation system (WAAS) provides the aviation industry with direct connection to GPS units. Capable of providing GPS calculation corrections in most circumstances, under extreme atmospheric ionization events, WAAS capabilities can be severely curtailed if not completely debilitated.
As implied above, the ionosphere is an important source of ionized particles. However, until recently, solar models and models of the Earth’s upper atmosphere could not fully replicate the complexity of interactions occurring between the ionosphere and magnetosphere. To better achieve this end, CMIT couples a model of the magnetosphere (Lyons-Fedder-Mobarry (LFM)), with NCAR’s Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM).
A recent update to the LFM by scientists working as part of the Center for Integrated Space-Weather Modeling (CISM), this model of the magnetosphere can now track a variety of the chemical species frequently ejected from the ionosphere into the magnetosphere. This advance means that the coupled CMIT model can now more realistically characterize the upper atmosphere, both in its steady state and when disruptions caused by solar-weather phenomena such as CMEs and geomagnetic substorms, which directs high levels of radiation toward the Earth.
The CMIT can simulate ionospheric activity by driving magnetospheric dynamics that, in turn, are driven by the solar winds. The CMIT framework connects these upper atmosphere’s linked systems and allows scientists to compare modeled outcomes with observed space weather events and characteristics. In doing this, new insights are being gained on the cascading effects of solar activity on Earth, which is particularly important for regions acutely affected by space weather.
NCAR’s Michael Wiltberger and colleagues from Dartmouth and CISM tested out the latest LFM version, called the Multi-Fluid LFM, by looking specifically at the dynamics of oxygen (O+) ions flowing from the magnetosphere toward the Earth’s lower atmosphere. The LFM more clearly shows the outflow of oxygen ions between the ionosphere and magnetosphere, such that when coupled with the TIE-GCM, researchers gain a new view on the dynamic exchanges of some of the charged materials that can affect Earth’s radio and communications’ function.
Observational data obtained from satellites like NASA’s Advanced Composition Explore (ACE) are also essential for realistic model output. These data provide researchers with information about solar wind – temperature, composition characteristics, speed, etc. – and geomagnetic storms within an hour of storm onset. Feeding these observations into the CMIT drives magnetospheric dynamics, which are used to better understand ionospheric behavior, and can isolate causes behind many of the Earth-bound space-weather anomalies, which range from variation in atmospheric chemistry to motion of ionospheric plasma. In their study, Wiltberger and colleagues used satellite observations to verify that the model runs showed realistic portrayals of ionosphere-magnetosphere O+ dynamics.
A recently published paper on CMIT appearing in Science includes simulations indicating that out-flowing oxygen ions may play an important role in driving observed responses in the magnetosphere. These responses, known as sawtooth intervals, are periods of recurring geomagnetic activity in the upper atmosphere, explains Wiltberger.
“This result is the first-ever indication of such an effect. With this outcome, we predict that a connection exists between the amount of outflow and the sawtooth period that, if confirmed by observational testing, will represent a significant change in this fundamental response mode of the magnetosphere to outflowing ions,” Wiltberger says.
CMIT is currently not used in real time and therefore cannot be used operationally to forecast space-weather events. Instead, it is used instead to enhance scientific insights. At some point soon, scientists hope to use the model in a predictive capacity. Currently, CMIT’s primary function is as an effective research model that improves scientific perspective on Sun-Earth interactions. It also assists with evaluating how the two models do both individually and as a coupled unit.