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Topology of Earth's Magnetic Shield: Modeled Properties and Applications
APS - Four Corners Fall Meeting (2019)
  • David Alan Smith, Utah State University
The open-closed boundary (OCB) defines the region where geomagnetic field
lines transition from being closed to open. A closed field line has both
foot points at or near Earth in opposing hemispheres. An open field line has
one foot point at Earth while the other maps to the interplanetary magnetic
field (IMF). Charged particles are able to follow these open field lines
into Earth's upper atmosphere. The altitude to which these charged particles
penetrate is a function of particle energy and latitude and is known as the
energy cutoff latitude (CL). Given sufficient energy, these charged
particles may reach the D-region of the ionosphere (about 100 km), causing
increased absorption of HF radio signals, especially over polar regions.
So-called polar cap absorption (PCA) events can, therefore, wreak havoc on
HF communications near the polar cap boundary. It has been estimated that in
excess of 7000 transpolar commercial flights occur each year. Hence, it is
an important public safety issue that reliable means exist to anticipate HF
communication conditions. Using the Tsyganenko model of the geomagnetic
field (T96) we were able to show that the OCB experiences a UT-dependent
variation. We are now prepared to demonstrate that this same UT-effect is
inherent in the CL. Understanding this UT-dependent variability is critical
to being able to accurately model HF communications disruptions due to PCA
  • open/closed boundary,
  • polar cap absorption,
  • cutoff latitude
Publication Date
Fall October 12, 2019
Prescott, AZ
Citation Information
David Alan Smith. "Topology of Earth's Magnetic Shield: Modeled Properties and Applications" APS - Four Corners Fall Meeting (2019)
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