A novel technique for rapid L* calculation using UBK coordinates

Kyungguk Min, Jacob Bortnik, Jeongwoo Lee

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The magnetic drift invariant (L*) is an important quantity used for tracking and organizing particle dynamics in the radiation belts, but its accurate calculation has been computationally expensive in the past, thus making it difficult to employ this quantity in real-time space weather applications. In this paper, we propose a new, efficient method to calculate L* using the principle of energy conservation. This method uses Whipple's (U, B, K) coordinates to quickly and accurately determine trajectories of particles at the magnetic mirror point from two-dimensional isoenergy contours. The method works for any magnetic field configuration and is able to accommodate constant electric potential along field lines. We compare the result of this method with those of International Radiation Belt Environment Modeling library (IRBEM-LIB) to demonstrate the performance of this new method. The method requires a preparation step, and thus may not be the optimal method for a single trajectory calculation; however, it presents a huge performance gain when adiabatically propagating a large population of particles in a given magnetic field configuration.

Original languageEnglish (US)
Pages (from-to)192-197
Number of pages6
JournalJournal of Geophysical Research: Space Physics
Issue number1
StatePublished - 2013

All Science Journal Classification (ASJC) codes

  • Space and Planetary Science
  • Geophysics


  • Generalized L value
  • L star


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