Betsy Hodges became the mayor of Minneapolis in 2014.
The L-shell , L-value , or McIlwain L-parameter -LRB- after Carl McIlwain -RRB- is a parameter describing a particular set of planetary magnetic field lines .. Carl McIlwain. Carl McIlwain. magnetic field lines. magnetic field lines. Colloquially , L-value often describes the set of magnetic field lines which cross the Earth 's magnetic equator at a number of Earth-radii equal to the L-value .. magnetic field lines. magnetic field lines. magnetic equator. magnetic equator. Earth-radii. Earth's radius. For example , '' '' describes the set of the Earth 's magnetic field lines which cross the Earth 's magnetic equator two earth radii from the center of the Earth .. magnetic field lines. magnetic field lines. magnetic equator. magnetic equator. L-shell parameters can also describe the magnetic fields of other planets .. In such cases , the parameter is renormalized for that planet 's radius and magnetic field model .. Although L-value is formally defined in terms of the Earth 's true instantaneous magnetic field -LRB- or a high-order model like IGRF -RRB- , it is often used to give a general picture of magnetic phenomena near the Earth , in which case it can be approximated using the dipole model of the Earth 's magnetic field .. IGRF. International Geomagnetic Reference Field