Events in Physics
Martin Laming (Space Science Division, Naval Research Laboratory): The First Ionization Potential (FIP) Effect in Open and Closed Magnetic Field
Location: PS128
The solar corona and both the slow and fast solar wind, originating from closed and
open field regions respectively, show a degree of elemental abundance
fractionation according to the First Ionization Potential (FIP) pattern.
Elements with FIP below about 10 eV (e.g. Fe, Si, Mg) are enhanced in
abundance relative to photospheric values, by a factor of about 3-4 in the
slow speed wind, and by about 1.5 in the fast wind, relative to those
elements (e.g. H, N, O, Ar) with higher FIP. Further, helium, the element
with highest FIP, is often observed to be depleted in abundance relative to
e.g. H, N, O, Ar, by varying amounts.
A compelling explanation for these abundance anomalies invokes the ponderomotive force
arising as Alfven and fast modes waves propagate through or reflect from the chromosphere.
These are fundamentally magnetic waves, and provide the necessary ion-neutral separation.
The different wave propagation in open and closed field regions of the solar corona reproduces
the observed variation in element abundances between fast and slow solar wind through the
naturally occurring variation in the ponderomotive force.
A careful consideration of the element abundance produced in a closed loop shows that the best
match to observed values arises for a wave resonant with the loop, i.e. the wave travel time from
one footpoint to the other is an integral number of wave half-periods. This strongly suggests a
coronal origin for the Alfven waves, where such a resonance would arise naturally, as opposed
to waves being generated in the photosphere or below and propagating up to the corona through
the loop footpoints, (as in open field regions). This scenario is investigated further, by evaluating the
their heating mechanism(s), and by consideration of the different fractionation and other observables
produced by shear and torsional Alfven waves, with a view to diagnosing the wave origin.
ponderomotive force arising in 3D compressible MHD simulations of coronal loops designed to understanding
their heating mechanism(s), and by consideration of the different fractionation and other observables
produced by shear and torsional Alfven waves, with a view to diagnosing the wave origin.
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