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SUMMARY:Element Fractionation by the Ponderomotive Force - J. Martin Lamin
 g\, Space Science Division Naval Research Laboratory
DTSTART:20221121T120000Z
DTEND:20221121T130000Z
UID:TALK185294@talks.cam.ac.uk
CONTACT:Callum William Fairbairn
DESCRIPTION:Since 1963\, we have known\, or at least suspected\, that elem
 ent abundances in the solar corona and wind are different to those in the 
 photosphere. Elements that are predominantly ionized in the photosphere an
 d chromosphere\, e.g. Fe\, Si\, Mg\, are observed to be enhanced in abunda
 nce in the corona and wind by a factor of typically 3-4. In the 1990’s w
 hen abundance measurements in stellar coronae became possible\, similar ef
 fects were seen in solar-like stars. An inverse effect\, the depletion of 
 Fe\, Si\, Mg\, etc was discovered in M dwarfs and more active binary stars
 . Due to the dependence on the ionization potential\, these phenomena have
  been dubbed the First Ionization Potential (FIP) Effect\, or the Inverse 
 FIP (IFIP) Effect. A model capturing both the FIP and IFIP effects invokes
  ion-neutral separation by the ponderomotive force due to Alfven and magne
 tosonic waves propagating through the chromosphere. More recently\, Invers
 e FIP effect has been identified in solar flares\, both in small regions o
 f otherwise FIP enhanced flare plasma\, and in bulk spatially unresolved s
 olar flares. The spatially resolved flare observations indicate a connecti
 on with sub-photospheric reconnection\, which is presumably a source of wa
 ves that become fast modes in the solar chromosphere. These selectively de
 plete ions through the ponderomotive force. Alfven waves have also been de
 tected in the chromosphere beneath an active region\, connected by magneti
 c field lines to coronal regions of strong FIP enhancement. These observat
 ions support the ponderomotive force model of the fractionation. Fractiona
 tion by such means is new to solar physics and astrophysics\, but is not n
 ew to science. Manipulation of atoms\, molecules\, biological samples\, et
 c. by the forces due to refraction of photons from lasers\, known as “op
 tical tweezers”\, has a rather long history in optical sciences\, and wo
 n Nobel Prizes for Steven Chu (in 1997) and Arthur Ashkin (in 2018). Our m
 odel is a precise analog of this work\, but with magnetohydrodynamic waves
  instead of optical photons. This connection leads to a better physical un
 derstanding of the mechanisms at work in FIP or Inverse FIP fractionated p
 lasma. Work supported by NASA Heliophysics Guest Investigator (80HQTR19T00
 29) and Supporting Research Programs (80HQTR20T0076)\, and by Basic Resear
 ch Funds of the Office of Naval Research.
LOCATION:In Person MR14 + Online
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