Post on 21-Dec-2015
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Hemispheric Comparison of Signatures of Flux Transfer Events
Kathryn McWilliams and Matt WesselUniversity of Saskatchewan
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
From Scholer, 1995
FTE ModelsFTE Models
kathryn.mcwilliams@usask.ca
FTEs at the MagnetopauseFTEs at the Magnetopause
(Russell & Elphic, 1979)
bipolar field variation
kathryn.mcwilliams@usask.ca2007 Fall AGU Meeting Physics & Engineering Physics, University of Saskatchewan
Magnetopause(Equator-S)
Ionosphere(SuperDARN)
(Neudegg et al., 2001)
Flux Transfer Events at the MagnetopauseFlux Transfer Events at the Magnetopause
bipolar boundary-normal FTE signatures
poleward moving radar auroral forms (PMRAFs)
kathryn.mcwilliams@usask.ca2007 Fall AGU Meeting Physics & Engineering Physics, University of Saskatchewan
Poleward Moving Radar Patches (STARE)Poleward Moving Radar Patches (STARE)
• poleward moving patches during Aug 28, 1978, storm
• patches emanate from polar cap boundary
(Sofko et al., 1979; 1985)
kathryn.mcwilliams@usask.ca2007 Fall AGU Meeting Physics & Engineering Physics, University of Saskatchewan
STARE Patches & GEOS-2 M’pause CrossingsSTARE Patches & GEOS-2 M’pause Crossings
(Sofko et al., 1979; 1985)
GEOS-2footprintin patch
upwellingions
GEOS-2footprintpolewardof patch
10X fewerupwelling
ions
kathryn.mcwilliams@usask.ca2007 Fall AGU Meeting Physics & Engineering Physics, University of Saskatchewan
Pulsed Ionospheric Flows (PIFs) vs. PMRAFsPulsed Ionospheric Flows (PIFs) vs. PMRAFs
oscillating flow magnitude(with continuous data)
discrete poleward movingpatches (with data gaps)
PMRAFsPMRAFs
PIFsPIFs
kathryn.mcwilliams@usask.ca
MHD Simulation – No Dipole TiltMHD Simulation – No Dipole Tilt
• Raeder, Annales Geophysicae, 2006
• “Stagnation line” – separates northward and southward flow
• Relatively smooth flow away from subsolar point (Earth-Sun line)
• No evident plasmoids
• Reconnection relatively smooth
Space & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
kathryn.mcwilliams@usask.ca
MHD Simulation – Large Dipole TiltMHD Simulation – Large Dipole Tilt
• Raeder, Annales Geophysicae, 2006
• “Stagnation line” located off Earth-Sun line, towards winter hemisphere
• Reconnection X-line forms winter-ward of Sun-Earth line
• Plasmoid forms in region of flow towards winter cusp
• Field lines draped around plasmoid from summer cusp form second X-line
• Plasmoid moves towards winter cusp
• No plasmoid observed in summer hemisphere
Space & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
kathryn.mcwilliams@usask.ca
3D Simulations – Development Along Magnetopause3D Simulations – Development Along Magnetopause
• Raeder, Annales Geophysicae, 2006
Space & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
kathryn.mcwilliams@usask.ca2007 Fall AGU Meeting Physics & Engineering Physics, University of Saskatchewan
2-D Electric Field in Footprint of Reconnection2-D Electric Field in Footprint of Reconnection• Patch of
SuperDARN backscatter:– footprint of
reconnected field lines
– measured by two overlapping SuperDARN radars (CUTLASS)
• Compared patch motion to ExB drift
(McWilliams et al., 2001)
kathryn.mcwilliams@usask.ca2007 Fall AGU Meeting Physics & Engineering Physics, University of Saskatchewan
• patch expands and moves azimuthally• convection speed differs from patch motion at first
2-D Electric Field in Footprint of Reconnection2-D Electric Field in Footprint of Reconnection
kathryn.mcwilliams@usask.ca2007 Fall AGU Meeting Physics & Engineering Physics, University of Saskatchewan
• Two phases of motion: (1) reconnection (2) convection
• FTEs are not necessarily “small”
2-D Electric Field in Footprint of Reconnection2-D Electric Field in Footprint of Reconnection
1
2
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Recent ObservationsRecent Observations
• Korotova & Sibeck, GRL, 2008
• Considered m’pause crossings
• Interball-1 on dayside only during northern summer months; north=summer, south=winter
• Included only FTEs during neg. IMF Bz– Bz < -1 nT
• Interball-1 FTEs observed exclusively in WINTER hemisphere
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Signatures of FTEsSignatures of FTEs
4 hours UT
Geotail FTEs
SuperDARN poleward moving forms 18 Jan 1999 (NH winter)
McWilliams et al., AG, 2004
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Survey of Poleward Moving Radar Auroral FormsSurvey of Poleward Moving Radar Auroral Forms
• only examined poleward moving forms (PMRAFs)
• no modulated continuous drifts (PIFs)
• Radar Frequency is important!
• Before 2002 used single day and single night transmitter frequency
• Con: You have to be lucky to get good propagation
• Pro: Motion of patches is geophysicalfrequency change
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Survey of SuperDARN PMRAFsSurvey of SuperDARN PMRAFs
• Noted days when PMRAFs evident (visual inspection)
• viewing angle important
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Comparing N&S Hem.Comparing N&S Hem.
• The “one hope” frequency makes things difficult
• Not guaranteed that radio wave will refract enough to scatter back from cusp/mantle patches
Kerguelen = SH
Hankasalmi = NH
Ker Han
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Question Answered!Question Answered!
• …sort of• Simultaneous poleward
moving form in winter and summer hemisphere
• This is RARE
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Seasonal Dependence?Seasonal Dependence?
• Hankasalmi data only – Does not run “sounding” mode, so patch motion is geophysical
• Visual inspection of PMRAFs over nearly a full solar cycle
• 1997 – 2006
• FTE: 1893 days
• No FTE: 3468 days
(~35% FTE)
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Probably Not…Probably Not…• Our day-frequency is not
optimized for season
• So we take what we can get
• The number of days with FTEs strongly resembles the amount of ionospheric backscatter overall throughout the year
• No seasonal trend in SuperDARN PMRAFs
kathryn.mcwilliams@usask.ca
Summary and Future WorkSummary and Future Work
• Study motivated by simulations and observations of FTEs in winter hemisphere– Modelled plasmoids form in on winter side of Sun-Earth line– Modelled plasmoids carried through winter cusp– FTEs detected in winter hemisphere by Interball-1
• Reconnection footprint should map to both hemispheres, so particles are expected to precipitate into both hemispheres, regardless of where plasmoid forms
• SuperDARN does not see seasonal dependence on occurrence of PMRAFs– Simultaneous observations by Hankasalmi and Kerguelen
• More sophisticated analysis of statistics is required– More detail on duration of PMRAFs, beams involved, etc.– Relationship to upstream IMF orientation
Space & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
kathryn.mcwilliams@usask.ca2007 Fall AGU Meeting Physics & Engineering Physics, University of Saskatchewan
• FTEs observed at Geotail only under certain IMF conditions (+By and +Bz).
• SuperDARN transients suggest FTEs occurred at all times, regardless of IMF orientation.
FTEs
SuperDARN PMRAFs
IMFBy
(McWilliams et al., 2004)
IMFBz
Geotail
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
kathryn.mcwilliams@usask.caSpace & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan