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[email protected] & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
Hemispheric Comparison of Signatures of Flux Transfer Events
Kathryn McWilliams and Matt WesselUniversity of Saskatchewan
[email protected] & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
From Scholer, 1995
FTE ModelsFTE Models
FTEs at the MagnetopauseFTEs at the Magnetopause
(Russell & Elphic, 1979)
bipolar field variation
[email protected] 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)
[email protected] 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)
[email protected] 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
[email protected] 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
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
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
3D Simulations – Development Along Magnetopause3D Simulations – Development Along Magnetopause
• Raeder, Annales Geophysicae, 2006
Space & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
[email protected] 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)
[email protected] 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
[email protected] 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
[email protected] & 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
[email protected] & 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
[email protected] & 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
[email protected] & 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
[email protected] & 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
[email protected] & 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
[email protected] & 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)
[email protected] & 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
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
[email protected] & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
[email protected] 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
[email protected] & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
[email protected] & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
[email protected] & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
[email protected] & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan
[email protected] & Atmospheric Studies Physics & Engineering Physics, University of Saskatchewan