Hemispheric Comparison of Signatures of Flux Transfer Events

[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


From Scholer, 1995

FTE ModelsFTE Models

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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)


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)


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


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

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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

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MHD Simulation – Large Dipole TiltMHD Simulation – Large Dipole Tilt


• “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


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3D Simulations – Development Along Magnetopause3D Simulations – Development Along Magnetopause




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)


• 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


• 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


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


Signatures of FTEsSignatures of FTEs

4 hours UT

Geotail FTEs

SuperDARN poleward moving forms 18 Jan 1999 (NH winter)

McWilliams et al., AG, 2004


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


Survey of SuperDARN PMRAFsSurvey of SuperDARN PMRAFs

• Noted days when PMRAFs evident (visual inspection)

• viewing angle important


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


Question Answered!Question Answered!

• …sort of• Simultaneous poleward

moving form in winter and summer hemisphere

• This is RARE


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)


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

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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



• 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

Hemispheric Comparison of Signatures of Flux Transfer Events

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