Phase Coherence on Open Field Lines Associated with FLRs

Abiyu Nedie, Frances Fenrich & Robert Rankin

University of AlbertaEdmonton, Alberta, Canada

2011 SuperDARN Meeting

HanoverMay 30 – June 3, 2011

Outline of the Talk

Introduction• Magnetospheric disturbances• Field Line Resonance & Excitation MechanismsEvents from our ObservationsSources of Pulsations • MHD waves in the solar windWhat we ‘ve learnt from this event

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Outline of the TalkIntroduction• Magnetospheric disturbances• Field Line Resonance & Excitation MechanismsEvents from our Observations• Phase Coherence on open field lines• 1st & 2nd order harmonic FLR signaturesSource of Pulsation • MHD waves in the solar windConclusions

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Magnetospheric disturbances The entire dayside MP & LLBL can map along the magnetic field lines in to

a relatively small area of the ionosphere

Disturbances in Magnetosphere can be followed by their signatures in the ionosphere

High latitude ionosphere provides a screen on which to view processes in the Magnetosphere & interactions b/n Magnetosphere, Solar wind, IMF

Ground based radars, magnetometers, optical instruments can be used to study magnetospheric disturbances

Significant advances in understanding the interaction b/n the SW & the Magnetosphere have been made through the study of ionospheric signatures (eg. Geotail & SuperDARN echoes will be used in this talk)

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Theory of MHD Waves and Field Line Resonance

There are two decoupled modes of MHD waves in homogeneous cold plasma.

1. Shear Alfven waves propagate along the magnetic field lines. and reflect back from the highly conducting ionospheres. As a result, the standing oscillation of the field lines could be driven 2. Fast compressional waves propagates across the magnetic field. Fast compressional waves in the outer magnetosphere can couple to shear Alfven Waves to drive the so-called FLRs.

FLR Excitation Mechanisms1. KH surface wave on the Magnetopause, Chen & Hasegawa (1974)2. Abrupt changes in the solar wind dynamic pressure excites compressional

waves, Kivelson & Southwood (1985, 1986) 3. MHD waves in the Solar wind, Walker (2002)

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Geotail Orbit, 2000/12/26, 0000-0400UT

Oscillations in time domain (Spacecraft and Radar data) , 0010-0210 UT

g=47

g=49

g=17

g=16

Frequency Spectra of Spacecraft and Radar data , 0010-0210 UT

Contour plot of 0.8 mHz wave from Kodiak HF radar, b=2-10, g=35-48, 0010-0210 UT

Contour plot of 0.8 mHz wave from Hanksalami HF radar, b=5-15, g=38-55, 0010-0210 UT

Ultraviolet Imager, OCB ≈ 71/72

≈ 73/74

SuperDARN swd OCB ≈ 71/72

OCB ≈ 73/74

0.8-mHz FLR from Pykkvibaer b=0-15, g=15-30, 0010-0210 UT

Contour plot of the power spectra at 0.8 -mHz from the Pykkvibaer, g=17, b=1-15

Spectral Power and Phase vs Latitude for the 0.8-mHz resonance from Pykkvibaer, g=17, b=1-15

Overlay of Pykkvibaer (b=13, g=16) and Geotail (Bz)

Cross power spectral density and and coherence of Pykkvibaer (b=13, g=16) with Geotail Bz time shifted to

(15min)

Comparison of convection flow speed and wave phase velocity

H

P

K

VpK≅670m/s500<Vc<1000m/s

VpP≅600m/s500<Vc<900m/s

VpH≅1440m/s400<Vc<700m/s

Conclusions• A completely new feature of phase coherence on open field lines

at exactly the same resonant frequency is found at the same time.

• Clear and discernible signatures of 1st and 2nd order harmonics at 0.8-mHz are observed

• Results in this study support the hypothesis that the coherent phase on open field lines and the discrete frequency FLR at 0.8-mHz were being driven at the same time by an external wave source in the solar wind at 0.8-mHz .

• SuperDARN could be used as a potential tool of providing a direct diagnostics on how MHD waves in the solar wind could enter into magnetosphere right at the boundary

-test various theories on how energy is transported into the boundary of the magnetosphere in a global scale view through continuous monitoring of the high latitude ionospheric convection

Conclusions• discernible FLR signatures at 0.8-mHz, extended azimuthally

along the latitude contour are found to be associated source in the Solar wind . A completely new feature of phase coherence on open field lines at exactly the same resonant frequency is found at the same time.

• Clear signatures of second harmonics are observed• Results in this study support the hypothesis that the coherent

phase on open field lines and the discrete frequency FLR at 0.8-mHz were being driven by an external wave source in the solar wind at the same discrete frequency.

• SuperDARN could be used as a potential tool of providing a direct diagnostics on how MHD waves in the solar wind could enter into magnetosphere right at the boundary

-test various theories on how energy is transported into the boundary of the magnetosphere through continuous monitoring of the high latitude ionospheric convection